Apparatus and method for producing insulating film on diamond substrate

Abstract

A manufacturing apparatus and a manufacturing method are provided that make it easy to dope hole carriers into the surface of a diamond substrate and that can form an insulating film having a sufficiently high dielectric strength on the diamond substrate. The present invention comprises a vacuum chamber (10), a support (14) for supporting a diamond substrate (1), a heating device (15) for heating the diamond substrate (1), and a device for heating the inside of the vacuum chamber (10) from atmospheric pressure to 2×10 within one hour. -3 The apparatus is equipped with a pressure reducing device that reduces the pressure to below Pa, a dopant supply device that supplies a dopant such as nitrogen dioxide to the vacuum chamber, a nitrogen supply device that supplies nitrogen to the vacuum chamber 10, an aluminum raw material supply device that supplies an organoaluminum compound to the vacuum chamber 10, a water vapor supply device that supplies water vapor to the vacuum chamber 10, and a control device 11 that controls these devices.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for producing an insulating film on a diamond substrate, which can be used in the manufacture of semiconductor devices using the diamond substrate. [Background technology]

[0002] Diamond semiconductors, which have a bandgap energy about five times that of silicon, are attracting attention as power semiconductor elements that can achieve low loss and high-temperature operation under high voltages, and are expected to be used in power semiconductor devices and microwave transmission semiconductor devices.

[0003] Patent Document 1 discloses a method for manufacturing a field effect transistor using diamond, in which a diamond crystal layer having p-type or n-type conductivity is formed using a CVD apparatus or the like, and then gold is evaporated to form source and drain electrodes. Next, oxygen gas, hydrogen gas, and trimethylaluminum are supplied to the diamond crystal layer in a depressurized CVD chamber, and an 8-nm thick Al(OH)3 or Al 1-x-y O x H y An insulating layer made of a compound is formed.

[0004] Patent Document 2 discloses a method for manufacturing a gate insulating film for a transistor, in which a semiconductor layer is formed by MOCVD on a substrate made of gallium nitride, silicon, silicon carbide, or the like, and a source electrode and a drain electrode are formed on the semiconductor layer. Thereafter, a gate insulating film made of aluminum oxide is formed on the semiconductor layer and the source electrode and the drain electrode by atomic deposition using trimethylaluminum (TMA), nitrogen gas, ozone, or the like as a reactive gas.

[0005] However, when an insulating film to be used as a gate insulating film or the like is formed on a diamond substrate, the following problems arise. The first problem was that even if an attempt was made to dope hole carriers into the surface of a diamond substrate by placing the diamond substrate in a vacuum chamber and introducing a dopant gas into the vacuum chamber, bonding between the dopant and the surface of the diamond substrate did not progress, making it difficult to dope hole carriers into the surface of the diamond substrate at a sufficient density.

[0006] The second problem was that when an aluminum oxide (Al2O3) layer was formed as an insulating film on a diamond substrate in a vacuum chamber, it was not possible to obtain the insulating properties necessary to realize a diamond semiconductor element. Due to the above problems, it is currently difficult to manufacture a diamond semiconductor element that has an insulating film with a sufficiently high dielectric strength and that can achieve a high operating current value.

[0007] Therefore, the inventors conducted detailed research into the above problems and discovered that, regarding the first problem, trace amounts of atmospheric components remain on the surface of the diamond substrate as impurities when the substrate is loaded into the atomic layer deposition system, and these remaining atmospheric components prevent the penetration of dopants and inhibit the doping of hole carriers into the surface of the diamond substrate. Furthermore, they discovered that the structure of the vacuum chamber and the setting of the degree of vacuum are important measures to avoid this phenomenon. Regarding the second problem, the inventors discovered that an aluminum oxide (Al2O3) layer formed on a diamond substrate contains residual methyl groups (CH3) and hydrogen atoms, which are impurities for Al2O3, and therefore an aluminum oxide layer having the insulating properties necessary to realize a diamond semiconductor element cannot be obtained, and they have come up with a solution that can reduce the amount of residual impurities. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-158612 [Patent Document 2] International Publication No. WO2014 / 010405A1 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention was made based on the above findings, and an object of the present invention is to provide a manufacturing apparatus and a manufacturing method that can easily dope hole carriers into the surface of a diamond substrate at a sufficient density and can form an insulating film having a sufficiently high dielectric strength voltage on the diamond substrate. [Means for solving the problem]

[0010] [Aspect 1] The apparatus for manufacturing an insulating film on a diamond substrate according to a first aspect of the present invention includes a vacuum chamber, a support for supporting the diamond substrate in the vacuum chamber, a heating device for heating the diamond substrate supported by the support, and a heating device for heating the inside of the vacuum chamber from atmospheric pressure to 2×10 within one hour. -3 the vacuum chamber; a dopant supply device that supplies one or more dopants selected from nitrogen dioxide (NO), nitric oxide (NO), sulfur dioxide (SO), and ozone (O) to the vacuum chamber; a nitrogen supply device that supplies nitrogen (N) to the vacuum chamber; an aluminum raw material supply device that supplies an organoaluminum compound to the vacuum chamber; a water vapor supply device that supplies water vapor (H0) to the vacuum chamber; and a control device that controls the decompression device, the dopant supply device, the nitrogen supply device, the aluminum raw material supply device, and the water vapor supply device.

[0011] [Aspect 2] Aspect 2 of the apparatus for producing an insulating film on a diamond substrate is in accordance with aspect 1, wherein the control device is programmed to perform the following steps in the following order: The pressure in the vacuum chamber was reduced from atmospheric pressure to 2×10 within one hour by the pressure reducing device. -3 Step A: reducing the pressure to below Pa; a step B of supplying the dopant into the vacuum chamber by the dopant supply device; a step C of supplying the nitrogen to the vacuum chamber by the nitrogen supply device; Step D: supplying an organoaluminum compound to the vacuum chamber using the aluminum source supply device; Step E of supplying the nitrogen to the vacuum chamber by the nitrogen supply device; a step F of supplying the water vapor to the vacuum chamber by the water vapor supply device; Step G of supplying the nitrogen to the vacuum chamber by the nitrogen supply device; and Step H is repeating steps D to G multiple times.

[0012] [Aspect 3] Aspect 3 of the apparatus for manufacturing an insulating film on a diamond substrate is in accordance with aspect 2, wherein the control device is programmed to perform step I, between step A and step B, in which steps D to G are repeated one or more times.

[0013] [Aspect 4] In the apparatus for manufacturing an insulating film on a diamond substrate of aspect 4, in aspect 2 or 3, the control device controls the supply time of the organoaluminum compound by the aluminum raw material supply device in step D to be 1 millisecond or more and 25 milliseconds or less, controls the supply time of water vapor by the water vapor supply device in step F to be 1 millisecond or more and 25 milliseconds or less, and controls the interval time between step D and step F to be 1 second or more and 20 seconds or less.

[0014] [Aspect 5] In the apparatus for producing an insulating film on a diamond substrate according to aspect 5, in any one of aspects 1 to 4, the pressure reducing device reduces the pressure in the vacuum chamber from atmospheric pressure to 2×10 -3 The vacuum chamber is depressurized to a pressure of 1.1 x 10 Pa or less, and the ultimate vacuum of the vacuum chamber is 1.1 x 10 -5 Pa or less.

[0015] [Aspect 6] A sixth aspect of the apparatus for producing an insulating film on a diamond substrate is in any one of the first to fifth aspects, wherein the aluminum source supply device supplies alkyl aluminum.

[0016] [Aspect 7] In the apparatus for manufacturing an insulating film on a diamond substrate of aspect 7, in any one of aspects 1 to 6, the vacuum chamber has a vacuum chamber body and a detachable part that can be separated from the vacuum chamber body, and a metal gasket is interposed at the separation surface between the vacuum chamber body and the detachable part.

[0017] [Aspect 8] A method for producing an insulating film on a diamond substrate according to an eighth aspect of the present invention comprises the steps of: The diamond substrate is placed in a vacuum chamber, the vacuum chamber is closed, and the pressure in the vacuum chamber is increased from atmospheric pressure to 2×10 -3 Step A: reducing the pressure to below Pa; Step B: supplying one or more dopants selected from nitrogen dioxide (NO), nitric oxide (NO), sulfur dioxide (SO), and ozone (O) into the vacuum chamber; Step C of supplying nitrogen into the vacuum chamber; Step D: supplying an organoaluminum compound to the vacuum chamber; Step E: supplying nitrogen into the vacuum chamber; a step F of supplying water vapor into the vacuum chamber; Step G of supplying nitrogen to the vacuum chamber; and The method is characterized by comprising a step H in which the steps D to G are repeated multiple times.

[0018] [Aspect 9] A ninth aspect of the method for producing an insulating film on a diamond substrate is the same as the eighth aspect, except that between the step A and the step B, a step I is performed in which the steps D to G are repeated one or more times.

[0019] [Aspect 10] A method for producing an insulating film on a diamond substrate according to aspect 10 is the same as that according to aspect 8 or 9, in which the supply time of the organoaluminum compound in step D is 1 millisecond or more and 25 milliseconds or less, the supply time of water vapor in step F is 1 millisecond or more and 25 milliseconds or less, and the interval time between step D and step F is 1 second or more and 20 seconds or less.

[0020] [Aspect 11] In the method for producing an insulating film on a diamond substrate according to aspect 11, in any one of aspects 8 to 10, in step A, the pressure inside the vacuum chamber is increased from atmospheric pressure to 2×10 -3 The vacuum chamber is depressurized to a pressure of 1.1 x 10 Pa or less, and the ultimate vacuum of the vacuum chamber is 1.1 x 10 -5 Pa or less.

[0021] [Aspect 12] A twelfth aspect of the method for producing an insulating film on a diamond substrate is the same as any one of the eighth to eleventh aspects, in which alkylaluminum is supplied as the organoaluminum compound in the step D.

[0022] [Aspect 13] A thirteenth aspect of the method for producing an insulating film on a diamond substrate is the same as any one of aspects 8 to 12, wherein in step D, the alkyl aluminum has an impurity concentration of less than 10 ppm.

[0023] [Aspect 14] A fourteenth aspect of the method for producing an insulating film on a diamond substrate is the method of any one of the eighth to thirteenth aspects, wherein the carrier gas for the organoaluminum compound and the water vapor is nitrogen (N2), and the purity of the nitrogen is 99.99995% or higher.

[0024] [Aspect 15] A fifteenth aspect of the method for producing an insulating film on a diamond substrate is any one of aspects 8 to 14, wherein in step B, the dopant is diluted with nitrogen (N2), and the concentration of the dopant in this diluted gas is 2% by volume (20,000 ppm) or more.

[0025] [Aspect 16] A method for producing an insulating film on a diamond substrate according to a sixteenth aspect is any one of aspects 8 to 15, in which in step B the diamond substrate is heated to 20 to 90°C to supply the dopant, in steps D to G when forming a first layer of aluminum oxide (Al2O3) film the diamond substrate is heated to 80 to 150°C, and in steps D to G when forming second and subsequent layers of aluminum oxide film the diamond substrate is heated to 200 to 260°C. In this specification, "numerical value A to numerical value B" refers to a value greater than or equal to numerical value A and less than or equal to numerical value B.

[0026] [Aspect 17] A seventeenth aspect of the present invention relates to a method for producing an insulating film on a diamond substrate, and is the same as any one of the eighth to sixteenth aspects, in which the insulating film produced is amorphous aluminum oxide, the insulating film has a dielectric strength of 8 MV / cm or more, and the surface of the diamond substrate is provided with a surface concentration of 5×10 13 cm -2 Higher hole carriers are generated, and the sheet resistance of the surface of the diamond substrate is 1 kΩ / □ or less for the (001) plane orientation of the diamond crystal, and 700 Ω / □ or less for the (111) plane orientation of the diamond crystal. [Effects of the Invention]

[0027] According to the manufacturing apparatus and method of the present invention for manufacturing an insulating film on a diamond substrate, it is easy to dope hole carriers into the surface of the diamond substrate at a high density, and it is also possible to form an insulating film on the diamond substrate that has a sufficiently high dielectric strength voltage. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a block diagram showing an embodiment of an apparatus for manufacturing an insulating film on a diamond substrate according to the present invention. [Figure 2] FIG. [Figure 3] 4 is a timing chart showing gas introduction timing in the embodiment. [Figure 4]1 is a longitudinal sectional view of a diamond substrate immediately after being loaded into a vacuum chamber in an embodiment of a method for producing an insulating film on a diamond substrate according to the present invention. FIG. [Figure 5] FIG. 2 is a longitudinal sectional view of the diamond substrate in step A of the same embodiment. [Figure 6] FIG. 2 is a longitudinal sectional view of a diamond substrate on which a dopant layer has been formed in step B of the same embodiment. [Figure 7] FIG. 10 is a longitudinal sectional view of a diamond substrate to which an organoaluminum compound is attached in step D of the same embodiment. [Figure 8] FIG. 10 is a longitudinal cross-sectional view of the diamond substrate showing a state in which organic components are removed by nitrogen molecules in step E of the same embodiment. [Figure 9] FIG. 10 is a longitudinal sectional view of a diamond substrate from which organic components have been removed by step E of the same embodiment. [Figure 10] FIG. 10 is a longitudinal sectional view of a diamond substrate to which water molecules have been attached in step F of the same embodiment. [Figure 11] FIG. 10 is a longitudinal sectional view of the diamond substrate showing a state in which hydrogen atoms are removed by nitrogen molecules in step G of the same embodiment. [Figure 12] FIG. 10 is a longitudinal sectional view of a diamond substrate on which hydrogen atoms have been removed and a single aluminum oxide layer has been formed in step G of the same embodiment. [Figure 13] FIG. 10 is a longitudinal sectional view of a diamond substrate on which an aluminum oxide layer has been laminated in step H of the same embodiment. [Figure 14] 10 is a timing chart showing the gas introduction timing in the second embodiment of the present invention. [Figure 15] FIG. 10 is a longitudinal cross-sectional view of a diamond substrate on which an aluminum oxide layer and a dopant layer have been laminated by steps A to H of the second embodiment. [Figure 16] 10 is a timing chart showing the gas introduction timing in a conventional method (Comparative Example 1). [Figure 17] FIG. 2 is a longitudinal cross-sectional view showing a method for measuring the current-voltage characteristics between the source electrode and the drain electrode of a field-effect transistor having no gate electrode in an embodiment of the present invention. [Figure 18] 1 is a graph showing the current-voltage characteristics between the source electrode and the drain electrode of a field effect transistor having no gate electrode in an embodiment of the present invention, and shows the difference depending on the oxygen impurity concentration in trimethylaluminum (TMA), which is the raw material of the Al2O3 insulating film. [Figure 19] 1 is a longitudinal sectional view showing a method for measuring output characteristics of a field effect transistor in an embodiment of the present invention. [Figure 20] 1 is a graph showing output characteristics of a field effect transistor in an example of the present invention. [Figure 21] 1 is a graph showing output characteristics of a field effect transistor in an example of the present invention. [Figure 22] 1 is a graph showing output characteristics of a field effect transistor in an example of the present invention. [Figure 23] 10 is a graph showing the output characteristics of a field effect transistor in a comparative example of the present invention. [Figure 24] 1 is a graph showing output characteristics of a field effect transistor in an example of the present invention. [Figure 25] 1 is a graph showing output characteristics of a field effect transistor in an example of the present invention. [Figure 26] 1 is a graph showing output characteristics of a field effect transistor in an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, an embodiment of an apparatus and method for manufacturing an insulating film on a diamond substrate according to the present invention will be described with reference to the drawings. Note that the dimensions of each part shown in the drawings do not reflect the dimensions of the actual product.

[0030] [Embodiment of an apparatus for manufacturing an insulating film on a diamond substrate] FIG. 1 is a block diagram showing one embodiment of an apparatus for producing an insulating film on a diamond substrate according to the present invention. This apparatus comprises a vacuum chamber 10, a support (support) 14 for supporting a diamond substrate 1 in the vacuum chamber 10, a heater 15 (FIG. 2; heating device) for heating the diamond substrate 1 supported by the support 14, and a device for heating the inside of the vacuum chamber 10 from atmospheric pressure to 2×10 -3 the vacuum chamber 10; a dopant supply device (88, 58, 90) that supplies one or more dopants selected from nitrogen dioxide (NO), nitric oxide (NO), sulfur dioxide (SO), and ozone (O) to the vacuum chamber 10; a nitrogen supply device (48, 52, 74, 56, 86, 60, 92) that supplies nitrogen (N) to the vacuum chamber 10; an aluminum raw material supply device (50, 62, 64, 66, 68, 70) that supplies an organoaluminum compound to the vacuum chamber 10; a water vapor supply device (54, 76, 78, 80, 81, 82, 84) that supplies water vapor (HO) to the vacuum chamber 10; and a control device 11 that controls the decompression device, the dopant supply device, the nitrogen supply device, the aluminum raw material supply device, and the water vapor supply device.

[0031] The vacuum chamber 10 has a cylindrical lower vacuum chamber portion 10b made of metal or the like, with a bottom, and a cylindrical upper vacuum chamber portion 10a made of metal or the like, with a closed top end, which closes the upper opening of the lower vacuum chamber portion 10b and can be separated when the diamond substrate 1 is loaded. A flange is formed at the dividing surface between the upper vacuum chamber portion 10a and the lower vacuum chamber portion 10b, and a ring-shaped metal gasket 12 is sandwiched between the flanges to maintain high airtightness. The metal gasket 12 is made entirely of a metal material, and the metal material is selected from stainless steel, titanium, Monel steel, and other materials with excellent corrosion resistance, as well as copper, aluminum, pure iron, and mild steel, which are well-suited. Conventionally, in atomic layer deposition (ALD) systems, a rubber O-ring or the like was thought to be sufficient for achieving airtightness. However, the present inventors have devised a method for replacing the O-ring with a metal gasket 12, which allows for a high degree of vacuum, as described below.

[0032] As shown in Figure 2, the support part 14 is equipped with a heater 15, which allows the diamond substrate 1 placed on the support part 14 via the support plate 13 to be heated to any desired temperature. A cylindrical sheath 16 is inserted into the lower end of the support part 14, which holds the support part 14 at an appropriate height within the vacuum chamber 10, and a thermocouple 17 is inserted through the sheath 16 to measure the temperatures of the support part 14 and the diamond substrate 1. Both the heater 15 and the thermocouple 17 are connected to the control device 11.

[0033] A water-cooled jacket 18 is attached to the outer periphery of the upper vacuum chamber 10a, and cooling water is circulated from a cooling water inlet 20 to a cooling water outlet 22 to cool the inside of the vacuum chamber 10. A gas inlet 24 is formed at the top end of the upper vacuum chamber 10a, and is connected to a gas introduction path 46 that leads to various gas supply sources.

[0034] Two pressure reducing devices are connected to the lower part 10b of the vacuum chamber. The first system of pressure reduction equipment is connected via a valve 26 leading to the lower part 10b of the vacuum chamber, and is equipped with a turbo molecular pump 28, a valve 30, a rotary pump 32, and an exhaust device 34 arranged in series in that order. It can achieve a higher degree of vacuum than the second system of pressure reduction equipment, but its exhaust speed is slower. The turbo molecular pump 28 is a mechanical vacuum pump, and its rotor, which is a rotating body with metallic turbine blades, rotates at high speed to eject gas molecules and thereby exhaust gas. The ultimate vacuum of the turbo molecular pump 28 is 1×10 -7 The pressure is preferably about 10 Pa. Since the operating pressure of the turbo molecular pump 28 is limited, a rotary pump 32 is used as an auxiliary pump. The rotary pump 32 is, for example, an oil rotary vacuum pump, and exhausts the gas by rotating internal blades. The ultimate vacuum level is not limited, but is, for example, 10 -1 The pressure is about Pa. The valve 26 , the turbomolecular pump 28 , the valve 30 , and the rotary pump 32 are connected to the control device 11 .

[0035] The second system of pressure reduction equipment is connected via a valve 36 leading to the lower part 10b of the vacuum chamber, and is equipped with a filter 38 for removing dust from inside the vacuum chamber 10, a pressure controller 40 for adjusting the degree of vacuum, a pump 42 for reducing the pressure in the vacuum chamber 10, and an exhaust device 44, arranged in series in this order. The pressure it achieves is higher (lower vacuum) than the first system of pressure reduction equipment, but its exhaust speed is faster. The degree of vacuum achieved by the pump 42 is 4.8 x 10 -1 The pressure controller 40 and the pump 42 are connected to the control device 11.

[0036] In the apparatus of this embodiment, the first system of pressure reduction devices is mainly used to remove atmospheric components 2 from the diamond substrate 1 by high vacuum, and the second system of pressure reduction devices is mainly used to introduce gas into the vacuum chamber 10 while evacuating it to maintain the desired pressure.

[0037] Next, the gas supply devices for the vacuum chamber 10 will be described. The gas supply devices all have a nitrogen purifier 48 as a common component. The nitrogen purifier 48 removes impurities from nitrogen gas supplied from a nitrogen source (not shown) to produce high-purity nitrogen gas. The purity of the nitrogen gas produced is not limited, but is preferably 99.99995% or higher. This purity facilitates the formation of an aluminum oxide film 7 with high insulating properties and is highly effective in suppressing doping inhibition due to the adhesion of atmospheric components 2.

[0038] The aluminum raw material supply device includes an MFC 50 (mass flow controller) connected to nitrogen purifier 48 and adjusting the flow rate of nitrogen gas as a carrier gas, a bubbling unit 68 for vaporizing the organoaluminum compound with nitrogen gas, a thermostatic bath 70 for keeping bubbling unit 68 at a temperature within the vaporization temperature range of the organoaluminum compound, valves 64 and 66 for opening and closing the inlet and outlet of bubbling unit 68, a valve 62 for short-circuiting the inlet and outlet of bubbling unit 68, and a valve 72 leading to gas introduction path 46. MFC 50 and valves 62, 64, 66, and 72 are connected to control device 11.

[0039] As the organoaluminum compound, for example, alkylaluminum can be used, and alkylaluminum includes trimethylaluminum, triethylaluminum, triisobutylaluminum, etc., among which trimethylaluminum (TMA) is particularly preferred for the present invention. The vaporization temperature range of trimethylaluminum at normal pressure is about 15 to 25°C.

[0040] The MFC 52 and valve 74 are provided as a first nitrogen supply device adjacent to the dopant supply device. The reason for being located adjacent to the dopant supply device is to quickly replace the inside of the path with nitrogen after the dopant is supplied. The MFC 52 and valve 74 are connected to the control device 11.

[0041] The water vapor supply device includes an MFC 54 connected to the nitrogen purifier 48 and adjusting the flow rate of nitrogen gas as a carrier gas, a bubbling unit 82 for vaporizing pure water with nitrogen gas, a thermostatic bath 84 for keeping the temperature of the bubbling unit 82 within the water vaporization temperature range, valves 78 and 80 for opening and closing the inlet and outlet of the bubbling unit 82, a valve 76 for bypassing the bubbling unit 82, and a valve 81 leading to the gas introduction path 46. The MFC 54 and the valves 76, 78, 80, and 81 are connected to the control device 11.

[0042] The MFC 56 and valve 86 are provided as a second nitrogen supply device adjacent to the water vapor supply device. The reason for being located adjacent to the water vapor supply device is to quickly replace the inside of the path with nitrogen after the water vapor is supplied. The MFC 56 and valve 86 are connected to the control device 11.

[0043] The dopant supply device is composed of a dopant tank 88 storing one or more dopants selected from nitrogen dioxide (NO2), nitric oxide (NO), sulfur dioxide (SO2), and ozone (O3), an MFC 58, and a valve 90. Nitrogen dioxide (NO2) is particularly preferred as a dopant used in the present invention. The MFC 58 and the valve 90 are connected to the control device 11.

[0044] The MFC 60 and valve 92 are provided as a third nitrogen supply device adjacent to the dopant supply device. The reason for being located adjacent to the dopant supply device is to quickly replace the inside of the path with nitrogen after the dopant is supplied. The MFC 60 and valve 92 are connected to the control device 11.

[0045] Next, a method for controlling the apparatus of the embodiment and a method for manufacturing an insulating film on the diamond substrate 1 will be specifically described with reference to Fig. 2. Fig. 2 shows a schematic diagram of the apparatus of Fig. 1, with the configuration of each part being simpler than that of Fig. 1. In Fig. 2, V1 denotes a valve that opens and closes the supply of an organoaluminum compound such as TMA from an aluminum raw material supply device, and when V1 is open (ON), this means that, in Fig. 1, MFC 50 is operated, valve 62 is closed, and valves 64, 66, and 72 are opened to perform bubbling in bubbling unit 68. When V1 is closed (OFF), this means, in Fig. 1, that MFC 50 is stopped, valve 62 is opened, and valves 64, 66, and 72 are closed to stop bubbling in bubbling unit 68.

[0046] V2 in Fig. 2 denotes a valve that opens and closes the supply of water vapor from the water vapor supply device, and when V2 is open (ON), this means that, in Fig. 1, MFC 54 is operated, valve 76 is closed, and valves 78, 80, and 81 are opened to perform bubbling in bubbling unit 82. When V2 is closed (OFF), this means, in Fig. 1, that MFC 54 is stopped, valve 76 is opened, and valves 78, 80, and 81 are closed to stop bubbling in bubbling unit 82.

[0047] V3 in Fig. 2 denotes a valve that opens and closes the supply of dopant from the dopant supply device, and when V3 is open (ON), it means that in Fig. 1, MFC 58 is operated and valve 90 is opened to supply dopant to vacuum chamber 10. When V3 is closed (OFF), it means that in Fig. 1, MFC 58 is stopped and valve 90 is closed to stop the supply of dopant.

[0048] V4 in Fig. 2 denotes a valve that operates the pressure reducing device of the second system, and when V4 is open (ON), this means that in Fig. 1, valve 36 is opened and air is evacuated from vacuum chamber 10 by pump 42 and exhaust device 44 through filter 38 and pressure controller 40. When V4 is closed (OFF), this means that in Fig. 1, valve 36 is closed and pump 42 and exhaust device 44 are stopped, thereby stopping evacuation from vacuum chamber 10.

[0049] V5 in Figure 2 represents a valve that operates the nitrogen supply device. When V5 is open (ON), at least one of MFCs 52, 56, and 60 in Figure 1 is operated, and the corresponding valves 74, 86, and 92 are opened to supply nitrogen gas to the vacuum chamber 10. The maximum flow rates of MFCs 52, 56, and 60 under standard conditions are 1 L per minute (1 sLm), 100 cc (100 sccm), and 100 cc (100 sccm), respectively. When V5 is closed (OFF), all of MFCs 52, 56, and 60 in Figure 1 are stopped, and all valves 74, 86, and 92 are also closed to stop the supply of nitrogen gas.

[0050] 2 denotes a valve that operates the first system pressure reducing device, and when V6 is open (ON), this means that in Fig. 1, valve 26 is opened, turbo molecular pump 28 and rotary pump 32 are operated, and air is exhausted from vacuum chamber 10 via valve 30 and exhaust device 34. When V6 is closed (OFF), this means that in Fig. 1, valve 26 is closed (the turbo molecular pump 28 and rotary pump 32 can be left operating), and exhaust from vacuum chamber 10 is stopped.

[0051] Figure 3 shows an example of sequence control of V1, V2, V3, and V5 by the control device 11 in the schematic diagram of Figure 2. In this sequence control, V1, V2, V3, V5, and other device components are controlled as follows. 1. The pressure in the vacuum chamber 10 is reduced from atmospheric pressure to 2 x 10 within one hour using a pressure reducing device. -3 Step A: reducing the pressure to below Pa; 2. Step B of supplying dopant into the vacuum chamber 10 using a dopant supply device; 3. Step C of supplying nitrogen to the vacuum chamber 10 using a nitrogen supply device; 4. Step D of supplying an organoaluminum compound to the vacuum chamber 10 using an aluminum raw material supply device; 5. Step E of supplying nitrogen to the vacuum chamber 10 using a nitrogen supply device; 6. Step F of supplying water vapor to the vacuum chamber 10 by a water vapor supply device; 7. Step G of supplying nitrogen to the vacuum chamber 10 by a nitrogen supply device; and 8. Step H: Repeating steps D to G multiple times.

[0052] [First embodiment of a method for manufacturing an insulating film on a diamond substrate] [Step A of reducing the pressure inside the vacuum chamber 10] First, the upper part 10a of the vacuum chamber 10 is opened, and the diamond substrate 1 is placed horizontally on the support part 14 via the support plate 13. Since the diamond substrate 1 is exposed to the atmosphere, atmospheric components 2 are adsorbed on the surface of the diamond substrate 1, as shown in Figure 4. The atmospheric components 2 are mainly N2, O2, CO2, H2O, etc.

[0053] The diamond substrate 1 is preferably made of a single crystal diamond, and the crystal orientation of the surface may be (100), (001), (110), or (111), with (110) or (111) being preferred, as this has the advantage of making it easier to improve the electrical characteristics of the semiconductor device ultimately obtained. The crystal orientation of the surface of the diamond substrate 1 may be tilted within ±3° from the above-mentioned plane orientation, more preferably within ±1°. The diamond substrate 1 may also be one in which a thin single crystal diamond layer is formed on a support such as SiC or polycrystalline diamond by CVD or PVD.

[0054] After the diamond substrate 1 is loaded into the vacuum chamber 10, the upper part 10a of the vacuum chamber is fixed to the lower part 10b of the vacuum chamber. The high level of airtightness of the annular metal gasket 12 interposed between the two parts keeps the inside of the vacuum chamber 10 at 1×10 -7It is possible to reduce the pressure to about Pa. In a typical atomic layer deposition (ALD) apparatus of this type, a rubber O-ring or the like is placed between the dividing surfaces of the vacuum chamber, which is thought to provide sufficient airtightness. However, according to the findings of the present inventors, it has been found that an O-ring cannot achieve a sufficient degree of vacuum to remove atmospheric components 2 from the diamond substrate 1.

[0055] Next, V6 is turned on, and the vacuum chamber 10 is placed in a high vacuum (2 × 10 -3 The chamber is rapidly evacuated to a pressure of 1.1 × 10 Pa or less within one hour. The turbomolecular pump 28 and rotary pump 32 arranged in series achieve a pressure of 1.1 × 10 Pa or less, which is difficult to achieve with conventional ALD. -5 As a result, a vacuum of 2×10 Pa or less can be achieved, and as shown in FIG. 5, atmospheric components 2 adsorbed on the surface of the diamond substrate 1 can be desorbed. -3 The inventors have found that even if the pressure reaches or exceeds 1.1×10 Pa, if it takes too long, the desorption of the atmospheric component 2 is likely to be insufficient. -5 Pa or less, and more preferably 1×10 -5 Pa or less, and more preferably 1×10 -6 Pa or less, preferably 1×10 -7 It is Pa.

[0056] [Step B of Supplying Dopant] Next, V6 is turned OFF and V3 is turned ON to introduce a dopant dilution gas, which is a mixture of a high-purity dopant and nitrogen gas as a carrier gas, into a clean vacuum chamber 10 under high vacuum. As a result, as shown in Figure 6, dopant molecules adhere to and deposit on the surface of the diamond substrate 1 to a thickness equivalent to one molecular layer, forming a dopant layer 3. The dopant is one or more selected from nitrogen dioxide (NO), nitric oxide (NO), sulfur dioxide (SO), and ozone (O). While any of these can be used, nitrogen dioxide is most preferred for its ability to enhance device performance. To ensure the doping effect of hole carriers on the surface of the diamond substrate 1, the dopant concentration in the dopant dilution gas is preferably 2% by volume (20,000 ppm) or higher, more preferably 10-100% by volume.

[0057] The period during which V3 is turned on is not limited in the present invention, but is preferably 1 millisecond or more and 25 milliseconds or less, more preferably 15 milliseconds or more and 20 milliseconds or less. With such a period, the doping effect of hole carriers on the surface of the diamond substrate 1 becomes more reliable. The heating temperature of the diamond substrate 1 by the heater 15 during the period during which V3 is turned on is preferably 100°C or more and 500°C or less, more preferably 150°C or more and 400°C or less. With such a temperature, the doping effect of hole carriers on the surface of the diamond substrate 1 becomes more reliable. The period during which V3 is turned on is not limited in the present invention, but the pressure in the vacuum chamber 10 is preferably 1.33×10 4 Pa or more 2.66×10 4 It is desirable that the pressure is not more than 1.7×10 Pa, and more desirably, it is not more than 1.7×10 4 Pa or more 2.3×10 4 In order to maintain the pressure in this range, V4 may be operated as appropriate.

[0058] [Nitrogen supply process C / 1st layer] Next, V3 is turned OFF, V5 is turned ON, and V4 is turned ON to exhaust the dopant diluted gas from the vacuum chamber 10 and introduce high-purity nitrogen gas. This removes the excess dopant adhering to the dopant layer 3 on the surface of the diamond substrate 1, and forms a single dopant layer 3 in which the molecules are arranged in an orderly manner.

[0059] Although not limited in the present invention, the period during which V5 is turned on is preferably 1 second or more and 20 seconds or less, more preferably 5 seconds or more and 10 seconds or less. This period ensures the effect of removing excess dopant. The heating temperature of the diamond substrate 1 by the heater 15 during the period during which V5 is turned on is preferably 80°C or more and 500°C or less, more preferably 120°C or more and 230°C or less. At such a temperature, the effect of removing excess dopant is ensured. Although not limited in the present invention, the pressure in the vacuum chamber 10 is preferably 0 Pa or more and 100 Pa or less, more preferably 0.1 Pa or more and 1 Pa or less. To maintain the pressure within this range, V4 is operated at an appropriate rotation speed.

[0060] [Process D for supplying organoaluminum compound / 1st layer] Next, V5 is turned OFF, V4 is left ON, and V1 is turned ON to exhaust the nitrogen gas from the vacuum chamber 10 and introduce an organoaluminum compound diluted gas, which is a mixture of a high-purity organoaluminum compound and nitrogen gas as a carrier gas, into the vacuum chamber 10. Examples of organoaluminum compounds that can be used include alkylaluminums, such as trimethylaluminum, triethylaluminum, and triisobutylaluminum. Among these, trimethylaluminum (TMA) is particularly preferred for the present invention. A TMA molecule consists of one aluminum atom 4A and three methyl groups 4B. As shown in Figure 7, TMA 4 is deposited on the dopant layer 3 as a monolayer. When other organoaluminum compounds are used, the terms organoaluminum compound 4, aluminum atom 4A, and organic functional group 4B should be used interchangeably.

[0061] The period during which V1 is turned on is not limited in the present invention, but is preferably 1 millisecond to 25 milliseconds, more preferably 15 milliseconds to 25 milliseconds. This period ensures that TMA4 adheres and accumulates as a monolayer on the dopant layer 3. The heating temperature of the diamond substrate 1 by the heater 15 during the period during which V1 is turned on is preferably 80°C to 500°C, more preferably 120°C to 230°C. At these temperatures, the effect of TMA4 adhering and accumulating as a monolayer on the dopant layer 3 is ensured. The period during which V1 is turned on is not limited in the present invention, but the pressure in the vacuum chamber 10 is preferably 0 Pa to 100 Pa, more preferably 0.1 Pa to 1 Pa. To maintain the pressure within this range, V4 is operated at an appropriate rotation speed.

[0062] [Nitrogen supply process E / 1st layer] Next, V1 is turned off, V4 is left on, and V5 is turned on to exhaust the organoaluminum compound diluted gas from the vacuum chamber 10 and introduce high-purity nitrogen gas. This removes excess TMA4 from the surface of the diamond substrate 1, and as shown in Figure 8, the methyl groups 4B of TMA4 are separated from the aluminum atoms 4A by nitrogen molecules 5 and removed from the surface of the diamond substrate 1. As shown in Figure 9, a monolayer of aluminum atoms 4A is formed on the dopant layer 3. The conditions for the period V5 is turned on, the heating temperature of the diamond substrate 1 by the heater 15, the pressure in the vacuum chamber 10, etc. may be the same as those in [Step C / First Layer of Nitrogen Supply].

[0063] [Steam supply process F / 1st layer] Next, V5 is turned OFF, V4 is left ON, and V2 is turned ON to exhaust the nitrogen gas from the vacuum chamber 10 and introduce a water vapor diluted gas, which is a mixture of high-purity water vapor and nitrogen gas as a carrier gas. As a result, water molecules 6 are deposited in a monolayer on the aluminum atoms 4A, as shown in Figure 10. Each water molecule 6 is composed of one oxygen atom 6A and two hydrogen atoms 6B.

[0064] The period during which V2 is turned on is not limited in the present invention, but is preferably 1 millisecond to 25 milliseconds, more preferably 15 milliseconds to 25 milliseconds. This period ensures that water molecules 6 adhere to and deposit in a monolayer on the aluminum atoms 4A. The heating temperature of the diamond substrate 1 by the heater 15 during the period during which V2 is turned on is preferably 80°C to 500°C, more preferably 120°C to 230°C. At these temperatures, the effect of water molecules 6 adhering to and depositing in a monolayer on the aluminum atoms 4A is ensured. During the period during which V5 is turned on, the pressure in the vacuum chamber 10 is preferably 0 Pa to 100 Pa, more preferably 0.1 Pa to 1 Pa. To maintain the pressure within this range, V4 is operated at an appropriate rotation speed.

[0065] [Nitrogen supply process G / 1st layer] Next, V2 is turned off, V4 is left on, and V5 is turned on to exhaust the water vapor-diluted gas from the vacuum chamber 10 and introduce high-purity nitrogen gas. This removes excess water molecules 6 from the surface of the diamond substrate 1. Furthermore, as shown in FIG. 11, the hydrogen atoms 6B of the water molecules 6 are separated from the oxygen atoms 6A by the nitrogen molecules 5 and removed from the surface of the diamond substrate 1. As shown in FIG. 12, a monolayer of oxygen atoms 6A is formed on the monolayer of aluminum atoms 4A. This completes the first monolayer of aluminum oxide. The conditions for the period V5 is turned on, the heating temperature of the diamond substrate 1 by the heater 15, and the pressure inside the vacuum chamber 10 may be the same as those in [Step C: Supplying Nitrogen for the First Layer].

[0066] [Process H: Repeating Processes D to G Multiple Times] Thereafter, the second and subsequent monolayer aluminum oxide films are repeatedly formed, until an aluminum oxide film 7, in which aluminum atoms 4A and oxygen atoms 6A are alternately stacked, is formed to the required thickness, as shown in FIG. 13. Since no methyl groups 4B or hydrogen atoms 6B remain in the aluminum oxide film 7 thus formed, it is possible to form a high-quality aluminum oxide film 7 with extremely few impurities. Note that the film formation conditions for the first layer and the second and subsequent layers are slightly different, and this will be explained below. Where not specifically explained, the same conditions as for the first layer can be used.

[0067] [Process D for supplying organoaluminum compounds / 2nd layer and onwards] By turning V5 OFF, V4 ON, and V1 ON, the nitrogen gas in the vacuum chamber 10 is exhausted and the organoaluminum compound diluted gas is introduced into the vacuum chamber 10, forming TMA4 on the aluminum oxide single layer. The period during which V1 is ON and the pressure in the vacuum chamber 10 can be the same as in [Step D / First Layer of Supplying the Organoaluminum Compound], but the heating temperature of the diamond substrate 1 using the heater 15 is preferably 80°C to 500°C, more preferably 120°C to 230°C. At such a temperature, the effect of depositing TMA4 as the second layer is more reliable. The reason why the deposition temperature for the second and subsequent layers is higher than that for the first layer is that the concentration of excess charge caused by impurities in the Al2O3 film is reduced.

[0068] [Nitrogen supply process E / 2nd layer onwards] Next, V1 is turned OFF, V4 is left ON, and V5 is turned ON to exhaust the organoaluminum compound diluted gas from the vacuum chamber 10 and introduce high-purity nitrogen gas. The conditions for the period V5 is ON and the pressure inside the vacuum chamber 10 may be the same as those in [Nitrogen Supply Step C / First Layer], but the heating temperature of the diamond substrate 1 by the heater 15 is preferably 80°C or higher and 500°C or lower, more preferably 120°C or higher and 230°C or lower. At such a temperature, the effect of removing the methyl group 4B of TMA4 in the second layer is more reliable.

[0069] [Steam supply process F / 2nd layer onwards] Next, V5 is turned off, V4 is left on, and V2 is turned on to exhaust the nitrogen gas from the vacuum chamber 10 and introduce a water vapor-diluted gas, which is a mixture of high-purity water vapor and nitrogen gas as a carrier gas. The period during which V2 is turned on and the pressure inside the vacuum chamber 10 can be the same as in [Water Vapor Supply Process F / First Layer], but the heating temperature of the diamond substrate 1 by the heater 15 is preferably 80°C to 500°C, more preferably 120°C to 230°C. At such a temperature, the effect of water molecules 6 adhering and accumulating in a single layer on the aluminum atoms 4A of the second and subsequent layers is more reliably achieved.

[0070] [Nitrogen supply process G / 2nd layer onwards] Next, V2 is turned off, V4 is left on, and V5 is turned on to exhaust the water vapor diluted gas from the vacuum chamber 10 and introduce high-purity nitrogen gas. This removes excess water molecules 6 adhering to the surface of the diamond substrate 1 and also removes the hydrogen atoms 6B of the water molecules 6. The conditions for the period V5 is turned on, the heating temperature of the diamond substrate 1 by the heater 15, the pressure inside the vacuum chamber 10, etc. may be the same as those in [Nitrogen Supply Process C / Second Layer and After].

[0071] According to the above-described apparatus and method for manufacturing an insulating film on a diamond substrate, the aluminum oxide film 7 is not contaminated with impurities such as methyl groups 4B and hydrogen atoms 6B, and therefore a high-quality aluminum oxide film 7 can be formed. Furthermore, since the dopant layer 3 can be formed on a clean diamond substrate 1, it is possible to manufacture semiconductor devices such as high-performance diamond MOSFETs.

[0072] [Second embodiment of the method for manufacturing an insulating film on a diamond substrate] Next, a second embodiment of the present invention will be described. This second embodiment is characterized in that the control device 11 is programmed to perform step I, in which steps D to G are repeated one or more times between step A and step B, as shown in FIG. 14. That is, after cleaning the diamond substrate 1 in step A, steps D to G are repeated one or more times to first form a first aluminum oxide film 7 to a predetermined thickness, then form a dopant layer 3, and then form a second aluminum oxide film 7. If the first aluminum oxide film 7 is thin, the dopant reaches the surface of the diamond substrate 1 from the dopant layer 3 through the first aluminum oxide film 7, and hole carrier doping is performed on the surface of the diamond substrate 1.

[0073] In the second embodiment, step A and steps D to G of the first layer when forming the first aluminum oxide film may be similar to those of the first layer in the first embodiment, and therefore the description of the first layer in the first embodiment is incorporated herein. Furthermore, steps D to G of the second and subsequent layers when forming the first aluminum oxide film and steps D to G of the second aluminum oxide film when forming the second aluminum oxide film may be similar to those of the second and subsequent layers in the first embodiment, and therefore the description of the second and subsequent layers in the first embodiment is incorporated herein.

[0074] [Step B of Supplying Dopant / Second Embodiment] The second embodiment differs from the first embodiment in the condition of step B, in which the dopant is supplied. When step B is performed in the second embodiment, the first aluminum oxide film 7 has already been formed, so the appropriate temperature conditions are different. When V6 is turned off and V3 is turned on, and a dopant dilution gas, in which a high-purity dopant is mixed with nitrogen gas as a carrier gas, is introduced into the clean vacuum chamber 10 in a high vacuum state, the heating temperature of the diamond substrate 1 by the heater 15 is preferably 80°C or higher and 500°C or lower, more preferably 120°C or higher and 230°C or lower. At such a temperature, the doping effect of hole carriers on the first aluminum oxide film 7 is more reliably achieved.

[0075] In the second embodiment, the number of times that steps D to G are repeated between step A and step B is not limited, but is preferably 18 times or more, and more preferably 37 times or more. This is because if the thickness of the first aluminum oxide film 7 is too thick, it becomes difficult to form hole carriers by the dopant. The film thickness per cycle may be, for example, 0.109 nm / cycle.

[0076] In the second embodiment, the dopant layer 3 is formed between the first and second aluminum oxide films 7 rather than directly on the surface of the diamond substrate 1, which has the advantage of suppressing the chemical reaction between hydrogen in the diamond and oxygen in the dopant layer compared to the first embodiment.

[0077] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it is possible to add other configurations of well-known technologies or to omit some of the configurations of well-known technologies. [Example]

[0078] Next, the effects of the present invention will be demonstrated by giving specific examples of the present invention. [Example 1] An apparatus for manufacturing an insulating film on a diamond substrate (atomic layer deposition (ALD) apparatus) shown in Figure 1 was actually created, and an aluminum oxide film 7 was formed on a diamond substrate 1. The internal volume of a vacuum chamber 10 was 8.2 L, and metal gaskets 12 made of oxygen-free copper were used on all dividing surfaces of the vacuum chamber 10.

[0079] A commercially available rectangular diamond single crystal with dimensions of 4.5 mm x 4.5 mm x 0.5 mm and a surface orientation within ±1° of the 001 orientation was used as the diamond substrate 1. A molybdenum substrate holder was used as the support plate 13. The support plate 13 with the diamond substrate 1 placed on it was set in the vacuum chamber 10, and V6 was operated to increase the vacuum chamber 10 from atmospheric pressure to 2 x 10 for one hour. -3 The pressure was reduced to 100 Pa.

[0080] Next, the temperature of the diamond substrate 1 was heated to 80°C by the heater 15, V6 was turned off, V4 was turned on to evacuate, and V3 was turned on to supply NO2 into the vacuum chamber 10 for 2 minutes. During this time, the degree of vacuum in the vacuum chamber 10 was 1×10 -2 After the supply time had elapsed, V3 was turned off to stop the supply of NO2, and V6 was turned on to pressurize the inside of the vacuum chamber 10 to 2 × 10 -3 The pressure was reduced to 0.2 Pa over 1 hour.

[0081] Next, bubbling unit 68 containing TMA was maintained at 20°C in thermostatic chamber 70, and bubbling unit 82 containing HO was maintained at 20°C in thermostatic chamber 84. V1 and V2 were alternately turned on for 20 milliseconds with a 5-second interval (rest period). During the interval, V5 was turned on to supply nitrogen gas to vacuum chamber 10.

[0082] When forming the first aluminum oxide film 7, when V1 was ON, TMA was bubbled with nitrogen gas of 99.99995% purity from the nitrogen purifier 48, and a TMA diluted gas obtained by diluting TMA with nitrogen was introduced into the vacuum chamber 10. The TMA concentration in the TMA diluted gas was 1.2% by volume, the degree of vacuum in the vacuum chamber 10 was maintained at 0.1 Pa, and the temperature of the diamond substrate 1 was set to 120°C.

[0083] When forming the first aluminum oxide film 7, with V2 ON, pure water was bubbled with nitrogen gas of 99.99995% purity from the nitrogen purifier 48, and a water vapor diluted gas prepared by diluting water vapor with nitrogen was introduced into the vacuum chamber 10. The water vapor concentration in the water vapor diluted gas was 2.3% by volume, the degree of vacuum in the vacuum chamber 10 was maintained at 0.1 Pa, and the temperature of the diamond substrate 1 was set to 120°C.

[0084] When forming the first aluminum oxide film 7, if V5 was ON, a route similar to the route of V1 or V2 used immediately before (MFC 52 → valve 74 or MFC 56 → valve 86) was selected to introduce nitrogen gas from the nitrogen purifier 48 into the vacuum chamber 10. The flow rate of nitrogen flowing into MFC 52 was set to 200 cc (200 sccm) per minute under standard conditions. The flow rate of nitrogen flowing into MFC 56 was set to 10 cc (10 sccm) per minute under standard conditions. The degree of vacuum in the vacuum chamber 10 was maintained at 0.1 Pa, and the temperature of the diamond substrate 1 was maintained at 120°C.

[0085] When forming the second and subsequent aluminum oxide films 7, the temperature of the diamond substrate 1 was maintained at 230°C when V1, V2, and V5 were turned ON. Other conditions were the same as those for the first layer. Under these conditions, the cycle was repeated 109 times to form aluminum oxide films 7 with a total thickness of 12 nm.

[0086] Heating by heater 15 was stopped, and after waiting for diamond substrate 1 to cool to room temperature, nitrogen gas was introduced into vacuum chamber 10 up to atmospheric pressure, and upper part 10a of the vacuum chamber was opened, and diamond substrate 1 with aluminum oxide film 7 formed thereon was removed together with support plate 13.

[0087] The sample obtained in the above process was set in a Toyo Corporation hole measurement device "ResiTest8300 / 8400" and the surface resistivity of the diamond substrate 1 was measured. The resistivity was 5 kΩ / □ for the (001) surface orientation of the diamond substrate 1 and 2.5 kΩ / □ for the (111) surface orientation of the diamond substrate 1, indicating that hole carrier doping by NO2 was performed well. The surface resistivity of the diamond substrate 1 can be measured either before or after the aluminum oxide film 7 is formed.

[0088] The characteristics of the diamond FET fabricated using the diamond substrate 1 of Example 1 were measured using the experimental apparatus shown in Figure 19. As shown in Figure 19, a dopant layer 3 and an aluminum oxide film 7 were formed on the diamond substrate 1 of Example 1, gold was evaporated onto the dopant layer 3 to form a source electrode 100 and a drain electrode 102, and gold was evaporated onto the aluminum oxide film 7 to form a gate electrode 116. Next, a power supply 108 and an ammeter 110 were connected between the source electrode 100 and the drain electrode 102, and the drain current I was measured with the ammeter 110 while changing the voltage of the power supply 108. D A power supply 112 and an ammeter 114 were connected between the source electrode 100 and the gate electrode 116, and the drain current I was measured with an ammeter 110 while changing the voltages of the power supplies 108 and 112, respectively. D Measure the gate-source voltage V with the ammeter 114. GS The results are shown in Figures 24 to 26.

[0089] FIG. 24 shows the output (drain voltage-current) characteristics of the diamond FET fabricated in Example 1. GS When the voltage is changed from -3V to 11V, the maximum drain current (I DMAX ) is 112.6mA / mm, and the on-resistance (R ON ) = 350 Ω·mm, which is a value sufficient for practical use as an FET. FIG. 25 shows the output (drain voltage-current) characteristics of the same diamond FET as FIG. 24 fabricated in Example 1. V GSWhen the drain voltage was set to 11V, the off-state breakdown voltage of the drain voltage was a high value of 4266V. FIG. 26 shows the V GS = -1V and V DS When continuously operated under the condition of =-10V, the drain current (I D ) and the absolute value of the gate current (|I G As shown in Figure 26, this diamond FET operated for up to 4050 hours without degradation, proving its long life.

[0090] [Comparative Example 1] Using the same atomic layer deposition (ALD) apparatus as in Example 1 shown in Figures 1 and 2, a dopant layer 3 and an aluminum oxide film 7 were formed using the same diamond substrate 1 as in Example 1 under sequence control as shown in Figure 16. The support plate 13 carrying the diamond substrate 1 was placed in the vacuum chamber 10, and V6 was operated to increase the vacuum chamber 10 from atmospheric pressure to 2×10 1 The pressure was reduced to 0.2 Pa.

[0091] Next, the temperature of the diamond substrate 1 was heated to 80°C by the heater 15, V6 was turned off, V4 was turned on to evacuate, and V3 was turned on to supply NO2 into the vacuum chamber 10 for 2 minutes. During this time, the degree of vacuum in the vacuum chamber 10 was 2 × 10 1 The pressure was maintained at 1 Pa. After the supply time had elapsed, V3 was turned OFF to stop the supply of NO2.

[0092] Next, bubbling unit 68 containing TMA was kept at 20°C in a thermostatic bath 70, and bubbling unit 82 containing H2O was kept at 20°C in a thermostatic bath 84, and V1 and V2 were alternately turned on for 20 milliseconds without an interval as shown in Figure 16. The other conditions were the same as in Example 1.

[0093] The comparative example 1 obtained by the above process was set in a hole measuring device "ResiTest8300 / 8400" manufactured by Toyo Corporation, and the resistivity of the surface of the diamond substrate 1 was measured. The resistivity was 15 kΩ / □ for the (001) plane orientation of the surface of the diamond substrate 1, and 12 kΩ / □ for the (111) plane orientation of the surface of the diamond substrate 1, indicating that the doping of hole carriers by NO2 was insufficient.

[0094] Furthermore, the diamond FET fabricated using the diamond substrate 1 of Comparative Example 1 had an on-resistance of 200 Ω·mm and an off-breakdown voltage of 200 V, which was not suitable for use as an FET.

[0095] [Example 2] In Example 2, a field effect transistor structure without a gate electrode was formed using high-purity TMA with an oxygen impurity concentration of less than 2 ppm, as shown in Figure 17. Under the same conditions as in Example 1, a dopant layer 3 and an aluminum oxide film 7 were formed on a diamond substrate 1, and gold was evaporated on the dopant layer 3 to form a source electrode 100 and a drain electrode 102.

[0096] [Example 3] On the other hand, in Example 3, a field effect transistor (MOSFET) without a gate electrode was formed using TMA with an oxygen impurity concentration of 10 ppm, as shown in Fig. 17. Under the same conditions as in Example 2 except for the TMA used, a dopant layer 3 and an aluminum oxide film 7 were formed on a diamond substrate 1, and gold was evaporated on the dopant layer 3 to form a source electrode 100 and a drain electrode 102.

[0097] Using the MOSFETs of Examples 2 and 3, a power supply 108 and an ammeter 110 were connected between the source electrode 100 and the drain electrode 102, and the drain current I was measured by the ammeter 110 while changing the voltage of the power supply 108. D was measured.

[0098] As a result, the graph shown in Figure 18 was obtained. In Example 2, where the oxygen concentration in the TMA was less than 2 ppm, the resistivity was 97 Ωmm, and in Example 3, where the oxygen concentration in the TMA was 10 ppm, the resistivity was 169 Ωmm. Both were usable as semiconductor elements, but Example 2, where the oxygen concentration in the TMA was less than 2 ppm, had particularly excellent characteristics as a diamond MOSFET.

[0099] [Example 4] In Example 4, a field effect transistor having a gate electrode 116 was formed using high-purity TMA with an oxygen impurity concentration of less than 2 ppm, as shown in Figure 19. Under the same conditions as in Example 1, a dopant layer 3 and an aluminum oxide film 7 were formed on a diamond substrate 1, and gold was evaporated on the dopant layer 3 to form a source electrode 100 and a drain electrode 102, and gold was evaporated on the aluminum oxide film 7 to form a gate electrode 116.

[0100] [Example 5] On the other hand, in Example 5, TMA with an oxygen impurity concentration of 10 ppm was used to form a field effect transistor having a gate electrode 116 as shown in Fig. 19. Under the same conditions as in Examples 1 and 4, a dopant layer 3 and an aluminum oxide film 7 were formed on a diamond substrate 1, and gold was evaporated on the dopant layer 3 to form a source electrode 100 and a drain electrode 102, and gold was evaporated on the aluminum oxide film 7 to form a gate electrode 116.

[0101] Using the MOSFETs of Examples 4 and 5, a power supply 108 and an ammeter 110 were connected between the source electrode 100 and the drain electrode 102, and the drain current I was measured by the ammeter 110 while changing the voltage of the power supply 108. D A power supply 112 and an ammeter 114 were connected between the source electrode 100 and the gate electrode 116, and the drain current I was measured with an ammeter 110 while changing the voltages of the power supplies 108 and 112, respectively. D Measure the gate-source voltage V with the ammeter 114. GS was measured.

[0102] 20 and 21 show the output characteristics (current-voltage characteristics) of the diamond MOSFETs of Example 4, in which the oxygen impurity concentration in the TMA was less than 2 ppm, and Example 5, in which the oxygen impurity concentration in the TMA was 10 ppm. DMAX The higher the drain current (I DMAX ) was 409 mA / mm, and Example 5 had the highest drain current (I DMAX ) was 234 mA / mm, and although both could be used as MOSFETs, the diamond MOSFET characteristics of Example 4 were superior.

[0103] [Example 6] A diamond MOSFET was fabricated as Example 6 using the same method and conditions as in Example 4, using the apparatus shown in FIGS.

[0104] Comparative Example 2 The diamond substrate 1 was heated to 1.01×10 s by using a separate processing furnace without sufficient initial decompression as in the present invention, instead of the apparatus shown in FIGS. 5 The diamond substrate 1 was doped with NO gas at 200 Pa, cooled to room temperature, and removed. The diamond substrate 1 was then loaded into the apparatus shown in Figures 1 and 2, and a diamond MOSFET was fabricated under the same conditions as in Example 6, resulting in Comparative Example 2.

[0105] 22 and 23 show the output characteristics (current-voltage characteristics) of the diamond MOSFETs of Example 6 and Comparative Example 2, respectively. DMAX ) was 213 mA / mm, while the maximum drain current (I DMAX ) was 125 mA / mm, and the diamond MOSFET characteristics of Example 6 were far superior to those of Comparative Example 2. [Industrial Applicability]

[0106] According to the apparatus and method for manufacturing an insulating film on a diamond substrate of the present invention, it is easy to dope hole carriers into the surface of the diamond substrate, and an insulating film having a sufficiently high dielectric strength voltage can be formed on the diamond substrate. This can be used in semiconductor devices and electronic components that can be used in various electronic devices, and therefore is industrially applicable. [Explanation of symbols]

[0107] 1. Diamond substrate 2. Atmospheric components 3 dopant layer 4 TMA 4A Aluminum atom 4B Methyl group 5 nitrogen molecules 6 water molecules 6A Oxygen atom 6B Hydrogen atom 7 Aluminum oxide film 10 Vacuum chamber 10a Upper part of vacuum chamber 10b Lower part of vacuum chamber 12 Metal gasket 13 Support plate 14 Support part 15 Heater 16 Sheath 17 Thermocouple 18 Water cooling jacket 20 Cooling water inlet 22 Cooling water outlet 24 Gas inlet 26 Valve 28 Turbomolecular pump 30 Valve 32 Rotary pump 34 Exhaust system 36 Valve 38 Filter 40 Pressure Controller 42 Pump 44 Exhaust system 46 Gas inlet 48 Nitrogen purifier 50 MFC 52 MFC 54 MFC 56 MFC 58 MFC 60 MFC 62 valves 64 valves 66 Valve 68 Bubbling unit 70 Thermostatic chamber 72 Valve 74 Valve 76 Valve 78 valves 80 valves 82 Bubbling unit 84 Thermostatic bath 86 Valve 88 Dopant tank 90 valve 92 valve 100 source electrode 102 drain electrode 108 Power supply 110 Ammeter 112 Power supply 114 Ammeter 116 Gate electrode

Claims

1. A vacuum chamber; a support for supporting a diamond substrate in the vacuum chamber; a heating device for heating the diamond substrate supported by the support; The pressure in the vacuum chamber was increased from atmospheric pressure to 2×10 within one hour. －３ a pressure reducing device for reducing the pressure to 0.2 Pa or less; Nitrogen dioxide (NO ２ ), nitric oxide (NO), sulfur dioxide (SO ２ ), and ozone (O ３ a dopant supply device that supplies one or more dopants selected from the group consisting of: Nitrogen (N ２ a nitrogen supply device that supplies nitrogen gas to the vacuum chamber; an aluminum raw material supply device that supplies an organoaluminum compound to the vacuum chamber; Water vapor (H ２ O) into the vacuum chamber; An apparatus for manufacturing an insulating film on a diamond substrate, comprising: a control device for controlling the pressure reducing device, the dopant supply device, the nitrogen supply device, the aluminum raw material supply device, and the water vapor supply device.

2. 2. The apparatus for manufacturing an insulating film on a diamond substrate according to claim 1, wherein the control device is programmed to perform the following steps in the following order: The pressure in the vacuum chamber was reduced from atmospheric pressure to 2×10 within one hour by the pressure reducing device. －３ Step A: reducing the pressure to 0.2 Pa or less; Step B: supplying the dopant into the vacuum chamber using the dopant supply device; Step C of supplying the nitrogen to the vacuum chamber by the nitrogen supply device; Step D: supplying an organoaluminum compound to the vacuum chamber using the aluminum source supply device; Step E: supplying the nitrogen to the vacuum chamber using the nitrogen supply device; a step F of supplying the water vapor to the vacuum chamber by the water vapor supply device; Step G of supplying the nitrogen to the vacuum chamber by the nitrogen supply device; and Step H: Repeating steps D to G multiple times.

3. The apparatus for manufacturing an insulating film on a diamond substrate as described in claim 2, characterized in that the control device is programmed to perform step I, which repeats steps D to G one or more times between step A and step B.

4. The control device controlling the supply time of the organoaluminum compound by the aluminum raw material supply device in the step D to be 1 millisecond or more and 25 milliseconds or less; The supply time of the water vapor by the water vapor supply device in the step F is controlled to 1 millisecond or more and 25 milliseconds or less, and 4. The apparatus for producing an insulating film on a diamond substrate according to claim 2, wherein the interval between the step D and the step F is controlled to be between 1 second and 20 seconds.

5. The pressure reducing device reduces the pressure in the vacuum chamber from atmospheric pressure to 2×10 within one hour. －３ The pressure is reduced to 1.1×10 Pa or less, and the ultimate vacuum of the vacuum chamber is 1.1×10 －５ 4. The apparatus for producing an insulating film on a diamond substrate according to claim 1, wherein the pressure is 0.05 Pa or less.

6. 4. The apparatus for producing an insulating film on a diamond substrate according to claim 1, wherein the aluminum raw material supply device supplies alkyl aluminum.

7. The apparatus for manufacturing an insulating film on a diamond substrate according to any one of claims 1 to 3, characterized in that the vacuum chamber has a vacuum chamber body and a detachable part that can be separated from the vacuum chamber body, and a metal gasket is interposed between the vacuum chamber body and the detachable part at the separation surface.

8. The diamond substrate is placed in a vacuum chamber, the vacuum chamber is closed, and the pressure in the vacuum chamber is increased from atmospheric pressure to 2×10 －３ Step A: reducing the pressure to 0.2 Pa or less; Nitrogen dioxide (NO ２ ), nitric oxide (NO), sulfur dioxide (SO ２ ), and ozone (O ３ Step B of supplying one or more dopants selected from: Step C: supplying nitrogen into the vacuum chamber; Step D: supplying an organoaluminum compound to the vacuum chamber; Step E: supplying nitrogen into the vacuum chamber; Step F of supplying water vapor into the vacuum chamber; Step G of supplying nitrogen to the vacuum chamber; and A method for producing an insulating film on a diamond substrate, comprising a step H in which the steps D to G are repeated a plurality of times.

9. 9. The method for producing an insulating film on a diamond substrate according to claim 8, wherein a step I is carried out between the step A and the step B, in which the steps D to G are repeated one or more times.

10. the supply time of the organoaluminum compound in the step D is 1 millisecond or more and 25 milliseconds or less; The supply time of the water vapor in the step F is 1 millisecond or more and 25 milliseconds or less, and 10. The method for producing an insulating film on a diamond substrate according to claim 8, wherein the interval between step D and step F is 1 second or more and 20 seconds or less.

11. In the step A, the pressure in the vacuum chamber is increased from atmospheric pressure to 2×10 －３ The pressure is reduced to 1.1×10 Pa or less, and the ultimate vacuum of the vacuum chamber is 1.1×10 －５ 10. The method for producing an insulating film on a diamond substrate according to claim 8, wherein the pressure is set to Pa or less.

12. 10. The method for producing an insulating film on a diamond substrate according to claim 8, wherein in step D, alkyl aluminum is supplied as the organic aluminum compound.

13. 13. The method for producing an insulating film on a diamond substrate according to claim 12, wherein in step D, the impurity concentration of the alkyl aluminum is less than 10 ppm.

14. The carrier gas for the organoaluminum compound and the water vapor is nitrogen (N ２ 10. The method for producing an insulating film on a diamond substrate according to claim 8, wherein the purity of the nitrogen is 99.99995% or more.

15. In the step B, the dopant is nitrogen (N ２ 10. The method for producing an insulating film on a diamond substrate according to claim 8, wherein the dopant is diluted with a dilution gas having a concentration of 2% by volume (20,000 ppm) or more.

16. In the step B, the diamond substrate is heated to 20 to 90° C. and the dopant is supplied; The first layer is aluminum oxide (Al ２ O ３ In the steps D to G of forming the film, the diamond substrate is heated to 80 to 150° C., 10. The method for manufacturing an insulating film on a diamond substrate according to claim 8, wherein in steps D to G when forming the second or subsequent aluminum oxide films, the diamond substrate is heated to 200 to 300°C.

17. The insulating film to be manufactured is amorphous aluminum oxide, and the insulating film has a dielectric strength of 8 MV / cm or more. The surface of the diamond substrate has a surface concentration of 5×10 １３ cm －２ 10. A method for producing an insulating film on a diamond substrate as described in claim 8 or 9, characterized in that higher hole carriers are generated, and the sheet resistance of the surface of the diamond substrate is 1 kΩ / □ or less for the (001) plane orientation of the diamond crystal, and 700 Ω / □ or less for the (111) plane orientation of the diamond crystal.

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