Matching circuit and semiconductor device

Abstract

To provide a matching circuit which can cope with a plurality of frequencies.SOLUTION: A matching circuit includes: a transistor; and an inductor. The matching circuit uses capacitance (hereinbelow, referred to as capacitance Cgsd) formed between a source / drain, and a gate of a transistor as a capacitor. The capacitance Cgsd has a feature of changing in accordance with voltage (hereinbelow, referred to as voltage Vgs) with respect to the source. The transistor included in the matching circuit is an OS transistor having a metal oxide material in a channel formation region. Since the OS transistor features larger variation in the capacitance Cgsd with respect to the voltage Vgs than a MOSFET that uses silicon, the matching circuit can cope with AC signals in a wide frequency range.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a matching circuit, and more particularly to a matching (also called impedance matching) circuit using a capacitor and an inductor, which is often used in high-frequency circuits.

[0002] One embodiment of the present invention relates to a semiconductor device. In this specification, the term "semiconductor device" refers to a device that utilizes semiconductor characteristics, such as a circuit including a semiconductor element (transistor, diode, photodiode, etc.) or a device having such a circuit. In this specification, the term "semiconductor device" refers to any device that can function by utilizing semiconductor characteristics, such as an integrated circuit, a chip including an integrated circuit, an electronic component with a chip housed in a package, or an electronic device including an integrated circuit.

[0003] Note that one aspect of the present invention is not limited to the above-mentioned technical fields. The technical fields of the invention disclosed in this specification relate to products, methods, or manufacturing methods. Alternatively, one aspect of the present invention relates to processes, machines, manufactures, or compositions of matter. [Background technology]

[0004] Portable information terminals such as smartphones and tablet devices are becoming increasingly popular. As information terminals become more popular, various communication standards have been established. For example, the LTE-Advanced standard, also known as the fourth generation (4G) standard, has begun operation.

[0005] In recent years, with the development of information technology such as IoT (Internet of Things), the amount of data handled by information terminals has tended to increase. Electronic devices such as mobile information terminals are required to have faster communication speeds.

[0006] To accommodate various information technologies such as IoT, the fifth generation (5G) communication standard is being considered, which will achieve faster communication speeds, more simultaneous connections, and shorter latency than 4G. In Japan, for example, 5G will use communication frequencies in the 3.7 GHz, 4.5 GHz, and 28 GHz bands.

[0007] 5G-compatible semiconductor devices are made using semiconductors that use a single element, such as Si, as their main component, or compound semiconductors that use multiple elements, such as Ga and As, as their main components. Furthermore, oxide semiconductors, a type of metal oxide, are attracting attention.

[0008] Oxide semiconductors have been found to have a c-axis aligned crystalline (CAAC) structure and a nanocrystalline (nc) structure, which are neither single crystalline nor amorphous (see Non-Patent Documents 1 and 2). Non-Patent Documents 1 and 2 disclose techniques for manufacturing transistors using oxide semiconductors having a CAAC structure. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] S. Yamazaki et al., “SID Symposium Digest of Technical Papers”, 2012, volume 43, issue 1, p.183-186 [Non-patent document 2] S. Yamazaki et al., “Japanese Journal of Applied Physics”, 2014, volume 53, Number 4S, p.04ED18-1-04ED18-10 Summary of the Invention [Problem to be solved by the invention]

[0010] To achieve high communication speeds, electrical circuits (also called radio frequency circuits) that handle high-frequency signals (radio frequency signals) are required. In radio frequency circuits, if the output impedance of the circuit that sends out the signal does not match the input impedance of the circuit that receives the signal, problems such as reflected waves can occur, so a matching circuit is used to match the output impedance and input impedance.

[0011] In high-frequency circuits, matching circuits using capacitors and inductors are known to be of L-type, T-type, π-type, etc., but once the capacitance of the capacitor and the inductance of the inductor are selected for a certain frequency, it is necessary to change either or both of the capacitance of the capacitor and the inductance of the inductor for frequencies other than that frequency, which means that either or both of the capacitor and the inductor must be replaced.

[0012] An object of one embodiment of the present invention is to provide a matching circuit that includes a transistor and an inductor and that can support multiple frequencies, or to provide a matching circuit that can support multiple frequencies without replacing either or both of the transistor and the inductor.

[0013] It should be noted that one embodiment of the present invention does not necessarily have to solve all of the above problems, but may solve at least one of the problems. Furthermore, the description of the above problems does not preclude the existence of other problems. Problems other than these will become apparent from the description in the specification, claims, drawings, etc., and other problems can be extracted from the description in the specification, claims, drawings, etc. [Means for solving the problem]

[0014] One aspect of the present invention is a matching circuit including a transistor and an inductor, wherein the transistor has a metal oxide in a channel forming region, and impedance matching is performed by changing the voltage of the gate of the transistor relative to the source.

[0015] Another aspect of the present invention is a matching circuit having a transistor, an inductor, and first and second input terminals. The first input terminal is electrically connected to the source and drain of the transistor, the gate of the transistor is electrically connected to the first terminal of the inductor, and the second terminal of the inductor is electrically connected to the second input terminal. The transistor has a metal oxide in a channel formation region, and performs impedance matching by changing the potential input to the second input terminal.

[0016] Another aspect of the present invention is a semiconductor device having a transistor, an inductor, and first and second input terminals. The first input terminal is electrically connected to a source and a drain of the transistor, the gate of the transistor is electrically connected to a first terminal of the inductor, and the second terminal of the inductor is electrically connected to a second input terminal. An AC signal is input to the first input terminal, and a predetermined potential is input to the second input terminal, and the predetermined potential changes when the frequency of the AC signal changes.

[0017] In the above-described embodiment, the transistor includes a metal oxide in a channel formation region. [Effects of the Invention]

[0018] According to one aspect of the present invention, it is possible to provide a matching circuit that has a transistor and an inductor and is capable of supporting multiple frequencies. Alternatively, it is possible to provide a matching circuit that is capable of supporting multiple frequencies without replacing either or both of the transistor and the inductor.

[0019] It should be noted that one embodiment of the present invention does not necessarily have to solve all of the above problems, but may solve at least one of the problems. Furthermore, the description of the above problems does not preclude the existence of other problems. Problems other than these will become apparent from the description in the specification, claims, drawings, etc., and other problems can be extracted from the description in the specification, claims, drawings, etc. [Brief explanation of the drawings]

[0020] [Figure 1] Fig. 1A is a circuit diagram showing an example of the configuration of a matching circuit. Fig. 1B is a block diagram showing the connection relationship between a device that outputs a signal, the matching circuit, and a device that inputs a signal. Fig. 1C is a diagram explaining the signals and potentials input to the matching circuit. [Figure 2] 2A is a conceptual diagram showing the relationship between the voltage of the gate relative to the source and the capacitance formed between the source and the gate, and between the drain and the gate. FIG. 2B and FIG. 2C are circuit diagrams showing examples of the configuration of a matching circuit. [Figure 3] FIG. 3 is a cross-sectional view showing an example of the configuration of a semiconductor device. [Figure 4] 4A, 4B, and 4C are cross-sectional views showing examples of the structure of a transistor. [Figure 5] 5A is a top view illustrating an example of the structure of a transistor, and FIGS. 5B and 5C are cross-sectional views illustrating the example of the structure of a transistor. [Figure 6] 6A is a top view illustrating an example of the structure of a transistor, and FIGS. 6B and 6C are cross-sectional views illustrating the example of the structure of a transistor. [Figure 7] 7A is a top view illustrating an example of the structure of a transistor, and FIGS. 7B and 7C are cross-sectional views illustrating the example of the structure of a transistor. [Figure 8] 8A is a top view illustrating an example of the structure of a transistor, and FIGS. 8B and 8C are cross-sectional views illustrating an example of the structure of a transistor. [Figure 9] 9A is a top view illustrating an example of the structure of a transistor, and FIGS. 9B and 9C are cross-sectional views illustrating an example of the structure of a transistor. [Figure 10] 10A is a top view illustrating an example of the structure of a transistor, and FIGS. 10B and 10C are cross-sectional views illustrating the example of the structure of a transistor. [Figure 11] 11A and 11B are cross-sectional views showing examples of the structure of a transistor. [Figure 12] FIG. 12 is a cross-sectional view showing an example of the configuration of a semiconductor device. [Figure 13] 13A and 13B are cross-sectional views showing examples of the structure of a transistor. [Figure 14] Fig. 14A is a diagram illustrating the classification of IGZO crystal structures, Fig. 14B is a diagram illustrating the XRD spectrum of a CAAC-IGZO film, and Fig. 14C is a diagram illustrating the electron microbeam diffraction pattern of a CAAC-IGZO film. [Figure 15] Figure 15 is an image diagram of factory automation. [Figure 16] FIG. 16 is a perspective view illustrating a structure of an OS transistor. [Figure 17] 17A and 17B are graphs showing Vgs-Cgsd characteristics of an OS transistor. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments will be described with reference to the drawings. However, it will be readily understood by those skilled in the art that the embodiments can be implemented in many different forms and that various changes in form and details can be made without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the following description of the embodiments.

[0022] In addition, the following multiple embodiments can be combined as appropriate. In addition, when multiple configuration examples are shown in one embodiment, the configuration examples can be combined with each other as appropriate.

[0023] In the drawings attached to this specification, the components are classified by function and shown as block diagrams that are independent of each other, but in reality, it is difficult to completely separate the components by function, and one component may be involved in multiple functions.

[0024] In addition, in the drawings, etc., the size, layer thickness, region, etc. may be exaggerated for clarity. Therefore, the drawings are not necessarily limited to the scale. The drawings are schematic illustrations of ideal examples, and are not limited to the shapes or values shown in the drawings.

[0025] In addition, in drawings, etc., identical elements or elements having similar functions, elements made of the same material, or elements formed at the same time may be given the same symbol, and repeated explanations may be omitted.

[0026] Furthermore, in this specification and the like, the terms "film" and "layer" can be interchangeable. For example, the term "conductive layer" can be changed to the term "conductive film." Or, for example, the term "insulating film" can be changed to the term "insulating layer."

[0027] Furthermore, in this specification and the like, terms indicating arrangement such as "above" and "below" do not limit the positional relationship of components to "directly above" or "directly below." For example, the expression "gate electrode on a gate insulating layer" does not exclude other components between the gate insulating layer and the gate electrode.

[0028] In addition, in this specification, ordinal numbers such as "first," "second," and "third" are used to avoid confusion of components and do not imply any numerical limitation.

[0029] Furthermore, in this specification, "electrically connected" includes a connection via "something that has some kind of electrical function." Here, "something that has some kind of electrical function" is not particularly limited as long as it enables the transmission and reception of electrical signals between the connected objects. For example, "something that has some kind of electrical function" includes electrodes and wiring, as well as switching elements such as transistors, resistive elements, inductors, capacitive elements, and other elements with various functions. Furthermore, even when something is expressed as "electrically connected," there may be no physical connection in the actual circuit, and only wiring may be extended.

[0030] Furthermore, in this specification and the like, the terms "electrode" and "wiring" do not limit the functionality of these components. For example, an "electrode" may be used as part of a "wiring," and vice versa.

[0031] In addition, in this specification, a "terminal" in an electric circuit refers to a part where a current or potential is input (or output) or a signal is received (or transmitted). Therefore, a part of a wiring or an electrode may function as a terminal.

[0032] Generally, a "capacitive element" has a configuration in which two electrodes face each other with an insulator (dielectric) interposed therebetween. In this specification, the term "capacitive element" also includes a configuration in which two wires face each other with an insulator interposed therebetween, or a configuration in which two wires are arranged with an insulator interposed therebetween, in addition to a configuration in which two electrodes face each other with an insulator interposed therebetween. In this specification, the "capacitive element" may also be referred to as a "condenser," "capacitor," or "capacitance."

[0033] In this specification, a "high frequency signal" refers to a signal with a high frequency (an AC signal). For example, in signal transmission, when the wavelength of the AC signal to be transmitted is a size that cannot be ignored compared to the distance between a device that outputs the signal and a device that inputs the signal, the AC signal may be called a high frequency signal.

[0034] Furthermore, in this specification and the like, the term "voltage" often refers to the potential difference between a certain potential and a reference potential (for example, ground potential). Therefore, the terms "voltage" and "potential difference" can be used interchangeably.

[0035] In this specification and the like, a transistor is an element having at least three terminals including a source, a drain, and a gate. A channel formation region is formed between the source (source terminal, source region, or source electrode) and the drain (drain terminal, drain region, or drain electrode), and a current can flow between the source and the drain through the channel formation region. In this specification and the like, the channel formation region refers to a region through which a current mainly flows.

[0036] Furthermore, the functions of the source and drain may be interchanged when transistors of different polarities are used, when the direction of current changes during circuit operation, etc. For this reason, the terms source and drain may be used interchangeably in this specification and the like.

[0037] In this specification and the like, unless otherwise specified, the off-state current refers to the drain current when a transistor is in an off state (also referred to as a non-conducting state or a cut-off state). Unless otherwise specified, the off-state refers to a state in which the gate voltage Vgs relative to the source is lower than the threshold voltage Vth for an n-channel transistor, and a state in which the gate voltage Vgs relative to the source is higher than the threshold voltage Vth for a p-channel transistor. In other words, the off-state current of an n-channel transistor may be referred to as the drain current when the gate voltage Vgs relative to the source is lower than the threshold voltage Vth.

[0038] In the above description of off-state current, the drain may be read as the source. That is, the off-state current may refer to the source current when a transistor is in an off state. The off-state current may also be referred to as leakage current, which has the same meaning as the off-state current. In this specification and the like, the off-state current may also refer to the current that flows between the source and drain when a transistor is in an off state.

[0039] In this specification and the like, the on-state current may refer to a current that flows between a source and a drain when a transistor is in an on state (also referred to as a conductive state).

[0040] In this specification and the like, the term "metal oxide" refers to an oxide of a metal in a broad sense. Metal oxides are classified into oxide insulators, oxide conductors (including transparent oxide conductors), oxide semiconductors, etc.

[0041] For example, when a metal oxide is used in a channel formation region of a transistor, the metal oxide may be referred to as an oxide semiconductor. That is, when a metal oxide has at least one of an amplifying function, a rectifying function, and a switching function, the metal oxide can be called a metal oxide semiconductor. That is, a transistor having a metal oxide in a channel formation region can be called an "oxide semiconductor transistor" or an "OS transistor." Similarly, a "transistor using an oxide semiconductor" is also a transistor having a metal oxide in a channel formation region.

[0042] In this specification and the like, a metal oxide containing nitrogen may also be referred to as a metal oxide. A metal oxide containing nitrogen may also be referred to as a metal oxynitride. Details of metal oxides will be described later.

[0043] (Embodiment 1) In this embodiment, a matching circuit according to an embodiment of the present invention will be described. The matching circuit according to an embodiment of the present invention is a circuit that can function by utilizing semiconductor characteristics, and can also be called a semiconductor device.

[0044] <Matching circuit configuration example 1> 1A is a circuit diagram showing an example of the configuration of a matching circuit 10 according to an embodiment of the present invention. The matching circuit 10 shown in FIG. 1A is an L-type matching circuit, and includes a transistor T11, an inductor L12, input terminals VDD_IN and SII_IN, and an output terminal SIO_OUT.

[0045] The input terminal SII_IN is electrically connected to the source and drain of the transistor T11, the gate of the transistor T11 is electrically connected to the first terminal of the inductor L12 and the output terminal SIO_OUT, and the second terminal of the inductor L12 is electrically connected to the input terminal VDD_IN.

[0046] In the matching circuit 10, a potential VDD is input to the input terminal VDD_IN, a signal SII is input to the input terminal SII_IN, and a signal SIO is output from the output terminal SIO_OUT. The signal SII can be, for example, an AC signal having an amplitude SII_A with respect to a potential Vref (see FIG. 1C).

[0047] Matching circuit 10 is provided between a device that outputs a signal and a device that inputs a signal. That is, an input terminal SII_IN of matching circuit 10 is electrically connected to an output terminal of device 20 that outputs a signal, and an output terminal SIO_OUT of matching circuit 10 is electrically connected to an input terminal of device 30 that inputs a signal. Figure 1B is a block diagram showing the connections between device 20 that outputs a signal, matching circuit 10, and device 30 that inputs a signal.

[0048] Matching circuit 10 is provided particularly when there is a mismatch between the output impedance of device 20 and the input impedance of device 30. This is because when there is a mismatch between the output impedance of device 20 and the input impedance of device 30, electrically connecting the output terminal of device 20 and the input terminal of device 30 can cause problems such as the generation of reflected waves and the inability to efficiently transmit and receive AC signals.

[0049] The devices 20 and 30 are not particularly limited as long as they can output or input a signal. For example, the devices 20 and 30 can be any of the above-mentioned devices having some electrical function. More specifically, the device 20 can be a buffer that outputs a signal, and the device 30 can be a wiring having a characteristic impedance.

[0050] <Example of input signal> 1C is a diagram illustrating the signal SII and the potential VDD, which are divided into periods D13 and D14.

[0051] During period D13, signal SII is an AC signal having an amplitude SII_A with respect to potential Vref, and the period of signal SII is period T13. During period D13, potential VDD is a constant potential, and the potential difference between potential VDD and potential Vref is potential difference VB1.

[0052] During period D14, signal SII is an AC signal having an amplitude SII_A with respect to potential Vref, and the period of signal SII is period T14. During period D14, potential VDD is a constant potential, and the potential difference between potential VDD and potential Vref is potential difference VB2.

[0053] In periods D13 and D14, the potential Vref and the amplitude SII_A do not change, and the period T14 is longer than the period T13. That is, the signal SII in period D14 is an AC signal with a lower frequency than the signal SII in period D13.

[0054] During periods D13 and D14, the potential difference between the potential VDD and the potential Vref changes from VB1 to VB2. The potential difference VB2 is larger than the potential difference VB1. Alternatively, the potential difference VB2 may be smaller than the potential difference VB1.

[0055] <Transistor> The transistor T11 is an OS transistor, which has the following characteristics: an extremely small off-state current, the off-state current is not likely to increase even in a high-temperature environment, it can be formed by stacking layers because it is a thin film transistor, and it can be manufactured at low cost because it can be manufactured using the same manufacturing equipment as a Si transistor (a transistor formed on a single-crystal silicon substrate).

[0056] The metal oxide used in the channel formation region of the OS transistor is preferably an oxide semiconductor containing at least one of indium (In) and zinc (Zn). A typical example of such an oxide semiconductor is an In-M-Zn oxide (wherein the element M is, for example, Al, Ga, Y, or Sn). By reducing impurities such as moisture and hydrogen, which serve as electron donors (donors), and by reducing oxygen vacancies, the oxide semiconductor can be made i-type (intrinsic) or substantially i-type. Such an oxide semiconductor can be called a highly purified oxide semiconductor. Details of the OS transistor will be described in Embodiments 2 and 3.

[0057] For example, the channel formation region of the transistor T11 can be made of a metal oxide containing any one of indium, element M (element M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.), and zinc. In particular, a metal oxide containing indium, gallium, and zinc is preferable.

[0058] The OS transistor also has a gate insulating film between the source and drain and the gate, and capacitance is formed between the source and drain and the gate. The capacitance formed between the source and drain and the gate can be used as a capacitor. The capacitance formed between the source and drain and the gate varies depending on the voltage Vgs of the gate relative to the source. Hereinafter, the voltage Vgs of the gate relative to the source will be referred to as voltage Vgs, and the capacitance formed between the source and drain and the gate will be referred to as capacitance Cgsd.

[0059] 2A is a conceptual diagram showing the relationship between voltage Vgs and capacitance Cgsd. As shown in FIG. 2A, capacitance Cgsd is almost constant when voltage Vgs is low, but increases when voltage Vgs is near the threshold voltage Vth of transistor T11 and above. The relationship between voltage Vgs and capacitance Cgsd in an OS transistor is similar to the relationship between voltage Vgs and capacitance Cgsd in a silicon-based MOS (Metal Oxide Semiconductor) FET (Field Effect Transistor). However, the OS transistor has a feature in which the amount of change in capacitance Cgsd is greater than that in a silicon-based MOS FET.

[0060] <Matching circuit configuration example 2> The transistor T11 may have a back gate. Fig. 2B is a circuit diagram showing an example configuration of a matching circuit 40 using a transistor T15 having a back gate. The matching circuit 40 is a modified example of the matching circuit 10, and to avoid repetition of explanation, differences from the matching circuit 10 will be mainly described.

[0061] The matching circuit 40 includes a transistor T15, an inductor L12, a line BKL, an input terminal VDD_IN, an input terminal SII_IN, and an output terminal SIO_OUT. The transistor T15 has a back gate in addition to a source, a drain, and a gate, and the back gate of the transistor T15 is electrically connected to the line BKL. The line BKL functions as a line for applying a predetermined potential to the back gate of the transistor T15, and applying an arbitrary potential to the line BKL can increase or decrease the threshold voltage of the transistor T15.

[0062] 2C is a circuit diagram showing an example configuration of matching circuit 50 using transistor T15 having a back gate. Matching circuit 50 is a modified example of matching circuit 10, and to avoid repetition of explanation, differences from matching circuit 10 will be mainly described.

[0063] The matching circuit 50 includes a transistor T15, an inductor L12, an input terminal VDD_IN, an input terminal SII_IN, and an output terminal SIO_OUT. The transistor T15 has a back gate in addition to a source, a drain, and a gate, and the back gate of the transistor T15 is electrically connected to the gate of the transistor T15, the first terminal of the inductor L12, and the output terminal SIO_OUT.

[0064] In the matching circuit 50, by electrically connecting the back gate of the transistor T15 to the gate of the transistor T15, the capacitance formed between the source / drain and the back gate can be used as a capacitor in addition to the capacitance formed between the source / drain and the gate, which increases the capacitance formed by the transistor T15.

[0065] The inductor L12 may be, for example, a coil. In particular, a coil for use in a high-frequency circuit, having an air-core structure and a high Q value (Quality Factor), is preferred. The coil that can be used for the inductor L12 may be configured using wiring or the like included in the semiconductor device, as described in the second embodiment.

[0066] <Matching circuit> In this embodiment, an L-type matching circuit 10 using a transistor and an inductor has been described. The capacitance formed between the source and drain of the transistor and the gate changes depending on the voltage of the gate relative to the source, so by changing the potential difference between the potential VDD and the potential Vref in the matching circuit 10, the matching circuit 10 can accommodate a plurality of frequencies.

[0067] That is, when the output impedance of device 20 and the input impedance of device 30 are matched using matching circuit 10 for an AC signal of a certain frequency (or period), even if the frequency of the AC signal changes, the impedance matching can be maintained by changing the potential difference between potential VDD and potential Vref in matching circuit 10. Alternatively, when the output impedance of device 20 and the input impedance of device 30 are matched using matching circuit 10 for an AC signal of a certain frequency, even if the frequency of the AC signal changes, it is not necessary to replace the components that make up matching circuit 10.

[0068] Furthermore, by using an OS transistor in matching circuit 10, the amount of change in capacitance Cgsd with respect to voltage Vgs of an OS transistor is large, and therefore matching circuit 10 can accommodate AC signals over a wide frequency range. Note that although the L-type matching circuit 10 has been described in this embodiment, the present invention can also be applied to other types of matching circuits, such as T-type and π-type.

[0069] Note that this embodiment mode can be implemented in appropriate combination with other embodiment modes described in this specification.

[0070] (Embodiment 2) In this embodiment, a structural example of a transistor constituting the matching circuit 10 described in the above embodiment will be described. Note that the OS transistor described in this embodiment has a structure in which it is stacked above a transistor formed on a semiconductor substrate. In addition, a capacitor (referred to as a capacitive element in this embodiment) is stacked above the OS transistor described in this embodiment. In this embodiment, the transistor, OS transistor, and capacitive element formed on the semiconductor substrate will be collectively referred to as a semiconductor device.

[0071] That is, matching circuit 10 may be fabricated on the same semiconductor substrate as device 20, device 30, or both of them described in the above embodiments. In this case, the "terminals" such as input terminals and output terminals described in the above embodiments may not be distinguishable from wiring, electrodes, etc.

[0072] The OS transistor described in this embodiment has a back gate (also referred to as a second gate or a bottom gate) in addition to a gate (also referred to as a first gate, a top gate, or a front gate).

[0073] <Configuration example of semiconductor device> 3 includes a transistor 300, a transistor 500, and a capacitor 600. Fig. 4A is a cross-sectional view of the transistor 500 in the channel length direction, Fig. 4B is a cross-sectional view of the transistor 500 in the channel width direction, and Fig. 4C is a cross-sectional view of the transistor 300 in the channel width direction.

[0074] The transistor 500 is an OS transistor having a metal oxide in a channel formation region. The transistor 500 is characterized by a large change in capacitance Cgsd between the gate voltage Vgs relative to the source and the capacitance Cgsd formed between the source, drain, and gate. Therefore, in the above embodiment, by using the transistor 500 in the matching circuit 10, the matching circuit 10 can support AC signals over a wide frequency range.

[0075] As shown in FIG. 3, in the semiconductor device described in this embodiment, the transistor 500 is provided above the transistor 300, and the capacitor 600 is provided above the transistors 300 and 500.

[0076] The transistor 300 is provided on a substrate 311 and includes a conductor 316, an insulator 315, a semiconductor region 313 made of part of the substrate 311, and low-resistance regions 314a and 314b that function as source and drain regions.

[0077] 4C , the upper surface and the side surfaces in the channel width direction of the semiconductor region 313 of the transistor 300 are covered with a conductor 316 via an insulator 315. By forming the transistor 300 as a fin type in this way, the effective channel width is increased, thereby improving the on-state characteristics of the transistor 300. Furthermore, the contribution of the electric field of the gate electrode can be increased, thereby improving the off-state characteristics of the transistor 300.

[0078] For example, a single crystal silicon substrate can be used as the substrate 311, and a Si transistor formed on the single crystal silicon substrate can be used as the transistor 300. Note that the transistor 300 may be either a p-channel type or an n-channel type.

[0079] The region where the channel of the semiconductor region 313 is formed, the region nearby, the low-resistance region 314a that serves as the source region or drain region, and the low-resistance region 314b preferably contain a semiconductor such as a silicon-based semiconductor, and preferably contain single-crystal silicon. Alternatively, they may be formed of a material containing Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), or the like. A configuration using silicon in which the effective mass is controlled by applying stress to the crystal lattice and changing the lattice spacing may also be used. Alternatively, the transistor 300 may be a HEMT (High Electron Mobility Transistor) by using GaAs and GaAlAs, or the like.

[0080] The low resistance region 314a and the low resistance region 314b contain, in addition to the semiconductor material applied to the semiconductor region 313, an element that imparts n-type conductivity, such as arsenic or phosphorus, or an element that imparts p-type conductivity, such as boron.

[0081] The conductor 316 functioning as the gate electrode can be made of a conductive material such as a semiconductor material, metal material, alloy material, or metal oxide material, such as silicon containing an element that imparts n-type conductivity, such as arsenic or phosphorus, or an element that imparts p-type conductivity, such as boron.

[0082] Since the work function is determined by the conductor material, the Vth of the transistor can be adjusted by changing the conductor material. Specifically, it is preferable to use materials such as titanium nitride and tantalum nitride for the conductor. Furthermore, in order to achieve both conductivity and embeddability, it is preferable to use a metal material such as tungsten or aluminum laminated on the conductor, and tungsten is particularly preferable in terms of heat resistance.

[0083] Note that the transistor 300 illustrated in FIG. 3 is just an example, and the structure is not limited to this example. An appropriate transistor may be used depending on the circuit configuration and driving method.

[0084] An insulator 320, an insulator 322, an insulator 324, and an insulator 326 are stacked in this order over the transistor 300.

[0085] The insulators 320, 322, 324, and 326 can be made of, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like.

[0086] The insulator 322 may function as a planarizing film that flattens steps caused by the transistor 300 or the like provided thereunder. For example, the top surface of the insulator 322 may be planarized by planarization treatment using a chemical mechanical polishing (CMP) method or the like to improve the flatness.

[0087] The insulator 324 is preferably a film having a barrier property that prevents hydrogen or impurities from diffusing from the substrate 311 or the transistor 300 to a region where the transistor 500 is provided.

[0088] An example of a film having a barrier property against hydrogen is silicon nitride formed by a CVD method. Here, hydrogen diffusion into a semiconductor element having an oxide semiconductor, such as the transistor 500, may degrade the characteristics of the semiconductor element. Therefore, it is preferable to use a film that suppresses hydrogen diffusion between the transistor 500 and the transistor 300. Specifically, the film that suppresses hydrogen diffusion is a film that releases a small amount of hydrogen.

[0089] The amount of desorbed hydrogen can be analyzed using, for example, thermal desorption spectroscopy (TDS analysis). For example, the amount of desorbed hydrogen from the insulator 324 is calculated as 10×10 per area of the insulator 324 when the surface temperature of the film is in the range of 50° C. to 500° C. in TDS analysis. 15 atoms / cm 2 Less than or equal to 5 x 10 15 atoms / cm2 The following is fine.

[0090] It is preferable that the insulator 326 has a lower dielectric constant than the insulator 324. For example, the relative dielectric constant of the insulator 326 is preferably less than 4, and more preferably less than 3. Furthermore, for example, the relative dielectric constant of the insulator 326 is preferably 0.7 times or less, and more preferably 0.6 times or less, the relative dielectric constant of the insulator 324. By using a material with a low relative dielectric constant as the interlayer film, the parasitic capacitance that occurs between wirings can be reduced.

[0091] Conductors 328 and 330, which connect to the capacitor 600 or the transistor 500, are embedded in the insulators 320, 322, 324, and 326. The conductors 328 and 330 function as plugs or wiring. A plurality of conductors that function as plugs or wiring may be collectively denoted by the same reference numeral. In this specification and the like, a wiring and a plug connected to the wiring may be integral. That is, a portion of a conductor may function as a wiring, and a portion of a conductor may function as a plug.

[0092] The materials for each plug and wiring (such as the conductor 328 and the conductor 330) can be a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material, and can be used in a single layer or a laminated layer. High-melting-point materials such as tungsten and molybdenum, which have both heat resistance and conductivity, are preferably used, and tungsten is preferred. Alternatively, they are preferably formed from a low-resistance conductive material such as aluminum or copper. The use of a low-resistance conductive material can reduce the wiring resistance.

[0093] A wiring layer may be provided over the insulator 326 and the conductor 330. For example, in FIG. 3, the insulator 350, the insulator 352, and the insulator 354 are stacked in this order. The conductor 356 is formed in the insulator 350, the insulator 352, and the insulator 354. The conductor 356 functions as a plug or wiring connected to the transistor 300. Note that the conductor 356 can be formed using a material similar to that of the conductor 328 and the conductor 330.

[0094] Note that, for example, the insulator 350 preferably uses an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 356 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 350 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0095] Note that, for example, tantalum nitride or the like is preferably used as the conductor having a barrier property against hydrogen. Stacking tantalum nitride and highly conductive tungsten can suppress diffusion of hydrogen from the transistor 300 while maintaining the conductivity of the wiring. In this case, a structure in which the tantalum nitride layer having a barrier property against hydrogen is in contact with the insulator 350 having a barrier property against hydrogen is preferable.

[0096] A wiring layer may be provided over the insulator 354 and the conductor 356. For example, in FIG. 3, the insulator 360, the insulator 362, and the insulator 364 are stacked in this order. The conductor 366 is formed in the insulator 360, the insulator 362, and the insulator 364. The conductor 366 functions as a plug or a wiring. The conductor 366 can be formed using the same material as the conductor 328 and the conductor 330.

[0097] Note that, for example, the insulator 360 preferably uses an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 366 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 360 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0098] A wiring layer may be provided over the insulator 364 and the conductor 366. For example, in FIG. 3, an insulator 370, an insulator 372, and an insulator 374 are stacked in this order. A conductor 376 is formed in the insulator 370, the insulator 372, and the insulator 374. The conductor 376 functions as a plug or a wiring. The conductor 376 can be formed using a material similar to that of the conductor 328 and the conductor 330.

[0099] Note that, for example, the insulator 370 preferably uses an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 376 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 370 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0100] A wiring layer may be provided over the insulator 374 and the conductor 376. For example, in FIG. 3, an insulator 380, an insulator 382, and an insulator 384 are stacked in this order. A conductor 386 is formed in the insulator 380, the insulator 382, and the insulator 384. The conductor 386 functions as a plug or a wiring. The conductor 386 can be formed using a material similar to that of the conductor 328 and the conductor 330.

[0101] Note that, for example, the insulator 380 preferably uses an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 386 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 380 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0102] Although the above describes a wiring layer including the conductor 356, a wiring layer including the conductor 366, a wiring layer including the conductor 376, and a wiring layer including the conductor 386, the semiconductor device according to this embodiment is not limited to this. There may be three or fewer wiring layers similar to the wiring layer including the conductor 356, or there may be five or more wiring layers similar to the wiring layer including the conductor 356.

[0103] An insulator 510, an insulator 512, an insulator 514, and an insulator 516 are stacked in this order on the insulator 384. Any of the insulator 510, the insulator 512, the insulator 514, and the insulator 516 is preferably made of a substance that has a barrier property against oxygen and hydrogen.

[0104] For example, the insulator 510 and the insulator 514 are preferably formed using a film having a barrier property that prevents hydrogen or impurities from diffusing from the substrate 311 or a region where the transistor 300 is provided to a region where the transistor 500 is provided. Therefore, a material similar to that of the insulator 324 can be used.

[0105] An example of a film having a barrier property against hydrogen is silicon nitride formed by a CVD method. Here, hydrogen diffusion into a semiconductor element having an oxide semiconductor, such as the transistor 500, may degrade the characteristics of the semiconductor element. Therefore, it is preferable to use a film that suppresses hydrogen diffusion between the transistor 500 and the transistor 300. Specifically, the film that suppresses hydrogen diffusion is a film that releases a small amount of hydrogen.

[0106] As a film having a barrier property against hydrogen, for example, the insulators 510 and 514 are preferably made of a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide.

[0107] In particular, aluminum oxide has a high blocking effect against both oxygen and impurities such as hydrogen and moisture, which can cause fluctuations in the electrical characteristics of a transistor. Therefore, aluminum oxide can prevent impurities such as hydrogen and moisture from entering the transistor 500 during and after the transistor manufacturing process. Furthermore, aluminum oxide can suppress the release of oxygen from the oxide that constitutes the transistor 500. Therefore, aluminum oxide is suitable for use as a protective film for the transistor 500.

[0108] For example, the insulator 512 and the insulator 516 can be formed using a material similar to that of the insulator 320. Using a material with a relatively low dielectric constant as an interlayer film can reduce parasitic capacitance between wirings. For example, the insulator 512 and the insulator 516 can be formed using a silicon oxide film, a silicon oxynitride film, or the like.

[0109] A conductor 518, a conductor constituting the transistor 500 (the conductor 503), and the like are embedded in the insulators 510, 512, 514, and 516. The conductor 518 functions as a plug or wiring connected to the capacitor 600 or the transistor 300. The conductor 518 can be formed using a material similar to that of the conductor 328 and the conductor 330.

[0110] In particular, the conductor 518 in the region in contact with the insulator 510 and the insulator 514 is preferably a conductor having a barrier property against oxygen, hydrogen, and water. With this structure, the transistor 300 and the transistor 500 can be separated by a layer having a barrier property against oxygen, hydrogen, and water, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0111] Above the insulator 516 is the transistor 500 .

[0112] As shown in FIGS. 4A and 4B, the transistor 500 includes a conductor 503 disposed so as to be embedded in an insulator 514 and an insulator 516, an insulator 520 disposed on the insulator 516 and the conductor 503, an insulator 522 disposed on the insulator 520, an insulator 524 disposed on the insulator 522, an oxide 530a disposed on the insulator 524, an oxide 530b disposed on the oxide 530a, conductors 542a disposed apart from each other on the oxide 530b, and and conductor 542b, an insulator 580 disposed on conductor 542a and conductor 542b and having an opening formed thereon overlapping between conductor 542a and conductor 542b, a conductor 560 disposed in the opening, an insulator 550 disposed among oxide 530b, conductor 542a, conductor 542b, and insulator 580, and conductor 560, and an oxide 530c disposed among oxide 530b, conductor 542a, conductor 542b, insulator 580, and insulator 550.

[0113] 4A and 4B, it is preferable that insulator 544 be disposed between oxide 530a, oxide 530b, conductor 542a, and conductor 542b and insulator 580. It is preferable that conductor 560 include conductor 560a disposed inside insulator 550 and conductor 560b disposed so as to be embedded inside conductor 560a. It is preferable that insulator 574 be disposed on insulator 580, conductor 560, and insulator 550, as shown in FIGS.

[0114] In the following, the oxide 530a, the oxide 530b, and the oxide 530c may be collectively referred to as the oxide 530. The conductor 542a and the conductor 542b may be collectively referred to as the conductor 542.

[0115] Although the transistor 500 has a three-layer structure including oxides 530a, 530b, and 530c in and around a channel region, the present invention is not limited to this structure. For example, the oxide 530 may have a four-layer or more layer structure. Although the conductor 560 has a two-layer structure in the transistor 500, the present invention is not limited to this structure. For example, the conductor 560 may have a single-layer structure or a three-layer or more layer structure. The transistor 500 shown in FIGS. 3, 4A, and 4B is merely an example, and the transistor is not limited to this structure. An appropriate transistor may be used depending on the circuit configuration and driving method.

[0116] Here, the conductor 560 functions as the gate electrode of the transistor, and the conductors 542a and 542b function as the source and drain electrodes, respectively. As described above, the conductor 560 is formed so as to be embedded in the opening of the insulator 580 and in the region sandwiched between the conductors 542a and 542b. The arrangement of the conductors 560, 542a, and 542b is selected in a self-aligned manner with respect to the opening of the insulator 580. That is, in the transistor 500, the gate electrode can be positioned between the source and drain electrodes in a self-aligned manner. Therefore, the conductor 560 can be formed without providing a margin for alignment, thereby reducing the area occupied by the transistor 500. This allows for miniaturization and high integration of semiconductor devices.

[0117] Furthermore, since the conductor 560 is formed in a self-aligned manner in the region between the conductor 542a and the conductor 542b, the conductor 560 does not have a region that overlaps with the conductor 542a or the conductor 542b. This reduces the parasitic capacitance formed between the conductor 560 and the conductor 542a and between the conductor 560 and the conductor 542b. This improves the switching speed of the transistor 500 and provides high frequency characteristics.

[0118] The conductor 560 may function as a first gate electrode. The conductor 503 may function as a second gate electrode. In this case, the Vth of the transistor 500 can be controlled by changing the potential applied to the conductor 503 independently of the potential applied to the conductor 560. In particular, applying a negative potential to the conductor 503 can increase the Vth of the transistor 500 above 0 V and reduce the off-state current. Therefore, applying a negative potential to the conductor 503 can reduce the drain current when the potential applied to the conductor 560 is 0 V compared to not applying a negative potential to the conductor 503.

[0119] The conductor 503 is arranged to overlap the oxide 530 and the conductor 560. In this way, when a potential is applied to the conductor 560 and the conductor 503, the electric field generated from the conductor 560 and the electric field generated from the conductor 503 are connected, and a channel formation region formed in the oxide 530 can be covered. In this specification and the like, a transistor structure in which the channel formation region is electrically surrounded by the electric fields of the first gate electrode and the second gate electrode is called a surrounded channel (S-channel) structure.

[0120] Furthermore, in this specification, the S-channel structure is characterized in that the side surfaces and peripheries of the oxide 530 in contact with the conductors 542a and 542b, which function as source and drain electrodes, are I-type, just like the channel formation region. Furthermore, the side surfaces and peripheries of the oxide 530 in contact with the conductors 542a and 542b are in contact with the insulator 544, so they can be I-type, just like the channel formation region. Note that in this specification, I-type can be treated as the same as high-purity intrinsic oxide, as described later. The S-channel structure disclosed in this specification differs from the fin structure and planar structure. The S-channel structure enhances resistance to the short-channel effect, in other words, makes it possible to create a transistor that is less susceptible to the short-channel effect.

[0121] Conductor 503 has the same configuration as conductor 518, with conductor 503a being formed in contact with the inner walls of the openings of insulators 514 and 516, and conductor 503b being formed further inside.

[0122] The insulators 520, 522, 524, and 550 function as gate insulating films.

[0123] Here, the insulator 524 in contact with the oxide 530 preferably contains more oxygen than the oxygen required for the stoichiometric composition. That is, an excess oxygen region is preferably formed in the insulator 524. By providing such an insulator containing excess oxygen in contact with the oxide 530, oxygen vacancies in the oxide 530 can be reduced and the reliability of the transistor 500 can be improved.

[0124] Specifically, it is preferable to use an oxide material from which a portion of oxygen is released by heating as an insulator having an excess oxygen region. The oxide material from which oxygen is released by heating is an oxide material from which the amount of released oxygen converted to oxygen atoms is 1.0 × 10 in TDS (Thermal Desorption Spectroscopy) analysis. 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 or more, or 3.0 x 10 20 atoms / cm 3 The oxide film is one having the above properties. The surface temperature of the film during the TDS analysis is preferably in the range of 100°C or higher and 700°C or lower, or 100°C or higher and 400°C or lower.

[0125] When the insulator 524 has an excess oxygen region, the insulator 522 preferably has a function of suppressing the diffusion of oxygen (for example, oxygen atoms, oxygen molecules, etc.) (preferably making the oxygen less permeable).

[0126] The insulator 522 preferably has a function of suppressing diffusion of oxygen and impurities, which prevents oxygen contained in the oxide 530 from diffusing toward the insulator 520. Furthermore, reaction of the conductor 503 with oxygen contained in the insulator 524 or the oxide 530 can be suppressed.

[0127] The insulator 522 is preferably a single layer or multilayer insulator containing, for example, aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3 (BST). As transistors become smaller and more highly integrated, thinner gate insulating films can cause problems such as leakage current. Using a high-k material for the insulator that functions as the gate insulating film makes it possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

[0128] In particular, an insulator containing an oxide of one or both of aluminum and hafnium, which is an insulating material that has the function of suppressing the diffusion of impurities and oxygen (i.e., is difficult for oxygen to permeate), is preferably used. Aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate) is preferably used as the insulator containing an oxide of one or both of aluminum and hafnium. When the insulator 522 is formed using such a material, the insulator 522 functions as a layer that suppresses oxygen release from the oxide 530 and the intrusion of impurities such as hydrogen into the oxide 530 from the periphery of the transistor 500.

[0129] Alternatively, for example, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide may be added to these insulators. Alternatively, these insulators may be nitrided. Silicon oxide, silicon oxynitride, or silicon nitride may be stacked on the above insulators.

[0130] Furthermore, it is preferable that the insulator 520 be thermally stable. For example, silicon oxide and silicon oxynitride are suitable because they are thermally stable. Furthermore, by combining a high-k insulator with silicon oxide or silicon oxynitride, it is possible to obtain the insulator 520 having a thermally stable layered structure with a high dielectric constant.

[0131] The insulators 520, 522, and 524 may each have a stacked structure of two or more layers. In this case, the stacked structures are not limited to those made of the same material, and may be those made of different materials.

[0132] In the transistor 500, a metal oxide functioning as an oxide semiconductor is preferably used for the oxide 530 including the channel formation region. For example, a metal oxide such as In-M-Zn oxide (wherein the element M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.) may be used for the oxide 530. Alternatively, an In-Ga oxide or an In-Zn oxide may be used for the oxide 530.

[0133] The metal oxide functioning as an oxide semiconductor may be formed by a sputtering method or an atomic layer deposition (ALD) method. The metal oxide functioning as an oxide semiconductor will be described in other embodiments.

[0134] Furthermore, it is preferable to use a metal oxide with a low carrier density for the transistor 500. To reduce the carrier density of a metal oxide, the impurity concentration in the metal oxide may be reduced to reduce the density of defect states. In this specification and the like, a low impurity concentration and a low density of defect states are referred to as high-purity intrinsic or substantially high-purity intrinsic. Examples of impurities in metal oxides include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, and silicon.

[0135] In particular, hydrogen contained in metal oxide reacts with oxygen bonded to metal atoms to form water, which can form oxygen vacancies in the metal oxide. If oxygen vacancies are present in the channel formation region of a metal oxide, the transistor may exhibit normally-on characteristics. Furthermore, defects in which hydrogen has entered the oxygen vacancies can function as donors, generating electrons as carriers. Furthermore, some of the hydrogen may bond with oxygen bonded to metal atoms to generate electrons as carriers. Therefore, transistors using metal oxides containing a large amount of hydrogen tend to exhibit normally-on characteristics.

[0136] Defects in which hydrogen has entered oxygen vacancies can function as donors for metal oxides. However, it is difficult to quantitatively evaluate such defects. Therefore, metal oxides are sometimes evaluated using carrier density rather than donor concentration. Therefore, in this specification and the like, carrier density assuming a state in which no electric field is applied may be used as a parameter for metal oxides, rather than donor concentration. In other words, the "carrier density" described in this specification and the like may sometimes be rephrased as "donor concentration."

[0137] Therefore, when a metal oxide is used for the oxide 530, it is preferable that the hydrogen in the metal oxide is reduced as much as possible. Specifically, in the metal oxide, the hydrogen concentration obtained by secondary ion mass spectrometry (SIMS) is set to 1×10 20 atoms / cm 3 Less than 1 x 10 19 atoms / cm 3 less than 5 × 10 18 atoms / cm 3 less than 1×10 18 atoms / cm 3 By using a metal oxide in which impurities such as hydrogen are sufficiently reduced for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0138] When a metal oxide is used for the oxide 530, the carrier density of the metal oxide in the channel formation region is 1×10 18 cm -3 Preferably, it is 1×10 or less. 17 cm -3 More preferably, it is less than 1×10 16 cm -3 More preferably, it is less than 1×10 13 cm -3 More preferably, it is less than 1×10 12 cm -3 The lower limit of the carrier density of the metal oxide in the channel formation region is not particularly limited, but is preferably, for example, 1×10 -9 cm -3 It can be said that:

[0139] Furthermore, when a metal oxide is used for the oxide 530, contact between the conductor 542 (conductor 542a and conductor 542b) and the oxide 530 may cause oxygen in the oxide 530 to diffuse into the conductor 542, resulting in the oxidation of the conductor 542. The oxidation of the conductor 542 is likely to result in a decrease in the conductivity of the conductor 542. The diffusion of oxygen in the oxide 530 into the conductor 542 can be rephrased as the conductor 542 absorbing the oxygen in the oxide 530.

[0140] Furthermore, oxygen in the oxide 530 may diffuse into the conductor 542 (conductor 542a and conductor 542b), forming a heterogeneous layer between the conductor 542a and the oxide 530b and between the conductor 542b and the oxide 530b. Since the heterogeneous layer contains more oxygen than the conductor 542, it is presumed that the heterogeneous layer has insulating properties. In this case, the three-layer structure of the conductor 542, the heterogeneous layer, and the oxide 530b can be regarded as a three-layer structure consisting of a metal, an insulator, and a semiconductor, and may be called an MIS (Metal-Insulator-Semiconductor) structure or a diode junction structure mainly based on the MIS structure.

[0141] It should be noted that the above-mentioned different layer is not limited to being formed between the conductor 542 and the oxide 530b, and for example, the different layer may be formed between the conductor 542 and the oxide 530c, between the conductor 542 and the oxide 530b, and between the conductor 542 and the oxide 530c.

[0142] The metal oxide that functions as a channel formation region in the oxide 530 preferably has a band gap of 2 eV or more, preferably 2.5 eV or more. By using a metal oxide with a wide band gap, the off-state current of the transistor can be reduced.

[0143] In addition, the semiconductor material that can be used for the oxide 530 is not limited to the above-mentioned metal oxides. A semiconductor material having a band gap (a semiconductor material that is not a zero-gap semiconductor) may also be used for the oxide 530. For example, a semiconductor of a simple element such as silicon, a compound semiconductor such as gallium arsenide, or a layered material that functions as a semiconductor (also called an atomic layer material or a two-dimensional material) is preferably used as the semiconductor material. In particular, a layered material that functions as a semiconductor is preferably used as the semiconductor material.

[0144] In this specification and the like, a layered material is a general term for a group of materials having a layered crystal structure. A layered crystal structure is a structure in which layers formed by covalent bonds or ionic bonds are stacked via bonds weaker than covalent bonds or ionic bonds, such as van der Waals forces. A layered material has high electrical conductivity within a unit layer, that is, high two-dimensional electrical conductivity. By using a material that functions as a semiconductor and has high two-dimensional electrical conductivity in the channel formation region, a transistor with a large on-current can be provided.

[0145] Layered materials include graphene, silicene, and chalcogenides. Chalcogenides are compounds containing chalcogen. Chalcogen is a general term for elements in Group 16, including oxygen, sulfur, selenium, tellurium, polonium, and livermorium. Chalcogenides also include transition metal chalcogenides and Group 13 chalcogenides.

[0146] It is preferable to use, for example, a transition metal chalcogenide that functions as a semiconductor as the oxide 530. Specific examples of transition metal chalcogenides that can be used as the oxide 530 include molybdenum sulfide (typically MoS2), molybdenum selenide (typically MoSe2), molybdenum tellurium (typically MoTe2), tungsten sulfide (typically WS2), tungsten selenide (typically WSe2), tungsten tellurium (typically WTe2), hafnium sulfide (typically HfS2), hafnium selenide (typically HfSe2), zirconium sulfide (typically ZrS2), and zirconium selenide (typically ZrSe2).

[0147] The oxide 530 has the oxide 530a below the oxide 530b, which can prevent impurities from diffusing from structures formed below the oxide 530a to the oxide 530b. Also, the oxide 530 has the oxide 530c on the oxide 530b, which can prevent impurities from diffusing from structures formed above the oxide 530c to the oxide 530b.

[0148] The oxide 530 preferably has a stacked structure of multiple oxide layers with different atomic ratios of the metal atoms. Specifically, the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530a is preferably greater than the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. The atomic ratio of the element M to In in the metal oxide used for the oxide 530a is preferably greater than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. The atomic ratio of In to M in the metal oxide used for the oxide 530b is preferably greater than the atomic ratio of In to M in the metal oxide used for the oxide 530a. The oxide 530c can be the same metal oxide as that used for the oxide 530a or the oxide 530b.

[0149] The oxides 530a and 530c preferably have a conduction band minimum energy higher than that of the oxide 530b, and the oxides 530a and 530c preferably have a lower electron affinity than that of the oxide 530b.

[0150] Here, the energy level of the conduction band minimum changes smoothly at the junction between the oxides 530a, 530b, and 530c. In other words, the energy level of the conduction band minimum at the junction between the oxides 530a, 530b, and 530c changes continuously or forms a continuous junction. To achieve this, it is preferable to reduce the defect level density of the mixed layers formed at the interface between the oxides 530a and 530b and at the interface between the oxides 530b and 530c.

[0151] Specifically, when the oxides 530a and 530b, and the oxides 530b and 530c, contain a common element (main component) other than oxygen, a mixed layer with a low density of defect states can be formed. For example, when the oxide 530b is an In-Ga-Zn oxide, the oxides 530a and 530c may be made of an In-Ga-Zn oxide, a Ga-Zn oxide, or a gallium oxide.

[0152] In this case, the oxide 530b serves as the main carrier path. By configuring the oxide 530a and the oxide 530c as described above, the defect state density at the interface between the oxide 530a and the oxide 530b and at the interface between the oxide 530b and the oxide 530c can be reduced. This reduces the effect of interface scattering on carrier conduction, allowing the transistor 500 to obtain a high on-state current.

[0153] Conductor 542 (conductor 542a and conductor 542b) functioning as a source electrode and a drain electrode are provided on oxide 530b. Conductor 542 is preferably made of a metal element selected from aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, or lanthanum, or an alloy containing any of the above metal elements or an alloy combining any of the above metal elements. For example, tantalum nitride, titanium nitride, tungsten, a nitride containing titanium and aluminum, a nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, an oxide containing strontium and ruthenium, or an oxide containing lanthanum and nickel is preferably used. In addition, tantalum nitride, titanium nitride, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, and oxides containing lanthanum and nickel are preferred because they are conductive materials that are resistant to oxidation or materials that maintain their conductivity even when they absorb oxygen.

[0154] 4A, a region 543 (regions 543a and 543b) may be formed as a low-resistance region at and near the interface between the oxide 530 and the conductor 542. In this case, the region 543a functions as one of a source region and a drain region, and the region 543b functions as the other of the source region and the drain region. A channel formation region is formed in the region sandwiched between the regions 543a and 543b.

[0155] Providing the conductor 542 so as to be in contact with the oxide 530 may reduce the oxygen concentration in the region 543. Also, a metal compound layer containing the metal contained in the conductor 542 and components of the oxide 530 may be formed in the region 543. In such a case, the carrier density in the region 543 increases, and the region 543 becomes a low-resistance region.

[0156] The insulator 544 is provided to cover the conductor 542 and suppresses oxidation of the conductor 542. In this case, the insulator 544 may be provided to cover the side surface of the oxide 530 and to be in contact with the insulator 524.

[0157] The insulator 544 can be a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, or the like.

[0158] In particular, it is preferable to use, as the insulator 544, an insulator containing an oxide of either or both of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate). Hafnium aluminate is particularly preferable because it has higher heat resistance than hafnium oxide film. Therefore, it is less likely to crystallize during heat treatment in a later process. Note that if the conductor 542 is made of a material that is resistant to oxidation or does not significantly decrease in conductivity even when it absorbs oxygen, the insulator 544 is not an essential component. It can be designed appropriately depending on the desired transistor characteristics.

[0159] The insulator 550 functions as a gate insulating film. The insulator 550 is preferably disposed in contact with the inside (top and side surfaces) of the oxide 530c. The insulator 550 is preferably formed using an insulator that releases oxygen when heated. For example, in TDS analysis, the amount of released oxygen converted into oxygen atoms is 1.0×10 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 or more, or 3.0 x 10 20 atoms / cm 3 The oxide film is as described above. The surface temperature of the film during the TDS analysis is preferably in the range of 100°C or higher and 700°C or lower.

[0160] Specifically, silicon oxide having excess oxygen, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, and silicon oxide having vacancies can be used. In particular, silicon oxide and silicon oxynitride are preferable because they are stable against heat.

[0161] By providing the insulator 550, which releases oxygen upon heating, in contact with the top surface of the oxide 530c, oxygen can be effectively supplied from the insulator 550 to the channel formation region of the oxide 530b through the oxide 530c. Similarly to the insulator 524, the insulator 550 preferably has a low concentration of impurities such as water or hydrogen. The thickness of the insulator 550 is preferably 1 nm to 20 nm.

[0162] Furthermore, a metal oxide may be provided between the insulator 550 and the conductor 560 to efficiently supply excess oxygen contained in the insulator 550 to the oxide 530. The metal oxide preferably suppresses oxygen diffusion from the insulator 550 to the conductor 560. By providing a metal oxide that suppresses oxygen diffusion, the diffusion of excess oxygen from the insulator 550 to the conductor 560 is suppressed. In other words, a decrease in the amount of excess oxygen supplied to the oxide 530 can be suppressed. Furthermore, oxidation of the conductor 560 due to excess oxygen can be suppressed. As the metal oxide, a material that can be used for the insulator 544 may be used.

[0163] The conductor 560 functioning as the first gate electrode is shown as having a two-layer structure in FIGS. 4A and 4B, but may have a single-layer structure or a laminated structure of three or more layers.

[0164] Conductor 560a is preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (NO, NO, NO, etc.), and copper atoms. Alternatively, conductive material that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.) is preferably used. Conductor 560a has the function of suppressing the diffusion of oxygen, which can suppress the oxidation of conductor 560b due to oxygen contained in insulator 550, thereby preventing a decrease in conductivity. As a conductive material that has the function of suppressing the diffusion of oxygen, for example, tantalum, tantalum nitride, ruthenium, or ruthenium oxide is preferably used.

[0165] The conductor 560b is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. Because the conductor 560b also functions as wiring, it is preferable to use a conductor with high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. The conductor 560b may have a layered structure, such as a layered structure of titanium or titanium nitride and the above-mentioned conductive material.

[0166] The insulator 580 is provided on the conductor 542 with the insulator 544 interposed therebetween. The insulator 580 preferably has an excess oxygen region. For example, the insulator 580 preferably includes silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide doped with fluorine, silicon oxide doped with carbon, silicon oxide doped with carbon and nitrogen, silicon oxide having voids, or a resin. Silicon oxide and silicon oxynitride are particularly preferred because they are thermally stable. Silicon oxide and silicon oxide having voids are particularly preferred because they allow for easy formation of an excess oxygen region in a later step.

[0167] Furthermore, by providing the insulator 580, which releases oxygen when heated, in contact with the oxide 530c, oxygen in the insulator 580 can be efficiently supplied to the oxide 530 through the oxide 530c. Note that the concentration of impurities such as water or hydrogen in the insulator 580 is preferably reduced.

[0168] The opening of the insulator 580 is formed to overlap the region between the conductor 542a and the conductor 542b, so that the conductor 560 is formed to be embedded in the opening of the insulator 580 and the region sandwiched between the conductor 542a and the conductor 542b.

[0169] When miniaturizing semiconductor devices, it is necessary to shorten the gate length, but it is also necessary to prevent the conductivity of the conductor 560 from decreasing. If the film thickness of the conductor 560 is increased to achieve this, the conductor 560 may have a shape with a high aspect ratio. In this embodiment, the conductor 560 is provided so as to be embedded in the opening of the insulator 580. Therefore, even if the conductor 560 has a shape with a high aspect ratio, the conductor 560 can be formed without collapsing during the process.

[0170] The insulator 574 is preferably provided in contact with the top surface of the insulator 580, the top surface of the conductor 560, and the top surface of the insulator 550. By forming the insulator 574 by a sputtering method, excess oxygen regions can be provided in the insulator 550 and the insulator 580. This allows oxygen to be supplied from the excess oxygen regions into the oxide 530.

[0171] For example, the insulator 574 can be a metal oxide containing one or more selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like.

[0172] In particular, aluminum oxide has high barrier properties and can suppress the diffusion of hydrogen and nitrogen even when it is a thin film with a thickness of 0.5 nm to 3.0 nm. Therefore, aluminum oxide formed by sputtering can function as both an oxygen source and a barrier film against impurities such as hydrogen.

[0173] An insulator 581 functioning as an interlayer film is preferably provided over the insulator 574. Like the insulator 524, the insulator 581 preferably has a reduced concentration of impurities such as water or hydrogen.

[0174] Furthermore, conductors 540a and 540b are arranged in openings formed in insulators 581, 574, 580, and 544. Conductor 540a and 540b are arranged opposite each other with conductor 560 interposed therebetween. Conductor 540a and 540b have the same configuration as conductors 546 and 548, which will be described later.

[0175] An insulator 582 is provided over the insulator 581. The insulator 582 is preferably formed using a substance that has a barrier property against oxygen and hydrogen. Therefore, the insulator 582 can be formed using a material similar to that of the insulator 514. For example, the insulator 582 is preferably formed using a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide.

[0176] In particular, aluminum oxide has a high blocking effect against both oxygen and impurities such as hydrogen and moisture, which can cause fluctuations in the electrical characteristics of a transistor. Therefore, aluminum oxide can prevent impurities such as hydrogen and moisture from entering the transistor 500 during and after the transistor manufacturing process. Furthermore, aluminum oxide can suppress the release of oxygen from the oxide that constitutes the transistor 500. Therefore, aluminum oxide is suitable for use as a protective film for the transistor 500.

[0177] An insulator 586 is provided over the insulator 582. The insulator 586 can be formed using a material similar to that of the insulator 320. Using a material with a relatively low dielectric constant as an interlayer film can reduce parasitic capacitance between wirings. For example, a silicon oxide film, a silicon oxynitride film, or the like can be used as the insulator 586.

[0178] Furthermore, conductors 546, 548, etc. are embedded in insulators 520, 522, 524, 544, 580, 574, 581, 582, and 586.

[0179] The conductor 546 and the conductor 548 function as a plug or a wiring that connects to the capacitor 600, the transistor 500, or the transistor 300. The conductor 546 and the conductor 548 can be formed using a material similar to that of the conductor 328 and the conductor 330.

[0180] Subsequently, a capacitor 600 is provided above the transistor 500. The capacitor 600 includes a conductor 610, a conductor 620, and an insulator 630.

[0181] A conductor 612 may be provided over the conductor 546 and the conductor 548. The conductor 612 functions as a plug or a wiring connected to the transistor 500. The conductor 610 functions as an electrode of the capacitor 600. Note that the conductor 612 and the conductor 610 can be formed at the same time.

[0182] A metal film containing an element selected from molybdenum, titanium, tantalum, tungsten, aluminum, copper, chromium, neodymium, and scandium, or a metal nitride film containing any of the above elements (tantalum nitride film, titanium nitride film, molybdenum nitride film, tungsten nitride film), etc. can be used for the conductor 612 and the conductor 610. Alternatively, a conductive material such as indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, or indium tin oxide with silicon oxide added can also be used.

[0183] 3, the conductor 612 and the conductor 610 are shown as single-layer structures, but are not limited to this configuration and may be a stacked structure of two or more layers. For example, a conductor having barrier properties and a conductor having high adhesion to the conductor having high conductivity may be formed between a conductor having barrier properties and a conductor having high conductivity.

[0184] The conductor 620 is provided so as to overlap with the conductor 610 with the insulator 630 interposed therebetween. Note that the conductor 620 can be made of a conductive material such as a metal material, an alloy material, or a metal oxide material. It is preferable to use a high-melting-point material such as tungsten or molybdenum that has both heat resistance and conductivity, and tungsten is particularly preferable. Furthermore, when the conductor 620 is formed simultaneously with other structures such as a conductor, a low-resistance metal material such as Cu (copper) or Al (aluminum) can be used.

[0185] An insulator 650 is provided over the conductor 620 and the insulator 630. The insulator 650 can be provided using a material similar to that of the insulator 320. The insulator 650 may also function as a planarizing film that covers the uneven shape underneath.

[0186] By using this structure, in a semiconductor device using a transistor including an oxide semiconductor, fluctuations in electrical characteristics can be suppressed and reliability can be improved. Alternatively, a transistor including an oxide semiconductor with a large on-state current can be provided. Alternatively, a transistor including an oxide semiconductor with a small off-state current can be provided. Alternatively, miniaturization or high integration of a semiconductor device using a transistor including an oxide semiconductor can be achieved.

[0187] <Example of transistor structure> Note that the transistor 500 of the semiconductor device described in this embodiment is not limited to the above structure. Structural examples that can be used for the transistor 500 are described below.

[0188] <Transistor structure example 1> An example structure of a transistor 510A will be described using Figures 5A, 5B, and 5C. Figure 5A is a top view of the transistor 510A. Figure 5B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 5A. Figure 5C is a cross-sectional view of the portion indicated by the dashed-dotted line W1-W2 in Figure 5A. Note that some elements have been omitted from the top view of Figure 5A for clarity.

[0189] 5A, 5B, and 5C show a transistor 510A and insulators 511, 512, 514, 516, 580, 582, and 584 which function as interlayer films. Also shown are a conductor 546 (conductor 546a and conductor 546b) which is electrically connected to the transistor 510A and functions as a contact plug, and a conductor 503 which functions as a wiring.

[0190] Transistor 510A has a conductor 560 (conductor 560a and conductor 560b) that functions as a first gate electrode, a conductor 505 (conductor 505a and conductor 505b) that functions as a second gate electrode, an insulator 550 that functions as a first gate insulating film, insulators 521, 522, and 524 that function as a second gate insulating film, an oxide 530 (oxide 530a, oxide 530b, and oxide 530c) that has a region where a channel is formed, a conductor 542a that functions as one of a source or a drain, a conductor 542b that functions as the other of the source or a drain, and an insulator 574.

[0191] 5, the oxide 530c, the insulator 550, and the conductor 560 are disposed in an opening in the insulator 580 with the insulator 574 interposed therebetween. The oxide 530c, the insulator 550, and the conductor 560 are disposed between the conductor 542a and the conductor 542b.

[0192] The insulators 511 and 512 function as interlayer films.

[0193] The interlayer film can be formed of a single layer or a stack of insulators such as silicon oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3 (BST). Alternatively, these insulators may contain, for example, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide. Alternatively, these insulators may be nitrided. Silicon oxide, silicon oxynitride, or silicon nitride may be stacked on the above insulators.

[0194] For example, the insulator 511 preferably functions as a barrier film that prevents impurities such as water or hydrogen from entering the transistor 510A from the substrate side. Therefore, the insulator 511 is preferably made of an insulating material that has a function of preventing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (i.e., the impurities are less likely to permeate through the insulator). Alternatively, the insulator 511 is preferably made of an insulating material that has a function of preventing the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.) (i.e., the oxygen is less likely to permeate through the insulator). Furthermore, for example, aluminum oxide or silicon nitride may be used as the insulator 511. This structure can prevent impurities such as hydrogen and water from diffusing from the substrate side toward the transistor 510A through the insulator 511.

[0195] For example, the insulator 512 preferably has a lower dielectric constant than the insulator 511. By using a material with a low dielectric constant as an interlayer film, parasitic capacitance occurring between wirings can be reduced.

[0196] The conductor 503 is formed so as to be embedded in the insulator 512. Here, the height of the top surface of the conductor 503 and the height of the top surface of the insulator 512 can be made approximately the same. Note that although the conductor 503 is shown as having a single layer structure, the present invention is not limited to this. For example, the conductor 503 may have a multilayer film structure of two or more layers. Note that the conductor 503 is preferably made of a highly conductive material containing tungsten, copper, or aluminum as a main component.

[0197] In the transistor 510A, the conductor 560 may function as a first gate electrode. The conductor 505 may function as a second gate electrode. In this case, the threshold voltage of the transistor 510A can be controlled by changing the potential applied to the conductor 505 independently of the potential applied to the conductor 560. In particular, applying a negative potential to the conductor 505 can increase the threshold voltage of the transistor 510A above 0 V and reduce the off-state current. Therefore, applying a negative potential to the conductor 505 can reduce the drain current when the potential applied to the conductor 560 is 0 V compared to not applying a negative potential to the conductor 505.

[0198] Furthermore, for example, by overlapping the conductor 505 and the conductor 560, when a potential is applied to the conductor 560 and the conductor 505, the electric field generated from the conductor 560 and the electric field generated from the conductor 505 can be connected and can cover the channel formation region formed in the oxide 530.

[0199] That is, the channel formation region can be electrically surrounded by the electric field of the conductor 560 functioning as the first gate electrode and the electric field of the conductor 505 functioning as the second gate electrode. That is, like the transistor 500 described above, this has a surrounded channel (S-channel) structure.

[0200] The insulators 514 and 516 function as interlayer films, similar to the insulator 511 or 512. For example, the insulator 514 preferably functions as a barrier film that prevents impurities such as water or hydrogen from entering the transistor 510A from the substrate side. This structure can prevent impurities such as hydrogen or water from diffusing from the substrate side toward the transistor 510A through the insulator 514. Furthermore, for example, the insulator 516 preferably has a lower dielectric constant than the insulator 514. Using a material with a low dielectric constant as an interlayer film can reduce parasitic capacitance between wirings.

[0201] The conductor 505 functioning as the second gate has a conductor 505a formed in contact with the inner walls of the openings of the insulator 514 and the insulator 516, and a conductor 505b formed further inside. Here, the height of the top surfaces of the conductor 505a and the conductor 505b can be made approximately the same as the height of the top surface of the insulator 516. Note that although the transistor 510A has a structure in which the conductor 505a and the conductor 505b are stacked, the present invention is not limited to this. For example, the conductor 505 may have a single layer structure or a stacked structure of three or more layers.

[0202] Here, the conductor 505a is preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (i.e., the impurities are less likely to permeate through it). Alternatively, it is preferably made of a conductive material that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.) (i.e., the oxygen is less likely to permeate through it). Note that in this specification, the function of suppressing the diffusion of impurities or oxygen refers to the function of suppressing the diffusion of any one or all of the impurities or oxygen.

[0203] For example, the conductor 505a has a function of suppressing the diffusion of oxygen, so that the conductor 505b can be prevented from being oxidized and its conductivity from decreasing.

[0204] Furthermore, when the conductor 505 also functions as a wiring, it is preferable that the conductor 505b be made of a highly conductive material containing tungsten, copper, or aluminum as a main component. In this case, the conductor 503 is not necessarily provided. Note that although the conductor 505b is illustrated as a single layer, it may have a multilayer structure, for example, a multilayer structure of titanium or titanium nitride and the above-mentioned conductive material.

[0205] The insulators 521, 522, and 524 function as a second gate insulating film.

[0206] The insulator 522 preferably has a barrier property. When the insulator 522 has a barrier property, it functions as a layer that prevents impurities such as hydrogen from entering the transistor 510A from the periphery of the transistor 510A.

[0207] The insulator 522 is preferably a single layer or multilayer insulator containing, for example, aluminum oxide, hafnium oxide, oxide containing aluminum and hafnium (hafnium aluminate), tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3 (BST). As transistors become smaller and more highly integrated, thinner gate insulating films can cause problems such as leakage current. Using a high-k material for the insulator that functions as the gate insulating film makes it possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

[0208] Furthermore, it is preferable that the insulator 521 be thermally stable. For example, silicon oxide and silicon oxynitride are suitable because they are thermally stable. Furthermore, by combining a high-k insulator with silicon oxide or silicon oxynitride, it is possible to obtain the insulator 521 having a thermally stable layered structure with a high dielectric constant.

[0209] 5 shows a three-layer stacked structure as the second gate insulating film, it may be a two-layer or less, or four-layer or more. In this case, it is not limited to a stacked structure made of the same material, and may be a stacked structure made of different materials.

[0210] The oxide 530 having a region functioning as a channel formation region includes an oxide 530a, an oxide 530b on the oxide 530a, and an oxide 530c on the oxide 530b. Having the oxide 530a below the oxide 530b can suppress impurity diffusion from structures formed below the oxide 530a to the oxide 530b. Having the oxide 530c on the oxide 530b can suppress impurity diffusion from structures formed above the oxide 530c to the oxide 530b. The oxide 530 can be made of an oxide semiconductor, which is one of the above-described metal oxides.

[0211] Note that the oxide 530c is preferably provided in an opening in the insulator 580 via the insulator 574. When the insulator 574 has a barrier property, it can prevent impurities from the insulator 580 from diffusing into the oxide 530.

[0212] One of the conductors 542 functions as a source electrode, and the other functions as a drain electrode.

[0213] The conductors 542a and 542b can be made of a metal such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, or tungsten, or an alloy containing any of these as its main component. In particular, a metal nitride film such as tantalum nitride is preferable because it has barrier properties against hydrogen or oxygen and is highly resistant to oxidation.

[0214] 5 shows a single-layer structure, the conductors 542a and 542b may have a stacked structure of two or more layers. For example, a tantalum nitride film and a tungsten film may be stacked. Alternatively, a titanium film and an aluminum film may be stacked. Alternatively, a two-layer structure in which an aluminum film is stacked on a tungsten film, a two-layer structure in which a copper film is stacked on a copper-magnesium-aluminum alloy film, a two-layer structure in which a copper film is stacked on a titanium film, or a two-layer structure in which a copper film is stacked on a tungsten film may be used.

[0215] Other examples include a three-layer structure in which a titanium film or titanium nitride film is laminated on the titanium film or titanium nitride film, an aluminum film or copper film is laminated on the titanium film or titanium nitride film, and a titanium film or titanium nitride film is further formed thereon, and a three-layer structure in which a molybdenum film or molybdenum nitride film is laminated on the molybdenum film or molybdenum nitride film, an aluminum film or copper film is laminated on the molybdenum film or molybdenum nitride film, and a molybdenum film or molybdenum nitride film is further formed thereon. Note that a transparent conductive material containing indium oxide, tin oxide, or zinc oxide may also be used.

[0216] A barrier layer may be provided over the conductor 542. The barrier layer is preferably formed using a substance that has a barrier property against oxygen or hydrogen. With this structure, oxidation of the conductor 542 can be suppressed when the insulator 574 is formed.

[0217] The barrier layer can be made of, for example, a metal oxide. In particular, it is preferable to use an insulating film that has barrier properties against oxygen and hydrogen, such as aluminum oxide, hafnium oxide, or gallium oxide. Silicon nitride formed by CVD may also be used.

[0218] The presence of the barrier layer can broaden the range of material options for the conductor 542. For example, materials with low oxidation resistance but high conductivity, such as tungsten or aluminum, can be used for the conductor 542. Also, for example, a conductor that is easy to form or process can be used.

[0219] The insulator 550 functions as a first gate insulating film. The insulator 550 is preferably provided in the opening provided in the insulator 580 with the oxide 530c and the insulator 574 interposed therebetween.

[0220] As transistors become more miniaturized and highly integrated, thinning of the gate insulating film can cause problems such as leakage current. In this case, the insulator 550 may have a stacked structure, similar to the second gate insulating film. By using a stacked structure of a high-k material and a thermally stable material for the insulator functioning as the gate insulating film, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness. Furthermore, a stacked structure that is thermally stable and has a high dielectric constant can be achieved.

[0221] The conductor 560 functioning as the first gate electrode includes a conductor 560a and a conductor 560b on the conductor 560a. As with the conductor 505a, the conductor 560a is preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms. Alternatively, the conductor 560a is preferably made of a conductive material that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms and oxygen molecules).

[0222] The conductor 560a has the function of suppressing oxygen diffusion, which widens the range of material options for the conductor 560b. That is, the presence of the conductor 560a suppresses oxidation of the conductor 560b, preventing a decrease in conductivity.

[0223] As a conductive material capable of suppressing oxygen diffusion, for example, tantalum, tantalum nitride, ruthenium, or ruthenium oxide is preferably used. Furthermore, an oxide semiconductor that can be used as the oxide 530 can be used as the conductor 560a. In this case, by forming the conductor 560b by a sputtering method, the electrical resistance of the conductor 560a can be reduced, making it a conductor. This can be called an OC (Oxide Conductor) electrode.

[0224] The conductor 560b is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. Furthermore, since the conductor 560b functions as wiring, it is preferable to use a conductor with high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. Furthermore, the conductor 560b may have a layered structure, for example, a layered structure of titanium or titanium nitride and the above-mentioned conductive material.

[0225] An insulator 574 is disposed between the insulator 580 and the transistor 510A. The insulator 574 is preferably an insulating material that has a function of suppressing diffusion of impurities such as water or hydrogen and oxygen. For example, aluminum oxide or hafnium oxide is preferably used. Other examples of the insulator include metal oxides such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and tantalum oxide, silicon nitride oxide, and silicon nitride.

[0226] The insulator 574 can prevent impurities such as water and hydrogen contained in the insulator 580 from diffusing to the oxide 530b through the oxide 530c and the insulator 550. The insulator 574 can also prevent the conductor 560 from being oxidized by excess oxygen contained in the insulator 580.

[0227] Insulators 580, 582, and 584 function as interlayer films.

[0228] Like the insulator 514, the insulator 582 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen from entering the transistor 510A from the outside.

[0229] Similarly to the insulator 516, the insulators 580 and 584 preferably have a lower dielectric constant than the insulator 582. By using a material with a low dielectric constant as an interlayer film, parasitic capacitance between wirings can be reduced.

[0230] Additionally, transistor 510A may be electrically connected to other structures through plugs or interconnects such as conductor 546 embedded in insulator 580, insulator 582, and insulator 584.

[0231] Similarly to the conductor 505, the conductor 546 can be made of a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material, either in a single layer or a stacked layer. For example, it is preferable to use a high-melting-point material such as tungsten or molybdenum, which has both heat resistance and conductivity. Alternatively, it is preferable to form the conductor 546 from a low-resistance conductive material such as aluminum or copper. The use of a low-resistance conductive material can reduce wiring resistance.

[0232] For example, by using a layered structure of tantalum nitride, a conductor that has barrier properties against hydrogen and oxygen, and tungsten, which has high conductivity, as the conductor 546, it is possible to suppress the diffusion of impurities from the outside while maintaining the conductivity as a wiring.

[0233] With the above structure, a transistor including an oxide semiconductor with high on-state current, a transistor including an oxide semiconductor with low off-state current, or a semiconductor device with reduced fluctuation in electrical characteristics, stable electrical characteristics, and improved reliability can be provided.

[0234] <Transistor structure example 2> An example structure of a transistor 510B will be described using Figures 6A, 6B, and 6C. Figure 6A is a top view of the transistor 510B. Figure 6B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 6A. Figure 6C is a cross-sectional view of the portion indicated by the dashed-dotted line W1-W2 in Figure 6A. Note that some elements have been omitted from the top view of Figure 6A for clarity.

[0235] The transistor 510B is a modified example of the transistor 510A, and therefore, to avoid repetition of explanation, the differences from the transistor 510A will be mainly described.

[0236] The transistor 510B has a region in which the conductor 542 (the conductor 542a and the conductor 542b) overlaps with the oxide 530c, the insulator 550, and the conductor 560. With this structure, a transistor with high on-state current and high controllability can be provided.

[0237] The conductor 560 functioning as the first gate electrode includes a conductor 560a and a conductor 560b on the conductor 560a. As with the conductor 505a, the conductor 560a is preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms. Alternatively, the conductor 560a is preferably made of a conductive material that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms and oxygen molecules).

[0238] The conductor 560a has the function of suppressing oxygen diffusion, which improves the material selectivity of the conductor 560b. In other words, the presence of the conductor 560a suppresses oxidation of the conductor 560b, preventing a decrease in conductivity.

[0239] Furthermore, it is preferable to provide an insulator 574 so as to cover the top surface and side surfaces of the conductor 560, the side surfaces of the insulator 550, and the side surfaces of the oxide 530c. Note that the insulator 574 is preferably made of an insulating material that has a function of suppressing the diffusion of impurities such as water or hydrogen and oxygen. For example, it is preferable to use aluminum oxide or hafnium oxide. Other examples that can be used include metal oxides such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and tantalum oxide, silicon nitride oxide, and silicon nitride.

[0240] Providing the insulator 574 can suppress oxidation of the conductor 560. Furthermore, including the insulator 574 can suppress diffusion of impurities such as water and hydrogen contained in the insulator 580 into the transistor 510B.

[0241] Furthermore, an insulator 576 (insulators 576a and 576b) having barrier properties may be disposed between the conductor 546 and the insulator 580. By providing the insulator 576, it is possible to prevent oxygen in the insulator 580 from reacting with the conductor 546 and oxidizing the conductor 546.

[0242] Furthermore, by providing the insulator 576 with barrier properties, the range of materials that can be used for the plugs and wirings can be expanded. For example, by using a metal material that has oxygen absorption properties and high conductivity for the conductor 546, a semiconductor device with low power consumption can be provided. Specifically, a material that has low oxidation resistance but high conductivity, such as tungsten or aluminum, can be used. Furthermore, for example, a conductor that is easy to form or process can be used.

[0243] <Transistor structure example 3> An example structure of a transistor 510C will be described using Figures 7A, 7B, and 7C. Figure 7A is a top view of the transistor 510C. Figure 7B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 7A. Figure 7C is a cross-sectional view of the portion indicated by the dashed-dotted line W1-W2 in Figure 7A. Note that some elements are omitted from the top view of Figure 7A for clarity.

[0244] The transistor 510C is a modified example of the transistor 510A, and therefore, to avoid repetition of explanation, the differences from the transistor 510A will be mainly described.

[0245] 7, a conductor 547a is disposed between the conductor 542a and the oxide 530b, and a conductor 547b is disposed between the conductor 542b and the oxide 530b. The conductor 542a (conductor 542b) extends beyond the top surface of the conductor 547a (conductor 547b) and the side surface on the conductor 560 side, and has a region in contact with the top surface of the oxide 530b. The conductor 547 may be any conductor that can be used for the conductor 542. Furthermore, the thickness of the conductor 547 is preferably at least thicker than that of the conductor 542.

[0246] 7 has the above-described structure, the conductor 542 can be closer to the conductor 560 than in the transistor 510A. Alternatively, the ends of the conductors 542a and 542b can overlap with the conductor 560. This shortens the effective channel length of the transistor 510C, thereby improving the on-state current and frequency characteristics.

[0247] The conductor 547a (conductor 547b) is preferably provided so as to overlap with the conductor 542a (conductor 542b). With this configuration, the conductor 547a (conductor 547b) functions as a stopper during etching to form an opening in which the conductor 546a (conductor 546b) is to be embedded, thereby preventing the oxide 530b from being over-etched.

[0248] 7 may have a structure in which an insulator 545 is provided on and in contact with the insulator 544. The insulator 544 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen or excess oxygen from entering the transistor 510C from the insulator 580. The insulator 545 can be any of the insulators that can be used for the insulator 544. The insulator 544 may be a nitride insulator such as aluminum nitride, aluminum titanium nitride, titanium nitride, silicon nitride, or silicon nitride oxide.

[0249] Unlike the transistor 510A shown in FIG. 5, the transistor 510C shown in FIG. 7 does not include the conductor 503 and may include the conductor 505 in a single-layer structure. In this case, an insulating film to serve as the insulator 516 may be formed on the patterned conductor 505, and the upper portion of the insulating film may be removed by CMP or the like until the top surface of the conductor 505 is exposed. Here, it is preferable to improve the flatness of the top surface of the conductor 505. For example, the average surface roughness (Ra) of the top surface of the conductor 505 may be 1 nm or less, preferably 0.5 nm or less, and more preferably 0.3 nm or less. This improves the flatness of the insulating layer formed on the conductor 505 and improves the crystallinity of the oxide 530b and the oxide 530c.

[0250] <Transistor structure example 4> An example structure of a transistor 510D will be described using Figures 8A, 8B, and 8C. Figure 8A is a top view of the transistor 510D. Figure 8B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 8A. Figure 8C is a cross-sectional view of the portion indicated by the dashed-dotted line W1-W2 in Figure 8A. Note that some elements have been omitted from the top view of Figure 8A for clarity.

[0251] The transistor 510D is a variation of the transistor described above, and therefore, to avoid repetition of the description, the differences from the transistor described above will be mainly described.

[0252] 8A to 8C, the conductor 503 is not provided, and the conductor 505, which functions as the second gate, also functions as a wiring. An insulator 550 is provided over the oxide 530c, and a metal oxide 552 is provided over the insulator 550. A conductor 560 is provided over the metal oxide 552, and an insulator 570 is provided over the conductor 560. An insulator 571 is provided over the insulator 570.

[0253] The metal oxide 552 preferably has a function of suppressing oxygen diffusion. By providing the metal oxide 552, which suppresses oxygen diffusion, between the insulator 550 and the conductor 560, the diffusion of oxygen into the conductor 560 is suppressed. That is, a decrease in the amount of oxygen supplied to the oxide 530 can be suppressed. Furthermore, oxidation of the conductor 560 by oxygen can be suppressed.

[0254] Note that the metal oxide 552 may function as a part of the first gate. For example, the oxide semiconductor that can be used as the oxide 530 can be used as the metal oxide 552. In this case, by forming the conductor 560 by a sputtering method, the electrical resistance of the metal oxide 552 can be reduced, making it a conductive layer. This can be called an OC (Oxide Conductor) electrode.

[0255] The metal oxide 552 may also function as part of the gate insulating film. Therefore, when silicon oxide or silicon oxynitride is used for the insulator 550, it is preferable to use a metal oxide, which is a high-k material with a high dielectric constant, for the metal oxide 552. This layered structure can be thermally stable and have a high dielectric constant. Therefore, it is possible to reduce the gate potential applied during transistor operation while maintaining the physical film thickness. Furthermore, it is possible to reduce the equivalent oxide thickness (EOT) of the insulating layer that functions as a gate insulating film.

[0256] Although the metal oxide 552 in the transistor 510D is shown as a single layer, it may have a stacked structure of two or more layers. For example, a metal oxide functioning as part of the gate electrode and a metal oxide functioning as part of the gate insulating film may be stacked.

[0257] When the metal oxide 552 functions as a gate electrode, the on-state current of the transistor 510D can be improved without weakening the influence of the electric field from the conductor 560. Alternatively, when the metal oxide 552 functions as a gate insulating film, the physical thickness of the insulator 550 and the metal oxide 552 can maintain a distance between the conductor 560 and the oxide 530, thereby suppressing leakage current between the conductor 560 and the oxide 530. Therefore, by providing a stacked structure of the insulator 550 and the metal oxide 552, the physical distance between the conductor 560 and the oxide 530 and the electric field strength applied from the conductor 560 to the oxide 530 can be easily adjusted as needed.

[0258] Specifically, by reducing the resistance of an oxide semiconductor that can be used for the oxide 530, it can be used as the metal oxide 552. Alternatively, a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like can be used.

[0259] In particular, it is preferable to use an insulating layer containing oxides of either or both aluminum and hafnium, such as aluminum oxide, hafnium oxide, or oxide containing aluminum and hafnium (hafnium aluminate). Hafnium aluminate is particularly preferable because it has higher heat resistance than hafnium oxide film and is therefore less likely to crystallize during heat treatment in a later step. Note that the metal oxide 552 is not an essential component. It may be designed appropriately depending on the desired transistor characteristics.

[0260] The insulator 570 is preferably made of an insulating material that has the function of suppressing the permeation of impurities such as water or hydrogen, and oxygen. For example, aluminum oxide or hafnium oxide is preferably used. This can suppress oxidation of the conductor 560 by oxygen from above the insulator 570. Furthermore, impurities such as water or hydrogen from above the insulator 570 can be prevented from being mixed into the oxide 530 through the conductor 560 and the insulator 550.

[0261] The insulator 571 functions as a hard mask. By providing the insulator 571, when the conductor 560 is processed, the side surface of the conductor 560 can be approximately perpendicular, specifically, the angle between the side surface of the conductor 560 and the surface of the substrate can be 75 degrees or more and 100 degrees or less, preferably 80 degrees or more and 95 degrees or less.

[0262] Note that the insulator 571 may also function as a barrier layer by using an insulating material that has a function of suppressing permeation of impurities such as water or hydrogen and oxygen. In that case, the insulator 570 is not necessary.

[0263] Using insulator 571 as a hard mask, portions of insulator 570, conductor 560, metal oxide 552, insulator 550, and oxide 530c can be selectively removed to roughly align their sides and expose a portion of the surface of oxide 530b.

[0264] Transistor 510D also has regions 531a and 531b on a portion of the exposed oxide 530b surface, with one of regions 531a or 531b functioning as the source region and the other as the drain region.

[0265] The regions 531a and 531b can be formed by introducing impurity elements such as phosphorus or boron into the exposed surface of the oxide 530b by, for example, ion implantation, ion doping, plasma immersion ion implantation, or plasma treatment. Note that in this embodiment and other examples, the term "impurity elements" refers to elements other than the main component elements.

[0266] Alternatively, a metal film can be formed after exposing a portion of the surface of oxide 530b, followed by heat treatment, thereby diffusing elements contained in the metal film into oxide 530b to form regions 531a and 531b.

[0267] The region of the oxide 530b into which the impurity element has been introduced has a reduced electrical resistivity, and therefore the region 531a and the region 531b are sometimes referred to as an "impurity region" or a "low-resistance region."

[0268] By using the insulator 571 and / or the conductor 560 as a mask, the regions 531a and 531b can be formed in a self-aligned manner. Therefore, the regions 531a and / or 531b do not overlap with the conductor 560, reducing parasitic capacitance. Furthermore, no offset region is formed between the channel formation region and the source / drain region (region 531a or region 531b). By forming the regions 531a and 531b in a self-aligned manner, it is possible to achieve an increase in on-current, a reduction in threshold voltage, an improvement in operating frequency, and the like.

[0269] To further reduce the off-state current, an offset region may be provided between the channel formation region and the source / drain region. The offset region is a region with high electrical resistivity, into which the impurity element described above is not introduced. The offset region can be formed by introducing the impurity element described above after forming the insulator 575. In this case, the insulator 575 also functions as a mask, similar to the insulator 571. Therefore, the impurity element is not introduced into the region of the oxide 530b that overlaps with the insulator 575, and the electrical resistivity of the region can be maintained high.

[0270] The transistor 510D also includes an insulator 575 on the side surfaces of the insulator 570, the conductor 560, the metal oxide 552, the insulator 550, and the oxide 530c. The insulator 575 is preferably an insulator with a low dielectric constant. For example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine has been added, silicon oxide to which carbon has been added, silicon oxide to which carbon and nitrogen have been added, silicon oxide having vacancies, or a resin is preferable. In particular, using silicon oxide, silicon oxynitride, silicon nitride oxide, or silicon oxide having vacancies for the insulator 575 is preferable because it allows for easy formation of an excess oxygen region in the insulator 575 in a later step. Silicon oxide and silicon oxynitride are also preferable because they are thermally stable. The insulator 575 preferably has a function of diffusing oxygen.

[0271] The transistor 510D also includes an insulator 574 over the insulator 575 and the oxide 530. The insulator 574 is preferably formed by a sputtering method. By using a sputtering method, an insulator with few impurities such as water or hydrogen can be formed. For example, aluminum oxide is preferably used as the insulator 574.

[0272] Note that an oxide film formed by a sputtering method may extract hydrogen from the structure to be deposited. Therefore, the insulator 574 absorbs hydrogen and water from the oxide 530 and the insulator 575, thereby reducing the hydrogen concentrations in the oxide 530 and the insulator 575.

[0273] <Transistor structure example 5> An example structure of a transistor 510E will be described with reference to FIGS. 9A to 9C. FIG. 9A is a top view of the transistor 510E. FIG. 9B is a cross-sectional view of a portion indicated by dashed-dotted line L1-L2 in FIG. 9A. FIG. 9C is a cross-sectional view of a portion indicated by dashed-dotted line W1-W2 in FIG. 9A. Note that some elements are omitted from the top view of FIG. 9A for clarity.

[0274] The transistor 510E is a modified example of the transistor described above, and therefore, to avoid repetition of the description, the differences from the transistor described above will be mainly described.

[0275] 9A to 9C, the conductor 542 is not provided, and the exposed oxide 530b has regions 531a and 531b on a portion of its surface. One of the regions 531a and 531b functions as a source region, and the other functions as a drain region. An insulator 573 is provided between the oxide 530b and the insulator 574.

[0276] 9, the region 531 (region 531a and region 531b) is a region in which the following elements are added to the oxide 530b: The region 531 can be formed by using a dummy gate, for example.

[0277] Specifically, a dummy gate is provided on the oxide 530b, and an element that reduces the resistance of the oxide 530b is added using the dummy gate as a mask. That is, the element is added to a region of the oxide 530b that does not overlap with the dummy gate, forming a region 531. The element can be added by ion implantation, which adds an ionized source gas after mass separation, ion doping, which adds an ionized source gas without mass separation, plasma immersion ion implantation, or the like.

[0278] Representative elements that reduce the resistance of the oxide 530 include boron and phosphorus. Hydrogen, carbon, nitrogen, fluorine, sulfur, chlorine, titanium, and rare gases may also be used. Representative examples of rare gases include helium, neon, argon, krypton, and xenon. The concentration of the element may be measured using secondary ion mass spectrometry (SIMS) or the like.

[0279] Boron and phosphorus are particularly preferred because they can be produced using equipment from production lines for low-temperature polysilicon, etc. Existing facilities can be reused, allowing for reduced capital investment.

[0280] Subsequently, an insulating film to be the insulator 573 and an insulating film to be the insulator 574 may be formed over the oxide 530b and the dummy gate. By stacking the insulating film to be the insulator 573 and the insulating film to be the insulator 574, a region can be formed in which the region 531 overlaps with the oxide 530c and the insulator 550.

[0281] Specifically, an insulating film to be the insulator 580 is provided on an insulating film to be the insulator 574, and then a CMP (chemical mechanical polishing) process is performed on the insulating film to be the insulator 580 to remove a portion of the insulating film to be the insulator 580 and expose the dummy gate. Subsequently, when removing the dummy gate, a portion of the insulator 573 in contact with the dummy gate may also be removed. Therefore, the insulators 574 and 573 are exposed on the side surfaces of the opening formed in the insulator 580, and a portion of the region 531 formed in the oxide 530b is exposed on the bottom surface of the opening. Next, an oxide film to be the oxide 530c, an insulating film to be the insulator 550, and a conductive film to be the conductor 560 are sequentially formed in the opening. Then, by performing a CMP process or the like until the insulator 580 is exposed, the oxide film to be the oxide 530c, the insulating film to be the insulator 550, and the conductive film to be the conductor 560 are partially removed, thereby forming the transistor shown in FIG. 9 .

[0282] Note that the insulators 573 and 574 are not essential components and may be appropriately designed depending on desired transistor characteristics.

[0283] The transistor shown in FIG. 9 can be an existing device and does not include the conductor 542, which contributes to cost reduction.

[0284] <Transistor structure example 6> An example structure of a transistor 510F will be described with reference to FIGS. 10A to 10C. FIG. 10A is a top view of the transistor 510F. FIG. 10B is a cross-sectional view of a portion indicated by dashed dotted line L1-L2 in FIG. 10A. FIG. 10C is a cross-sectional view of a portion indicated by dashed dotted line W1-W2 in FIG. 10A. Note that some elements are omitted from the top view of FIG. 10A for clarity.

[0285] The transistor 510F is a modified example of the transistor 510A, and therefore, to avoid repetition of the description, the differences from the above transistor will be mainly described.

[0286] In transistor 510A, a portion of insulator 574 is provided in an opening provided in insulator 580 and is provided so as to cover the side surface of conductor 560. On the other hand, in transistor 510F, an opening is formed by removing a portion of insulator 580 and insulator 574.

[0287] Furthermore, an insulator 576 (insulators 576a and 576b) having barrier properties may be disposed between the conductor 546 and the insulator 580. By providing the insulator 576, it is possible to prevent oxygen in the insulator 580 from reacting with the conductor 546 and oxidizing the conductor 546.

[0288] When an oxide semiconductor is used for the oxide 530, the oxide 530 preferably has a stacked structure of multiple oxide layers with different atomic ratios of metal atoms. Specifically, the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530a is preferably larger than the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. The atomic ratio of the element M to In in the metal oxide used for the oxide 530a is preferably larger than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. The atomic ratio of In to M in the metal oxide used for the oxide 530b is preferably larger than the atomic ratio of In to M in the metal oxide used for the oxide 530a. The oxide 530c can be the same metal oxide as can be used for the oxide 530a or the oxide 530b.

[0289] The oxide 530a, the oxide 530b, and the oxide 530c preferably have crystallinity, and CAAC-OS is particularly preferable. Crystalline oxides such as CAAC-OS have few impurities and defects (such as oxygen vacancies), and have a highly crystalline and dense structure. This can prevent the source or drain electrode from extracting oxygen from the oxide 530b. This reduces the extraction of oxygen from the oxide 530b even during heat treatment, making the transistor 510F stable against high temperatures (or thermal budgets) during the manufacturing process.

[0290] When the oxide 530 is a stack of oxides 530a, 530b, and 530c, the conduction band minimums of the oxides 530a and 530c are preferably higher than the conduction band minimum of the oxide 530b. In other words, the electron affinities of the oxides 530a and 530c are preferably lower than the electron affinity of the oxide 530b. In this case, the oxide 530c is preferably a metal oxide that can be used for the oxide 530a. Specifically, the atomic ratio of the element M among the constituent elements of the metal oxide used for the oxide 530c is preferably greater than the atomic ratio of the element M among the constituent elements of the metal oxide used for the oxide 530b. Furthermore, the atomic ratio of the element M to In in the metal oxide used for the oxide 530c is preferably greater than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. In addition, in the metal oxide used for oxide 530b, the atomic ratio of In to element M is preferably larger than the atomic ratio of In to element M in the metal oxide used for oxide 530c.

[0291] Here, the energy level of the conduction band minimum changes smoothly at the junction between the oxides 530a, 530b, and 530c. In other words, the energy level of the conduction band minimum at the junction between the oxides 530a, 530b, and 530c changes continuously or forms a continuous junction. To achieve this, it is preferable to reduce the defect level density of the mixed layers formed at the interface between the oxides 530a and 530b and at the interface between the oxides 530b and 530c.

[0292] Specifically, the oxides 530a and 530b, and the oxides 530b and 530c, may have a common element other than oxygen (as a main component), thereby forming a mixed layer with a low density of defect states. For example, when the oxide 530b is an In-Ga-Zn oxide, the oxides 530a and 530c may be made of In-Ga-Zn oxide, Ga-Zn oxide, gallium oxide, or the like. The oxide 530c may also have a stacked structure. For example, a stacked structure of In-Ga-Zn oxide and Ga-Zn oxide on the In-Ga-Zn oxide, or a stacked structure of In-Ga-Zn oxide and gallium oxide on the In-Ga-Zn oxide, may be used. In other words, the oxide 530c may have a stacked structure of In-Ga-Zn oxide and an oxide not containing In.

[0293] Specifically, oxide 530a may be a metal oxide having an atomic ratio of In:Ga:Zn=1:3:4 or 1:1:0.5. Oxide 530b may be a metal oxide having an atomic ratio of In:Ga:Zn=4:2:3 or 3:1:2. Oxide 530c may be a metal oxide having an atomic ratio of In:Ga:Zn=1:3:4, In:Ga:Zn=4:2:3, Ga:Zn=2:1, or Ga:Zn=2:5. Specific examples of the oxide 530c having a layered structure include a layered structure of In:Ga:Zn=4:2:3 [atomic ratio] and Ga:Zn=2:1 [atomic ratio], a layered structure of In:Ga:Zn=4:2:3 [atomic ratio] and Ga:Zn=2:5 [atomic ratio], and a layered structure of In:Ga:Zn=4:2:3 [atomic ratio] and gallium oxide.

[0294] In this case, the oxide 530b serves as the main carrier path. The oxide 530a and the oxide 530c are configured as described above, thereby reducing the defect state density at the interface between the oxide 530a and the oxide 530b and at the interface between the oxide 530b and the oxide 530c. This reduces the effect of interface scattering on carrier conduction, allowing the transistor 510F to achieve a high on-state current and high frequency characteristics. Note that when the oxide 530c has a stacked structure, in addition to reducing the defect state density at the interface between the oxide 530b and the oxide 530c, it is expected to prevent the constituent elements of the oxide 530c from diffusing toward the insulator 550. More specifically, the oxide 530c has a stacked structure, and an oxide not containing In is positioned above the stacked structure, thereby preventing In from diffusing toward the insulator 550. The insulator 550 functions as a gate insulator, and diffusion of In leads to poor transistor characteristics. Therefore, by forming the oxide 530c into a stacked structure, a highly reliable semiconductor device can be provided.

[0295] A metal oxide that functions as an oxide semiconductor is preferably used for the oxide 530. For example, a metal oxide that serves as a channel formation region of the oxide 530 preferably has a band gap of 2 eV or more, preferably 2.5 eV or more. By using such a metal oxide with a wide band gap, the off-state current of the transistor can be reduced.

[0296] <Transistor structure example 7> 11A and 11B will be used to describe a structural example of a transistor 510G. The transistor 510G is a variation of the transistor 500. Therefore, to avoid repetition of the description, differences from the above transistor will be mainly described. Note that the structures illustrated in FIGS. 11A and 11B can also be applied to other transistors included in a semiconductor device of one embodiment of the present invention, such as the transistor 300.

[0297] 11A is a cross-sectional view of the transistor 510G in the channel length direction, and FIG. 11B is a cross-sectional view of the transistor 510G in the channel width direction. The transistor 510G shown in FIGS. 11A and 11B differs from the transistor 500 shown in FIGS. 4A and 4B in that the transistor 510G includes an insulator 402 and an insulator 404. The transistor 510G also differs from the transistor 500 shown in FIGS. 4A and 4B in that the insulator 551 is provided in contact with the side surface of the conductor 540a and the insulator 551 is provided in contact with the side surface of the conductor 540b. The transistor 510G also differs from the transistor 500 shown in FIGS. 4A and 4B in that the insulator 520 is not provided.

[0298] 11A and 11B, the insulator 402 is provided over the insulator 512. The insulator 404 is provided over the insulator 574 and the insulator 402.

[0299] 11A and 11B, the insulators 514, 516, 522, 524, 544, 580, and 574 are patterned, and the insulator 404 covers them. That is, the insulator 404 is in contact with the top surface of the insulator 574, the side surface of the insulator 574, the side surface of the insulator 580, the side surface of the insulator 544, the side surface of the insulator 524, the side surface of the insulator 522, the side surface of the insulator 516, the side surface of the insulator 514, and the top surface of the insulator 402. As a result, the oxide 530 and the like are isolated from the outside by the insulators 404 and 402.

[0300] The insulators 402 and 404 preferably have a high function of suppressing diffusion of hydrogen (for example, at least one of hydrogen atoms and hydrogen molecules) or water molecules. For example, silicon nitride or silicon nitride oxide, which are materials with high hydrogen barrier properties, are preferably used for the insulators 402 and 404. This can suppress diffusion of hydrogen and the like into the oxide 530, thereby suppressing deterioration in the characteristics of the transistor 510G. Therefore, the reliability of the semiconductor device of one embodiment of the present invention can be improved.

[0301] The insulator 551 is provided in contact with the insulator 581, the insulator 404, the insulator 574, the insulator 580, and the insulator 544. The insulator 551 preferably has a function of suppressing diffusion of hydrogen or water molecules. For example, the insulator 551 is preferably formed using an insulator with high hydrogen barrier properties, such as silicon nitride, aluminum oxide, or silicon nitride oxide. Silicon nitride is particularly suitable for use as the insulator 551 because it has high hydrogen barrier properties. Using a material with high hydrogen barrier properties for the insulator 551 can suppress diffusion of impurities such as water or hydrogen from the insulator 580 or the like to the oxide 530 through the conductors 540a and 540b. Furthermore, oxygen contained in the insulator 580 can be suppressed from being absorbed by the conductors 540a and 540b. Thus, the reliability of the semiconductor device of one embodiment of the present invention can be improved.

[0302] 12 is a cross-sectional view illustrating a configuration example of a semiconductor device in which the transistor 500 and the transistor 300 have the configurations shown in FIGS. 11A and 11B. An insulator 551 is provided on the side surface of the conductor 546.

[0303] 13A and 13B illustrate modifications of the transistor 510G shown in FIGS. 11A and 11B. FIG. 13A is a cross-sectional view of the transistor in the channel length direction, and FIG. 13B is a cross-sectional view of the transistor in the channel width direction. The transistor shown in FIGS. 13A and 13B differs from the transistor shown in FIGS. 11A and 11B in that the oxide 530c has a two-layer structure of oxides 530c1 and 530c2.

[0304] The oxide 530c1 contacts the top surface of the insulator 524, the side surface of the oxide 530a, the top surface and side surface of the oxide 530b, the side surfaces of the conductors 542a and 542b, the side surface of the insulator 544, and the side surface of the insulator 580. The oxide 530c2 contacts the insulator 550.

[0305] Oxide 530c1 can be, for example, an In-Zn oxide. Oxide 530c2 can be made of the same material as that used for oxide 530c when oxide 530c has a single-layer structure. For example, oxide 530c2 can be made of a metal oxide with an atomic ratio of In:Ga:Zn=1:3:4, Ga:Zn=2:1, or Ga:Zn=2:5.

[0306] By forming the oxide 530c as a two-layer structure of the oxide 530c1 and the oxide 530c2, the on-state current of the transistor can be increased compared to when the oxide 530c has a single-layer structure. Therefore, the transistor can be, for example, a power MOS transistor. The oxide 530c of the transistor shown in FIGS. 4A and 4B can also have a two-layer structure of the oxide 530c1 and the oxide 530c2.

[0307] The transistors shown in FIGS. 13A and 13B can be applied to, for example, the transistor 500, the transistor 300, or both.

[0308] Note that this embodiment mode can be implemented in appropriate combination with other embodiment modes described in this specification.

[0309] (Embodiment 3) In this embodiment, a metal oxide (hereinafter also referred to as an oxide semiconductor) that can be used for the OS transistor described in the above embodiment will be described.

[0310] The metal oxide preferably contains at least indium or zinc. It is particularly preferable that it contains indium and zinc. It is also preferable that it contains aluminum, gallium, yttrium, tin, or the like in addition to these. It may also contain one or more elements selected from boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, cobalt, and the like.

[0311] <Classification of crystal structures> First, classification of crystal structures in oxide semiconductors will be described with reference to Fig. 14A, which is a diagram for explaining classification of crystal structures of oxide semiconductors, typically IGZO (metal oxide containing In, Ga, and Zn).

[0312] As shown in FIG. 14A, oxide semiconductors are broadly classified into "amorphous," "crystalline," and "crystal." "Amorphous" includes completely amorphous. "Crystalline" includes c-axis-aligned crystalline (CAAC), nanocrystalline (nc), and cloud-aligned composite (CAC). The "Crystalline" classification excludes single crystal, polycrystal, and completely amorphous. "Crystalline" includes single crystal and polycrystal.

[0313] The structure within the bold frame in Figure 14A is an intermediate state between "amorphous" and "crystal," and is a structure that belongs to a new boundary region (new crystalline phase). In other words, this structure can be said to be completely different from the energetically unstable "amorphous" and "crystal."

[0314] The crystalline structure of a film or substrate can be evaluated using X-ray diffraction (XRD) spectroscopy. Figure 14B shows the XRD spectrum obtained by GIXD (Grazing-Incidence XRD) measurement of a CAAC-IGZO film classified as "Crystalline." The GIXD method is also known as the thin-film method or the Seemann-Bohlin method. Hereinafter, the XRD spectrum obtained by GIXD measurement shown in Figure 14B will be simply referred to as the XRD spectrum. The composition of the CAAC-IGZO film shown in Figure 14B is approximately In:Ga:Zn = 4:2:3 [atomic ratio]. The thickness of the CAAC-IGZO film shown in Figure 14B is 500 nm.

[0315] In Figure 14B, the horizontal axis is 2θ [deg.] and the vertical axis is intensity [au]. As shown in Figure 14B, a peak indicating clear crystallinity is detected in the XRD spectrum of the CAAC-IGZO film. Specifically, a peak indicating c-axis orientation is detected near 2θ = 31° in the XRD spectrum of the CAAC-IGZO film. Note that, as shown in Figure 14B, the peak near 2θ = 31° is asymmetrical with respect to the angle at which the peak intensity is detected.

[0316] The crystalline structure of a film or substrate can be evaluated by the diffraction pattern (also called the nanobeam electron diffraction pattern) observed using nanobeam electron diffraction (NBED). Figure 14C shows the diffraction pattern of a CAAC-IGZO film. Figure 14C shows a diffraction pattern observed using NBED, in which an electron beam is incident parallel to the substrate. The composition of the CAAC-IGZO film shown in Figure 14C is approximately In:Ga:Zn = 4:2:3 [atomic ratio]. In nanobeam electron diffraction, electron diffraction is performed using a probe diameter of 1 nm.

[0317] As shown in FIG. 14C, multiple spots indicating c-axis orientation are observed in the diffraction pattern of the CAAC-IGZO film.

[0318] <<Oxide semiconductor structure>> Note that oxide semiconductors may be classified differently from those shown in FIG. 14A when focusing on their crystal structures. For example, oxide semiconductors are divided into single-crystal oxide semiconductors and other non-single-crystal oxide semiconductors. Examples of non-single-crystal oxide semiconductors include the above-mentioned CAAC-OS and nc-OS. Non-single-crystal oxide semiconductors include polycrystalline oxide semiconductors, amorphous-like oxide semiconductors (a-like OSs), amorphous oxide semiconductors, and the like.

[0319] Here, the above-mentioned CAAC-OS, nc-OS, and a-like OS will be described in detail.

[0320] [CAAC-OS] CAAC-OS is an oxide semiconductor having multiple crystalline regions, each with its c-axis aligned in a specific direction. The specific direction can be the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, a crystalline region can also be a region with a uniform lattice arrangement. Furthermore, CAAC-OS has a region where multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. Note that distortion refers to a location where the lattice arrangement changes between a region with a uniform lattice arrangement and a region with a different uniform lattice arrangement in the region where multiple crystalline regions are connected. In other words, CAAC-OS is an oxide semiconductor with a c-axis aligned but no clear orientation in the ab-plane direction.

[0321] Each of the multiple crystalline regions is composed of one or more minute crystals (crystals with a maximum diameter of less than 10 nm). When a crystalline region is composed of one minute crystal, the maximum diameter of the crystalline region is less than 10 nm. When a crystalline region is composed of many minute crystals, the size of the crystalline region may be several tens of nm.

[0322] In an In-M-Zn oxide (wherein element M is one or more elements selected from aluminum, gallium, yttrium, tin, titanium, etc.), the CAAC-OS tends to have a layered crystal structure (also referred to as a layered structure) in which a layer containing indium (In) and oxygen (hereinafter referred to as an In layer) and a layer containing element M, zinc (Zn), and oxygen (hereinafter referred to as an (M, Zn) layer) are stacked. Note that indium and element M are mutually substituted. Therefore, the (M, Zn) layer may contain indium. Furthermore, the In layer may contain element M. Furthermore, the In layer may contain Zn. The layered structure is observed as a lattice image in a high-resolution TEM image, for example.

[0323] When the CAAC-OS film is subjected to structural analysis using, for example, an XRD apparatus, a peak indicating c-axis orientation is detected at or near 2θ=31° in out-of-plane XRD measurement using θ / 2θ scan. Note that the position of the peak indicating c-axis orientation (2θ value) may vary depending on the type and composition of the metallic elements constituting the CAAC-OS.

[0324] Furthermore, for example, in the electron diffraction pattern of a CAAC-OS film, multiple bright spots are observed, and the spots are observed at positions that are point-symmetric with respect to the spot of the incident electron beam that has passed through the sample (also called the direct spot).

[0325] When the crystalline region is observed from the specific direction, the lattice arrangement within the crystalline region is basically a hexagonal lattice, but the unit cell is not necessarily a regular hexagon and may be non-regular hexagonal. Furthermore, the distortion may have a pentagonal, heptagonal, or other lattice arrangement. In the CAAC-OS, no clear grain boundaries are observed even near the distortion. This indicates that the formation of grain boundaries is suppressed by the distortion of the lattice arrangement. This is thought to be because the CAAC-OS can tolerate distortion due to the lack of close-packed oxygen atom arrangement in the ab-plane direction and the change in interatomic bond distance caused by metal atom substitution.

[0326] A crystal structure with clear grain boundaries is called polycrystalline. Grain boundaries act as recombination centers, trapping carriers and potentially causing a decrease in the on-state current and field-effect mobility of a transistor. Therefore, CAAC-OS, which lacks clear grain boundaries, is one of the crystalline oxides with a crystal structure suitable for use in the semiconductor layer of a transistor. Zn is preferred for use in CAAC-OS. For example, In-Zn oxide and In-Ga-Zn oxide are suitable because they can suppress the generation of grain boundaries more effectively than In oxide.

[0327] CAAC-OS is an oxide semiconductor with high crystallinity and no clear grain boundaries. Therefore, it can be said that the decrease in electron mobility due to grain boundaries is unlikely to occur in CAAC-OS. Furthermore, since the crystallinity of oxide semiconductors can be reduced by impurities or defects, CAAC-OS can be said to be an oxide semiconductor with few impurities or defects (such as oxygen vacancies). Therefore, oxide semiconductors with CAAC-OS have stable physical properties. Therefore, oxide semiconductors with CAAC-OS are heat-resistant and highly reliable. Furthermore, CAAC-OS is stable against high temperatures (or thermal budgets) during the manufacturing process. Therefore, using CAAC-OS in OS transistors allows for greater flexibility in the manufacturing process.

[0328] [nc-OS] The nc-OS has periodic atomic arrangement in a microscopic region (e.g., a region of 1 nm to 10 nm, particularly a region of 1 nm to 3 nm). In other words, the nc-OS has microcrystalline structures. The size of these microcrystalline structures is, for example, 1 nm to 10 nm, particularly 1 nm to 3 nm, and therefore these microcrystalline structures are also called nanocrystalline structures. Furthermore, the nc-OS exhibits no regularity in the crystal orientation between different nanocrystalline structures. Therefore, the entire film lacks orientation. Therefore, depending on the analytical method, the nc-OS may be indistinguishable from an a-like OS or an amorphous oxide semiconductor. For example, when a structural analysis of an nc-OS film is performed using an XRD system, no peaks indicating crystallinity are detected in out-of-plane XRD measurements using θ / 2θ scanning. Furthermore, when an nc-OS film is subjected to electron diffraction (also known as selected-area electron diffraction) using an electron beam with a probe diameter larger than that of nanocrystalline structures (e.g., 50 nm or larger), a halo-like diffraction pattern is observed. On the other hand, when electron diffraction (also known as nanobeam electron diffraction) is performed on an nc-OS film using an electron beam with a probe diameter close to or smaller than the size of the nanocrystals (for example, 1 nm to 30 nm), an electron diffraction pattern can be obtained in which multiple spots are observed within a ring-shaped region centered on the direct spot.

[0329] [a-like OS] The a-like OS is an oxide semiconductor having a structure between the nc-OS and the amorphous oxide semiconductor. The a-like OS has a pore or low-density region. That is, the a-like OS has lower crystallinity than the nc-OS and CAAC-OS. Furthermore, the a-like OS has a higher hydrogen concentration in the film than the nc-OS and CAAC-OS.

[0330] <<Oxide semiconductor structure>> Next, the above-mentioned CAC-OS will be described in detail, which relates to the material composition.

[0331] [CAC-OS] CAC-OS is a material structure in which elements constituting a metal oxide are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a similar size range. Hereinafter, a metal oxide in which one or more metal elements are unevenly distributed and the regions containing the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a similar size range, is also referred to as a mosaic or patch state.

[0332] Furthermore, CAC-OS has a mosaic structure in which the material is separated into first and second regions, and the first regions are distributed throughout the film (hereinafter also referred to as a cloud structure). That is, CAC-OS is a composite metal oxide having a structure in which the first and second regions are mixed.

[0333] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In-Ga-Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0334] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be rephrased as a region whose main component is In. The second region can be rephrased as a region whose main component is Ga.

[0335] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0336] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) confirms that the CAC-OS has a structure in which a region mainly composed of In (first region) and a region mainly composed of Ga (second region) are unevenly distributed and mixed.

[0337] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act in a complementary manner, thereby providing the CAC-OS with a switching function (the ability to turn on and off). In other words, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), high field-effect mobility (μ), and good switching behavior can be achieved.

[0338] Oxide semiconductors have a variety of structures, each with different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0339] <Transistors containing oxide semiconductors> Next, a case where the oxide semiconductor is used in a transistor will be described.

[0340] By using the oxide semiconductor for a transistor, a transistor with high field-effect mobility and high reliability can be realized.

[0341] For the transistor, an oxide semiconductor with a low carrier concentration is preferably used. For example, the carrier concentration of the oxide semiconductor is 1×10 17 cm -3 Less than 1 × 10 15 cm -3 or less, more preferably 1 × 10 13 cm -3 Less than 1×10, more preferably 11 cm -3 or less, more preferably 1 × 10 10 cm -3 Less than 1 x 10 -9 cm-3 The above is the case. Note that in order to reduce the carrier concentration of an oxide semiconductor film, the impurity concentration in the oxide semiconductor film may be reduced to reduce the density of defect states. In this specification and the like, a semiconductor having a low impurity concentration and a low density of defect states is referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor. Note that an oxide semiconductor having a low carrier concentration may also be referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor.

[0342] Furthermore, a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states, and therefore the density of trap states may also be low.

[0343] Furthermore, charges trapped in the trap states of an oxide semiconductor take a long time to disappear and may behave like fixed charges. Therefore, a transistor in which a channel formation region is formed in an oxide semiconductor with a high density of trap states may have unstable electrical characteristics.

[0344] Therefore, in order to stabilize the electrical characteristics of a transistor, it is effective to reduce the impurity concentration in the oxide semiconductor. Furthermore, in order to reduce the impurity concentration in the oxide semiconductor, it is preferable to also reduce the impurity concentration in the adjacent film. Examples of impurities include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, and silicon.

[0345] <Impurities> Here, the influence of each impurity in an oxide semiconductor will be described.

[0346] When an oxide semiconductor contains silicon or carbon, which is one of the Group 14 elements, defect levels are formed in the oxide semiconductor. Therefore, the concentrations of silicon or carbon in the oxide semiconductor and those near the interface with the oxide semiconductor (concentrations obtained by secondary ion mass spectrometry (SIMS)) are calculated as follows: 18 atoms / cm 3 Less than or equal to 2 x 10 17atoms / cm 3 The following applies.

[0347] Furthermore, when an oxide semiconductor contains an alkali metal or alkaline earth metal, defect levels may be formed and carriers may be generated. Therefore, a transistor using an oxide semiconductor containing an alkali metal or alkaline earth metal is likely to have normally-on characteristics. For this reason, when the concentration of the alkali metal or alkaline earth metal in the oxide semiconductor obtained by SIMS is 1×10 18 atoms / cm 3 Less than or equal to 2 x 10 16 atoms / cm 3 Do the following:

[0348] Furthermore, when nitrogen is contained in an oxide semiconductor, electrons serving as carriers are generated, the carrier concentration increases, and the semiconductor is likely to become n-type. As a result, a transistor using an oxide semiconductor containing nitrogen is likely to have normally-on characteristics. Alternatively, when nitrogen is contained in an oxide semiconductor, trap states may be formed. As a result, the electrical characteristics of the transistor may become unstable. For this reason, the nitrogen concentration in the oxide semiconductor obtained by SIMS is set to 5×10 19 atoms / cm 3 Less than 5 x 10 18 atoms / cm 3 Less than 1×10, more preferably 18 atoms / cm 3 Less than 5 × 10, more preferably 17 atoms / cm 3 Do the following:

[0349] Furthermore, hydrogen contained in an oxide semiconductor may react with oxygen bonded to a metal atom to form water, which may form an oxygen vacancy. When hydrogen enters the oxygen vacancy, electrons serving as carriers may be generated. Furthermore, some of the hydrogen may bond with oxygen bonded to a metal atom to generate electrons serving as carriers. Therefore, a transistor using an oxide semiconductor containing hydrogen is likely to have normally-on characteristics. For this reason, it is preferable to reduce the amount of hydrogen in the oxide semiconductor as much as possible. Specifically, the hydrogen concentration in an oxide semiconductor measured by SIMS is 1×10 20 atoms / cm 3 Less than 1 x 10 19 atoms / cm 3 less than 5 × 10 18 atoms / cm 3 less than 1×10 18 atoms / cm 3 Make it less than.

[0350] When an oxide semiconductor with sufficiently reduced impurities is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0351] Note that this embodiment mode can be implemented in appropriate combination with other embodiment modes described in this specification.

[0352] (Fourth embodiment) In this embodiment, an example of an electronic component or electronic device in which the matching circuit 10 described in the above embodiment can be incorporated will be described.

[0353] For example, FIG. 15 shows an image diagram of factory automation. In FIG. 15, a factory 884 is connected to a cloud 883 via an Internet line. Furthermore, the cloud 883 is connected to a home 881 and an office 882 via the Internet line. The Internet line may be a wired communication system or a wireless communication system. For example, in the case of a wireless communication system, a fourth-generation mobile communication system (4G) or a fifth-generation mobile communication system (5G) may be used. Furthermore, the factory 884 may be connected to a factory 885 and a factory 886 via the Internet line.

[0354] The factory 884 has a master device (control device) 831. The master device 831 has a function of connecting to a cloud (server) 883 and transmitting and receiving information. The master device 831 is also connected to a plurality of industrial robots 842 included in an IoT terminal device (also called an endpoint microcomputer) 841 via an M2M (Machine to Machine) interface 832. As the M2M interface 832, for example, industrial Ethernet ("Ethernet" is a registered trademark), which is a type of wired communication method, or local 5G, which is a type of wireless communication method, may be used.

[0355] A factory manager can connect to a factory 884 via a cloud 883 from a home 881 or office 882 to know the operating status, etc. He can also check for incorrect or missing items, give instructions on where to put them, measure takt time, etc.

[0356] In recent years, the introduction of IoT into factories has been progressing worldwide under the name of "smart factories." In smart factory cases, there have been reported cases where endpoint microcomputers are used not only for simple inspection and auditing but also for fault detection and anomaly prediction.

[0357] In the above-mentioned example of factory automation, a matching circuit 10 according to an embodiment of the present invention can be incorporated into electronic components constituting communication devices such as a fourth-generation mobile communication system (4G), a fifth-generation mobile communication system (5G), industrial Ethernet, local 5G, etc., PCs (Personal Computers) used in the home 881 and the office 882, CPUs (Central Processing Units) used in the master device 831, etc., motherboards, high-speed serial interfaces such as PCI Express (sometimes abbreviated as PCIe; "PCI Express" and "PCIe" are registered trademarks), etc.

[0358] Note that this embodiment mode can be implemented in appropriate combination with other embodiment modes described in this specification. [Example]

[0359] In this example, the OS transistor described in the above embodiment was fabricated and the relationship between the voltage Vgs and the capacitance Cgsd was measured. In addition, the relationship between the voltage Vgs and the capacitance Cgsd of a silicon MOS FET was simulated and compared with the relationship between the voltage Vgs and the capacitance Cgsd of an OS transistor (hereinafter referred to as the Vgs-Cgsd characteristic).

[0360] The channel length of the fabricated OS transistor is 60 nm, and the channel width is also 60 nm. The channel length of the MOS FET used in the simulation is 60 nm, and the channel width is 80 nm.

[0361] 16 is a perspective view showing the structure of a prototype OS transistor. The transistor has a structure similar to that of the transistor 500 described in the above embodiment, including a top gate electrode (TGE), a gate insulating layer (TGI) on the top gate electrode side, a back gate electrode (BGE), a gate insulating layer (BGI) on the back gate electrode side, electrodes (S / D) functioning as source or drain, and an oxide. The transistor is a transistor containing an In-Ga-Zn oxide having a CAAC structure in a channel formation region.

[0362] Figure 17A shows the Vgs-Cgsd characteristics of an OS transistor and a silicon MOS FET side by side. The horizontal axis of Figure 17A represents the gate voltage Vgs relative to the source, and the vertical axis represents the capacitance Cgsd formed between the source and the drain and the gate. Figure 17B shows the Vgs-Cgsd characteristics of the OS transistor and the MOS FET in Figure 17A, normalized per 1 μm of channel length and channel width.

[0363] 17A and 17B show that the capacitance Cgsd of an OS transistor is not significantly different from the capacitance Cgsd of a silicon MOS FET in the low voltage Vgs region, but the difference becomes larger in the region where the voltage Vgs is higher than the threshold voltage Vth of the OS transistor. In the high voltage Vgs region, the capacitance Cgsd of the OS transistor is up to 30 times larger than the capacitance Cgsd of a silicon MOS FET. This shows that the capacitance Cgsd of an OS transistor changes more than the capacitance Cgsd of a silicon MOS FET.

[0364] This embodiment can be implemented in appropriate combination with other embodiment modes described in this specification. [Explanation of symbols]

[0365] L12: inductor, T11: transistor, T15: transistor, VDD_IN: input terminal, SII_IN: input terminal, SIO_OUT: output terminal, 10: matching circuit, 20: device, 30: device, 40: matching circuit, 50: matching circuit, 300: transistor, 311: substrate, 313: semiconductor region, 314a: low resistance region, 314b: low resistance region, 315: insulator, 316: conductor, 320: insulator, 322: insulator, 324: insulator, 326: insulator, 328: conductor, 330: conductor, 350: insulator, 352: insulator, 354: insulator, 356: conductor Conductor, 360: Insulator, 362: Insulator, 364: Insulator, 366: Conductor, 370: Insulator, 372: Insulator, 374: Insulator, 376: Conductor, 380: Insulator, 382: Insulator, 384: Insulator, 386: Conductor, 402: Insulator, 404: Insulator, 500: Transistor, 503: Conductor, 503a: Conductor, 503b: Conductor, 505: Conductor, 505a: Conductor, 505b: Conductor, 510: Insulator, 510A: Transistor, 510B: Transistor, 510C: Transistor, 510D: Transistor, 510E: Transistor, 510 F: transistor, 510G: transistor, 511: insulator, 512: insulator, 514: insulator, 516: insulator, 518: conductor, 520: insulator, 521: insulator, 522: insulator, 524: insulator, 530: oxide, 530a: oxide, 530b: oxide, 530c: oxide, 530c1: oxide, 530c2: oxide, 531: region, 531a: region, 531b: region, 540a: conductor, 540b: conductor, 542: conductor, 542a: conductor, 542b: conductor, 543: region, 543a: region, 543b: region, 544: insulator, 54 5: insulator, 546: conductor, 546a: conductor, 546b: conductor, 547: conductor, 547a: conductor, 547b: conductor, 548: conductor, 550: insulator, 551: insulator, 552: metal oxide, 560: conductor, 560a: conductor, 560b: conductor, 570: insulator, 571: insulator, 573: insulator, 574: insulator, 575: insulator, 576: insulator, 576a: insulator, 576b: insulator, 580: insulator, 581: insulator, 582: insulator, 584: insulator, 586: insulator, 600: capacitor, 610: conductor, 612: conductor,620: Conductor, 630: Insulator, 650: Insulator, 831: Master device, 832: M2M interface, 841: IoT end device, 842: Industrial robot, 881: Home, 882: Office, 883: Cloud, 884: Factory, 885: Factory, 886: Factory,

Claims

1. A transistor, an inductor; a first input terminal and a second input terminal; an output terminal; the first input terminal is electrically connected to the source and drain of the transistor; a gate and a back gate of the transistor are electrically connected to the first terminal of the inductor and the output terminal; a second terminal of the inductor electrically connected to the second input terminal; the transistor has a metal oxide in a channel formation region; a matching circuit that performs impedance matching by changing the potential input to the second input terminal;

2. A transistor, an inductor; a first input terminal and a second input terminal; an output terminal; the first input terminal is electrically connected to the source and drain of the transistor; a gate and a back gate of the transistor are electrically connected to the first terminal of the inductor and the output terminal; a second terminal of the inductor electrically connected to the second input terminal; An AC signal is input to the first input terminal, a first potential is input to the second input terminal; When the frequency of the AC signal changes, the first potential is changed.

3. In claim 2, The semiconductor device, wherein the transistor has a metal oxide in a channel formation region.

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