Apparatus and method for manufacturing insulating film on a diamond substrate

Abstract

The present invention provides a manufacturing apparatus and method that facilitates doping the surface of a diamond substrate with hole carriers and enables the formation of an insulating film having a sufficiently high dielectric strength on the diamond substrate. [Solution] A vacuum chamber 10, a support 14 for supporting the diamond substrate 1, a heating device 15 for heating the diamond substrate 1, and a 2x10 vacuum chamber 10 that is heated from atmospheric pressure within 1 hour. -3 The system comprises a vacuum pressure device that reduces the pressure to below Pa, a dopant supply device that supplies dopants 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 organoaluminum compounds to the vacuum chamber 10, a steam supply device that supplies steam 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 manufacturing an insulating film on a diamond substrate, which can be used in the manufacture of semiconductor devices using a diamond substrate. [Background technology]

[0002] Diamond semiconductors, with a bandgap energy approximately five times that of silicon, are attracting attention as power semiconductor devices that achieve low loss and high-temperature operation under high voltage, and are expected to have applications 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 this method, a diamond crystal layer having p-type or n-type conductivity is formed using a CVD apparatus, and then gold is deposited to form the source electrode and drain electrode. Next, oxygen gas, hydrogen gas, and trimethylaluminum are supplied to the diamond crystal layer in a reduced-pressure CVD chamber, and an 8 nm thick layer of Al(OH)3 or Al is deposited in the gate portion between the source electrode and the drain electrode. 1-x-y O x H y An insulating layer made of compounds is formed.

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

[0005] By the way, when forming insulating films used as gate insulating films, etc., on a diamond substrate, the following problems arose. The first problem was that even when attempting to dope hole carriers on the surface of a diamond substrate by placing the diamond substrate in a vacuum chamber and introducing a dopant gas into the vacuum chamber, the bonding between the dopant and the surface of the diamond substrate did not progress, making it difficult to dope hole carriers on 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 impossible to obtain the insulating properties necessary to realize a diamond semiconductor device. Due to the above problems, it is currently difficult to manufacture a diamond semiconductor device having an insulating film with a sufficiently high breakdown voltage and capable of achieving a high operating current value.

[0007] Therefore, the present inventors conducted detailed research on each of the above problems. Regarding the first problem, they discovered that when the diamond substrate was carried into an atomic layer deposition apparatus, trace amounts of atmospheric components remained as impurities on the surface of the diamond substrate, and this residual atmospheric component hindered the intrusion of the dopant, inhibiting the doping of hole carriers on the surface of the diamond substrate. Further, as a countermeasure against this phenomenon, they found that the structure of the vacuum chamber and the setting of the degree of vacuum were important. In addition, regarding the second problem, the present inventors discovered that methyl groups (CH3) and hydrogen atoms, which are impurities for Al2O3, remained in the aluminum oxide (Al2O3) layer formed on the diamond substrate, and thus it was impossible to obtain an aluminum oxide layer having the insulating properties necessary to realize a diamond semiconductor device. They then found a solution to reduce the residual amount of these impurities.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

[0009] The present invention has been made based on the above findings, and an object thereof is to provide a manufacturing apparatus and a manufacturing method that can easily dope hole carriers at a sufficient density on the surface of a diamond substrate and can form an insulating film having a sufficiently high breakdown voltage on the diamond substrate. Means for Solving the Problems

[0010] [Aspect 1] The manufacturing apparatus for an insulating film on a diamond substrate according to Aspect 1 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, a decompression device for decompressing the inside of the vacuum chamber from atmospheric pressure to 2×10 -3 Pa or less within 1 hour, a dopant supply device for supplying at least one dopant selected from nitrogen dioxide (NO2), nitric oxide (NO), sulfur dioxide (SO2), and ozone (O3) to the vacuum chamber, a nitrogen supply device for supplying nitrogen (N2) to the vacuum chamber, an aluminum raw material supply device for supplying an organic aluminum compound to the vacuum chamber, a water vapor supply device for supplying water vapor (H2O) to the vacuum chamber, and a control device for controlling 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] The manufacturing apparatus for an insulating film on a diamond substrate according to Aspect 2 is programmed in Aspect 1 such that the control device performs the following steps in the following order. Step A of decompressing the inside of the vacuum chamber from atmospheric pressure to 2×10 -3 Pa or less within 1 hour by the decompression device; Step B of supplying the dopant into the vacuum chamber by the dopant supply device; Step C: Supplying the nitrogen to the vacuum chamber using the nitrogen supply device; Step D: Supplying an organoaluminum compound to the vacuum chamber using the aluminum raw material supply device; Step E: Supplying the nitrogen to the vacuum chamber using the nitrogen supply device; Step F: Supplying the steam to the vacuum chamber using the steam supply device; Step G: supplying the nitrogen to the vacuum chamber using the nitrogen supply device; and Step H is a process that repeats steps D to G multiple times.

[0012] [Aspect 3] In the apparatus for manufacturing an insulating film on a diamond substrate according to Embodiment 3, in Embodiment 2, the control device is programmed to perform a step I between step A and step B, repeating steps D to G one or more times.

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

[0014] [Aspect 5] The apparatus for manufacturing an insulating film on a diamond substrate according to Embodiment 5, in any of Embodiments 1 to 4, wherein the vacuum device reduces the pressure inside the vacuum chamber from atmospheric pressure to 2 × 10 within 1 hour. -3 The pressure is reduced to below Pa, and the ultimate vacuum of the vacuum chamber is 1.1 × 10⁻⁶ -5 It is below Pa.

[0015] [Aspect 6] In the apparatus for manufacturing an insulating film on a diamond substrate according to embodiment 6, in any of embodiments 1 to 5, the aluminum raw material supply apparatus supplies alkylaluminum.

[0016] [Aspect 7] In the apparatus for manufacturing an insulating film on a diamond substrate according to Embodiment 7, in any of Embodiments 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 between the vacuum chamber body, the detachable part, and the dividing surface.

[0017] [Aspect 8] The method for manufacturing an insulating film on a diamond substrate according to aspect 8 of the present invention is: A diamond substrate is placed inside a vacuum chamber and the vacuum chamber is closed. The inside of the vacuum chamber is heated from atmospheric pressure to 2 × 10 within 1 hour. -3 Process A: Depressurizing to below Pa; Step B: Supplying one or more dopants selected from nitrogen dioxide (NO2), nitric oxide (NO), sulfur dioxide (SO2), and ozone (O3) into the vacuum chamber; Step C: Supplying nitrogen to the vacuum chamber; Step D: Supplying an organic aluminum compound to the vacuum chamber; Step E: Supplying nitrogen to the vacuum chamber; Step F: Supplying water vapor to 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 above steps D to G are repeated multiple times.

[0018] [Aspect 9] The method for manufacturing an insulating film on a diamond substrate according to embodiment 9 is to perform step I, in embodiment 8, between step A and step B, by repeating steps D to G one or more times.

[0019] [Aspect 10] The method for manufacturing an insulating film on a diamond substrate according to embodiment 10 is as follows: in embodiment 8 or 9, 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] The method for manufacturing an insulating film on a diamond substrate according to Embodiment 11 is, in any one of Embodiments 8 to 10, in the step A, the inside of the vacuum chamber is depressurized from atmospheric pressure to 2×10 -3 Pa or less within 1 hour, and the ultimate vacuum degree of the vacuum chamber is 1.1×10 -5 Pa or less.

[0021] [Embodiment 12] The method for manufacturing an insulating film on a diamond substrate according to Embodiment 12 is, in any one of Embodiments 8 to 11, in the step D, an alkylaluminum is supplied as the organoaluminum compound.

[0022] [Embodiment 13] The method for manufacturing an insulating film on a diamond substrate according to Embodiment 13 is, in any one of Embodiments 8 to 12, in the step D, the impurity concentration of the alkylaluminum is less than 10 ppm.

[0023] [Embodiment 14] The method for manufacturing an insulating film on a diamond substrate according to Embodiment 14 is, in any one of Embodiments 8 to 13, the carrier gas for the organoaluminum compound and the water vapor is nitrogen (N2), and the purity of the nitrogen is 99.99995% or more.

[0024] [Embodiment 15] The method for manufacturing an insulating film on a diamond substrate according to Embodiment 15 is, in any one of Embodiments 8 to 14, in the step B, the dopant is diluted with nitrogen (N2), and the concentration of the dopant in this dilution gas is 2% by volume (20000 ppm) or more.

[0025] [Embodiment 16]<The method for manufacturing an insulating film on a diamond substrate according to Embodiment 16 is as follows, in any of Embodiments 8 to 15, in step B the diamond substrate is heated to 20 to 90°C and the dopant is supplied; in steps D to G when forming the 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 the 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" means a value greater than or equal to numerical value A and less than or equal to numerical value B.

[0026] [Aspect 17] The method for manufacturing an insulating film on a diamond substrate according to Embodiment 17 is as follows: in any of Embodiments 8 to 16, the insulating film to be manufactured is amorphous aluminum oxide, the dielectric breakdown voltage of the insulating film is 8 MV / cm or more, and the surface of the diamond substrate has a surface density of 5 × 10⁻¹⁶ 13 cm -2 Higher hole carriers are generated, and the sheet resistance of the surface of the diamond substrate is 1 kΩ / □ or less in the (001) plane orientation of the diamond crystal, and 700 Ω / □ or less in the (111) plane orientation of the diamond crystal. [Effects of the Invention]

[0027] According to the apparatus and method for manufacturing an insulating film on a diamond substrate of the present invention, it is easy to dope the surface of the diamond substrate with hole carriers at a high density, and an insulating film having a sufficiently high dielectric strength can be formed on the diamond substrate. [Brief explanation of the drawing]

[0028] [Figure 1] This is a block diagram showing one embodiment of the apparatus for manufacturing an insulating film on a diamond substrate according to the present invention. [Figure 2] This is a schematic diagram showing the same embodiment. [Figure 3] This is a timing chart showing the gas introduction timing in the same embodiment. [Figure 4]This is a longitudinal cross-sectional view of a diamond substrate immediately after being placed in a vacuum chamber, according to one embodiment of the method for manufacturing an insulating film on a diamond substrate according to the present invention. [Figure 5] This is a longitudinal cross-sectional view of the diamond substrate in step A of the same embodiment. [Figure 6] This is a longitudinal cross-sectional view of a diamond substrate in which a dopant layer has been formed in step B of the same embodiment. [Figure 7] This is a longitudinal cross-sectional view of a diamond substrate to which an organoaluminum compound has been attached in step D of the same embodiment. [Figure 8] This is a longitudinal cross-sectional view of a diamond substrate showing the state in which organic components are removed by nitrogen molecules in step E of the same embodiment. [Figure 9] This is a longitudinal cross-sectional view of a diamond substrate from which organic components have been removed by step E of the same embodiment. [Figure 10] This is a longitudinal cross-sectional view of a diamond substrate to which water molecules have been attached by step F of the same embodiment. [Figure 11] This is a longitudinal cross-sectional view of a diamond substrate showing the state in which hydrogen atoms are removed by nitrogen molecules in step G of the same embodiment. [Figure 12] This is a longitudinal cross-sectional view of a diamond substrate in which a single layer of aluminum oxide has been formed by removing hydrogen atoms in step G of the same embodiment. [Figure 13] This is a longitudinal cross-sectional view of a diamond substrate in which aluminum oxide layers have been laminated by process H of the same embodiment. [Figure 14] This is a timing chart showing the gas introduction timing in a second embodiment of the present invention. [Figure 15] This is a longitudinal cross-sectional view of a diamond substrate in which an aluminum oxide layer and a dopant layer have been laminated by steps A to H of the second embodiment. [Figure 16] This is a timing chart showing the gas introduction timing in the conventional method (Comparative Example 1). [Figure 17] This is a longitudinal cross-sectional view showing a method for measuring the current-voltage characteristics between the source electrode and drain electrode of a field-effect transistor without a gate electrode, according to an embodiment of the present invention. [Figure 18] This graph shows the current-voltage characteristics between the source and drain electrodes of a field-effect transistor without a gate electrode in an embodiment of the present invention, illustrating the differences due to the oxygen impurity concentration in the trimethylaluminum (TMA) raw material of the Al2O3 insulating film. [Figure 19] This is a longitudinal cross-sectional view showing a method for measuring the output characteristics of a field-effect transistor in an embodiment of the present invention. [Figure 20] This graph shows the output characteristics of a field-effect transistor in an embodiment of the present invention. [Figure 21] This graph shows the output characteristics of a field-effect transistor in an embodiment of the present invention. [Figure 22] This graph shows the output characteristics of a field-effect transistor in an embodiment of the present invention. [Figure 23] This graph shows the output characteristics of a field-effect transistor in a comparative example of the present invention. [Figure 24] This graph shows the output characteristics of a field-effect transistor in an embodiment of the present invention. [Figure 25] This graph shows the output characteristics of a field-effect transistor in an embodiment of the present invention. [Figure 26] This graph shows the output characteristics of a field-effect transistor in an embodiment of the present invention. [Modes for carrying out the invention]

[0029] The following describes embodiments of the manufacturing apparatus and manufacturing method for insulating films on diamond substrates according to the present invention, using drawings. Note that the dimensions of the parts shown in the drawings do not reflect the dimensions of actual products.

[0030] [Embodiment of an apparatus for manufacturing insulating film on a diamond substrate] Figure 1 is a block diagram showing one embodiment of the apparatus for manufacturing an insulating film on a diamond substrate according to the present invention. This apparatus comprises a vacuum chamber 10, a support part (support) 14 for supporting the diamond substrate 1 inside the vacuum chamber 10, a heater 15 (Figure 2; heating device) for heating the diamond substrate 1 supported by the support part 14, and a vacuum chamber 10 that is heated from atmospheric pressure to 2 × 10 within 1 hour. -3 The system comprises a vacuum pressure device (28, 30, 32, 34) for reducing the pressure to below Pa, a dopant supply device (88, 58, 90) for supplying one or more dopants selected from nitrogen dioxide (NO2), nitric oxide (NO), sulfur dioxide (SO2), and ozone (O3) to the vacuum chamber 10, a nitrogen supply device (48, 52, 74, 56, 86, 60, 92) for supplying nitrogen (N2) to the vacuum chamber 10, an aluminum raw material supply device (50, 62, 64, 66, 68, 70) for supplying organoaluminum compounds to the vacuum chamber 10, a steam supply device (54, 76, 78, 80, 81, 82, 84) for supplying steam (H2O) to the vacuum chamber 10, and a control device 11 for controlling the vacuum pressure device, the dopant supply device, the nitrogen supply device, the aluminum raw material supply device, and the steam supply device.

[0031] The vacuum chamber 10 has a bottomed cylindrical vacuum chamber lower section 10b made of metal or the like, and a closed-topped cylindrical vacuum chamber upper section 10a made of metal or the like, which closes the upper end opening of the vacuum chamber lower section 10b and is separable when inserting the diamond substrate 1. A flange is formed on the dividing surface between the vacuum chamber upper section 10a and the vacuum chamber lower section 10b, and an annular metal gasket 12 is sandwiched between the flanges to maintain high airtightness. The metal gasket 12 is a gasket made only of metal material, and the metal material is selected from stainless steel, titanium, Monel steel, which have excellent corrosion resistance, or copper, aluminum, pure iron, mild steel, etc. which have good compatibility. Conventionally, in this type of atomic layer deposition apparatus (ALD), it was thought that sufficient airtightness could be obtained by interposing rubber O-rings or the like on the dividing surface of the vacuum chamber, but by installing a metal gasket 12 instead of an O-ring as invented by the inventor, a high vacuum level can be achieved as described later.

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

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

[0034] Two vacuum pressure devices are connected to the lower part 10b of the vacuum chamber. The first pressure reducing system is connected via a valve 26 leading to the bottom 10b of the vacuum chamber and comprises a turbomolecular pump 28, a valve 30, a rotary pump 32, and an exhaust device 34 in series in that order. It can achieve a higher vacuum than the second pressure reducing system, but the exhaust speed is lower. The turbomolecular pump 28 is a mechanical vacuum pump in which a rotor, a rotating body with metal turbine blades, rotates at high speed, ejecting gas molecules and thereby exhausting the gas. The ultimate vacuum of the turbomolecular pump 28 is 1 × 10⁻⁶. -7 A pressure of approximately Pa is desirable. Since the operating pressure of the turbomolecular pump 28 is limited, a rotary pump 32 is used as an auxiliary pump. The rotary pump 32 is, for example, an oil-sealed rotary vacuum pump, which exhausts gas by scraping it out with its rotating internal blades, and the ultimate vacuum is not limited, but for example 10 -1 The pressure is approximately Pa. Valve 26, turbomolecular pump 28, valve 30, and rotary pump 32 are connected to control device 11.

[0035] The second pressure reducing system is connected via a valve 36 leading to the bottom 10b of the vacuum chamber and includes a filter 38 for removing dust from inside the vacuum chamber 10, a pressure controller 40 for adjusting the vacuum level, a pump 42 for reducing the pressure in the vacuum chamber 10, and an exhaust device 44, all connected in series in this order. Although it achieves a higher pressure (lower vacuum) than the first pressure reducing system, it has a higher exhaust speed. The ultimate vacuum level achieved by the pump 42 is 4.8 × 10⁻⁶. -1 A pressure of around Pa is sufficient. The pressure controller 40 and the pump 42 are connected to the control device 11.

[0036] In this embodiment of the apparatus, the first pressure reducing device is mainly used to remove atmospheric components 2 from the diamond substrate 1 by high vacuum, and the second pressure reducing device is mainly used to maintain the desired pressure by introducing gas into the vacuum chamber 10 while exhausting.

[0037] Next, the gas supply equipment group for the vacuum chamber 10 will be described. The gas supply equipment group is equipped with a nitrogen purifier 48 as a common component. The nitrogen purifier 48 removes impurities from the nitrogen gas supplied from a nitrogen source (not shown) to produce high-purity nitrogen gas. The purity of the produced nitrogen gas is not limited, but it is preferably 99.99995% or higher. This purity makes it easy to form an aluminum oxide film 7 with high insulating performance and has a high effect 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 a nitrogen purifier 48 to adjust the flow rate of nitrogen gas, which is the carrier gas; a bubbling unit 68 for vaporizing organoaluminum compounds with nitrogen gas; a constant temperature bath 70 for maintaining the bubbling unit 68 at the vaporization temperature range of the organoaluminum compounds; valves 64 and 66 for opening and closing the inlet and outlet of the bubbling unit 68; a valve 62 for short-circuiting the inlet and outlet of the bubbling unit 68; and a valve 72 leading to the gas introduction passage 46. The MFC 50 and valves 62, 64, 66, and 72 are connected to the control device 11.

[0039] For example, alkylaluminum compounds can be used as organoaluminum compounds. Alkylaluminum compounds include trimethylaluminum, triethylaluminum, and triisobutylaluminum, but trimethylaluminum (TMA) is particularly preferred for the present invention. The vaporization temperature range of trimethylaluminum at atmospheric pressure is approximately 15 to 25°C.

[0040] Adjacent to the dopant supply device, an MFC52 and valve 74 are provided as a first nitrogen supply device. The reason for their proximity to the dopant supply device is to quickly replace the path with nitrogen after dopant supply. The MFC52 and valve 74 are connected to the control device 11.

[0041] The steam supply device includes an MFC 54 connected to the nitrogen purifier 48 to adjust the flow rate of nitrogen gas, which is the carrier gas; a bubbling unit 82 for vaporizing pure water with nitrogen gas; a constant temperature bath 84 for keeping the bubbling unit 82 at 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 passage 46. The MFC 54 and valves 76, 78, 80, and 81 are connected to the control device 11.

[0042] A second nitrogen supply device, consisting of an MFC56 and a valve 86, is provided in close proximity to the steam supply device. The reason for its proximity to the steam supply device is to quickly replace the path with nitrogen after steam is supplied. The MFC56 and valve 86 are connected to the control device 11.

[0043] The dopant supply device consists 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 the dopant used in the present invention. The MFC 58 and the valve 90 are connected to the control device 11.

[0044] Adjacent to the dopant supply device, a third nitrogen supply device consisting of an MFC 60 and a valve 92 is provided. The reason for its proximity to the dopant supply device is to quickly replace the path with nitrogen after dopant supply. The MFC 60 and valve 92 are connected to the control device 11.

[0045] Next, the control method of the apparatus of the above embodiment and the method for manufacturing the insulating film on the diamond substrate 1 will be specifically explained using Figure 2. Figure 2 schematically shows the apparatus of Figure 1, and the configuration of each part is simplified compared to Figure 1. In Figure 2, V1 represents a valve that opens and closes the supply of organic aluminum compounds such as TMA from the aluminum raw material supply device. When V1 is open (ON), it means that in Figure 1, the MFC 50 is operated, valve 62 is closed, and valves 64, 66, and 72 are opened to perform bubbling in the bubbling unit 68. When V1 is closed (OFF), it means that in Figure 1, the MFC 50 is stopped, valve 62 is opened, and valves 64, 66, and 72 are closed to stop bubbling in the bubbling unit 68.

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

[0047] In Figure 2, V3 represents a valve that opens and closes the supply of dopant from the dopant supply device. When V3 is open (ON), in Figure 1, it means that the MFC 58 is operated, opening valve 90 and supplying dopant to the vacuum chamber 10. When V3 is closed (OFF), in Figure 1, it means that the MFC 58 is stopped, closing valve 90 and stopping the supply of dopant.

[0048] In Figure 2, V4 represents the valve that operates the second pressure reducing device. When V4 is open (ON), in Figure 1, it means that valve 36 is opened, and the vacuum chamber 10 is evacuated through the filter 38 and pressure controller 40 by the pump 42 and exhaust device 44. When V4 is closed (OFF), in Figure 1, it means that valve 36 is closed, and the pump 42 and exhaust device 44 are stopped, thus stopping the evacuation from the vacuum chamber 10.

[0049] In Figure 2, V5 represents the valve that operates the nitrogen supply device. When V5 is open (ON), in Figure 1, it means that at least one of the MFCs 52, 56, and 60 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 (1 sLm), 100 cc (100 sccm), and 100 cc (100 sccm), respectively. When V5 is closed (OFF), in Figure 1, it means that all of the MFCs 52, 56, and 60 are stopped, and all of the valves 74, 86, and 92 are closed, stopping the supply of nitrogen gas.

[0050] In Figure 2, V6 represents the valve that operates the first pressure reducing device. When V6 is open (ON), in Figure 1, it means that valve 26 is opened, the turbomolecular pump 28 and rotary pump 32 are activated, and the vacuum chamber 10 is evacuated via valve 30 and exhaust device 34. When V6 is closed (OFF), in Figure 1, it means that valve 26 is closed (the turbomolecular pump 28 and rotary pump 32 may remain operating), and the evacuation from the 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 parts of the device are controlled as follows. 1. Using a vacuum device, reduce the pressure inside the vacuum chamber 10 from atmospheric pressure to 2 × 10 within 1 hour. -3 Process A: Depressurizing to below Pa; 2. Step B: Supplying dopants into the vacuum chamber 10 using a dopant supply device; 3. Step C: Supplying nitrogen to the vacuum chamber 10 using a nitrogen supply device; 4. Step D: Supplying organoaluminum compounds to the vacuum chamber 10 using an aluminum raw material supply device; 5. Step E: Supplying nitrogen to the vacuum chamber 10 using a nitrogen supply device; 6. Step F: Supplying steam to the vacuum chamber 10 using a steam supply device; 7. Step G of supplying nitrogen to the vacuum chamber 10 using a nitrogen supply device; and 8. Process H is a process that repeats processes D to G multiple times.

[0052] [First Embodiment of a Method for Manufacturing an Insulating Film on a Diamond Substrate] [Step A: Depressurizing the inside of 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. Atmospheric components 2 mainly consist of N2, O2, CO2, H2O, etc.

[0053] The diamond substrate 1 is preferably made of a single diamond crystal, 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 easily improving the electrical properties of the final semiconductor device. The crystal orientation of the surface of the diamond substrate 1 may be tilted within ±3° from the aforementioned crystal orientation, and more preferably within ±1°. The diamond substrate 1 may also be one on which a thin single diamond crystal layer has been deposited on a support such as SiC or polycrystalline diamond by CVD or PVD.

[0054] Once the diamond substrate 1 is placed inside the vacuum chamber 10, the upper part 10a of the vacuum chamber is fixed to the lower part 10b of the vacuum chamber. Due to the high airtightness of the annular metal gasket 12 interposed between the two, the inside of the vacuum chamber 10 is 1 × 10 -7It becomes possible to reduce the pressure to approximately Pa. In typical atomic layer deposition (ALD) apparatuses of this type, rubber O-rings are interposed on the dividing surfaces of the vacuum chamber, and it is believed that sufficient airtightness can be achieved with these. However, according to the inventor's findings, it has been found that O-rings do not achieve a vacuum level sufficient to remove atmospheric components 2 from the diamond substrate 1.

[0055] Next, turn on V6 and set vacuum chamber 10 to high vacuum (2 x 10 -3 The system rapidly evacuates to below Pa within one hour. The series-arranged turbomolecular pump 28 and rotary pump 32 achieve a vacuum of 1.1 × 10⁻¹⁶, which is difficult to achieve with conventional ALDs. -5 A vacuum level of less than Pa can be achieved, and as shown in Figure 5, it is possible to desorb atmospheric components 2 adsorbed on the surface of the diamond substrate 1. -3 The inventors have found that even if a vacuum of Pa or less is achieved, if it takes too long, the desorption of atmospheric component 2 tends to be insufficient. The final vacuum level attained in the vacuum chamber 10 by turning on V6 is preferably 1.1 × 10⁻⁶. -5 Pa or less, fer 1 × 10 -5 Pa or less, and more preferably 1 × 10⁻⁶ -6 Pa or less, 1 x 10 if possible. -7 It is Pa.

[0056] [Process B: Supplying the dopant] Next, V6 is turned OFF and V3 is turned ON to introduce a dopant dilution gas, which is a mixture of high-purity dopant and nitrogen gas as a carrier gas, into a clean vacuum chamber 10 under high vacuum conditions. As a result, as shown in Figure 6, the dopant molecules adhere to and deposit on the surface of the diamond substrate 1 to a thickness of one molecular layer, forming a dopant layer 3. The dopant is one or more selected from nitrogen dioxide (NO2), nitric oxide (NO), sulfur dioxide (SO2), and ozone (O3), and any of them can be used, but from the viewpoint of easily improving device performance, nitrogen dioxide is the most preferred. In order to ensure the doping effect of hole carriers on the surface of the diamond substrate 1, the concentration of dopant in the dopant dilution gas is preferably 2 volume% (20000 ppm) or more, and more preferably 10 to 100 volume%.

[0057] The duration for which V3 is ON is not limited in this invention, but is preferably 1 millisecond to 25 milliseconds, and more preferably 15 milliseconds to 20 milliseconds. Such a duration ensures a more reliable doping effect of hole carriers on the surface of the diamond substrate 1. The heating temperature of the diamond substrate 1 by the heater 15 during the period when V3 is ON is preferably 100°C to 500°C, and more preferably 150°C to 400°C. Such a temperature ensures a more reliable doping effect of hole carriers on the surface of the diamond substrate 1. While not limited in this invention, the pressure inside the vacuum chamber 10 during the period when V3 is ON is 1.33 × 10⁻⁶. 4 Pa or more 2.66×10 4 It is preferable that it be less than or equal to Pa, and more preferably 1.7 × 10⁻⁶ 4 Pa or more 2.3×10 4 The pressure is below Pa. V4 may be activated as needed to maintain the pressure within this range.

[0058] [Process C for supplying nitrogen / Layer 1] Next, by turning V3 OFF, V5 ON, and V4 ON, the dopant dilution gas in the vacuum chamber 10 is discharged, and high-purity nitrogen gas is introduced. This removes excess dopant adhering to the dopant layer 3 on the surface of the diamond substrate 1, forming a single layer dopant layer 3 with neatly arranged molecules.

[0059] While not limited in this invention, the duration for which V5 is ON is preferably between 1 second and 20 seconds, and more preferably between 5 seconds and 10 seconds. Such a duration ensures a more reliable effect in removing excess dopant. The heating temperature of the diamond substrate 1 by the heater 15 during the period when V5 is ON is preferably between 80°C and 500°C, and more preferably between 120°C and 230°C. Such a temperature ensures a more reliable effect in removing excess dopant. While not limited in this invention, the pressure inside the vacuum chamber 10 during the period when V5 is ON is preferably between 0 Pa and 100 Pa, and more preferably between 0.1 Pa and 1 Pa. V4 is operated at an appropriate rotational speed to maintain the pressure within this range.

[0060] [Process D / 1st layer for supplying organoaluminum compounds] Next, by turning V5 OFF and leaving V4 ON, and then turning V1 ON, the nitrogen gas in the vacuum chamber 10 is discharged, and a diluted organoaluminum compound gas, which is a mixture of a high-purity organoaluminum compound with nitrogen gas as a carrier gas, is introduced into the vacuum chamber 10. Examples of organoaluminum compounds that can be used include alkylaluminum, which includes trimethylaluminum, triethylaluminum, and triisobutylaluminum, but trimethylaluminum (TMA) is particularly preferred for this invention. A TMA molecule consists of one aluminum atom 4A and three methyl groups 4B, and as shown in Figure 7, TMA4 is deposited and stacked on the dopant layer 3 as a monolayer. When using other organoaluminum compounds, these should be read as organoaluminum compound 4, aluminum atom 4A, and organic functional group 4B, respectively.

[0061] The duration for which V1 is ON is not limited in this invention, but is preferably 1 millisecond to 25 milliseconds, and more preferably 15 milliseconds to 25 milliseconds. Such a duration ensures that the TMA4 adheres to and laminates on the dopant layer 3 as a monolayer. The heating temperature of the diamond substrate 1 by the heater 15 during the period when V1 is ON is preferably 80°C to 500°C, and more preferably 120°C to 230°C. Such a temperature ensures that the TMA4 adheres to and laminates on the dopant layer 3 as a monolayer. During the period when V1 is ON, the pressure inside the vacuum chamber 10 is preferably 0 Pa to 100 Pa, and more preferably 0.1 Pa to 1 Pa. V4 is operated at an appropriate rotational speed to maintain the pressure within this range.

[0062] [Process E for supplying nitrogen / Layer 1] Next, by turning V1 OFF, leaving V4 ON, and then turning V5 ON, the organoaluminum compound dilution gas in the vacuum chamber 10 is discharged, and high-purity nitrogen gas is introduced. This removes excess TMA4 adhering to the surface of the diamond substrate 1, and further, as shown in Figure 8, the methyl groups 4B of TMA4 are separated from the aluminum atoms 4A by the nitrogen molecules 5 and removed from the surface of the diamond substrate 1, and as shown in Figure 9, a single layer of aluminum atoms 4A is formed on the single layer of dopant layer 3. During the period when V5 is ON, the heating temperature of the diamond substrate 1 by the heater 15, the pressure in the vacuum chamber 10, and other conditions may be the same as in [Process C / 1st layer for supplying nitrogen].

[0063] [Process F for supplying water vapor / 1st layer] Next, by turning V5 OFF, leaving V4 ON, and then turning V2 ON, the nitrogen gas in the vacuum chamber 10 is discharged, and a water vapor dilution gas, which is a mixture of high-purity water vapor with the nitrogen gas used as a carrier gas, is introduced. As a result, as shown in Figure 10, water molecules 6 are deposited on the aluminum atoms 4A in a single layer. Each water molecule 6 consists of one oxygen atom 6A and two hydrogen atoms 6B.

[0064] The duration for which V2 is ON is preferably 1 millisecond to 25 milliseconds, and more preferably 15 milliseconds to 25 milliseconds, although this invention is not limited thereto. Such a duration makes it more certain that water molecules 6 will adhere to and deposit on the aluminum atoms 4A in a single layer. The heating temperature of the diamond substrate 1 by the heater 15 during the period when V2 is ON is preferably 80°C to 500°C, and more preferably 120°C to 230°C. Such a temperature makes it more certain that water molecules 6 will adhere to and deposit on the aluminum atoms 4A in a single layer. During the period when V5 is ON, the pressure inside the vacuum chamber 10 is preferably 0 Pa to 100 Pa, and more preferably 0.1 Pa to 1 Pa, although this invention is not limited thereto. V4 is operated at an appropriate rotational speed to maintain the pressure within this range.

[0065] [Process G for supplying nitrogen / Layer 1] Next, V2 is turned OFF, V4 is left ON, and V5 is turned ON to discharge the water vapor dilution gas in the vacuum chamber 10 and introduce high-purity nitrogen gas. This removes excess water molecules 6 attached to the surface of the diamond substrate 1, and further, as shown in Figure 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 Figure 12, a single layer of oxygen atoms 6A is formed on the single layer of aluminum atoms 4A, thus completing the first single layer film of aluminum oxide. During the period when V5 is ON, the heating temperature of the diamond substrate 1 by the heater 15, the pressure inside the vacuum chamber 10, and other conditions can be the same as in [Process C / First layer supplying nitrogen].

[0066] [Process H is a process that repeats processes D through G multiple times] The following steps involve repeatedly forming two or more single layers of aluminum oxide to create an aluminum oxide film 7 with alternating layers of aluminum atoms 4A and oxygen atoms 6A, as shown in Figure 13, to the required thickness. Since no methyl groups 4B or hydrogen atoms 6B remain in the aluminum oxide film 7 formed in this way, a high-quality aluminum oxide film 7 with extremely few impurities can be formed. Note that the film formation conditions differ slightly between the first layer and the second and subsequent layers, so these points will be explained. Unless otherwise specified, the conditions can be the same as for the first layer.

[0067] [Process D for supplying organoaluminum compounds / from the second layer onwards] By turning V5 OFF, leaving V4 ON, and then turning V1 ON, nitrogen gas is discharged from the vacuum chamber 10, and organoaluminum compound diluent gas is introduced into the vacuum chamber 10 to form TMA4 on a single layer of aluminum oxide. The period during which V1 is ON and the pressure inside the vacuum chamber 10 may be the same as in [Process D / 1st layer for supplying organoaluminum compound], but the heating temperature of the diamond substrate 1 by the heater 15 is preferably 80°C to 500°C, and more preferably 120°C to 230°C. Such temperatures make the effect of laminating TMA4 as the second layer more reliable. It is preferable to have a higher film deposition temperature for the second and subsequent layers than for the first layer because it reduces the concentration of excess charge caused by impurities in the Al2O3 film.

[0068] [Process E for supplying nitrogen / from the second layer onwards] Next, V1 is turned OFF, V4 is left ON, and V5 is turned ON to discharge the organoaluminum compound dilution gas from the vacuum chamber 10 and introduce high-purity nitrogen gas. The duration for which V5 is ON and the pressure conditions inside the vacuum chamber 10 may be the same as in [Process C for supplying nitrogen / 1st layer], but the heating temperature of the diamond substrate 1 by the heater 15 is preferably 80°C to 500°C, and more preferably 120°C to 230°C. At such temperatures, the effect of removing the methyl group 4B of the second layer TMA4 becomes more reliable.

[0069] [Process F for supplying water vapor / from the second layer onwards] Next, by turning V5 OFF and leaving V4 ON, and then turning V2 ON, the nitrogen gas in the vacuum chamber 10 is discharged, and a water vapor dilution gas, which is a mixture of high-purity water vapor with nitrogen gas as a carrier gas, is introduced. The period during which V2 is ON and the pressure inside the vacuum chamber 10 may be the same as in the [water vapor supply process F / 1st layer], but the heating temperature of the diamond substrate 1 by the heater 15 is preferably 80°C to 500°C, and more preferably 120°C to 230°C. At such temperatures, the effect of water molecules 6 adhering to and depositing in a single layer on the aluminum atoms 4A of the second layer and above becomes more reliable.

[0070] [Process G for supplying nitrogen / from the second layer onwards] Next, by turning V2 OFF, leaving V4 ON, and then turning V5 ON, the water vapor dilution gas in the vacuum chamber 10 is discharged, and high-purity nitrogen gas is introduced. This removes excess water molecules 6 adhering to the surface of the diamond substrate 1, and also removes the hydrogen atoms 6B from the water molecules 6. During the period when V5 is ON, the heating temperature of the diamond substrate 1 by the heater 15, the pressure inside the vacuum chamber 10, and other conditions can be the same as in [Process C for supplying nitrogen / 2nd layer and beyond].

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

[0072] [Second Embodiment of a Method for Manufacturing an Insulating Film on a Diamond Substrate] Next, a second embodiment of the present invention will be described. In this second embodiment, the control device 11 is programmed to perform a step I between step A and step B, repeating steps D to G one or more times, as shown in Figure 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 a dopant layer 3 is formed, and then a second aluminum oxide film 7 is formed. 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, steps A and steps D to G for the first layer during the formation of the first aluminum oxide film may be the same as those for the first layer in the first embodiment, so the explanation for the first layer in the first embodiment will be used by reference. Also, steps D to G for the second and subsequent layers during the formation of the first aluminum oxide film, and steps D to G during the formation of the second aluminum oxide film may be the same as those for the second and subsequent layers in the first embodiment, so the explanation for the second and subsequent layers in the first embodiment will be used by reference.

[0074] [Process B for supplying the dopant / Second embodiment] In the second embodiment, the difference in conditions from the first embodiment lies in step B, the step of supplying the dopant. In the second embodiment, when step B is performed, 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, which is a mixture of high-purity dopant and nitrogen gas as a carrier gas, is introduced into a 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 to 500°C, and more preferably 120°C to 230°C. At such temperatures, the doping effect of hole carriers on the first aluminum oxide film 7 becomes more reliable.

[0075] In the second embodiment, the number of times 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, instead of forming the dopant layer 3 directly on the surface of the diamond substrate 1, the dopant layer 3 can be formed between the first and second aluminum oxide films 7. This provides 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 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 components of well-known technologies or omit some components of well-known technologies. [Examples]

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

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

[0080] Next, the diamond substrate 1 was heated to 80°C by heater 15, V6 was turned OFF, V4 was turned ON to create a vacuum, and V3 was turned ON to supply NO2 into the vacuum chamber 10 for 2 minutes. During this time, the vacuum level inside the vacuum chamber 10 was 1 × 10⁻⁶. -2 The pressure was maintained at Pa. After the supply time had elapsed, V3 was turned OFF to stop the supply of NO2, and V6 was turned ON to create a 2x10 vacuum chamber in the 10 chamber. -3 The pressure was reduced to Pa in one hour.

[0081] Next, the bubbling unit 68 containing TMA was kept at 20°C in the constant temperature bath 70, and the bubbling unit 82 containing H2O was kept at 20°C in the constant temperature bath 84. With a 5-second interval (pause period), V1 and V2 were alternately turned ON for 20 milliseconds each. During the interval, V5 was also turned ON to supply nitrogen gas to the vacuum bath 10.

[0082] When forming the first layer of aluminum oxide film 7, when V1 was ON, TMA was bubbling with 99.99995% pure nitrogen gas from the nitrogen purifier 48, and the 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 maintained at 1.2 volume%, the vacuum level 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 layer of aluminum oxide film 7, if V2 was ON, pure water was bubbled with 99.99995% pure nitrogen gas from the nitrogen purifier 48, and water vapor diluted with nitrogen was introduced into the vacuum chamber 10. The water vapor concentration in the water vapor dilution gas was maintained at 2.3 volume%, the vacuum level of 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 layer of aluminum oxide film 7, if V5 was ON, a path similar to the path taken immediately before (MFC52 → valve 74 or MFC56 → valve 86) was selected to introduce nitrogen gas from the nitrogen purifier 48 into the vacuum chamber 10. The nitrogen flow rate through MFC52 was set to 200 cc / min (200 sccm) under standard conditions. The nitrogen flow rate through MFC56 was set to 10 cc / min (10 sccm) under standard conditions. The vacuum level of 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 layers of aluminum oxide film 7, the temperature of the diamond substrate 1 was maintained at 230°C when V1, V2, and V5 were turned ON. All other conditions were the same as for the first layer. Under these conditions, 109 cycles were repeated to form an aluminum oxide film 7 with a total thickness of 12 nm.

[0086] After stopping the heating by the heater 15 and waiting for the diamond substrate 1 to cool to room temperature, nitrogen gas was introduced into the vacuum chamber 10 to atmospheric pressure, the top 10a of the vacuum chamber was opened, and the diamond substrate 1 with the aluminum oxide film 7 formed on it was removed together with the support plate 13.

[0087] The sample obtained in the above process was set in a Toyo Technica Hall resistivity measuring device "ResiTest8300 / 8400" and the resistivity of the surface of the diamond substrate 1 was measured. The results were 5 kΩ / □ for the (001) plane orientation of the surface of the diamond substrate 1 and 2.5 kΩ / □ for the (111) plane orientation of the surface of the diamond substrate 1, indicating that the doping of hole carriers with NO2 was successful. The resistivity of the surface of the diamond substrate 1 can be measured both before and after the formation of the aluminum oxide film 7.

[0088] Furthermore, the characteristics of the diamond FET fabricated using the diamond substrate 1 of Example 1 were measured using the experimental setup 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 deposited on the dopant layer 3 to form the source electrode 100 and drain electrode 102, and gold was deposited on the aluminum oxide film 7 to form the 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 using the ammeter 110 while varying the voltage of the power supply 108. D The following was measured: 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 using the ammeter 110 while varying the voltages of power supply 108 and power supply 112, respectively. D Measure the gate-source voltage V with ammeter 114. GS The following measurements were taken. The results are shown in Figures 24 to 26.

[0089] Figure 24 shows the output (drain voltage / current) characteristics of the diamond FET fabricated according to Example 1, V GS When the voltage is changed from -3V to 11V, the maximum drain current (I DMAX The current is 112.6mA / mm, and the on-resistance (R ON The resistance was 350Ω·mm, which was a value that was perfectly practical for use as a FET. Figure 25 shows the output (drain voltage / current) characteristics of the same diamond FET as in Figure 24, fabricated according to Example 1, V GSWhen the voltage was set to 11V, the off-voltage of the drain voltage was a high value of 4266V. Figure 26 shows the same diamond FET as in Figures 24 and 25, fabricated in Example 1, at room temperature 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 The time evolution of |) is shown. As shown in Figure 26, this diamond FET operated without degradation for up to 4050 hours, demonstrating its long lifespan.

[0090] [Comparative Example 1] Using the same atomic layer deposition (ALD) apparatus as in Example 1 shown in Figures 1 and 2, and with the same sequence control as shown in Figure 16, a dopant layer 3 and an aluminum oxide film 7 were formed on the same diamond substrate 1 as in Example 1. A support plate 13 with a diamond substrate 1 on it is placed inside the vacuum chamber 10, and V6 is activated to lower the vacuum chamber 10 from atmospheric pressure to 2 × 10⁻¹⁰⁻¹ 1 The pressure was reduced to Pa.

[0091] Next, the diamond substrate 1 was heated to 80°C by heater 15, V6 was turned OFF, V4 was turned ON to create a vacuum, and V3 was turned ON to supply NO2 into the vacuum chamber 10 for 2 minutes. During this time, the vacuum level inside the vacuum chamber 10 was 2 × 10⁻⁶. 1 The pressure was maintained at Pa. After the supply time had elapsed, V3 was turned OFF to stop the supply of NO2.

[0092] Next, the bubbling unit 68 containing TMA was kept at 20°C in the constant temperature bath 70, and the bubbling unit 82 containing H2O was kept at 20°C in the constant temperature bath 84. As shown in Figure 16, V1 and V2 were turned ON alternately for 20 milliseconds each without any interval. Other conditions were the same as in Example 1.

[0093] Comparative Example 1, obtained through the above process, was placed in a Toyo Technica Hall resistivity measuring device "ResiTest8300 / 8400" and the resistivity of the surface of the diamond substrate 1 was measured. The results were 15kΩ / □ for the (001) plane orientation of the surface of the diamond substrate 1 and 12kΩ / □ for the (111) plane orientation of the surface of the diamond substrate 1, indicating that the doping of hole carriers with 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-voltage of 200 V, which was unsuitable for use as a FET.

[0095] [Example 2] As 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 the diamond substrate 1, and gold was deposited on the dopant layer 3 to form the source electrode 100 and 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 a TMA with an oxygen impurity concentration of 10 ppm, as shown in Figure 17. Except for the TMA used, all conditions were the same as in Example 2, and a dopant layer 3 and an aluminum oxide film 7 were formed on the diamond substrate 1, and gold was deposited on the dopant layer 3 to form the source electrode 100 and drain electrode 102.

[0097] Using the MOSFETs of Example 2 and Example 3, a power supply 108 and an ammeter 110 are connected between the source electrode 100 and the drain electrode 102, and the drain current I is measured by the ammeter 110 while varying the voltage of the power supply 108. D We measured it.

[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 Ω mm, and in Example 3, where the oxygen concentration in the TMA was 10 ppm, it was 169 Ω mm. Both were usable as semiconductor devices, but Example 2, with an oxygen concentration in the TMA of less than 2 ppm, showed particularly excellent characteristics as a diamond MOSFET.

[0099] [Example 4] As 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 deposited on the dopant layer 3 to form the source electrode 100 and drain electrode 102, and gold was deposited on the aluminum oxide film 7 to form the gate electrode 116.

[0100] [Example 5] On the other hand, in Example 5, a field-effect transistor having a gate electrode 116 was formed using TMA with an oxygen impurity concentration of 10 ppm, as shown in Figure 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 deposited on the dopant layer 3 to form the source electrode 100 and drain electrode 102, and gold was deposited on the aluminum oxide film 7 to form the gate electrode 116.

[0101] Using the MOSFETs of Examples 4 and 5, a power supply 108 and an ammeter 110 are connected between the source electrode 100 and the drain electrode 102, and the drain current I is measured using the ammeter 110 while varying the voltage of the power supply 108. D The following was measured: 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 using the ammeter 110 while varying the voltages of power supply 108 and power supply 112, respectively. D Measure the gate-source voltage V with ammeter 114. GS We measured it.

[0102] Figures 20 and 21 show the output characteristics (current-voltage characteristics) of the diamond MOSFETs in Example 4, where the oxygen impurity concentration in the TMA was less than 2 ppm, and in Example 5, where the oxygen impurity concentration in the TMA was 10 ppm, respectively. Maximum drain current (I DMAX A higher value indicates a superior MOSFET. Example 4 shows the highest drain current (I DMAX ) is 409 mA / mm, and Example 5 has a maximum drain current (I DMAX Both have a capacitance of 234 mA / mm and can be used as MOSFETs, but Example 4 showed superior characteristics as a diamond MOSFET.

[0103] [Example 6] Using the same method and conditions as in Example 4, a diamond MOSFET was fabricated using the apparatus shown in Figures 1 and 2, which was designated as Example 6.

[0104] [Comparative Example 2] The diamond substrate 1 is processed using a different furnace without sufficient initial depressurization, as in the present invention, rather than using the apparatus shown in Figures 1 and 2, resulting in a 1.01 × 10⁻¹⁰ 5 The diamond substrate 1, which was doped with NO2 gas at Pa and then removed at room temperature, was again placed in the apparatus shown in Figures 1 and 2, and a diamond MOSFET was fabricated under the same conditions as in Example 6, which was then designated as Comparative Example 2.

[0105] Figures 22 and 23 show the output characteristics (current-voltage characteristics) of the diamond MOSFETs of Example 6 and Comparative Example 2, respectively. Example 6 has a maximum drain current (I DMAX ) was 213 mA / mm, but Comparative Example 2 had a maximum drain current (I DMAX The current ratio was 125 mA / mm, and the diamond MOSFET in Example 6 had significantly better characteristics than in Comparative Example 2. [Industrial applicability]

[0106] According to the present invention's apparatus and method for manufacturing insulating films on diamond substrates, it is easy to dope the surface of a diamond substrate with hole carriers, and an insulating film having a sufficiently high dielectric strength can be formed on the diamond substrate. This film can be used in semiconductor devices and electronic components that can be used in various electronic devices, and therefore has industrial applications. [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-cooled jacket 20 Coolant inlet 22 Cooling water outlet 24 Gas inlet 26 Valves 28 Turbomolecular pumps 30 Valves 32 Rotary Pump 34 Exhaust system 36 Valves 38 Filters 40 Pressure Controllers 42 Pump 44 Exhaust system 46 Gas introduction path 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 Constant temperature bath 72 Valves 74 valves 76 valves 78 valves 80 valves 82 Bubbling unit 84 Constant temperature 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 Shuttle bus stop

Claims

1. Vacuum chamber and A support for the diamond substrate within the vacuum chamber, A heating device for heating a diamond substrate supported on the aforementioned support, The vacuum chamber is subjected to atmospheric pressure for 2 × 10 within 1 hour. －３ A vacuum device that reduces pressure to below Pa, 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 ) to the vacuum chamber, Nitrogen (N ２ A nitrogen supply device that supplies ) to the vacuum chamber, An aluminum raw material supply device that supplies organoaluminum compounds to the vacuum chamber, Water vapor (H ２ A steam supply device that supplies O) to the vacuum chamber, An apparatus for manufacturing an insulating film on a diamond substrate, comprising a vacuum device, a dopant supply device, a nitrogen supply device, an aluminum raw material supply device, and a control device for controlling the water vapor supply device.

2. The apparatus for manufacturing an insulating film on a diamond substrate according to claim 1, characterized in that the control device is programmed to perform the following steps in the following order. The vacuum device reduces the pressure inside the vacuum chamber from atmospheric pressure to 2 × 10 within 1 hour. －３ Step A: Depressurizing to below Pa; Step B: Supplying the dopant into the vacuum chamber using the dopant supply device; Step C: Supplying the nitrogen to the vacuum chamber using the nitrogen supply device; Step D: Supplying an organoaluminum compound to the vacuum chamber using the aluminum raw material supply device; Step E: Supplying the nitrogen to the vacuum chamber using the nitrogen supply device; Step F: Supplying the steam to the vacuum chamber using the steam supply device; Step G of supplying the nitrogen to the vacuum chamber using the nitrogen supply device; and Step H is a process that repeats steps D to G multiple times.

3. The apparatus for manufacturing an insulating film on a diamond substrate according to 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 is The supply time of the organoaluminum compound by the aluminum raw material supply device in step D is controlled to be between 1 millisecond and 25 milliseconds. The steam supply time by the steam supply device in step F is controlled to be between 1 millisecond and 25 milliseconds, and The apparatus for manufacturing an insulating film on a diamond substrate according to claim 2 or 3, characterized in that the interval time between step D and step F is controlled to be 1 second or more and 20 seconds or less.

5. The pressure reducing device reduces the pressure inside the vacuum chamber from atmospheric pressure to 2×10 －３ Pa or less within 1 hour, and the ultimate vacuum degree of the vacuum chamber is 1.1×10 －５ Pa or less. The manufacturing apparatus for an insulating film on a diamond substrate according to any one of claims 1 to 3, characterized by this.

6. The apparatus for manufacturing an insulating film on a diamond substrate according to any one of claims 1 to 3, characterized in that the aluminum raw material supply device supplies alkylaluminum.

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, the detachable part, and the dividing surface.

8. A diamond substrate is placed inside a vacuum chamber and the vacuum chamber is closed. Within one hour, the inside of the vacuum chamber is heated from atmospheric pressure to 2 × 10⁻¹⁶ －３ Step A: Depressurizing to below Pa; Nitrogen dioxide (NOx) into the vacuum chamber ２ ), nitric oxide (NO), sulfur dioxide (SO ２ ), and ozone (O ３ Step B: Supplying one or more dopants selected from ) Step C: Supplying nitrogen to the vacuum chamber; Step D: Supplying an organic aluminum compound to the vacuum chamber; Step E: Supplying nitrogen to the vacuum chamber; Step F: Supplying water vapor to the vacuum chamber; Step G of supplying nitrogen to the vacuum chamber; and A method for manufacturing an insulating film on a diamond substrate, characterized by comprising step H, which involves repeating steps D to G multiple times.

9. The method for manufacturing an insulating film on a diamond substrate according to claim 8, characterized in that step I is performed between step A and step B, in which steps D to G are repeated one or more times.

10. The supply time of the organoaluminum compound in step D is 1 millisecond or more and 25 milliseconds or less. The steam supply time in step F is 1 millisecond or more and 25 milliseconds or less, The method for manufacturing an insulating film on a diamond substrate according to 8 or 9, characterized in that the interval time between step D and step F is 1 second or more and 20 seconds or less.

11. In step A, the inside of the vacuum chamber is heated from atmospheric pressure to 2 × 10 within 1 hour. －３ The pressure is reduced to below Pa, and the ultimate vacuum level of the vacuum chamber is 1.1 × 10⁻⁶. －５ A method for manufacturing an insulating film on a diamond substrate according to claim 8 or 9, characterized in that the pressure is Pa or less.

12. The method for producing an insulating film on a diamond substrate according to 8 or 9, characterized in that alkylaluminum is supplied as an organoaluminum compound in step D.

13. The method for manufacturing an insulating film on a diamond substrate according to claim 12, characterized in that, in step D, the impurity concentration of the alkylaluminum is less than 10 ppm.

14. The carrier gas for the organoaluminum compound and the water vapor is nitrogen (N ２ The method for manufacturing an insulating film on a diamond substrate according to 8 or 9, characterized in that the nitrogen has a purity of 99.99995% or higher.

15. In step B, the dopant is nitrogen (N ２ A method for manufacturing an insulating film on a diamond substrate according to claim 8 or 9, characterized in that the dopant is diluted with a dilution gas and the concentration of the dopant in the dilution gas is 2% by volume (20,000 ppm) or more.

16. In 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 steps D to G when forming the film, the diamond substrate is heated to 80 to 150°C. The method for manufacturing an insulating film on a diamond substrate according to 8 or 9, characterized in that in steps D to G when forming the second and subsequent layers of aluminum oxide film, the diamond substrate is heated to 200 to 300°C.

17. The insulating film to be manufactured is amorphous aluminum oxide, the dielectric breakdown voltage of the insulating film is 8 MV / cm or more, and the surface density of the diamond substrate is 5 × 10⁻¹⁶. １３ cm －２ A method for manufacturing an insulating film on a diamond substrate according to claim 8 or 9, characterized in that a higher number of hole carriers are generated, and the sheet resistance of the surface of the diamond substrate is 1 kΩ / □ or less in the (001) plane orientation of the diamond crystal and 700 Ω / □ or less in the (111) plane orientation of the diamond crystal.

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