Semiconductor equipment

Abstract

To provide a semiconductor device using diamond semiconductors that is suitable for low-loss, high-current, high-speed, and high-voltage operation, as well as for miniaturization and weight reduction of devices. [Solution] In the semiconductor device 101, a film (HEA film) 13 made of a high electron affinity material is formed in contact with at least a part of the surface of the diamond semiconductor 11. The high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is energetically lower than the upper end of the valence band of the diamond semiconductor at the interface, and the HEA film has a structure in which it is made of a single crystal or polycrystalline film in at least some locations.

Description

[Technical Field]

[0001] This invention relates to a semiconductor device, and more particularly to a semiconductor device using a diamond semiconductor. [Background technology]

[0002] As a semiconductor, diamond has a wide bandgap energy (5.47 eV), a low relative permittivity (5.7), a high dielectric breakdown field strength (10 MV / cm), and a high carrier saturation rate (1.5–2.7 × 10⁻¹⁰ for electrons and holes, respectively). 7 cm / s and 0.85~1.2 × 10 7 (cm / s), high thermal conductivity (22 W / (cm·K)) and high carrier mobility (4500 cm for electrons and holes, respectively). 2 / (V·s) and 3800cm 2 It possesses several remarkable physical properties, such as (V·s). Here, the above characteristic values ​​are for room temperature. For this reason, semiconductor devices using diamond are highly anticipated as they can be semiconductor devices that possess high power operation, high speed and high frequency operation, and high voltage resistance characteristics.

[0003] In recent years, hydrogen-terminated diamond semiconductors have been actively studied in the field of diamond semiconductors (see Non-Patent Documents 1, 2, and 3). This is because when the surface of a diamond semiconductor is hydrogen-terminated, an electrically conductive region is created near the surface of the diamond semiconductor, resulting in a p-type semiconductor. In diamond semiconductors, the activation energy of dopants is high, making it difficult to achieve both carrier density and mobility at room temperature, but surface conductivity in hydrogen-terminated diamond can be one way to solve this problem. When diamonds are manufactured by vapor phase synthesis, the diamond surface is automatically almost completely hydrogen-terminated due to the hydrogen process gas, which is essential in the vapor phase synthesis process. Hydrogen-terminated diamond semiconductors have the advantage of reducing the number of manufacturing steps, and because the hydrogen termination is almost complete, it is easier to obtain high quality. In recent years, studies have also been underway on elements such as silicon (Si) that bond to the unbonded hands of carbon on the outermost surface of diamond (Non-Patent Document 3).

[0004] Furthermore, studies have been conducted on semiconductor devices having a heterostructure composed of a hydrogen-terminated diamond layer and a high electron affinity oxide layer by depositing an oxide film having a high electron affinity such as amorphous MoO3 or V2O5 on the surface of the hydrogen-terminated diamond. For example, the disclosure is found in Non-Patent Documents 2, 4, and 5. This is because when an oxide film having a high electron affinity is formed on the surface of the hydrogen-terminated diamond, this oxide film extracts electrons, and it is thought that a high-density hole carrier such as 10 13 ~10 14 cm -2 might be induced, opening the way to higher output and lower loss.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, semiconductor devices using diamond terminated with hydrogen, especially semiconductor devices using hydrogen-terminated diamond having a heterostructure, are expected to have excellent material properties as semiconductor devices with excellent electrical and physical properties. However, when a sample of a heterostructure composed of hydrogen-terminated diamond and a high electron affinity oxide film is made and experiments are conducted, the mobility is 70 cm 2 V-1 s -1 Less than, or there was a problem that the sheet resistance was higher than 9 kΩ and it was not suitable for low conduction loss and high current operation. Also, when holes in the diamond were depleted, there was a problem that it was difficult to increase the breakdown voltage because there were electrons trapped in the high electron affinity oxide film.

[0007] Furthermore, when this heterostructure is used in the channel region of a diamond field-effect transistor (FET), the low mobility means that it is necessary to increase the channel width or increase the gate insulation film capacitance per unit area in order to obtain conduction characteristics such as equivalent mutual conductance, and the gate-source and gate-drain capacitances increase and do not contribute to high-speed operation or low switching loss. These problems ultimately make it difficult to miniaturize peripheral electronic components and simplify the cooling system, and there is a problem that the miniaturization and weight reduction of power electronics devices and high-power high-frequency amplifiers using diamond FETs cannot be advanced.

[0008] The problem to be solved by the present invention is to provide a semiconductor device using a diamond semiconductor suitable for low loss, high current, high speed, high breakdown voltage operation and miniaturization and weight reduction of the device. By using this in the channel, access or drift region of a diamond FET, low loss, high current, and high-speed operation can be expected compared to the past. In particular, by using it in the access or drift region, conduction and switching losses can be reduced, and a uniform electric field distribution can be obtained at off-time, and an improvement in the breakdown voltage can be expected. The present invention will open the way for high-power high-frequency amplification for large-capacity communication and low-loss power electronics.

Means for Solving the Problem

[0009] The configuration of the present invention is shown below. (Configuration 1) A film (HEA film) made of a high electron affinity substance is formed in contact with at least a part of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. The HEA film is a single crystal film, and the semiconductor device has a structure in at least some locations. (Configuration 2) A film made of a highly electron-affinity material (HEA film) is formed in contact with at least a portion of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. A semiconductor device having a structure in at least some locations, wherein the HEA film is a film made of single crystal or polycrystalline material. (Composition 3) A film made of a highly electron-affinity material (HEA film) is formed in contact with at least a portion of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. The room-temperature mobility of the charge carriers generated at the interface between the diamond semiconductor and the HEA film is 200 cm². 2 V -1 s -1 More than 3800cm 2 V -1 s -1 A semiconductor device having the following characteristics, and having a structure in at least some location where the sheet resistance is 0.3kΩ or more and 6kΩ or less. (Composition 4) It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. The HEA film is a single crystal film, and the semiconductor device has a structure in at least some locations. (Composition 5) It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. A semiconductor device having a structure in at least some locations, wherein the HEA film is a film made of single crystal or polycrystalline material. (Composition 6) It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. The room-temperature mobility of the charge carriers generated at the interface between the diamond semiconductor and the insulating film is 200 cm². 2 V -1 s -1 More than 3800cm 2 V -1 s -1 A semiconductor device having the following characteristics, and having a structure in at least some location where the sheet resistance is 0.3kΩ or more and 6kΩ or less. (Composition 7) It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. A semiconductor device having a structure in which the sheet resistance of the surface of the HEA film is higher than 0 Ω and 500 MΩ or less in at least some locations. (Composition 8) A film made of a highly electron-affinity material (HEA film) is formed in contact with at least a portion of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. A semiconductor device having a structure in which, when holes in the diamond semiconductor become depleted, electrons in the HEA film are also depleted in at least some locations. (Composition 9) It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. A semiconductor device having a structure in which, when holes in the diamond semiconductor become depleted, electrons in the HEA film are also depleted in at least some locations. (Composition 10) The semiconductor device according to any one of the configurations 1 to 9, wherein the surface of the diamond semiconductor is terminated with one or more elements selected from the group consisting of hydrogen, silicon, or oxygen. (Composition 11) The HEA film is made of MoO3, and the semiconductor device is as described in any one of the configurations 1 to 9. (Composition 12) The HEA film is made of α-MoO3, and the semiconductor device is as described in any one of the configurations 1 to 9. (Composition 13) The HEA film is made of V2O5, and the semiconductor device is as described in any one of items 1 to 9. (Composition 14) The HEA film is made of α-V2O5, and the semiconductor device is as described in any one of items 1 to 9. [Effects of the Invention]

[0010] According to the present invention, a semiconductor device made of diamond semiconductors is provided that is suitable for low-loss, high-current, high-speed, and high-voltage operation, as well as for miniaturization and weight reduction of the device. [Brief explanation of the drawing]

[0011] [Figure 1] A cross-sectional view showing the basic structure of the semiconductor device of the present invention. [Figure 2] Band diagrams of the semiconductor layer and HEA film of the first invention. [Figure 3] Band diagrams of the semiconductor layer, HEA film, and insulating film of the second invention. [Figure 4] A cross-sectional view showing the structure of the second semiconductor device of the present invention. [Figure 5] A cross-sectional view showing the structure of the third semiconductor device of the present invention. [Figure 6] A cross-sectional view showing the structure of the fourth semiconductor device of the present invention. [Figure 7] A cross-sectional view showing the structure of the fifth semiconductor device of the present invention. [Figure 8] This diagram illustrates the operating principle of the semiconductor device of the present invention in comparison with the operating principle of a conventional device. Here, (a) shows the ON state and (b) shows the OFF state, and the circled plus and minus marks represent positive charge (hole) and negative charge (electron), respectively. [Figure 9] A schematic diagram visualizing the crystal structure when α-MoO3 is used as the high electron affinity material and (001) hydrogen-terminated diamond is used as the diamond. [Figure 10] Optical microscope image of α-MoO3 crystals picked up with a stamp. The circled areas were transferred. [Figure 11] A top view photograph of the semiconductor device fabricated in the example. [Figure 12] A characteristic diagram showing the electrical characteristics of the semiconductor device fabricated in the example. [Modes for carrying out the invention]

[0012] (Embodiment 1) The embodiments for carrying out the present invention will be described below with reference to the drawings. In this text, "A to B" means "A or greater and B or less," including the upper and lower limits.

[0013] <Concept> Previous research has shown that the emergence of p-type electrical conductivity in hydrogen-terminated diamond semiconductors is due to the contribution of negative charges present in molecules adsorbed on the surface of the diamond semiconductor or in insulating films formed in contact with the diamond semiconductor. For example, when hydrogen-terminated diamond is exposed to the atmosphere, water containing carbon dioxide, water containing oxygen, or nitrogen dioxide (NO2) molecules from the atmosphere are adsorbed, and these become negatively charged, generating holes in the diamond (Non-Patent Literature 1, 2, 3). Also, when an Al2O3 film is deposited on the surface of hydrogen-terminated diamond, defects in the Al2O3 film become negatively charged, inducing holes near the diamond surface and resulting in electrical conductivity (Non-Patent Literature 1, 2, 3). This mechanism, in which negative charges are generated in the material in contact with the surface of hydrogen-terminated diamond, leading to the generation of holes in the diamond and the emergence of electrical conductivity, is generally called surface transfer doping or simply transfer doping.

[0014] The integral of the volume density of negative charges in the material in contact with the surface of hydrogen-terminated diamond, perpendicular to the interface, i.e., the surface density, is approximately equal to the surface density of holes in the diamond. (More precisely, the integral of the volume density of negative charges in the material in contact with the surface of hydrogen-terminated diamond, perpendicular to the interface, i.e., the surface density, is equal to the integral of the net positive charge density of holes and other positively ionized nitrogen in the diamond, perpendicular to the interface.) A more fundamental reason why transfer doping occurs on such hydrogen-terminated surfaces is that the upper end of the valence band of hydrogen-terminated diamond is at a high energy level (approximately -4.2V from the vacuum level). Hydrogen-terminated diamond has a large negative electron affinity (approximately -1.3eV), and due to its 5.5eV band gap, the upper end of the valence band is located at approximately -4.2eV from the vacuum level. When a substance with unoccupied energy levels at a lower energy level is adsorbed or deposited on the diamond surface, electrons move from the diamond's valence band to the unoccupied energy levels of that substance, creating holes in the diamond.

[0015] Considering this transfer doping mechanism, it is expected that depositing a material with high electron affinity, i.e., one in which the lower end of the conduction band is energetically lower than the vacuum level and also has a high work function, onto the surface of hydrogen-terminated diamond will induce a high density of holes in the diamond due to the high density of unoccupied levels located below the upper end of the valence band of the hydrogen-terminated diamond. From this perspective, extensive research has been conducted on semiconductor devices in which highly electron-affinity oxides such as molybdenum oxide (MoO3), vanadium oxide (V2O5), tungsten oxide (WO3), and niobium oxide (Nb2O5) are deposited on the surface of hydrogen-terminated diamond. For example, MoO3 has an electron affinity of approximately 6.6 eV, and the lower end of the conduction band is located at approximately -6.6 eV from the vacuum level. In other words, the lower end of the conduction band of MoO3 is energetically about 2.4 eV lower than the upper end of the valence band of hydrogen-terminated diamond.

[0016] To date, in heterostructure samples consisting of hydrogen-terminated diamond and a high electron affinity oxide film (HEA film), a hole density of 10 13 ~10 14 cm -2 High values ​​such as the above have been disclosed as results of Hall effect measurements (Non-patent documents 2, 4, 5). However, the room-temperature mobility of holes is 10-70 cm². 2 V -1 s -1Furthermore, the room-temperature mobility of bulk high-purity diamonds is reported to be 3800 cm². 2 V -1 s -1 It is significantly lower in comparison. Furthermore, in a diamond FET in which a gate electrode is placed on top of a heterostructure of hydrogen-terminated diamond and MoO3, a highly electron-affinity oxide, 200 cm 2 V -1 s -1 Although the above mobility is disclosed, the hole density is low when this mobility is observed, and the sheet resistance is higher than 9 kΩ (Non-Patent Literature 6).

[0017] The inventors hypothesized that the reason why the expected properties, such as mobility, have not been obtained in the previously reported heterostructures of hydrogen-terminated diamond and HEA films is that electrons that move to the unoccupied levels of the HEA film are localized at spatially random positions, and the holes conducting through the diamond are scattered by the heterogeneous Coulomb potential formed by these electrons. More specifically, they hypothesized that conventionally used HEA films are formed by vapor deposition and have an amorphous structure, causing the area near the lower end of the conduction band to blur and become localized, and that there are also numerous localized states within the energy gap, trapping electrons in these states and localizing them at spatially random positions. In fact, previous studies have shown that the HEA film side does not have conductivity (Non-Patent Documents 2, 4, 5).

[0018] Therefore, the inventor investigated a structure that would provide a spatially uniform electron system within the HEA film without causing scattering. It was hypothesized that this structure could be realized by creating a heterostructure using a polycrystalline or single-crystal HEA film, thereby reducing the density of localized energy levels within the HEA film, and moving electrons from the localized energy levels within the HEA film to the conduction band levels (located higher than the mobility edge and contributing to conduction), thereby generating holes in the diamond. As shown in the examples, the device characteristics were evaluated when using a single-crystal HEA film, specifically α-MoO3, to confirm the effect of the present invention, namely the improvement in mobility. Furthermore, during this investigation, it was discovered that using the semiconductor device of the present invention in the access or drift region of a diamond FET reduces conduction and switching losses, and also allows for a uniform electric field distribution during the off state, thereby improving the dielectric breakdown voltage.

[0019] As shown in Figure 1(a), the semiconductor device of the present invention has a structure in which a single-crystal or polycrystalline HEA film 13 is formed in contact with a diamond semiconductor 11 on which a diamond semiconductor terminal surface (terminal layer) 12 is formed as a first main surface, and as shown in Figure 2, the HEA film 13 belongs to a semiconductor device in which the lower end of its conduction band at the interface is located below the upper end of the valence band of the diamond semiconductor 11, resulting in a type III (broken gap) band alignment. Here, Figure 2(a) shows the band diagram when the diamond layer (layer A) and the high electron affinity material layer (layer B) are separated by a distance, and (b) shows the band diagram when layers A and B are in contact. In this configuration, as shown in Figure 2(b), holes are generated on the diamond side and electrons on the HEA film side through electron transfer.

[0020] By using single-crystal or polycrystalline HEA films, electrons generated on the HEA film side occupy the conduction band, exhibiting conductivity. This reduces Coulomb scattering due to localized electrons, which was considered a problem with conventional amorphous HEA films, and increases the mobility of holes in diamond from the conventional 10 to 70 cm⁻¹. 2 V -1 s-1 Compared to that, it's more than double at 200cm 2 V -1 s -1 It can be improved significantly more than this. In particular, by creating a heterostructure using hydrogen-terminated diamond, which is atomically flat and has a low defect density, and a HEA film that is a single crystal with a layered structure and few defects, charged impurity scattering, including that caused by the localized electrons mentioned above, and interfacial roughness scattering are reduced to the absolute minimum, the bulk 3800 cm⁻¹, which is rate-limited by acoustic and optical phonon scattering, is reduced. 2 V -1 s -1 It is possible to obtain a high mobility close to 5 × 10. Furthermore, not only this high mobility, but also at least 5 × 10 12 cm -2 A hole density exceeding this level makes it possible to obtain low sheet resistances of 0.3 kΩ or more and 6 kΩ or less. Furthermore, holes on the diamond side and electrons on the HEA film side are confined by the electric field and potential barrier perpendicular to the interface, and their motion in this direction is quantized, leading to the formation of subbands. Therefore, they can be considered as two-dimensional hole systems and two-dimensional electron systems, respectively. When the HEA film is thin, around 10 nm thick, it forms a quantum well structure sandwiched between the potential barriers of the surface in contact with the diamond and the surface on the opposite side.

[0021] Furthermore, the present invention includes not only a semiconductor device 101 having a HEA film 13 formed in contact with a terminalized diamond semiconductor 11, but also a semiconductor device 102 in which an insulating film 16 is interposed between the terminalized diamond semiconductor 11 and the HEA film 13, and the band structure is as shown in Figure 3. Here, Figure 3(a) shows the band diagram when the diamond layer (layer A), the high electron affinity material layer (layer B), and the insulating film (layer C) are separated by a distance from each other, while Figure 3(b) shows the band diagram when they are formed in contact. This band diagram shows that the high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film 16 and the HEA film 13 is at an energetically lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor 11 and the insulating film 16. Furthermore, the lower end of the conduction band of the insulating film 16 is energetically higher than the upper end of the valence band of the diamond semiconductor 11 at the interface between the insulating film 16 and the diamond semiconductor 11, and the upper end of the valence band of the insulating film 16 is energetically lower than the lower end of the conduction band of the HEA film 13 at the interface between the insulating film 16 and the HEA film 13. In the case of the semiconductor device 102, as in the case of the semiconductor device 101, Coulomb scattering due to localized electrons can be suppressed, improving mobility and reducing sheet resistance. However, if there are defects that trap electrons and holes inside the insulating film (C layer) and at the interface between the diamond semiconductor 11 and the HEA film 13, they become scattering sources and cause a decrease in mobility, so it is preferable to have as few such defects as possible. Also, as the thickness of the insulating film increases, the density of holes and electrons generated in the diamond semiconductor 11 and the HEA film 13 decreases, so the thickness should be determined according to the purpose.

[0022] As elements constituting the termination of the diamond semiconductor 11, one or more can be selected from the group consisting of hydrogen (H), oxygen (O), nitrogen (N), fluorine (F), aluminum (Al), and silicon (Si). Among these, hydrogen (H) is preferred because it has a low surface energy level density and a high energy at the top of the valence band, making it easy to increase the hole density. Terminations consisting of silicon (Si) and oxygen (O) are also preferred because they can reduce the surface energy level density. The electron affinity of diamond and the magnitude of the band offset with the HEA film change depending on the termination, so they should be selected according to the purpose.

[0023] Here, the HEA film 13 is not particularly limited as long as it is a material that exhibits the above-mentioned band alignment with the diamond semiconductor 11, but examples include MoO3, V2O5, WO3, ReO3, CrO3, and Nb2O5. Polycrystalline or single crystal forms of these materials are particularly preferred. In the case of polycrystalline materials, as with single crystals, in regions (grains) with a crystalline structure, unlike conventional amorphous films, electrons that move from the valence band of diamond occupy the conduction band levels, which have conductivity, rather than localized levels in the HEA film, thus improving mobility. However, a larger grain size is preferable to avoid the influence of grain boundaries, including localized energy levels. For example, when applied to diamond FETs, a grain size of 1 μm or larger is preferable considering the gate length. A grain size of 10 μm or larger is even more preferable. Furthermore, when fabricating a layered structure by cleaving a single crystal material and attaching it to a diamond surface, layered single crystals of these materials are preferred. For example, α-MoO3 is an example of MoO3 that takes on a layered structure. The work function tends to increase in the order of Nb2O5, CrO3, ReO3, WO3, MoO3, and V2O5, and the hole density induced in diamond is expected to increase in this order. It is preferable to select an appropriate material depending on the purpose.

[0024] The insulating film 16 is not particularly limited as long as it is a material that exhibits the band alignment described above with the diamond semiconductor 11 and the HEA film 13, but examples include boron nitride and calcium fluoride. In particular, it is preferable that there are no defects that trap electrons and holes in the interior and at the interface with the diamond semiconductor 11 and the HEA film 13. Hexagonal boron nitride single crystals are preferred because they have few such defects.

[0025] In the HEA film 13 made of single crystal or polycrystalline oxide of the present invention, a spatially uniform electron system that is not localized and has conductivity is formed, thereby suppressing the effect of Coulomb scattering and increasing the mobility of holes on the diamond surface. Furthermore, by using this hole-electron coexistence system in the drift region of a transistor, conduction and switching losses can be reduced, and a uniform electric field distribution can be obtained when the transistor is off, improving the dielectric breakdown voltage.

[0026] Examples of device configurations include field-effect transistors (FETs) 201 and 201a (Figure 4), in which a HEA film 13 and a gate electrode 17 are stacked on a diamond semiconductor 11 treated with a termination layer 12, with the active portion positioned between a source electrode 14 and a drain electrode 15; FETs 301 and 301a (Figure 5), in which an insulating film 16 is formed between the diamond semiconductor 11 and the HEA film 13, in contact with both; and FETs 401 and 401a (Figure 6), in which an insulating film 18 is formed between the gate electrode 17 and the HEA film 13. Here, the difference between (a) and (b) in Figures 4 to 6 is the length of the gate electrode 17, where (a) is a structure that controls the entire HEA film 13, and (b) is a structure that controls a part of the HEA film 13.

[0027] In semiconductor devices 501 and 502, a two-dimensional hole system (on the diamond 11 side) and a two-dimensional electron system (on the HEA film 13 side) are formed. In conventional amorphous high-work-function oxides produced by methods such as conventional vapor deposition, electrons are spatially non-uniformly localized. In contrast, in the present invention (semiconductor devices 501 and 502), a spatially uniform electron system is formed that does not localize and exhibits conductivity. As a result, the effect of Coulomb scattering is suppressed, and the mobility of holes on the diamond surface is increased. Not only is semiconductor device 501 used by directly forming single crystals or polycrystals of high work function oxides on a hydrogen-terminated diamond surface, but as seen in semiconductor device 502, a structure can also be created with an insulating film, such as hexagonal boron nitride, sandwiched in between. This allows for electrode contacts in both the hole system and the electron system. By using this structure in the access or drift region of an FET, a structure similar to a superjunction can be created, resulting in low resistance when on and a uniform electric field distribution when off, thereby improving the dielectric breakdown voltage.

[0028] In the conventional method shown in Figure 8, when the FET is in the off state, i.e., when holes near the diamond surface between the gate and drain are depleted, the rate of change of the electric field between the gate and drain increases as the density of localized negative charge within the HEA increases. Therefore, the higher the negative charge density, i.e., the higher the hole density and the lower the resistance in the on state, the easier it is for the electric field near the gate electrode to exceed the dielectric breakdown field, making it difficult to increase the breakdown voltage (voltage is the x-integral of the electric field; the area of ​​the triangle in Figure 8).

[0029] In contrast, in the present invention, as shown in Figure 8, when the device is off, not only are the holes in the diamond between the gate and drain depleted, but the electrons in the HEA are also depleted. (The electrons in the HEA are discharged from the gate due to their conductivity.) Therefore, the electric field in the off state is independent of the negative charge density, i.e., the hole density, in the HEA when the device is on. As a result, it is possible to achieve both low resistance and high breakdown voltage. While similar in concept to superjunctions, in the case of superjunctions, if the dopant concentrations are not balanced, a net space charge remains when the device is in the off state, requiring a high-precision balance of the donor and acceptor concentrations for both n-type and p-type devices. On the other hand, the present invention does not require dopants and has the significant advantage of not generating a space charge from ionized donors and acceptors when the carriers are depleted. [Examples]

[0030] The present invention will be described in more detail below with reference to examples, but these examples are provided solely to aid in understanding the present invention and are not intended to limit the present invention to them.

[0031] In the example, a heterostructure sample 101 was fabricated in which a HEA film 13 made of α-MoO3 was formed in contact with a hydrogen-terminated diamond semiconductor. The electrical properties of the sample were measured to evaluate the sheet resistance, carrier density, and mobility.

[0032] <Element Structure> The sample fabricated in the example is the semiconductor device 101 shown in Figure 1. The surface of the diamond semiconductor 11 is a hydrogen-terminated surface 12, on which electrodes 14 and 15 are formed, each consisting of sequentially stacked titanium (Ti) and platinum (Pt) layers with a thickness of 5 nm. A HEA film 13 using α-MoO3 as a high electron affinity material is formed between electrodes 14 and 15. Although Figure 1 shows two terminals for electrodes 14 and 15, in order to accurately evaluate the carrier density and mobility, a sample with a six-terminal Hall bar structure for Hall effect measurement was actually fabricated.

[0033] <Manufacturing method> 1. Prepare the circuit board. After preparing a Type IIa single-crystal diamond (100) substrate (manufactured by Element Six), ultrasonic cleaning was performed sequentially for 5 minutes each with pure water, 2-propanol (IPA), acetone, IPA, and pure water.

[0034] 2. Element Isolation Hole bar patterns were drawn using a maskless exposure system (DL-1000, manufactured by Nano System Solutions Co., Ltd.). The photoresist used was ZPN1150 (manufactured by Zeon Corporation). The resist treatment was performed by dropping the ZPN1150 resist, linearly increasing the spin coat rotation speed to 5000 rpm over 5 seconds, fixing it at 5000 rpm and rotating for 60 seconds, and then baking at 110°C for 2 minutes. After pattern exposure, post-exposure baking was performed at 120°C for 5 minutes, followed by development with 2.38 wt% tetramethylammonium hydroxide (TMAH) for 130 seconds and rinsing with ultrapure water for 60 seconds.

[0035] Subsequently, nitrogen ion implantation was performed on the diamond substrate surface using a hole bar pattern made of the ZPN1150 resist described above as a mask. The ion implantation conditions were nitrogen (N), 10.0 keV, and 1,000 × 10⁻¹⁶ ion species, implantation energy, implantation amount, beam current, implantation time, and tilt angle, respectively. 14 atoms / cm 2 The current was 0.59 μA, the duration was 490.9 seconds, and the duration was 0 degrees. The substrate was not heated during implantation. Nitrogen ion implantation was performed to deconduct the portion of the hole bar shape other than the channel region. After nitrogen ion implantation, the sample was immersed in a beaker containing N-methyl-2-pyrrolidone (NMP), and the beaker was heated in a water bath heated to 80°C to remove the resist. Subsequently, the sample was rinsed by immersion in acetone and IPA, and then blown with nitrogen. Furthermore, it was acid washed by immersion in a solution of nitric acid and sulfuric acid mixed in a 1:3 volume ratio at a liquid temperature of 200°C for 30 minutes. After acid washing, organic washing was performed in the following order: pure water, 2-propanol (IPA), acetone, IPA, and pure water.

[0036] 3. Electrode formation After forming a pattern using lithography with a maskless exposure system, electrodes were deposited using an electron gun type deposition system (ADS-E810, R-DEC). A two-layer photoresist consisting of LOR5A and AZ5214E ​​was used. For LOR5A spin coating, the rotation speed was increased to 3000 rpm in 10 seconds, then rotated at 3000 rpm for 60 seconds, and then baked at 180°C for 5 minutes. For AZ5214E ​​spin coating, the rotation speed was increased to 3000 rpm in 10 seconds, then rotated at 3000 rpm for 60 seconds, and then baked at 110°C for 2 minutes. The electrode pattern was exposed so as to be in contact with the hole bar, developed with 2.38 wt% TMAH for about 70 seconds, and then rinsed with ultrapure water for 60 seconds. Subsequently, Ti (5 nm) / Pt (5 nm) electrodes were deposited using an electron gun type deposition system. The deposition rate for titanium (Ti) was 0.1 nm / s, and the deposition rate for platinum (Pt) was 0.05 nm / s. The vacuum level during deposition was 10°C. -5 ~10 -6 The pressure was Pa. After Ti / Pt deposition, the resist was removed and lifted off by immersing the beaker in a beaker containing NMP and then immersing the beaker in a water bath heated to 80°C. After lift-off, the electrodes were formed by rinsing with acetone and IPA, followed by blowing with nitrogen.

[0037] 4. Annealing and hydrogen termination Electrode annealing and hydrogen termination of the diamond surface were performed using a microwave plasma chemical vapor deposition apparatus. The electrode annealing conditions were 650°C, 500 sccm, 80 Torr, and 35 minutes, respectively, for temperature, hydrogen flow rate, pressure, and time. The heating rate during annealing was 1°C / 3 sec. After annealing, the electrode was cooled to 570°C and treated with hydrogen plasma for 15 minutes at a hydrogen flow rate, pressure, and microwave power of 500 sccm, 27 Torr, and 270 W, respectively. After hydrogen termination, the sample was transported to a glove box using a transport chamber maintained under vacuum by an NEG pump.

[0038] 5. Making polymer stamps A polymer stamp was fabricated to transfer a thin α-MoO3 flake, cleaved from a Si substrate, onto hydrogen-terminated diamond. The polymer stamp was fabricated on a glass slide. The microscope slides were treated with a water vapor plasma cleaning system (AQ-500, Samco) to remove organic contaminants from the surface. The RF output, oxygen gas flow rate, and treatment time were set to 250W, 20 sccm, and 10 minutes, respectively. After oxygen plasma treatment of the microscope slides, a gel sheet (PF-60-X4, Gel Pak) approximately 1 mm square was attached, and polydimethylsiloxane (PDMS) was spin-coated. For the PDMS spin-coating, the rotation speed was increased to 3000 rpm in 10 seconds, then rotated at 3000 rpm for 60 seconds, and finally baked at 70°C for 5 hours. The PDMS base and hardener (SYLGARD) were then applied. TM 184 Silicone Elastomer Kit (manufactured by Dow) was mixed in a mass ratio of 10:1, air bubbles were removed, and then PDMS was spin-coated onto the mixture.

[0039] After spin-coating PDMS, the surface of the PDMS was treated with oxygen plasma using a parallel plate RIE apparatus (RIE-200NL, Samco), and then polypropylene carbonate (PPC) was spin-coated. The conditions for the plasma treatment of PDMS were RF output, oxygen gas flow rate, and treatment time of 120 W, 50 sccm, and 10 minutes, respectively. PPC (Sigma-Aldrich) was diluted with anisole at a weight ratio of 15 wt% and stirred using a stirrer. For the PPC spin-coating, the rotation speed was increased to 1500 rpm in 10 seconds, then rotated at 1500 rpm for 60 seconds, and then baked at 110°C for 5 minutes. For degassing treatment of the PPC / PDMS stamp, three argon gas replacements and vacuuming for more than one day were performed in a pass box. Furthermore, it was baked at 110°C for 5 minutes in a glove box.

[0040] 6. Cleavage of α-MoO3 As the HEA film, we used single-crystal α-MoO3 (manufactured by 2D Semiconductors) synthesized by chemical vapor transport. α-MoO3, a material with high electron affinity, was cleaved using adhesive tape (manufactured by Nitto Denko Corporation) in a glove box under an argon gas atmosphere. To degass the tape, three argon gas replacements and vacuuming for more than one day were performed in a pass box connected to the glove box. While heating a Si substrate at 90°C on a stage inside the glove box, the tape with the α-MoO3 cleaved was attached for 5 minutes to cleave the α-MoO3 onto the Si substrate. Before placing the Si substrate into the glove box, organic contaminants on the Si substrate surface were removed using a water vapor plasma cleaning system (AQ-500, manufactured by Samco) with a plasma treatment of 250W RF output, 20 sccm oxygen gas, and a processing time of 5 minutes. After oxygen plasma treatment of the Si substrate, the passbox underwent three argon gas replacements and vacuuming for more than one day. Before cleaving α-MoO3 onto the Si substrate, vacuum annealing was performed at 300°C for 2 hours in an annealing tubular furnace connected to the glove box. After cleaving α-MoO3 onto a Si substrate, a relatively flat α-MoO3 thin section with the desired thickness was searched for using an optical microscope in a glove box. A thin section of α-MoO3 with dimensions of approximately 30 μm (length), 15 μm (width), and 40 nm (thickness) was obtained. The thickness of the α-MoO3 thin section can be estimated from the color of the optical microscope image.

[0041] 7. Transfer of α-MoO3 Using a PPC / PDMS stamp fabricated on a glass slide, thin flakes of α-MoO3 were picked up from a Si substrate in a glove box and transferred to hydrogen-terminated diamond. The α-MoO3 pickup and transfer were performed using a manipulator movable in the XYZ axis direction with the stamp attached, and a stage movable in the XY axis and rotation axis direction, with the Si substrate or hydrogen-terminated diamond fixed in a vacuum chuck. For reference, Figure 9 shows the crystal structure of α-MoO3, and Figure 10 shows an optical microscope image of the α-MoO3 crystal picked up by the stamp. The crystals seen inside the circle in Figure 10 are the α-MoO3 crystals targeted for heterostructure fabrication. During α-MoO3 pickup, the stamp and α-MoO3 were aligned under an optical microscope. The stamp was brought into contact with the target α-MoO3 at room temperature, and the stage was heated to 70°C. After reaching 70°C, a 5-minute wait was taken, and then the stage was cooled to 38°C. After reaching 38°C and waiting for 5 minutes, the target α-MoO3 was picked up from the Si substrate by slowly lifting the stamp from the Si substrate. During the transfer of α-MoO3, the positions of the α-MoO3 picked up on the stamp and the hydrogen-terminated diamond were aligned under an optical microscope. The α-MoO3 was bonded to the hydrogen-terminated diamond at room temperature, and the stage was heated to 110°C. After reaching 110°C and waiting for 5 minutes, the stamp was quickly lifted to transfer the α-MoO3 to the hydrogen-terminated diamond, and a semiconductor device 101 with a heterostructure in which a HEA film (13) made of α-MoO3 was formed between electrodes (14,15) and in contact with a hydrogen-terminated (12) diamond semiconductor (11) was fabricated, as shown in Figure 1(a). For reference, a microscope image of the fabricated semiconductor device 101 taken from above is shown in Figure 11.

[0042] <Characteristic Evaluation> 1. Sheet resistance For sheet resistance measurement, a two-terminal measurement was performed inside a glove box under an argon gas atmosphere immediately after hydrogen termination. The sheet resistance at that time was 40 GΩ. Next, after transferring a thin film of α-MoO3 onto hydrogen-terminated diamond, the film was transported into a glove box under a nitrogen atmosphere using a vacuum transport chamber, and four-terminal measurements were performed. As a result, the sheet resistance after transferring α-MoO3 was 4.7 kΩ, and a significant decrease in sheet resistance was observed due to the heterostructure in which the single-crystal HEA film of the present invention, α-MoO3, was stacked on a hydrogen-terminated diamond semiconductor.

[0043] 2. Carrier density and mobility After measuring the sheet resistance using four terminals, the Hall effect was measured using a prober equipped with a tungsten needle, applying a magnetic field of -0.5 to 0.5 T perpendicular to the substrate (Figure 12; Rxx (The values ​​shown are before applying the shape factor and converting to sheet resistance.) As a result, the carrier density and mobility calculated assuming a single carrier are 5.7 × 10⁻⁶, respectively, at room temperature. 12 cm -2 and 230cm 2 V -1 s -1 And it was excellent. As mentioned in the background section, the conventional method had a mobility of 70 cm. 2 V -1 s -1 The figures were even lower, less than one-third of those in the examples. The measuring instruments used for these measurements included a function generator 33210A (Agilent Technologies), amplifiers 1201 (2 units) and 1211 (DL Instruments), a digital multimeter 34410A (Agilent Technologies), and digital multimeters 34461A (2 units) (Keysight Technologies).

[0044] Samples were also prepared by transferring α-MoO3 to a region of diamond implanted with nitrogen ions, using the same method as described above. The longitudinal sheet resistance of the α-MoO3 crystal was approximately 500 MΩ, and conductivity was observed. In the nitrogen ion-implanted region, nitrogen acts as a deep donor, preventing the formation of holes within the diamond (the sheet resistance of a hydrogen-terminated diamond surface implanted with nitrogen ions under the same conditions as described above remained approximately 10 after 17 hours of exposure to air). 11 (It showed a high value of Ω). Therefore, this conduction is thought to represent electron conduction within α-MoO3. In other words, unlike conventional methods, it was shown that electrons that moved from the valence band of diamond to α-MoO3 occupy the conduction band levels that contribute to conduction. Furthermore, from these experimental results, the low sheet resistance of 4.7 kΩ and high mobility of 230 cm observed in the prototype semiconductor device 101 mentioned above were confirmed. 2 V -1 s -1 It was shown that this was due to holes in the diamond.

[0045] On the other hand, a sample prepared by transferring α-MoO3 onto a silicon substrate with a 90 nm thick thermal oxide film exhibited a resistance higher than the measurement limit, and conductivity could not be obtained. This is thought to be because the upper end of the valence band of SiO2 is at a low energy position (similar to the upper end of the valence band of MoO3), thus preventing transfer doping. [Industrial applicability]

[0046] The present invention provides a semiconductor device made of diamond semiconductors that is suitable for low-loss, high-current, high-speed, and high-voltage operation, as well as for miniaturization and weight reduction of devices. In particular, when used in the access or drift region, conduction and switching losses can be reduced, and a uniform electric field distribution can be obtained when off, which is expected to improve the dielectric breakdown voltage. Therefore, the present invention opens the way for high-power high-frequency amplification and low-loss power electronics for high-capacity communications, and is expected to be widely used in industry. [Explanation of Symbols]

[0047] 11: Diamond semiconductor 12: Diamond semiconductor termination surface (termination layer) 13: Single-crystal or polycrystalline high electron affinity material films (HEA films) 13b: Amorphous high electron affinity material film 14: Electrode (Source electrode) 15: Electrode (Drain electrode) 16: Insulating film (also serves as gate insulating film) 17: Electrode (gate electrode) 18: Insulating Film 101: Semiconductor Device 102: Semiconductor Equipment 201: Semiconductor Equipment 201a: Semiconductor equipment 301: Semiconductor Equipment 301a: Semiconductor device 401: Semiconductor Device 401a: Semiconductor device 501: Semiconductor Equipment 502: Semiconductor Equipment

Claims

1. A film made of a highly electron-affinity material (HEA film) is formed in contact with at least a portion of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. The HEA film is a film made of a single crystal, and the semiconductor device has a structure in at least some locations.

2. A film made of a highly electron-affinity material (HEA film) is formed in contact with at least a portion of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. A semiconductor device having a structure in at least some locations, wherein the HEA film is a film made of single crystal or polycrystalline material.

3. A film made of a highly electron-affinity material (HEA film) is formed in contact with at least a portion of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. The room-temperature mobility of the charge carriers generated at the interface between the diamond semiconductor and the HEA film is 200 cm². ２ V －１ s －１ More than 3800cm ２ V －１ s －１ A semiconductor device having the following characteristics, and having a structure in at least some location where the sheet resistance is 0.3 kΩ or more and 6 kΩ or less.

4. It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. The HEA film is a film made of a single crystal, and the semiconductor device has a structure in at least some locations.

5. It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. A semiconductor device having a structure in at least some locations, wherein the HEA film is a film made of single crystal or polycrystalline material.

6. It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. The mobility of the charge carriers generated at the interface between the diamond semiconductor and the insulating film at room temperature is 200 cm ２ V －１ s －１ or more and 3800 cm ２ V －１ s －１ or less, and a semiconductor device having a structure with a sheet resistance of 0.3 kΩ or more and 6 kΩ or less in at least some locations.

7. It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. A semiconductor device having a structure in which the sheet resistance of the surface of the HEA film is higher than 0 Ω and 500 MΩ or less in at least some locations.

8. A film made of a highly electron-affinity material (HEA film) is formed in contact with at least a portion of the surface of the diamond semiconductor. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the diamond semiconductor and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface. A semiconductor device having a structure in which, when holes in the diamond semiconductor become depleted, electrons in the HEA film are also depleted in at least some locations.

9. It has a layered structure in which a diamond semiconductor, an insulating film, and a film (HEA film) made of a high electron affinity material are sequentially in contact and stacked. The aforementioned high electron affinity material is a material in which the lower end of the conduction band at the interface between the insulating film and the HEA film is at an energy lower position than the upper end of the valence band of the diamond semiconductor at the interface between the diamond semiconductor and the insulating film. A semiconductor device having a structure in which, when holes in the diamond semiconductor become depleted, electrons in the HEA film are also depleted in at least some locations.

10. The semiconductor device according to any one of claims 1 to 9, wherein the surface of the diamond semiconductor is terminated with one or more elements selected from the group consisting of hydrogen, silicon, or oxygen.

11. The aforementioned HEA film is MoO ３ A semiconductor device according to any one of claims 1 to 9, comprising the above.

12. The aforementioned HEA film is α-MoO ３ A semiconductor device according to any one of claims 1 to 9, comprising the above.

13. The HEA film is V ２ O ５ A semiconductor device according to any one of claims 1 to 9, comprising the above.

14. The aforementioned HEA film is α-V ２ O ５ A semiconductor device according to any one of claims 1 to 9, comprising the above.

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