Film formation method, film formation device, and production method for oxide film

Abstract

Provided is a novel method for forming an oxide film that includes indium oxide and gallium oxide.　A film formation method according to the present invention includes a step for using microwave remote plasma to form an oxide film that includes indium oxide and gallium oxide on a substrate.

Description

Film forming method, film forming apparatus, and method for producing oxide film

[0001] The present invention relates to a method for forming a film of multiple materials, a film forming apparatus, and a method for producing an oxide film.

[0002] In the process of depositing the channel layer of a thin-film transistor using an oxide semiconductor containing an indium-gallium-zinc-oxide (IGZO)-based material, plasma-enhanced atomic layer deposition (PEALD) is used to deposit indium oxide channels because it allows deposition even in low-temperature environments.

[0003] Regarding technology related to semiconductor devices using IGZO-based oxide semiconductors, Patent Document 1 discloses a method for fabricating a semiconductor device in which a metal oxide is formed on a substrate using a plasma-assisted ALD method, which is a film formation method that uses plasma. The fabrication method disclosed in Patent Document 1 includes the steps of introducing a first precursor containing indium into a chamber in which a substrate is provided, introducing a first oxidizing agent after the introduction of the first precursor, introducing a second precursor containing at least one of zinc and gallium after the introduction of the first oxidizing agent, and introducing the second oxidizing agent after the introduction of the second precursor.

[0004] JP 2024-56943 A

[0005] In the plasma-assisted ALD method, a plasma-excited oxidant is introduced. While methods for generating plasma include capacitively coupled plasma (CCP), inductively coupled plasma (ICP), and electron cyclotron resonance (ECR), when using these plasma sources, ions in the plasma collide with the substrate, potentially causing heating of the substrate or defects in the substrate or the formed film. A new film formation method that can prevent ions in the plasma from reaching the substrate is desired.

[0006] A primary object of the present disclosure is to provide a new method for forming an oxide film containing indium oxide and gallium oxide.

[0007] The aspects of the present disclosure that solve the above problems are as follows.

[0008] [1] A film formation method including a step of forming an oxide film containing indium oxide and gallium oxide on a substrate using microwave remote plasma. [2] The film formation method according to [1], wherein the oxide film is formed by plasma-assisted ALD using microwave remote plasma. [3] The film formation method according to [1] or [2], wherein the step includes the steps of: supplying a precursor containing indium to a chamber in which a substrate is placed; supplying an oxidizing gas plasmatized in a plasma generation unit separate from the chamber to the chamber to form an oxide film containing indium oxide; supplying a precursor containing gallium to the chamber; and supplying the oxidizing gas plasmatized in the plasma generation unit to the chamber to form an oxide film containing gallium oxide. [4] The film formation method according to any one of [1] to [3], wherein the substrate surface reacted with the precursor containing indium or gallium is plasma-oxidized for an oxidation time of 10 seconds or more in the step. [5] The film formation method according to any one of [1] to [4], wherein the step is performed under conditions where the substrate temperature is 100°C to 500°C. [6] A film formation apparatus for forming an oxide film containing indium oxide and gallium oxide on a substrate, comprising: a chamber having a mounting table for mounting the substrate and a temperature control mechanism, a microwave remote plasma device connected to an upper part of the chamber, and a control unit for controlling operation of the film formation apparatus, the microwave remote plasma device having a microwave generation unit for generating microwaves and a plasma generation unit for generating plasma by the microwaves generated in the microwave generation unit, a precursor supply source connected to the chamber, and an oxidant supply source connected to the plasma generation unit. [7] A method for producing an oxide film, comprising a step of forming an oxide film containing indium oxide and gallium oxide on a substrate by microwave remote plasma.

[0009] According to the present disclosure, a new method for forming an oxide film containing indium oxide and gallium oxide can be provided.

[0010] FIG. 1 is an explanatory diagram illustrating a film formation method of the present embodiment; FIG. 2 is a diagram illustrating an example of a configuration of a film formation apparatus used in the film formation method of the present embodiment; FIG. 3 is a flowchart illustrating an example of a film formation method of the present embodiment; FIG. 4 is a flowchart illustrating an example of a film formation method of the present embodiment; FIG. 5 is a diagram illustrating processing conditions and evaluation results of an experimental example and a comparative experimental example; FIG. 6 is a diagram illustrating the configuration of FETs in each experimental example and a comparative experimental example; FIG. 7 is an optical microscope photograph of the FETs in the experimental examples; and FIG. 8 is a diagram illustrating the transfer characteristics of the FETs in experimental examples 1 to 7. g 1 is a diagram showing the field-effect mobility calculated from the transfer characteristics of the FET of Experimental Example 2. 2 is a diagram showing the relationship between oxidation time and field-effect mobility for the FETs of Experimental Examples 1 to 7 and Comparative Experimental Examples 1 to 5. 3 is a diagram showing the relationship between oxidation time and threshold voltage for the FETs of Experimental Examples 1 to 7 and Comparative Experimental Examples 1 to 5. 4 is a diagram showing the relationship between oxidation time and SS for the FETs of Experimental Examples 1 to 7 and Comparative Experimental Examples 1 to 5. 5 is a diagram showing the results of XPS analysis of oxide films of Experimental Examples. 6 is a diagram showing the results of XPS analysis of oxide films of Experimental Examples. 7 is a diagram showing XRD patterns of oxide films of Experimental Examples 1 to 3. 8 is a diagram showing the results of surface observation by atomic force microscope for the oxide films of Experimental Example 1 and Comparative Experimental Example 1. 9 is a diagram showing the relationship between oxidation time and mean square roughness of the surface for the oxide films of Experimental Examples 1 to 3 and 5 and Comparative Experimental Examples 1 to 3 and 5.

[0011] Preferred embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. The elements listed below can be combined in any way, and the scope of the present invention is intended to include all modifications within the scope of the claims and ranges equivalent to the claims. Furthermore, in this specification, the upper and lower limits exemplified for numerical ranges can be combined in any way to form new numerical ranges. For example, when "A or more and B or less" and "C or more and D or less" are described, the ranges "A or more and D or less" and "C or more and B or less" can also be included in the numerical range.

[0012] The film formation method of this embodiment includes a step of forming an oxide film containing indium oxide and gallium oxide on a substrate by microwave remote plasma.

[0013] The present inventors have investigated a method for forming an oxide film of an IGZO-based material containing indium oxide and gallium oxide on a semiconductor substrate by plasma-assisted ALD.

[0014] The ALD method is a film formation technique that deposits atomic layers one by one on a substrate through a surface chemical reaction between a precursor and an oxidizing gas. While sputtering is known as one of the film formation techniques, the deposited oxide film has poor step coverage. To deposit multiple materials, such as IGZO-based materials, using sputtering may require multiple sputtering targets and multiple chambers. Furthermore, sputtered particles and ions may cause film damage or introduce stress into the thin film. The ALD method achieves good step coverage with less damage than sputtering, and is believed to be able to provide semiconductor devices with good electrical properties.

[0015] Among these, plasma-assisted ALD, which uses plasma, has a higher oxidizing power than thermal ALD and allows for film formation at lower temperatures. In the oxidation process of plasma-assisted ALD, an oxidizing gas is converted into plasma to oxidize a precursor adsorbed on a substrate. The time required for the oxidation process varies depending on the type of precursor. While easily oxidizable materials can be oxidized within approximately one second, resistant materials require several tens of seconds or more. Trimethylgallium, contained in IGZO-based materials, is one type of resistant material. Therefore, for IGZO-based materials containing gallium oxide, the oxidation process in the ALD method takes a long time. The inventors have confirmed that if a material is continuously exposed to plasma after oxidation is complete, ions in the plasma heat the semiconductor substrate and cause defects in the substrate or deposited film, resulting in degradation of the electrical characteristics of the device.

[0016] Conventionally, CCP, ICP, and ECR have been used as plasma sources. However, when these plasmas are used, ions generated in the plasma source collide with the semiconductor substrate, causing heating and defects in the semiconductor substrate, and therefore, processing in a short time is desirable.

[0017] The above-mentioned phenomenon, which leads to degradation of electrical properties, is more likely to occur when forming an IGZO-based film composed of multiple materials, including a material that is difficult to oxidize in a short time. The inventors have confirmed that ion defects in the oxide film increase over time during the long-term oxidation process of a difficult-to-oxidize material. Specifically, if the oxidation time required for a second material is longer than that required for a first material, defects will occur in the oxide layer of the first material formed earlier during the oxidation process of the second material, degrading the electrical properties of devices using this oxide film, such as field-effect transistors (FETs). For this reason, a plasma source for the plasma-assisted ALD method used to form IGZO-based materials is required that has the oxidizing power to oxidize the difficult-to-oxidize material while preventing ions from reaching the substrate. After extensive research, the inventors have come up with the novel idea of ​​using microwave remote plasma as a plasma source for the ALD method.

[0018] The plasma source used in plasma-assisted ALD is a remote plasma, which allows separation of the gas reactor chamber and the plasma generation unit that generates the plasma. This allows ions in the plasma to be deactivated before they reach the substrate to be processed. This reduces heating and defects in the substrate caused by ions, and prevents deterioration of the electrical characteristics of the device. Furthermore, using microwave plasma as the plasma generation source allows for the decomposition of more gases and the supply of a sufficient amount of radicals for oxidizing difficult-to-oxidize materials.

[0019] In the film forming method of the present embodiment, an oxide film containing an IGZO-based material is formed on the surface of a substrate to be processed. In this specification, the oxide film containing an IGZO-based material is an oxide film containing indium oxide (In2O 3 The oxide film containing an IGZO-based material may further contain zinc oxide (ZnO). The oxide film containing an IGZO-based material may further contain oxides of aluminum, yttrium, scandium, tin, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, or the like. In this specification, an oxide film containing an IGZO-based material refers to a semiconductor thin film having a crystalline structure or an amorphous structure, and may be selected appropriately depending on the required characteristics of the semiconductor device. In the film formation method of this embodiment, two or more oxide films made of different IGZO-based materials may be stacked.

[0020] In this specification, the terms "film," "thin film," or "oxide film" and the term "layer" may be interchangeable in some cases. Also, in this specification, the terms "channel film" and "indium oxide film" may be interchangeable in some cases.

[0021] Fig. 1 is an explanatory diagram illustrating a film formation method according to the present embodiment. Fig. 2 is a diagram illustrating an example of the configuration of a film formation apparatus 20 used in the film formation method according to the present embodiment. The film formation method according to the present embodiment will be described in detail with reference to Figs. 1 and 2.

[0022] The film formation method of this embodiment includes the steps of (1) preparing a substrate to be processed, (2) forming an oxide film containing indium oxide on the substrate, and (3) forming an oxide film containing gallium oxide on the substrate.

[0023] In step 1, a substrate is prepared. Step 1 includes, for example, a step of forming hydroxyl groups on the surface of the substrate by cleaning the substrate before film formation. Step 1 may also include a step of placing the substrate 10 inside the film formation apparatus 20. The substrate on which film formation is performed is not particularly limited, and examples thereof include a semiconductor substrate, an insulator substrate, a conductor substrate, etc., with a semiconductor substrate being preferred. Examples of materials for the semiconductor substrate include silicon, germanium, silicon carbide, silicon germanium, gallium arsenide, gallium nitride, diamond, etc., with silicon being preferred. Examples of materials for the insulator substrate include glass, quartz, resin, etc. Examples of materials for the conductor substrate include graphite, metal, alloy, etc.

[0024] As the substrate, various substrates on which semiconductor materials, insulating materials, or conductive materials are deposited, and substrates whose surfaces are covered with a plurality of materials including semiconductor materials, insulating materials, and conductive materials can also be used.

[0025] An insulating film may be formed on the substrate. Examples of insulating films include silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum nitride, scandium nitride, hafnium oxide, zirconium oxide, aluminum oxide, tantalum oxide, lanthanum oxide, yttrium oxide, titanium oxide, strontium tantalate, and lead zirconate titanate, with silicon oxide being preferred. An insulating film formed by stacking a plurality of the insulating films described above, or a composite oxide film, composite nitride film, or composite oxynitride film formed by mixing a plurality of the insulating films described above may be formed on the substrate. The method for forming the insulating film on the substrate is not particularly limited, and any appropriate film formation method such as chemical vapor deposition (CVD), atomic layer deposition (ALD), or sputtering may be used.

[0026] In this embodiment, the substrate to be processed is a silicon substrate, and a silicon oxide film is formed on one surface of the substrate.

[0027] In steps 2 and 3, a film is formed using a film formation apparatus 20. The film formation apparatus 20 of this embodiment is an apparatus for forming a film by a plasma-assisted ALD method using microwave remote plasma. As shown in FIG. 2 , the film formation apparatus 20 includes a chamber 21, a microwave remote plasma device 22 disposed outside the chamber 21, and a control unit 23 that controls the operation of the film formation apparatus 20.

[0028] The chamber 21 has, for example, a substantially cylindrical shape. A mounting table 211 on which a substrate is placed is provided inside the chamber 21. The silicon substrate is placed in the chamber 21 while being supported by the mounting table 211. A temperature adjustment mechanism 212 including, for example, a heater, a coolant flow path, etc. is provided inside the mounting table 211. By operating the temperature adjustment mechanism 212, it is possible to adjust the temperatures of the mounting table 211 and the silicon substrate.

[0029] A plasma inlet 213 is provided at the top of the chamber 21, through which plasma generated by the microwave remote plasma device 22 is introduced. A gas inlet 214, which is connected to a gas supply source (precursor supply source) (not shown) and through which a process gas supplied from the gas supply source is introduced, is provided at one side wall of the chamber 21. A gas outlet 215, which discharges gas from the chamber 21, is provided at the other side wall of the chamber 21. An exhaust device such as a vacuum pump is connected to the gas outlet 215 via an exhaust pipe (not shown). By operating the exhaust device, the pressure inside the chamber 21 can be reduced to a predetermined level.

[0030] The microwave remote plasma device 22 generates plasma for exciting a process gas using microwaves. The microwave remote plasma device 22 includes a plasma generation unit 221 connected to the upper part of the chamber 21, a microwave generation unit 222 that generates microwaves, and a waveguide 223 that guides the microwaves generated by the microwave generation unit 222 to the plasma generation unit 221.

[0031] A gas inlet 224 connected to an oxidizing gas supply source (not shown) for introducing oxidizing gas supplied from the oxidizing gas supply source is provided on the side wall of the plasma generating unit 221. A pipe 225 is provided on the bottom of the plasma generating unit 221 for introducing plasma generated in the microwave remote plasma device 22 into the chamber 21 through the plasma inlet 213 of the chamber 21.

[0032] The control unit 23 is a computer and includes a processor such as a central processing unit (CPU) (not shown), a memory, an input / output interface, etc. The control unit 23 receives settings of processing conditions and outputs control signals according to the received conditions to the temperature adjustment mechanism 212, the microwave generation unit 222, the plasma generation unit 221, etc., to control their operation. The control unit 23 controls, for example, the set temperature of the temperature adjustment mechanism 212, the pressure of the oxidizing gas in the microwave remote plasma device 22, the microwave frequency, the microwave power, the plasma ignition time, etc.

[0033] Step 2 includes the steps of (2-1) supplying a precursor for forming indium oxide as a process gas into chamber 21 in which a silicon substrate is placed, (2-2) discharging excess precursor, reaction products, etc. from chamber 21, (2-3) supplying an oxidizing gas into chamber 21 to oxidize the precursor on the silicon substrate, and (2-4) discharging excess oxidizing gas, reaction products, etc. from chamber 21. Steps 2-1, 2-2, 2-3, and 2-4 are performed in this order.

[0034] In step 2-1, under a predetermined reduced pressure, a precursor (process gas) is introduced into the chamber 21 while the mounting table 211 on which the silicon substrate is placed is heated to a predetermined temperature. Examples of the precursor include trimethylindium, triethylindium, and cyclopentadienylindium, and triethylindium is preferred. In the following description, the precursor is assumed to be triethylindium.

[0035] In step 2-1, triethylindium is supplied to the surface of the silicon substrate on which hydroxy groups have been formed. When the ethyl groups of triethylindium come into contact with the hydroxy groups on the substrate, methane, ethane, or an intermediate product is produced, and the product is released into the space (or vacuum space) within chamber 21. At the same time, a bond is formed between an indium atom and an oxygen atom.

[0036] In step 2-2, while an inert gas is flowing into the chamber 21, the surplus precursor not used in the reaction in step 2-1 and the product methane or ethane or intermediate product are discharged (exhausted) from the gas outlet 215 of the chamber 21. As the inert gas, for example, N 2 , Ar, etc., and preferably N 2 In step 2-2, the precursor and methane or ethane or intermediate product may be discharged by a method such as vacuum evacuation.

[0037] In step 2-3, an oxidizing gas is introduced into the plasma generating unit 221 through the gas inlet 224. The oxidizing gas may be, for example, O 2 , H 2 O, O 3 and the like, and preferably O 2 The oxidizing gas may be used alone or in combination of two or more. 2 , N 2 may be added.

[0038] In step 2-3, the oxidizing gas in the plasma generating unit 221 is converted into plasma by microwaves introduced from the microwave generating unit 222, and is introduced into the chamber 21 through the plasma inlet 213. The oxidizing gas in plasma oxidizes the surface of the silicon substrate, forming hydroxyl groups that are in a bonded state capable of reacting with the ethyl groups of the triethylindium.

[0039] In step 2-4, while an inert gas is flowing into the chamber 21, the excess oxidizing gas that was not used in the reaction in step 2-3 and the product methane or ethane or intermediate products are discharged (exhausted) from the gas outlet 215 of the chamber 21. As the inert gas, for example, N 2 , Ar, etc. In step 2-4, the precursor and ethane may be discharged by a method such as evacuation.

[0040] As processing conditions for steps 2-1 to 2-4, the temperatures of the mounting table 211 and the silicon substrate are, for example, 100°C to 500°C, preferably 150°C to 300°C, and more preferably 150°C to 200°C. The above temperatures may be determined taking into consideration the ALD window of the precursor. The ALD window is an appropriate temperature range in which the self-terminating mechanism of the surface chemical reaction operates and atomic layers can be formed one by one. The ALD window varies depending on the type of precursor and the type of oxidizer. When forming films using multiple types of precursors sequentially, as in this embodiment, it is preferable to set the processing conditions to a temperature range that falls within the ALD windows of all precursors. In the case of precursors containing indium-based materials, such as triethylindium, the ALD window is relatively narrow, but by using microwave remote plasma, processing can be performed effectively even under such temperature conditions.

[0041] The treatment conditions in step 2-3 include an oxidation gas pressure of, for example, 0.1 Pa to 150 Pa. The microwave frequency is, for example, 2.4 GHz to 2.5 GHz, and the microwave power is 50 W to 3000 W, preferably 100 W to 1000 W, and more preferably 200 W to 450 W. The oxidation time is, for example, 1 sec to 300 sec, preferably 10 sec to 100 sec, and more preferably 10 sec to 60 sec. The oxidation time is the treatment time (plasma ignition time) of the plasma oxidation treatment in step 2-3.

[0042] Step 3 includes the steps of (3-1) supplying a precursor for forming gallium oxide into the chamber 21, (3-2) discharging excess precursor, reaction products, etc. from the chamber 21, (3-3) supplying an oxidizing gas into the chamber 21 to oxidize the precursor on the silicon substrate, and (3-4) discharging excess oxidizing gas, reaction products, etc. from the chamber 21. Steps 3-1, 3-2, 3-3, and 3-4 are performed in this order.

[0043] Examples of precursors in step 3-1 include trimethylgallium, triethylgallium, dimethylchlorogallium, and diethylchlorogallium, with trimethylgallium being preferred. Steps 3-1 to 3-4 are similar to step 2 except that the precursor is replaced with a gallium source, and therefore detailed explanations will be omitted. Note that the processing conditions may be appropriately set depending on the type of precursor.

[0044] As shown in FIG. 1, a series of processes from steps 2-1 to 2-4 forms an indium oxide layer 12 (In 2 O 3 Furthermore, a gallium oxide layer 13 (GaO layer) containing gallium and oxygen is formed on the indium oxide layer 12 by a series of processes from step 3-1 to step 3-4. 2 O 3 One layer (layer) is formed.

[0045] The film formation method of this embodiment may further include a step (4) of forming an oxide film containing a component other than indium oxide and gallium oxide on the substrate. Examples of the component other than indium oxide and gallium oxide include components that can be contained in the oxide film containing the above-mentioned IGZO-based material, and zinc oxide is preferred. Hereinafter, step 4 will be referred to as the step of forming an oxide film containing zinc oxide.

[0046] Step 4 includes the steps of (4-1) supplying a precursor for forming zinc oxide into the chamber 21, (4-2) discharging excess precursor, reaction products, etc. from the chamber 21, (4-3) supplying an oxidizing gas into the chamber 21 to oxidize the precursor on the silicon substrate, and (4-4) discharging excess oxidizing gas, reaction products, etc. from the chamber 21. Steps 4-1, 4-2, 4-3, and 4-4 are performed in this order.

[0047] Examples of precursors in step 4-1 include dimethyl zinc and diethyl zinc. Steps 4-1 to 4-4 are the same as step 2 except that the precursor is changed to zinc, and therefore detailed explanations will be omitted. A zinc oxide layer containing zinc and oxygen is formed on the silicon substrate 10 by a series of processes from step 4-1 to 4-4.

[0048] 1 shows an example in which an indium oxide layer 12 and a gallium oxide layer 13 are stacked in this order on a silicon substrate 10, but in the film formation method of this embodiment, the order in which steps 2 to 4 are performed and the number of times they are performed are not limited. For example, the steps may be performed in the order of step 4, step 3, and step 2, or in the order of step 3, step 2, and step 4. Furthermore, a specific step may be repeated multiple times before the next step is performed. The film thickness can be adjusted by adjusting the number of repetitions.

[0049] In the film forming method of this embodiment, the total thickness of the oxide film formed on the substrate is, for example, 1 nm to 10 nm, and preferably 3 nm to 7 nm.

[0050] 3 and 4 are flowcharts showing an example of the film forming method of this embodiment. In step S10, a substrate having hydroxy groups formed thereon is prepared (step 1). In step S20, a first oxide film (e.g., an indium oxide film) is formed on the substrate using a first precursor (e.g., triethylindium) (step 2). Step S20 includes the steps of supplying the first precursor to chamber 21 (step 2-1) in step S21, supplying an inert gas to chamber 21 and discharging excess gas in step S22 (step 2-2), oxidizing the first precursor on the substrate with plasmatized oxidizing gas in step S23 (step 2-3), and supplying the inert gas to chamber 21 and discharging excess gas in step S24 (step 2-4).

[0051] Next, in step S25, it is determined whether the number of repetitions of steps S21 to S24 has reached a preset number. If the number of repetitions has not reached the preset number (S25: NO), the process returns to step S20. If the number of repetitions has reached the preset number (S25: YES), it is determined in step S26 whether the thickness of the oxide film on the substrate has not reached the preset thickness. If the thickness has reached the preset thickness (S26: NO), the film formation process is terminated. If the thickness has not reached the preset thickness (S26: YES), the process proceeds to forming a second oxide film.

[0052] In step S30, a second oxide film (e.g., a gallium oxide film) is formed on the substrate using a second precursor (e.g., trimethylgallium) (step 3). Step S30 includes the steps of supplying the second precursor to chamber 21 in step S31 (step 3-1), supplying an inert gas to chamber 21 and discharging excess gas in step S32 (step 3-2), oxidizing the second precursor on the substrate with plasmatized oxidizing gas in step S33 (step 3-3), and supplying the inert gas to chamber 21 and discharging excess gas in step S34 (step 3-4).

[0053] Next, in step S35, it is determined whether the number of repetitions of steps S31 to S34 has reached a preset number. If the number of repetitions has not reached the preset number (S35: NO), the process returns to step S30. If the number of repetitions has reached the preset number (S35: YES), it is determined in step S36 whether the thickness of the oxide film on the substrate has not reached the preset thickness. If the thickness has reached the preset thickness (S36: NO), the film formation process is terminated. If the thickness has not reached the preset thickness (S36: YES), the process proceeds to step S37.

[0054] In step S37, it is determined whether a third oxide film (e.g., zinc oxide) is to be formed on the substrate using a third precursor. If a third precursor is not to be used (S37: NO), the process returns to step S20. If a third precursor is to be used (S37: YES), the process proceeds to the formation of a third oxide film.

[0055] In step S40, a third oxide film is formed on the substrate using a third precursor (step 3). Step S40 includes the steps of supplying the third precursor to chamber 21 in step S41 (step 4-1), supplying an inert gas to chamber 21 and discharging excess gas in step S42 (step 4-2), oxidizing the third precursor on the substrate with plasmatized oxidizing gas in step S43 (step 4-3), and supplying the inert gas to chamber 21 and discharging excess gas in step S44 (step 4-4).

[0056] Next, in step S45, it is determined whether the number of repetitions of steps S41 to S44 has reached a preset number. If the number of repetitions has not reached the preset number (S45: NO), the process returns to step S40. If the number of repetitions has reached the preset number (S45: YES), it is determined in step S46 whether the thickness of the oxide film on the substrate has reached a preset thickness. If the thickness has not reached the preset thickness (S46: NO), the process returns to step S20, and the first oxide film is formed again. If the thickness has reached the preset thickness (S46: YES), the film formation process ends.

[0057] According to the film formation method of the present embodiment, it is possible to form an oxide film containing an IGZO-based material having good electrical properties on a substrate while suppressing heating of the substrate and the occurrence of ion defects in the substrate or the deposited film, and therefore the method can be suitably applied to film formation on substrates used for field-effect transistors (FETs), thin-film transistors (TFTs), semiconductor memories, chemical sensors, etc.

[0058] The present embodiment provides a method for producing an oxide film, which includes forming an oxide film containing indium oxide and gallium oxide on a substrate by microwave remote plasma.

[0059] The present invention will be explained in more detail below based on experimental examples and comparative experimental examples, but it is not intended that the present invention be limited to these experimental examples.

[0060] [Experimental Examples 1 to 10] A Si substrate was prepared, and SiO was formed on the Si substrate by thermal oxidation. 2 The Si substrate is a low-resistance substrate with a high concentration of impurities added, and therefore can be used as an electrode, corresponding to the gate electrode of the device shown in this example. 2 The Si substrate having the film is cleaned with a solution of sulfuric acid and hydrogen peroxide, and then SiO 2 The film surface was subjected to UV / O3 treatment. 2 On the film, an indium oxide film (In) was deposited by the ALD apparatus using microwave remote plasma according to the procedure of step 2 described above. 2 O 3 A film (film, thickness approximately 5 nm) was formed. The precursor used in the film formation was triethylindium (TEIn), the inert gas was N2, and the oxidizing gas was O2. Figure 5 shows the processing conditions and evaluation results of an experimental example and a comparative experimental example. In order to investigate the effects of the film formation conditions, oxidation time, and microwave power on the device characteristics, samples were fabricated by changing the film formation conditions, oxidation time, and microwave power as shown in Figure 5.

[0061] Fig. 6 shows an example of a time chart for the oxide film formation process. Fig. 6 shows an example in which the oxidation time (plasma ignition time) was set to 20 seconds. As shown in Fig. 6, the oxide film was formed by sequentially performing (step 2-1) supplying triethylindium, (step 2-2) purging with N2, (step 2-3) oxidation with O2, and (step 2-4) purging with N2.

[0062] After the film formation, the indium oxide was patterned by photolithography and wet etching using an oxalic acid solution or dilute hydrochloric acid, and the indium oxide film was crystallized by atmospheric annealing at 450° C. for 2 hours. 2 Membrane and In 2 O 3 A photoresist pattern for the source and drain electrodes was formed on a portion of the film, and a platinum / tungsten (Pt / W, thickness 20 / 80 nm) laminated film was deposited by sputtering, and the source / drain electrodes were formed by lift-off. After that, an indium oxide film and SiO 2 A gallium oxide film (Ga 2 O 3 After the film formation, contact holes were formed on the source / drain electrodes by photolithography and wet etching with a tetramethylammonium hydroxide solution. 2 Annealing was carried out to obtain the FETs of Experimental Examples 1 to 10. The electrical characteristics of the fabricated FETs were measured at room temperature in a dark place using a probe box and a semiconductor device analyzer.

[0063] Comparative Experimental Examples 1 to 5 FETs of Comparative Experimental Examples 1 to 5 were fabricated in the same manner as Experimental Example 1, except that in forming the indium oxide film, the plasma source in the plasma-assisted ALD method was changed to CCP and the oxidation time was set as shown in FIG. 5 .

[0064] Fig. 7 shows the structure of the FETs of each experimental example and comparative example. Fig. 8 shows an optical microscope photograph of the FETs of the experimental examples. The channel length and channel width of the FETs in Fig. 8 are 90 and 10 μm, respectively.

[0065] <Performance Evaluation> The transfer characteristics (I d -V g The transfer characteristics were measured by applying a drain voltage V between the source and drain electrodes with the source electrode as the reference potential. d = 0.1V [V] is applied between the source and gate in this state. g The measurement was performed by applying a gate voltage V g was swept from -20 [V] to 20 [V] at 50 [mV] intervals. d is the current (drain current) flowing between the source and drain electrodes. Based on the measured transfer characteristics, the following characteristic values ​​were calculated. The transfer characteristics were measured for 10 elements with a channel width W of 90 μm and a channel length L of 10 μm (see FIG. 7) under each set of conditions. The calculation results are shown in FIG. 5. For each FET, FIG. 5 shows the average value±standard deviation of each characteristic value calculated from the measurement results of 10 elements.

[0066] (field-effect mobility μ FE ) Field-effect mobility μ FE [cm 2 / Vs] is calculated by the following formula (1): FE is V normalized using the threshold voltage g -V th The field effect mobility μ FEThe larger the value, the better the performance of the device.

[0067]

[0068] In formula (1), g m is the transconductance [S], W is the channel width [μm], L is the channel length [μm], C i is the gate insulating film (SiO 2 Capacitance per unit area of ​​the film [F / cm 2 ], V d is the drain voltage [V]. m can be calculated by differentiating the drain current obtained by measuring the transfer characteristics with respect to the gate voltage. i is SiO 2 The film thickness (80 nm), relative dielectric constant (3.9), and dielectric constant of vacuum (8.854 × 10 -12 [F / m]).

[0069] (threshold voltage V th ) Threshold voltage V th [V] is the gate voltage V g When the drain current I d The gate voltage V when g In this experimental example, the value of I in the transfer characteristics of the FET d = 1 [nA] when V g is the threshold voltage V th It was defined as follows.

[0070] (SS (Subthreshold Swing)) SS [mV / decade] is the value of the drain current I d The gate voltage V required to increase by one order of magnitude g SS is calculated by the following formula (2). In this experimental example, I d The minimum value of the calculated value in the range of 10 pA to 100 pA was defined as the subthreshold swing SS. The smaller the SS value, the more the SiO 2 In-film and semiconductor / SiO 2 This means that the defect density at the film interface is low.

[0071]

[0072] 9 is a diagram showing the transfer characteristics of the FETs of Experimental Examples 1 to 7. In FIG. 9, the horizontal axis represents the gate voltage V g [V], and the left vertical axis represents the drain current I d The W / L (channel width / channel length of the FET) shown in the figure is determined by the aspect ratio of the source / drain electrodes and the channel film, and V d is the drain voltage V d The channel length L is defined by the distance between the source / drain electrodes and the source electrode, and the channel width W is defined by the width of the indium oxide channel film. The drain current I d is the gate voltage V g A rise from the off-state current was observed near 0 V, and good switching characteristics were confirmed under all oxidation time conditions.

[0073] FIG. 10 shows the output characteristics of the FET of Experimental Example 2, with respect to the gate voltage V g In FIG. 10, the horizontal axis represents the drain voltage V d [V], and the vertical axis represents the drain current I d As can be seen from FIG. 10, the drain current I d It can be seen that is saturated.

[0074] 11 is a graph showing the field-effect mobility calculated from the transfer characteristics of the FET of Experimental Example 2. In FIG. 11, the horizontal axis represents the gate voltage V g [V], and the left vertical axis represents the drain current I d [A], and the right vertical axis represents the field-effect mobility μ FE [cm 2 In FIG. 11, the solid line represents the transfer characteristic, and the dashed line represents the field-effect mobility μ calculated from the transfer characteristic shown by the solid line. FE As shown in the transfer characteristic, the drain current I d is the gate voltage V g This indicates that the drain current I d V g It was confirmed that the indium oxide channel film functioned as a semiconductor.g With the increase of FE It is clear that the performance of the device is improved by the injection of carriers into the channel region due to the field effect.

[0075] 12 is a graph showing the relationship between oxidation time and field-effect mobility for the FETs of Experimental Examples 1 to 7 and Comparative Experimental Examples 1 to 5. In FIG. 12, the horizontal axis represents oxidation time [sec], and the vertical axis represents field-effect mobility μ FE [cm 2 In the FET of the experimental example using microwave remote plasma, the field effect mobility μ FE In other words, it can be seen that even if the oxidation time is extended, the device performance does not deteriorate. Although the mechanism is not clear, it is presumed that the long oxidation time reduces unreacted precursor components and impurities that cause scattering of conduction electrons. On the other hand, in the FET of the comparative experiment using CCP, the field effect mobility μ FE The results showed that the oxidation time was long, which is thought to be due to increased ion bombardment of the device and semiconductor channel film, resulting in a deterioration in film quality. These results confirmed that the use of microwave remote plasma can reduce damage to devices caused by ion bombardment, and suppress deterioration in device performance, even when the oxidation time is long.

[0076] 13 is a graph showing the relationship between oxidation time and threshold voltage for the FETs of Experimental Examples 1 to 7 and Comparative Experimental Examples 1 to 5. In FIG. 13, the horizontal axis represents oxidation time [sec], and the vertical axis represents threshold voltage V th In the case of the FET of the experimental example, the threshold voltage V th However, in the case of the FET of the comparative experiment, the threshold voltage V th It can be seen that the variation in threshold voltage V th The variation is evident.

[0077] FIG. 14 is a diagram showing the relationship between oxidation time and SS for the FETs of Experimental Examples 1 to 7 and Comparative Experimental Examples 1 to 5. In FIG. 14, the horizontal axis represents oxidation time [sec], and the vertical axis represents SS [mV / decade]. In the FETs of the Experimental Examples, no increase in SS was observed even when the oxidation time was increased, and it can be seen that no deterioration in device performance occurred. In contrast, in the FET of the Comparative Experimental Example, SS increased significantly at an oxidation time of 60 seconds, which means that the rise characteristics deteriorate as the oxidation time increases. The smaller the SS value, the greater the amount of SiO in the semiconductor channel film. 2 In-film and semiconductor / SiO 2 This suggests a low defect density at the film interface, and it was confirmed that the use of microwave remote plasma can reduce damage caused by ion bombardment to the semiconductor channel film, even when the oxidation time is long, thereby suppressing deterioration of device performance.

[0078] The indium oxide film used in the FET of the experimental example was analyzed by X-ray photoelectron spectroscopy (XPS). 2 O 3 The chemical bonding state of the film surface was confirmed. Figures 15 and 16 show the results of XPS analysis of the oxide film of Experimental Example. The upper left of Figure 15 is an XPS wide scan profile of the surface of the FET of Experimental Example 2. The upper right, lower left, and lower right of Figure 15 are O1s spectra obtained by XPS analysis of the FETs of Experimental Example 2 (oxidation time: 20 seconds), Experimental Example 3 (oxidation time: 10 seconds), and Experimental Example 5 (oxidation time: 5 seconds), respectively. In the upper right, lower left, and lower right of Figure 15, circles (○) represent values ​​measured using XPS, and the solid lines represent the spectra of O-In, Ov, and O-C or O-H, and the spectra (composite function) fitted by combining the composite spectrum. Figure 16 shows the percentage of the area of ​​each of the spectra of O-In, Ov, and O-C or O-H to the total area.

[0079] From the XPS wide scan profile, a spectrum originating from indium oxide was confirmed on the surface of the indium oxide film used in the FET of Experimental Example 2. Furthermore, a comparison of the O1s spectra for each oxidation time reveals that as the oxidation time increases, the proportion of O—In increases, and the proportions of Ov, O—C, or O—H caused by oxygen defects decrease. From these results, it is inferred that as the oxidation progresses, impurities and oxygen defects decrease, and high-purity indium oxide with few defects is formed on the substrate, thereby improving the field-effect mobility of the FET.

[0080] In order to identify the crystal structure of the indium oxide film used in the FETs of the experimental examples, X-ray diffraction (XRD) measurements were carried out. Figure 17 shows the XRD patterns of the oxide films of Experimental Examples 1 to 3. As shown in Figure 17, the In 2 Diffraction peaks due to the bixbyite structure of O3 were confirmed. Furthermore, as can be seen from Figure 17, the longer the oxidation time, the better the crystallinity. Therefore, even a long oxidation time does not significantly reduce the crystallinity of the channel film. Furthermore, since the 400 peak in particular becomes clearer as the oxidation time increases, it is believed that indium oxide with higher purity and better crystallinity is growing, which is presumed to contribute to improving the field-effect mobility of the FET.

[0081] The indium oxide films used in the FETs of the experimental and comparative experimental examples were examined by atomic force microscope (AFM) immediately after deposition. 2 O 3 The surface shapes of the films were confirmed. Figure 18 is a diagram showing the results of surface observation by atomic force microscope of the oxide films of Experimental Example 1 and Comparative Experimental Example 1. The upper left and lower left of Figure 18 are respectively a three-dimensional diagram and a two-dimensional diagram of the surface observation results of the indium oxide film obtained by Experimental Example 1. The upper right and lower right of Figure 18 are respectively a three-dimensional diagram and a two-dimensional diagram of the surface observation results of the indium oxide film obtained by Comparative Experimental Example 1. Figure 18 shows that the surface of the indium oxide film formed using microwave remote plasma in the Experimental Example is flat, but multiple irregularities are confirmed on the surface of the indium oxide film of the Comparative Experimental Example using CCP, making it rough.

[0082] FIG. 19 shows the relationship between the oxidation time and the root mean square roughness R ｑ 1 is a diagram showing the relationship between the mean square roughness R ｑ is a value calculated from the surface shape observed using software attached to the AFM measurement, and a smaller value indicates a flatter surface shape. From FIG. 19, in the experimental example using microwave remote plasma, the mean square surface roughness R ｑ On the other hand, in the comparative experiment using CCP, the root mean square surface roughness R of the indium oxide film increases with increasing oxidation time. ｑ It can be seen that the surface roughness increases and the surface shape becomes rougher. Therefore, by using microwave remote plasma, it is possible to maintain a flat surface shape of the channel film even over a long oxidation time. Surface roughness of the channel film not only reduces the voltage resistance of the FET device, but is also thought to be a factor in scattering of conduction electrons. Therefore, it was confirmed that by using microwave remote plasma, damage to the semiconductor channel film caused by ion bombardment and unintentional heating of the substrate can be reduced, and deterioration of device performance can be suppressed, even over a long oxidation time.

[0083] In the above experimental example, only an indium oxide film was deposited using microwave remote plasma. However, because the plasma ALD window for gallium oxide film deposition is wider than that for indium oxide, it is fully expected that gallium oxide films can also be successfully deposited using microwave remote plasma, just like indium oxide films. Furthermore, because the oxidation time required for gallium oxide film deposition is longer than that for indium oxide, there are concerns about the impact on already formed indium oxide films. However, as described above, it has been confirmed that, in this deposition method, even if the oxidation time is extended, the field-effect mobility, which represents the electrical characteristics of FETs, improves or does not decrease, and the SS improves or does not increase. Furthermore, because electron transport in oxide semiconductors is primarily carried out by indium, the state of the indium oxide film dominates the field-effect mobility. Therefore, it is fully expected that the field-effect mobility characteristics of FETs in which an indium oxide film and a gallium oxide film are deposited using remote plasma will also exhibit results similar to those of the above experimental example.

[0084] 20 Film forming device 21 Chamber 22 Microwave remote plasma device 23 Control unit

Claims

1. A film formation method comprising the step of forming an oxide film containing indium oxide and gallium oxide on a substrate using microwave remote plasma.

2. The film forming method according to claim 1, wherein in the step, the oxide film is formed by plasma-assisted ALD using microwave remote plasma.

3. A film forming method according to claim 1 or claim 2, wherein the steps include: supplying a precursor containing indium to a chamber in which a substrate is placed; supplying an oxidizing gas that has been converted into plasma in a plasma generating section separate from the chamber to the chamber to form an oxide film containing indium oxide; supplying a precursor containing gallium to the chamber; and supplying the oxidizing gas that has been converted into plasma in the plasma generating section to the chamber to form an oxide film containing gallium oxide.

4. A film forming method according to any one of claims 1 to 3, wherein in the step, the substrate surface that has reacted with the precursor containing indium or gallium is plasma oxidized for an oxidation time of 10 seconds or more.

5. A film forming method according to any one of claims 1 to 4, wherein the process is carried out under conditions where the substrate temperature is 100°C to 500°C.

6. A film formation apparatus for forming an oxide film containing indium oxide and gallium oxide on a substrate, comprising: a chamber having a stage for placing a substrate thereon and a temperature control mechanism; a microwave remote plasma device connected to an upper part of the chamber; and a control unit for controlling the operation of the film formation apparatus, wherein the microwave remote plasma device comprises a microwave generation unit for generating microwaves and a plasma generation unit for generating plasma using the microwaves generated by the microwave generation unit, and wherein a precursor supply source is connected to the chamber and an oxidant supply source is connected to the plasma generation unit.

7. A method for producing an oxide film, comprising the step of forming an oxide film containing indium oxide and gallium oxide on a substrate by microwave remote plasma.

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