METHOD FOR PROCESSING SiC SUBSTRATE, METHOD FOR REMOVING PROCESSING-AFFECTED LAYER OF SiC SUBSTRATE, AND METHOD FOR REDUCING SURFACE ROUGHNESS OF SiC SUBSTRATE

Abstract

Provided is a novel method for processing a SiC substrate. Provided is a method for processing a SiC substrate, the method comprising: an annealing step S2 for heating a SiC substrate 1 in an inert gas environment; and an etching step S3 for etching the SiC substrate 1 that has undergone the annealing step S2 in an environment including a gas composed of one or both of a Si element and a C element.

Description

Method for treating SiC substrate, method for removing process-affected layer of SiC substrate, and method for reducing surface roughness of SiC substrate

[0001] The present invention relates to a method for processing a SiC substrate.

[0002] In the manufacture of SiC semiconductor devices, it is extremely important to process the SiC substrate (as-sliced ​​substrate) cut from the ingot and flatten the substrate surface at the atomic level. Conventional SiC substrate processing involves steps such as lapping and / or grinding and polishing to gradually reduce surface roughness.

[0003] However, it is known that mechanical damage remains on SiC substrates processed in this way. This damage manifests itself not only as scratches on the surface, but also as crystal distortion in the surface layer up to a certain depth. The layer containing this damage is called the "process-affected layer," and it has a significant adverse effect on the performance of SiC semiconductor devices.

[0004] The present inventors have invented a method for reducing surface roughness by non-contact processing, which differs from conventional processing steps. Patent Document 1 describes a method for reducing macrostep bunching on a substrate surface by heating and etching a SiC substrate in an environment with the vapor pressure of a gas phase species containing Si and a gas phase species containing C. Patent Document 2 describes a method for reducing a process-affected layer on a substrate by heating and etching a SiC substrate in an environment with the vapor pressure of a gas phase species containing Si and a gas phase species containing C.

[0005] International Publication No. 2020 / 179793 International Publication No. 2020 / 179794

[0006] The intermediate and final stages of conventional processing can be substituted by the methods described in Patent Documents 1 and 2. However, in the initial stage of processing, it is required to roughly reduce the surface roughness from a state where the surface roughness is very large. For this reason, it has been recognized in the technical field that the initial stage of processing must still be performed by contact treatment such as grinding or polishing.

[0007] In this situation, the inventors have discovered the following problem: the initial stage of processing causes the formation and expansion of a process-affected layer on the SiC substrate, making it difficult to remove this process-affected layer in the middle and final stages of processing. Furthermore, significant raw material loss occurs in the initial stage of processing, which is a factor that reduces the sustainability of SiC semiconductor device manufacturing.

[0008] Therefore, an object of the present invention is to provide a new processing method for SiC substrates. More specifically, an object of the present invention is to provide a non-contact processing method that can replace the initial stage of conventional SiC substrate processing. Another object of the present invention is to provide a processing method that can reduce raw material loss that occurs in this initial stage of processing.

[0009] One embodiment of the present invention for achieving the above object is a method for processing a SiC substrate, which is the following methods [1] to

[82] .

[0010] Method [1] is a SiC substrate processing method comprising an annealing step in which a SiC substrate is heated in an inert gas environment, and an etching step in which the SiC substrate that has undergone the annealing step is etched in an environment containing a gas composed of one or both of Si and C elements. Method [1] strongly promotes both sublimation and recrystallization reactions on the surface of the SiC substrate, thereby vigorously exchanging atoms between the surface layer of the SiC substrate and the environment, i.e., strongly promoting the metabolism of atoms constituting the surface layer of the SiC substrate. This allows the process-affected layer contained in the surface layer to be removed in a short time. Furthermore, the surface layer of the SiC substrate is smoothed during the metabolism process, resulting in a SiC substrate with reduced surface roughness. By subsequently etching the SiC substrate, even SiC substrates with high surface roughness can be produced using non-contact processing.

[0011] Method [2] is a method for treating a SiC substrate according to method [1], wherein the annealing step includes heating the SiC substrate inside a crucible made of SiC, and the inside of the crucible is maintained in an inert gas environment during the annealing step.

[0012] Method [3] is a method of treating a SiC substrate according to method [1] or [2], wherein the annealing step includes etching one surface of the SiC substrate and simultaneously growing the other surface of the SiC substrate.

[0013] Method [4] is a method for treating a SiC substrate according to method [3], in which the annealing step includes making the etching amount on one surface approximately equal to the growth amount on the other surface, thereby making the substrate thickness of the SiC substrate approximately equal before and after the annealing step.

[0014] Method [5] is a method for treating a SiC substrate according to method [3] or [4], in which the annealing step includes increasing the thickness of the SiC substrate before and after the annealing step by reducing the amount of etching on one surface relative to the amount of growth on the other surface.

[0015] Method [6] is a method for treating a SiC substrate, which is any one of methods [2] to [5], in which, in the annealing step, the crucible includes a base having an opening and a lid, and the interior of the crucible is formed by covering the opening of the base with the lid.

[0016] The method [7] is any one of the methods [2] to [6], wherein in the annealing step, the SiC substrate is supported by a substrate support.

[0017] The method [8] is any one of the methods [2] to [7], wherein the pressure inside the crucible in the annealing step is 1 kPa or more.

[0018] The method [9] is any one of the methods [2] to [7], wherein the pressure inside the crucible is 5 kPa or more in the annealing step.

[0019] The method

[10] is any one of the methods [2] to [7], wherein the pressure inside the crucible in the annealing step is 10 kPa or more.

[0020] Method

[11] is any one of methods [2] to

[10] , wherein the temperature inside the crucible is 1800° C. or higher in the annealing step.

[0021] The method

[12] is any one of the methods [2] to

[10] , wherein the temperature inside the crucible is 2000° C. or higher in the annealing step.

[0022] The method

[13] is any one of the methods [2] to

[10] , wherein the temperature inside the crucible is 2200° C. or higher in the annealing step.

[0023] Method

[14] is any one of methods [2] to

[13] , wherein the combination of pressure and temperature inside the crucible in the annealing step is 1 kPa or more and 1800°C or more.

[0024] Method

[15] is any one of methods [2] to

[13] , wherein the combination of pressure and temperature inside the crucible in the annealing step is 5 kPa or more and 2000°C or more.

[0025] Method

[16] is any one of methods [2] to

[13] , wherein the combination of the pressure and temperature inside the crucible in the annealing step is 5 kPa or more and 2200°C or more.

[0026] Method

[17] is any one of methods [2] to

[13] , wherein the combination of the pressure and temperature inside the crucible in the annealing step is 10 kPa or more and 2200°C or more.

[0027] Method

[18] is any one of methods [2] to

[17] , wherein in the annealing step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate.

[0028] Method

[19] is a method for treating a SiC substrate according to method

[18] , wherein in the annealing step, the temperature gradient is formed such that the temperature decreases from the C-face side of the SiC substrate toward the Si-face side.

[0029] Method

[20] is any one of methods [2] to

[19] , in which the annealing step includes a housing step of housing the SiC substrate inside a crucible, and in the annealing step, the crucible includes a base having an opening and a lid, and the housing step includes placing the SiC substrate through the opening of the base and placing the lid on the base to cover the opening of the base, thereby housing the SiC substrate inside the crucible.

[0030] Method

[21] is any one of methods [2] to

[20] , in which the annealing step includes a housing step of housing the SiC substrate inside a crucible, and the housing step includes supporting the SiC substrate in the hollow inside the crucible with a substrate support.

[0031] Method

[22] is any one of methods [2] to

[21] , in which the annealing step includes a heating step of heating a crucible, and the heating step includes heating the crucible and generating a source gas composed of one or both of Si element and C element from the crucible into the interior of the crucible.

[0032] Method

[23] is any one of methods [2] to

[22] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes introducing an inert gas into the crucible and maintaining the pressure inside the crucible at 1 kPa or more.

[0033] Method

[24] is any one of methods [2] to

[22] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes introducing an inert gas into the crucible and maintaining the pressure inside the crucible at 5 kPa or more.

[0034] Method

[25] is any one of methods [2] to

[22] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes introducing an inert gas into the crucible and maintaining the pressure inside the crucible at 10 kPa or more.

[0035] Method

[26] is any one of methods [2] to

[25] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes heating the crucible and maintaining the temperature inside the crucible at 1800°C or higher.

[0036] Method

[27] is any one of methods [2] to

[25] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes heating the crucible and maintaining the temperature inside the crucible at 2000°C or higher.

[0037] Method

[28] is any one of methods [2] to

[25] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes heating the crucible and maintaining the temperature inside the crucible at 2200°C or higher.

[0038] Method

[29] is any one of methods [2] to

[28] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes introducing an inert gas into the crucible to maintain a pressure inside the crucible at 1 kPa or higher, and heating the crucible to maintain a temperature inside the crucible at 1800°C or higher.

[0039] Method

[30] is any one of methods [2] to

[28] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes introducing an inert gas into the crucible to maintain a pressure inside the crucible at 5 kPa or higher, and heating the crucible to maintain a temperature inside the crucible at 2000°C or higher.

[0040] Method

[31] is any one of methods [2] to

[28] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes introducing an inert gas into the crucible to maintain a pressure inside the crucible at 5 kPa or higher, and heating the crucible to maintain a temperature inside the crucible at 2200°C or higher.

[0041] Method

[32] is any one of methods [2] to

[28] , in which the annealing step includes a heating step of heating a crucible, and the heating step includes introducing an inert gas into the crucible to maintain a pressure inside the crucible at 10 kPa or higher, and heating the crucible to maintain a temperature inside the crucible at 2200°C or higher.

[0042] Method

[33] is any one of methods [2] to

[32] , wherein the annealing step includes a heating step of heating a crucible, and the heating step includes forming a temperature gradient inside the crucible in a direction penetrating the SiC substrate.

[0043] Method

[34] is a method for treating a SiC substrate according to method

[33] , wherein the heating step includes forming a temperature gradient such that the temperature decreases from the C-face side of the SiC substrate toward the Si-face side.

[0044] The method

[35] is any one of the methods [1] to

[34] , in which a protective film is not formed on the surface of the SiC substrate in the annealing step.

[0045] Method

[36] is any one of methods [1] to

[35] , wherein the etching step includes heating the SiC substrate inside a crucible made of SiC, and the inside of the crucible is maintained in an environment containing a gas containing one or both of Si element and C element during the etching step.

[0046] The method

[37] is the method

[36] for treating a SiC substrate, wherein the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment during the etching step.

[0047] Method

[38] is the method for treating a SiC substrate according to method

[37] , wherein the temperature inside the crucible is 1600°C or higher and 2000°C or lower in the etching step.

[0048] Method

[39] is the method for treating a SiC substrate according to method

[38] , wherein the temperature inside the crucible in the etching step is lower than the temperature inside the crucible in the annealing step.

[0049] The method

[40] is the method

[36] for treating a SiC substrate, wherein the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment during the etching step.

[0050] The method

[41] is the method

[40] for treating a SiC substrate, wherein the temperature inside the crucible is 1800°C or more and 2000°C or less in the etching step.

[0051] Method

[42] is the method for treating a SiC substrate according to method

[41] , wherein the temperature inside the crucible in the etching step is lower than the temperature inside the crucible in the annealing step.

[0052] Method

[43] is any one of methods

[36] to

[42] , wherein in the etching step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases from the C-face side to the Si-face side of the SiC substrate.

[0053] Method

[44] is any one of methods

[36] to

[39] or

[43] , in which the etching step includes an etching accommodation step of accommodating the SiC substrate in a crucible, and an etching heating step of heating the crucible, and the etching heating step includes maintaining the inside of the crucible in a SiC-C equilibrium vapor pressure environment.

[0054] Method

[45] is the method for treating a SiC substrate according to method

[44] , wherein the etching heating step includes heating the crucible and generating a gas composed of one or both of Si element and C element from the crucible into the interior of the crucible, thereby maintaining the interior of the crucible in a SiC-C equilibrium vapor pressure environment.

[0055] Method

[46] is a method for treating a SiC substrate according to method

[44] or

[45] , wherein the etching heating step includes heating a crucible and maintaining the temperature inside the crucible at 1600°C or more and 2000°C or less.

[0056] Method

[47] is the method for treating a SiC substrate according to method

[46] , wherein the etching heating step includes heating the crucible and maintaining the temperature inside the crucible lower than the temperature inside the crucible in the annealing step.

[0057] Method

[48] is any one of methods

[36] or

[40] to

[43] , in which the etching step includes an etching accommodation step of accommodating the SiC substrate in a crucible, and an etching heating step of heating the crucible, and the etching heating step includes maintaining the inside of the crucible in a SiC-Si equilibrium vapor pressure environment.

[0058] Method

[49] is a method for treating a SiC substrate according to method

[48] , in which the etching accommodation step includes accommodating a Si gas source together with the SiC substrate inside the crucible, and the etching heating step includes heating the crucible together with the Si gas source to generate a gas composed of one or both of Si element and C element from the crucible into the interior of the crucible, and generating Si gas from the Si gas source inside the crucible, thereby maintaining the interior of the crucible in a SiC-Si equilibrium vapor pressure environment.

[0059] Method

[50] is a method for treating a SiC substrate according to method

[48] or

[49] , wherein the etching heating step includes heating a crucible and maintaining the temperature inside the crucible at 1800°C or more and 2000°C or less.

[0060] Method

[51] is a method for treating a SiC substrate according to method

[50] , wherein the etching heating step includes heating a crucible and maintaining the temperature inside the crucible lower than the temperature inside the crucible in the annealing step.

[0061] Method

[52] is any one of methods

[36] to

[51] , in which the etching step includes an etching heating step of heating a crucible, and the etching heating step includes forming a temperature gradient inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases from the C-face side to the Si-face side of the SiC substrate.

[0062] The method

[53] is any one of the methods

[36] to

[52] , which is a method for processing a SiC substrate, and does not include a step of performing a mechanical treatment on the SiC substrate after the etching step.

[0063] Method

[54] is any one of methods

[36] to

[53] , in which the etching step is performed at least twice, that is, a first etching step and a second etching step, the first etching step includes etching a SiC substrate that has been subjected to an annealing step, and the second etching step includes etching a SiC substrate that has been subjected to the first etching step, and in the first etching step, the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment, and in the second etching step, the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment.

[0064] Method

[55] is the method for treating a SiC substrate according to method

[54] , wherein in the first etching step, the temperature inside the crucible is 1600°C or more and 2000°C or less, and in the second etching step, the temperature inside the crucible is 1800°C or more and 2000°C or less.

[0065] Method

[56] is the method of processing a SiC substrate according to method

[55] , wherein the temperature inside the crucible in the first etching step is lower than the temperature inside the crucible in the annealing step, and the temperature inside the crucible in the second etching step is lower than the temperature inside the crucible in the annealing step and higher than the temperature inside the crucible in the first etching step.

[0066] Method

[57] is any one of methods

[54] to

[56] , wherein in the first etching step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases as the temperature moves from the C-face side to the Si-face side of the SiC substrate; and in the second etching step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases as the temperature moves from the C-face side to the Si-face side of the SiC substrate.

[0067] Method

[58] is any one of methods

[54] to

[57] , which does not include a step of performing a mechanical treatment on the SiC substrate after the second etching step.

[0068] Method

[59] is any one of methods [1] to

[58] , and is a method for treating a SiC substrate, comprising: a growth step of growing a SiC substrate that has been subjected to an etching step in an environment containing a gas composed of one or both of Si and C elements.

[0069] Method

[60] is a method for treating a SiC substrate according to method

[59] , wherein the growing step includes heating the SiC substrate inside a crucible made of SiC, and during the growing step, the inside of the crucible is maintained in an environment containing a gas consisting of one or both of Si element and C element.

[0070] The method

[61] is the method of processing a SiC substrate according to the method

[60] , wherein the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment during the growth step.

[0071] Method

[62] is the method for treating a SiC substrate according to method

[61] , wherein the temperature inside the crucible in the growing step is 1600°C or more and 2000°C or less.

[0072] Method

[63] is a method for treating a SiC substrate according to method

[62] , wherein the temperature inside the crucible in the growing step is lower than the temperature inside the crucible in the annealing step.

[0073] Method

[64] is a method for treating a SiC substrate according to method

[60] , wherein the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment during the growth step.

[0074] Method

[65] is the method for treating a SiC substrate according to method

[64] , wherein the temperature inside the crucible is 1800°C or more and 2000°C or less in the growing step.

[0075] Method

[66] is the method for treating a SiC substrate according to method

[65] , wherein the temperature inside the crucible in the growing step is lower than the temperature inside the crucible in the annealing step.

[0076] Method

[67] is any one of methods

[60] to

[66] , wherein in the growth step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases from the Si-face side to the C-face side of the SiC substrate.

[0077] Method

[68] is any one of methods

[60] to

[63] or

[67] , in which the growing step includes a growth containing step of containing the SiC substrate inside a crucible, and a growth heating step of heating the crucible, and the growth heating step includes maintaining the inside of the crucible in a SiC-C equilibrium vapor pressure environment.

[0078] Method

[69] is a method for treating a SiC substrate according to method

[68] , wherein the growth heating step includes heating the crucible and generating a gas composed of one or both of Si element and C element from the crucible into the interior of the crucible, thereby maintaining the interior of the crucible in a SiC-C equilibrium vapor pressure environment.

[0079] Method

[70] is a method for treating a SiC substrate according to method

[68] or

[69] , wherein the growth heating step includes heating a crucible and maintaining the temperature inside the crucible at 1600°C or more and 2000°C or less.

[0080] Method

[71] is a method of treating a SiC substrate according to method

[70] , wherein the growth heating step includes heating a crucible and maintaining the temperature inside the crucible lower than the temperature inside the crucible in the annealing step.

[0081] Method

[72] is any one of methods

[60] or

[64] to

[67] , in which the growing step includes a growth containing step of containing the SiC substrate inside a crucible, and a growth heating step of heating the crucible, and the growth heating step includes maintaining the inside of the crucible in a SiC-Si equilibrium vapor pressure environment.

[0082] Method

[73] is a method for treating a SiC substrate according to method

[72] , in which the growth accommodation step includes accommodating a Si gas source together with the SiC substrate inside the crucible, and the growth heating step includes heating the crucible together with the Si gas source to generate a gas composed of one or both of Si element and C element from the crucible into the interior of the crucible, and generating Si gas from the Si gas source inside the crucible, thereby maintaining the interior of the crucible in a SiC-Si equilibrium vapor pressure environment.

[0083] Method

[74] is a method for treating a SiC substrate according to method

[72] or

[73] , wherein the growth heating step includes heating a crucible and maintaining the temperature inside the crucible at 1800°C or more and 2000°C or less.

[0084] Method

[75] is a method of treating a SiC substrate according to method

[74] , wherein the growth heating step includes heating a crucible and maintaining the temperature inside the crucible lower than the temperature inside the crucible in the annealing step.

[0085] Method

[76] is any one of methods

[60] to

[75] , wherein the growing step includes a growth heating step of heating a crucible, and the growth heating step includes forming a temperature gradient inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases from the Si-face side to the C-face side of the SiC substrate.

[0086] Method

[77] is any one of methods

[60] to

[76] , wherein the method does not include a step of mechanically processing the SiC substrate after the growth step.

[0087] Method

[78] is any one of methods

[60] to

[77] , wherein the growing step is performed at least twice, that is, a first growing step and a second growing step, the first growing step includes growing a SiC substrate that has been subjected to an etching step, and the second growing step includes growing a SiC substrate that has been subjected to the first growing step, wherein the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment in the first growing step, and the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment in the second growing step.

[0088] Method

[79] is the method for treating a SiC substrate according to method

[78] , wherein in the first growth step, the temperature inside the crucible is 1600°C or more and 2000°C or less, and in the second growth step, the temperature inside the crucible is 1800°C or more and 2000°C or less.

[0089] Method

[80] is the method of processing a SiC substrate according to method

[79] , wherein the temperature inside the crucible in the first growth step is lower than the temperature inside the crucible in the annealing step, and the temperature inside the crucible in the second growth step is lower than the temperature inside the crucible in the annealing step and higher than the temperature inside the crucible in the first growth step.

[0090] Method

[81] is any one of methods

[78] to

[80] , wherein in the first growth step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and such that the temperature decreases as the temperature moves from the Si-face side to the C-face side of the SiC substrate; and in the second growth step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and such that the temperature decreases as the temperature moves from the Si-face side to the C-face side of the SiC substrate.

[0091] Method

[82] is any one of methods

[78] to

[81] , wherein the method does not include a step of performing a mechanical treatment on the SiC substrate after the second etching step.

[0092] One embodiment of the present invention for achieving the above object is a method for removing a process-affected layer from a SiC substrate, which is the following methods

[83] to

[85] .

[0093] The method

[83] is a method for removing a process-affected layer from a SiC substrate, comprising performing any one of the methods [1] to

[82] on a SiC substrate having a process-affected layer to remove the process-affected layer.

[0094] Method

[84] is a method for removing a work-affected layer from a SiC substrate, which is method

[83] , and includes performing any one of methods [1] to

[82] on a SiC substrate on which a work-affected layer has been formed by mechanical processing.

[0095] Method

[85] is a method for removing a process-affected layer of a SiC substrate according to method

[83] or

[84] , wherein the annealing step includes exchanging atoms between a surface layer of the SiC substrate and an inert gas environment to remove the process-affected layer.

[0096] Furthermore, one embodiment of the present invention for achieving the above object is a method for reducing the surface roughness of a SiC substrate, which is the following methods

[86] to

[88] .

[0097] The method

[86] is a method for reducing the surface roughness of a SiC substrate, which comprises carrying out any one of the methods [1] to

[82] on a SiC substrate having an arithmetic mean roughness Ra of the Si surface of 15 nm or more, thereby reducing the arithmetic mean roughness Ra.

[0098] Method

[87] is a method for reducing the surface roughness of a SiC substrate, which is the same as method

[86] , and includes performing any one of methods [1] to

[82] on a SiC substrate that has undergone mechanical processing.

[0099] Method

[88] is a method for reducing the surface roughness of a SiC substrate according to method

[86] or

[87] , wherein the annealing step includes exchanging atoms between the surface of the SiC substrate and an inert gas environment to smooth the surface.

[0100] According to the present invention, a novel processing method for SiC substrates can be provided. More specifically, a non-contact processing method can be provided that can replace the initial stage of conventional SiC substrate processing. Furthermore, a processing method can be provided that can reduce raw material loss that occurs in this initial stage of processing.

[0101] FIG. 1 is an explanatory diagram of the concept of a processing method according to an embodiment of the present invention. ... a first preferred embodiment of the present invention. FIG. 2 is an explanatory diagram of a modification of the first preferred embodiment of the present invention. FIG. 1 is an explanatory diagram of the first preferred embodiment of the present invention. FIG. 2 is an explanatory diagram of the second preferred embodiment of the present invention. FIG. 3 is an explanatory diagram of the second preferred embodiment of the present invention. FIG. 4 is an explanatory diagram of the third preferred embodiment of the present invention. FIG. 5 is an explanatory diagram of the result of an example of the present invention. FIG. 1 is an explanatory diagram of the result of an example of the present invention.

[0102] One embodiment of the present invention is a method for processing a SiC substrate, which includes an annealing step of heating the SiC substrate inside a crucible made of SiC.

[0103] In the annealing step of this processing method, the inside of the crucible is maintained in an inert gas environment. The term "inert gas environment" refers to an environment containing an inert gas. Examples of inert gas include Ar gas and N2 gas. The inert gas environment of this processing method contains Ar gas as the inert gas. Here, it is preferable that the majority of the inert gas is Ar gas, and it is also preferable that the inert gas is substantially entirely Ar gas. Note that a portion of the inert gas may be N2 gas. In other words, the annealing step of this processing method can be said to be a step of annealing a SiC substrate in an inert gas environment.

[0104] The concept of this processing method will be described in detail below with reference to FIGS. 1 to 5. FIGS. 1 to 5 show a SiC substrate 1, a surface 11 (Si-face 111 and C-face 112) of the SiC substrate, a process-affected layer 12 of the SiC substrate, a crucible 2 made of SiC, and a base 21 and lid 22 of the crucible 2. The term "process-affected layer" refers to a layer that includes damage caused by mechanical processing and is likely to adversely affect the performance of a SiC semiconductor device. An example of a process-affected layer is a surface layer that has undergone mechanical processing on the Si-face 111 side where a device will be formed. The term "mechanical processing" refers to a process that physically destroys the atomic arrangement of the substrate. Examples of mechanical processing include ingot cutting (e.g., multi-wire saw cutting, laser cutting, and electric discharge cutting), grinding, and polishing (e.g., mechanical polishing and chemical-mechanical polishing).

[0105] Heating the SiC substrate 1 causes, for example, the reactions represented by Chemical Formulas 1 to 3. That is, heating the SiC substrate 1 causes the source gas to sublimate from the SiC substrate 1 and recrystallize on the SiC substrate 1. The term "source gas" refers to a gas composed of one or both of Si and C elements. Examples of source gases include Si gas, SiC2 gas, Si2C gas, and a mixture of these gases.

[0106]

[0107]

[0108]

[0109] The reaction of Chemical Formula 1 corresponds to a thermal decomposition reaction. In the thermal decomposition reaction, Si gas is desorbed from the SiC substrate 1, and C remains in the SiC substrate 1. When the thermal decomposition reaction is dominant, the SiC substrate 1 is carbonized.

[0110] The reaction of Chemical Formula 2 corresponds to a sublimation reaction. In the sublimation reaction, C in the SiC substrate 1 sublimes as a source gas. When the sublimation reaction is dominant, the SiC substrate 1 is etched.

[0111] The reaction of Chemical Formula 3 corresponds to a recrystallization reaction. In the recrystallization reaction, the source gas is recrystallized into the SiC substrate 1. When the recrystallization reaction is dominant, the SiC substrate 1 grows.

[0112] This processing method is based on the idea of ​​strongly promoting both sublimation and recrystallization reactions, thereby vigorously exchanging atoms between the surface layer of the SiC substrate 1 and the annealing environment, that is, strongly promoting the metabolism of atoms that make up the surface layer of the SiC substrate 1. The term "surface layer" refers to the layer ranging from the surface to a predetermined depth.

[0113] As shown in FIG. 1 , this processing method involves inducing the metabolism of atoms constituting the surface layer ranging from the surface 11 to a depth d. The depth d depends on the intensity of the sublimation and recrystallization reactions. This allows the damaged layer 12 included in the range from the surface 11 to the depth d to be removed in a short time. Furthermore, the surface layer of the SiC substrate 1 is smoothed during the metabolism process, resulting in a SiC substrate 1 with low surface roughness. In other words, this processing method can be used both to remove the damaged layer 12 of the SiC substrate 1 and to reduce the roughness of the surface 11 of the SiC substrate 1.

[0114] When the sublimation reaction is dominant over the recrystallization reaction, the atoms constituting the surface layer of the SiC substrate 1 are macroscopically reduced, and the surface 11 is etched. Here, in the etching by this processing method, the balance between the reduction and increase of microscopic atoms is biased toward the reduction, resulting in the macroscopic reduction of atoms. In contrast, in conventional etching, the macroscopic reduction of atoms is caused by repeated reduction of microscopic atoms.

[0115] When the recrystallization reaction is dominant over the sublimation reaction, the atoms constituting the surface layer of the SiC substrate 1 increase macroscopically, and the surface 11 grows. Here, in the growth by this processing method, the balance between the decrease and increase of microscopic atoms is biased toward the increase, resulting in the macroscopic increase of atoms. In contrast, in conventional growth, the macroscopic increase of atoms occurs due to repeated increases in microscopic atoms.

[0116] The etching and growth processes of this processing method always remove the damaged layer 12 within the range from the surface 11 to a depth d. Thus, the etching process of this processing method can remove the damaged layer 12 over a range wider than the etching range. Furthermore, the growth process of this processing method can form a grown layer free of the effects of the damaged layer 12 in a single process. In contrast, conventional etching cannot remove the damaged layer outside the etching range, and conventional growth cannot remove the damaged layer at all. In other words, to eliminate the adverse effects of the damaged layer on the device using conventional methods, it is necessary to etch the entire surface layer in the range containing the damaged layer and then form a grown layer.

[0117] The present processing method includes controlling the macroscopic flow of the source gas to control the etching and growth of the surface 11. Examples of means for controlling the macroscopic flow of the source gas include controlling the temperature gradient and controlling the source gas concentration gradient.

[0118] As shown in Figure 2, when a temperature gradient is formed such that the temperature decreases with increasing distance from the surface 11, the macroscopic flow of the source gas is directed away from the surface 11. At this time, the sublimation reaction becomes dominant over the recrystallization reaction, and the surface 11 is etched. On the other hand, as shown in Figure 3, when a temperature gradient is formed such that the temperature decreases with increasing distance from the surface 11, the macroscopic flow of the source gas is directed toward the surface 11. At this time, the recrystallization reaction becomes dominant over the sublimation reaction, and the surface 11 grows.

[0119] This processing method involves inducing the metabolism of atoms constituting the surface layer of the SiC substrate 1 on both the Si face 111 and the C face 112, i.e., simultaneously processing both the Si face 111 and the C face 112. As shown in FIG. 4 , when a temperature gradient is formed in which the temperature decreases from the C face 112 side toward the Si face 111 side, the macroscopic flow of the source gas is directed away from the Si face 111 and toward the C face 112. At this time, the Si face 111 is etched, and simultaneously, the C face 112 grows. On the other hand, as shown in FIG. 5 , when a temperature gradient is formed in which the temperature decreases from the Si face 111 side toward the C face 112 side, the macroscopic flow of the source gas is directed toward the Si face 111 and away from the C face 112. At this time, the Si face 111 grows, and simultaneously, the C face 112 is etched.

[0120] This processing method involves simultaneously processing both the Si face 111 and the C face 112 of the SiC substrate 1 while maintaining the substrate thickness. The etching rate or growth rate on the surface 11 largely depends on the temperature gradient near the surface 11. Here, although the temperature gradient itself changes over time, the Si face 111 and the C face 112 are spatially very close to each other (e.g., about 400 μm apart), so the temperature gradients on the Si face 111 and the C face 112 are always substantially the same. As a result, the etching rate on one surface 11 and the growth rate on the other surface 11 are always substantially the same. In other words, regardless of the magnitude and direction of the temperature gradient or its changes over time, the etching amount on one surface 11 and the growth amount on the other surface 11 are substantially the same, and the substrate thickness of the SiC substrate 1 is maintained. This allows for the loss of material within the substrate during processing of the SiC substrate 1 to be substantially zero.

[0121] <Processing Method X> A first preferred embodiment of the present processing method will be described in detail with reference to Figures 6 to 8. In Figures 6 to 8, the same components as those shown in Figures 1 to 5 are designated by the same reference numerals. Hereinafter, this first preferred embodiment of the present processing method will be referred to as Processing Method X.

[0122] <Preparation Step S1> The processing method X includes a preparation step S1 of preparing a SiC substrate 1. Note that the preparation step S1 may include preparing a plurality of SiC substrates 1.

[0123] The preparation step S1 may include preparing a substrate having a work-affected layer as the SiC substrate 1. This substrate may be a substrate (e.g., an as-sliced ​​substrate) on which a work-affected layer has been formed through mechanical processing (e.g., ingot cutting, grinding, mechanical polishing, chemical mechanical polishing). That is, the processing method X can be used as a method for removing the work-affected layer 12 from the SiC substrate 1.

[0124] The preparation step S1 may include preparing a substrate having an arithmetic mean roughness Ra of the Si surface of 15 nm or more (or exceeding 15 nm) as the SiC substrate 1. This arithmetic mean roughness Ra may be 30 nm or more (or exceeding 30 nm) or 100 nm or more (or exceeding 100 nm). While there is no particular upper limit to the arithmetic mean roughness Ra, it is preferably 500 nm or less (or less than 500 nm). The "arithmetic mean roughness Ra" is calculated as the average absolute difference between the contour line and its mean line in an AFM image (10 μm × 10 μm) of the substrate surface (excluding the edge). This SiC substrate may also be a SiC substrate that has undergone mechanical processing (e.g., ingot cutting, grinding). In other words, the processing method X can be used as a method for reducing the roughness of the surface 11 of the SiC substrate 1.

[0125] The preparation step S1 includes preparing a substrate having no protective film formed on its surface as the SiC substrate 1. This allows both the Si surface 111 and the C surface 112 to be processed simultaneously.

[0126] <Annealing Step S2> As shown in FIG. 6, the processing method X includes an annealing step S2 in which the SiC substrate 1 is heated inside the crucible 2.

[0127] The inner wall of the crucible 2 is made of SiC (for example, polycrystalline SiC or single crystal SiC). It is also preferable that the crucible 2 is made almost entirely of SiC. This SiC is preferably polycrystalline SiC.

[0128] The crucible 2 includes a base 21 having an opening and a lid 22. The interior of the crucible 2 is formed by covering the opening of the base 21 with the lid 22. The SiC substrate 1 is placed inside the crucible 2 with the opening of the base 21 facing upward and the lid 22 placed on the base 21 to cover the opening of the base 21.

[0129] The SiC substrate 1 is supported by a substrate support 3. The substrate support 3 is formed integrally with the base 21 or the lid 22. Here, the substrate support 3 may be provided from the inner wall of the base 21 or from the inner wall of the lid 22. The substrate support 3 may also be formed separately from the base 21 or the lid 22. Here, the substrate support 3 is preferably placed on the inner bottom of the base 21.

[0130] The substrate support 3 is preferably made of SiC (for example, polycrystalline SiC or single crystal SiC).

[0131] The SiC substrate 1 is supported by the substrate support 3 from below the C-face 112 with the Si-face 111 facing up and the C-face 112 facing down. Alternatively, the substrate may be supported by the substrate support 3 from below the Si-face 111 with the Si-face 111 facing down and the C-face 112 facing up.

[0132] The SiC substrate 1 is supported by the substrate support 3 via a small contact area, and as a result, is supported in the hollow interior of the crucible 2. The SiC substrate 1 may be supported at three or more points, or may be supported along a line such as a circle. The SiC substrate 1 is preferably supported in the hollow interior of the crucible 2 so that one surface 11 directly faces the inner wall of the crucible 2 and the other surface 11 directly faces the inner wall of the crucible 2. The term "directly facing" refers to two components facing each other without being obstructed by other components. The SiC substrate 1 is preferably supported in the hollow and positioned approximately in the center of the interior of the crucible 2.

[0133] The interior of the crucible 2 is maintained in an inert gas environment. The pressure inside the crucible 2 is 1 kPa or more (or more than 1 kPa). This pressure may be 5 kPa or more (or more than 5 kPa), 10 kPa or more (or more than 10 kPa), or 100 kPa or more (or more than 100 kPa). There is no particular upper limit to this pressure, but it is preferably 300 kPa or less (or less than 300 kPa). The temperature inside the crucible 2 is 1800°C or more (or more than 1800°C). This temperature is preferably 1900°C or more (or more than 1900°C), preferably 2000°C or more (or more than 2000°C), preferably 2100°C or more (or more than 2100°C), and preferably 2200°C or more (or more than 2200°C). There is no particular upper limit to this temperature, but it is preferably 2300°C or less (or less than 2300°C). A preferred combination of pressure and temperature inside the crucible 2 is 1 kPa or more (or more than 1 kPa) and 1800°C or more (or more than 1800°C). This combination is preferably 1 kPa or more (or more than 1 kPa) and 1900°C or more (or more than 1900°C), and more preferably 1 kPa or more (or more than 1 kPa) and 2000°C or more (or more than 2000°C). The combination is preferably a combination of 10 kPa or more (or more than 10 kPa) and 1800°C or more (or more than 1800°C), a combination of 10 kPa or more (or more than 10 kPa) and 1900°C or more (or more than 1900°C), or a combination of 10 kPa or more (or more than 10 kPa) and 2000°C or more (or more than 2000°C).

[0134] A particularly preferred combination of pressure and temperature inside the crucible 2 is 5 kPa or more (or more than 5 kPa) and 2000°C or more (or more than 2000°C). This combination is preferably 5 kPa or more (or more than 5 kPa) and 2200°C or more (or more than 2200°C), more preferably 10 kPa or more (or more than 10 kPa) and 2000°C or more (or more than 2200°C), and more preferably 10 kPa or more (or more than 10 kPa) and 2200°C or more (or more than 2200°C).

[0135] A temperature gradient is formed inside the crucible 2. A temperature difference is also formed between the base 21 and the lid 22. There is no particular limit to the magnitude of this temperature gradient. This temperature gradient is formed in a direction penetrating the SiC substrate 1. This temperature gradient is formed in a direction in which the temperature decreases from the C-face 112 side toward the Si-face 111 side. Note that this temperature gradient may also be formed in a direction in which the temperature decreases from the Si-face 111 toward the C-face 112.

[0136] In processing method X, by annealing the SiC substrate 1 inside the crucible 2, the Si face 111 can be etched while maintaining the substrate thickness of the SiC substrate 1, and the C face 112 can be grown at the same time. As a result, the damaged layer 12 included in the surface layer on the Si face 111 side can be sufficiently removed, and the roughness of both the Si face 111 and the C face 112 can be reduced. Note that if the temperature gradient is reversed, the Si face 111 can be grown while maintaining the substrate thickness of the SiC substrate 1, and the C face 112 can be etched at the same time. As a result, the damaged layer 12 included in the surface layer on the Si face 111 side can be removed, and a growth layer can be formed on the Si face 111 at the same time.

[0137] In the processing method X, since the SiC substrate 1 is supported inside the crucible 2 in the above-described manner, etching or growth of the surface 11 can be carried out under suitable conditions.

[0138] Since the crucible 2 and the substrate support 3 are made of SiC, raw material gas is generated from the crucible 2 and the substrate support 3 inside the crucible 2, and a sufficient amount of raw material gas is maintained inside the crucible 2. As a result, both the sublimation reaction and the recrystallization reaction can be strongly promoted. Here, in the crucible 2, as in the SiC substrate 1, both the sublimation reaction and the recrystallization reaction are strongly promoted, thereby suppressing carbonization of the crucible 2. Furthermore, gas that does not recrystallize in the SiC substrate 1 can be recrystallized in the crucible 2 and the substrate support 3 and recovered. As a result, raw material loss can be substantially reduced to zero in the crucible 2 and the entire interior of the crucible 2. In addition, because the crucible 2 is made of polycrystalline SiC, the amount of source gas generated per unit area of ​​the crucible 2 is greater than the amount of source gas generated per unit area of ​​the SiC substrate 1, which is single-crystal SiC, so the amount of etching of the Si-face 111 is slightly smaller and the amount of growth of the C-face 112 is slightly larger. As a result, the thickness of the SiC substrate 1 can be slightly increased before and after heating.

[0139] The interior of the crucible 2 is formed by placing the lid 22 on the base 21, and while the interior of the crucible 2 is a closed environment, gas (e.g., inert gas) can pass between the inside and outside of the crucible 2 through the small gap between the base 21 and the lid 22. In other words, the gas inside the crucible 2 can be adjusted without opening the crucible 2.

[0140] Since the SiC substrate 1 is supported by the substrate support 3 as described above, a macroscopic flow of the source gas from the inner wall of the crucible 2 to the C-face 112 and a macroscopic flow of the source gas from the Si-face 111 to the inner wall of the crucible 2 are formed. As a result, the source gas is steadily exchanged between the SiC substrate 1 and the inner wall of the crucible 2 via an inert gas environment, thereby forming an annealing environment in which a balance is maintained throughout the entire interior of the crucible 2 and the crucible 2. Furthermore, since the macroscopic flow of the source gas from the inner wall of the crucible 2 to the C-face and the macroscopic flow of the source gas from the Si-face 111 to the inner wall of the crucible 2 are substantially the same, the etching amount of the Si-face 111 and the growth amount on the C-face 112 can be made substantially the same, and the substrate thickness of the SiC substrate 1 can be made substantially the same before and after heating.

[0141] In the processing method X, the inside of the crucible 2 is maintained in an inert gas environment in the above-described manner, so that etching or growth of the surface 11 can be carried out under suitable conditions.

[0142] By maintaining the interior of crucible 2 in an inert gas environment as described above, the diffusion of the source gas sublimated from SiC substrate 1 is suppressed, the source gas concentration in the vicinity of SiC substrate 1 increases, and the thermal motion of the source gas becomes intense. As a result, both the sublimation reaction and the recrystallization reaction are strongly promoted on surface 11 of SiC substrate 1.

[0143] As shown in FIG. 7, the crucible 2 may be placed inside a large crucible 4 .

[0144] The inner wall of the large crucible 4 is made of a C-element occluding material. The term "C-element occluding material" refers to a material that occludes the C element when heated. Examples of C-element occluding materials include Ta and TaC. It is also preferable that substantially the entire large crucible 4 is made of a C-element occluding material.

[0145] The inner wall of the large crucible 4 is preferably made of a Si gas-generating material. The term "Si gas-generating material" refers to a material that generates Si gas when heated. Examples of Si gas-generating materials include Si and tantalum silicide. Substantially the entire large crucible 4 may be made of the Si gas-generating material.

[0146] A Si gas source may be disposed inside the large crucible 4 and outside the crucible 2. The term "Si gas source" refers to a component that generates Si gas when heated. An example of a Si gas source is Si (e.g., Si chips).

[0147] The large crucible 4 includes a large base 41 having an opening and a large lid 42. The interior of the large crucible 4 is formed by covering the opening of the large base 41 with the large lid 42. The crucible 2 is placed inside the large crucible 4 with the opening of the large base 41 facing upward and the large lid 42 placed on the large base 41 to cover the opening of the large base 41.

[0148] In the processing method X, the crucible 2 is disposed inside the large crucible 4 in the above-described manner, so that etching or growth of the surface 11 can be carried out under suitable conditions.

[0149] Since the inner wall of the large crucible 4 is configured to contain a C element occluding material, the C element is removed from the raw material gas generated from the crucible 2, and the outside of the crucible 2 becomes an environment dominated by the Si element. As a result, carbonization of the crucible 2 can be suppressed.

[0150] The inner wall of the large crucible 4 is configured to contain a Si gas generating material or a Si gas source is disposed inside the large crucible 4 and outside the crucible 2, so that the outside of the crucible 2 becomes an environment dominated by Si elements. As a result, carbonization of the crucible 2 can be suppressed.

[0151] The steps included in the annealing step S2 will be described in detail below. <Accommodating Step S21> The annealing step S2 includes an accommodating step S21 of accommodating the SiC substrate 1 inside the crucible 2.

[0152] The accommodation step S21 includes placing the SiC substrate 1 through the opening of the base 21 and placing the lid 22 on the base 21 to cover the opening of the base 21, thereby accommodating the SiC substrate 1 inside the crucible 2.

[0153] The accommodating step S21 includes supporting the SiC substrate 1 in the hollow interior of the crucible 2 with the substrate support 3, so that one surface 11 directly faces the inner wall of the crucible 2 and the other surface 11 directly faces the inner wall of the crucible 2. The accommodating step S21 includes supporting the SiC substrate 1 with the Si face 111 facing up and the C face 112 facing down with the substrate support 3 from below the C face 112. Here, the accommodating step S21 includes supporting the SiC substrate 1 with the substrate support 3 via a small contact area. The accommodation step S21 preferably includes supporting the SiC substrate 1 in the hollow interior of the crucible 2 and positioning it approximately at the center of the interior of the crucible 2, thereby forming a macroscopic flow of the raw material gas from the inner wall of the crucible 2 to the C-face and a macroscopic flow of the raw material gas from the Si-face 111 to the inner wall of the crucible 2 that are approximately identical.

[0154] The accommodation step S21 preferably includes accommodating the crucible 2 inside a heating furnace. Here, the heating furnace preferably includes a line through which an inert gas can be introduced and a line through which a vacuum can be drawn.

[0155] It is preferable that no members containing materials other than SiC are placed inside the crucible 2. More specifically, it is preferable that no members other than the SiC substrate 1 are placed inside the crucible 2. When the substrate support 3 is formed separately from the base 21 or the lid 22, it is preferable that no members other than the SiC substrate 1 and the substrate support 3 made of SiC are placed inside the crucible 2. This makes it possible to maintain a favorable environment inside the crucible 2 during heating.

[0156] For example, it is preferable that no heat source is disposed inside the crucible 2. This can prevent impurities originating from the heat source from being mixed into the environment inside the crucible 2. In addition, it can prevent the closed environment inside the crucible 2 from being lost due to a feed-through of the heat source.

[0157] The accommodation step S21 may include accommodating the crucible 2 inside the large crucible 4. Here, the accommodation step S21 includes placing the crucible 2 through the opening of the large base 41, and placing the large lid 42 on the large base 41 to cover the opening of the large base 41, thereby accommodating the crucible 2 inside the large crucible 4.

[0158] <Heating Step S22> After the accommodation step S21, the annealing step S2 includes a heating step S22 of heating the crucible 2. The heating step S22 includes heating the crucible 2 to heat the SiC substrate 1 accommodated inside the crucible 2.

[0159] The heating step S22 includes heating the crucible 2 to generate a source gas from the crucible 2 inside the crucible 2.

[0160] The heating step S22 includes introducing an inert gas into the crucible 2 and maintaining the pressure inside the crucible 2 at 1 kPa or more (or more than 1 kPa). This pressure may be 5 kPa or more (or more than 5 kPa), 10 kPa or more (or more than 10 kPa), or 100 kPa or more (or more than 100 kPa). There is no particular upper limit to this pressure, but it is preferably 300 kPa or less (or less than 300 kPa). Here, the heating step S22 includes introducing an inert gas into the heating furnace, thereby introducing the inert gas into the crucible 2 accommodated inside the heating furnace.

[0161] The heating step S22 includes heating the crucible 2 and maintaining the temperature inside the crucible 2 at 1800°C or higher (or above 1800°C). This temperature is preferably 1900°C or higher (or above 1900°C), preferably 2000°C or higher (or above 2000°C), preferably 2100°C or higher (or above 2100°C), and preferably 2200°C or higher (or above 2200°C). There is no particular upper limit to this temperature, but it is preferably 2300°C or lower (or lower than 2300°C).

[0162] The heating step S22 includes maintaining the combination of pressure and temperature inside the crucible 2 at 1 kPa or higher (or more than 1 kPa) and 1800°C or higher (or more than 1800°C). This combination is preferably 1 kPa or higher (or more than 1 kPa) and 1900°C or higher (or more than 1900°C), and more preferably 1 kPa or higher (or more than 1 kPa) and 2000°C or higher (or more than 2000°C). This combination is preferably 10 kPa or higher (or more than 10 kPa) and 1800°C or higher (or more than 1800°C), and more preferably 10 kPa or higher (or more than 10 kPa) and 1900°C or higher (or more than 1900°C), and more preferably 10 kPa or higher (or more than 10 kPa) and 2000°C or higher (or more than 2000°C).

[0163] In the heating step S22, a particularly preferred combination of pressure and temperature inside the crucible 2 is 5 kPa or more (or more than 5 kPa) and 2000°C or more (or more than 2000°C). This combination is preferably 5 kPa or more (or more than 5 kPa) and 2200°C or more (or more than 2200°C), more preferably 10 kPa or more (or more than 10 kPa) and 2000°C or more (or more than 2200°C), and more preferably 10 kPa or more (or more than 10 kPa) and 2200°C or more (or more than 2200°C).

[0164] In the heating step S22, the heating time of the crucible 2 is 10 minutes or more (or more than 10 minutes). This heating time is preferably 30 minutes or more (or more than 30 minutes), and preferably 1 hour or more (or more than 1 hour). There is no particular upper limit to this time, but it is preferably 3 hours or less (or less than 3 hours), and preferably 2 hours or less (or less than 2 hours).

[0165] The heating step S22 includes forming a temperature gradient inside the crucible 2 in a direction penetrating the SiC substrate 1, thereby forming a macroscopic flow of the source gas inside the crucible 2. Here, the heating step S22 preferably includes forming a temperature gradient inside the crucible 2 by creating a temperature difference between the base 21 and the lid 22. Although SiC is a material with high thermal conductivity, the contact area between the base 21 and the lid 22 creates thermal resistance, which can create a temperature difference between the base 21 and the lid 22. This temperature difference is formed so that the base 21 is hot and the lid 22 is cold. This creates a temperature gradient in which the temperature decreases from the C-face 112 side toward the Si-face 111 side, resulting in etching the Si-face 111 and simultaneously growing the C-face 112. This temperature difference may also be formed so that the base 21 is cold and the lid 22 is hot. This creates a temperature gradient in which the temperature decreases from the Si surface 111 side toward the C surface 112 side, resulting in the Si surface 111 growing and simultaneously etching the C surface 112.

[0166] The heating step S22 includes heating the crucible 2 using a heating furnace as a heat source. This allows the inside of the crucible 2 to be heated from the outside of the crucible 2. In addition, by providing a difference in heating output between the upper and lower parts of the heating furnace, a desired temperature gradient can be formed inside the crucible 2.

[0167] The flow of processing method X is as shown in Figure 8. Processing method X includes a preparation step S1 followed by an annealing step S2. The annealing step S2 includes a housing step S21 followed by a heating step S22. Processing method X may include a step of performing any processing after the annealing step S2. Here, processing method X preferably does not include a step of performing mechanical processing after the annealing step S2.

[0168] <Processing Method Y> A second preferred embodiment of the present processing method will be described in detail with reference to Figures 9 and 10. In Figures 9 and 10, the same components as those shown in Figures 1 to 8 are designated by the same reference numerals. Hereinafter, this second preferred embodiment of the present processing method will be referred to as Processing Method Y.

[0169] <Preparation Step S1> Processing method Y includes a preparation step S1 of preparing a SiC substrate 1. Since preparation step S1 is similar to preparation step S1 of processing method X, a description thereof will be omitted.

[0170] <Annealing Step S2> Processing method Y includes an annealing step S2 in which the SiC substrate 1 is annealed inside a crucible 2 made of SiC. The annealing step S2 is similar to the annealing step S2 of processing method X, and therefore a description thereof will be omitted.

[0171] <Etching Step S3> Processing method Y includes an etching step S3 in which the SiC substrate 1 that has been subjected to the annealing step S2 is etched.

[0172] The etching in the etching step S3 is similar to conventional etching in that the reduction of atoms is caused macroscopically by repeated microscopic reduction of atoms. That is, it differs from the etching in the annealing step S2. At this time, the surface 11 of the SiC substrate 1 is precisely etched, resulting in a SiC substrate 1 with significantly reduced surface roughness.

[0173] The arrangement of the components is substantially the same as that in the annealing step S2, but as shown in FIG. 7, it is preferable that a large crucible 4 is used in addition to the SiC substrate 1, crucible 2, and substrate support 3.

[0174] The interior of the crucible 2 is maintained in a source gas phase equilibrium environment. The term "source gas phase equilibrium environment" refers to an environment in which the source gas pressure is such that the SiC substrate and the source gas are in approximate phase equilibrium. Examples of source gas phase equilibrium environments include a SiC-C equilibrium vapor pressure environment in which the C element is dominant, and a SiC-Si equilibrium vapor pressure environment in which the Si element is dominant. In other words, the etching step of this processing method can be said to be a step of etching the SiC substrate in a source gas phase equilibrium environment.

[0175] The temperature inside the crucible 2 maintained in the SiC-C equilibrium vapor pressure environment is preferably 1600°C or higher (or higher than 1600°C), and preferably 1700°C or higher (or higher than 1700°C). This temperature is preferably 2000°C or lower (or lower than 2000°C), and preferably 1900°C or lower (or lower than 1900°C). This temperature is preferably lower than the temperature inside the crucible 2 in the annealing step S2.

[0176] The temperature inside the crucible 2 maintained in the SiC-Si equilibrium vapor pressure environment is preferably 1800°C or higher (or higher than 1800°C), and more preferably 1900°C or higher (or higher than 1900°C). This temperature is preferably 2000°C or lower (or lower than 2000°C). This temperature is preferably lower than the temperature inside the crucible 2 in the annealing step S2.

[0177] 9, when a Si gas source 5 (e.g., Si pieces) is disposed inside the crucible 2, a SiC-Si equilibrium vapor pressure environment is formed inside the crucible 2. On the other hand, when a Si gas source 5 is not disposed inside the crucible 2, as shown in FIG. 7, a SiC-C equilibrium vapor pressure environment is formed inside the crucible 2.

[0178] A temperature gradient is formed inside the crucible 2. The magnitude of this temperature gradient is 0.1 mm / K or more and 5 mm / K or less. This temperature gradient is formed in a direction penetrating the SiC substrate 1. This temperature gradient is formed in a direction in which the temperature decreases from the C-face 112 toward the Si-face 111.

[0179] In the processing method Y, the inside of the crucible 2 is maintained in a source gas phase equilibrium environment in the above-described manner, so that etching of the Si surface 111 can be carried out under suitable conditions.

[0180] By maintaining the interior of the crucible 2 in a source gas phase equilibrium environment as described above, the sublimation reaction and the recrystallization reaction are gently balanced with a slight bias toward the sublimation reaction, and the source gas gradually sublimes from the Si surface 111. As a result, the Si surface 111 can be precisely etched, and the surface roughness of the Si surface 111 can be significantly reduced.

[0181] The steps included in the etching step S3 will be described in detail below.

[0182] <Etching Accommodation Step S31> The etching step S3 includes an etching accommodation step S31 in which the SiC substrate 1 is accommodated in the crucible 2. The etching accommodation step S31 is substantially similar to the accommodation step S21 of the processing method X, except that, when etching is performed in a SiC-C equilibrium vapor pressure environment, the Si gas source 5 is not disposed in the crucible 2, as shown in FIG. 7 . When etching the SiC substrate in a SiC-Si equilibrium vapor pressure environment, the Si gas source 5 is disposed in the crucible 2, as shown in FIG. 9 . Note that, in the etching accommodation step S31, the crucible 2 may be the same as or different from the crucible 2 used in the accommodation step S21. Here, instead of accommodating the SiC substrate 1 in the crucible 2, the etching accommodation step S31 may include preparing the crucible 2 that has been subjected to the annealing step S2, with the SiC substrate 1 still accommodated therein.

[0183] <Etching and Heating Step S32> The etching step S3 includes, after the etching and accommodating step S31, an etching and heating step S32 of heating the crucible 2. The etching and heating step S32 includes heating the crucible 2 to heat the SiC substrate 1 accommodated inside the crucible 2.

[0184] The etching and heating step S32 preferably includes maintaining a SiC-C equilibrium vapor pressure environment inside the crucible 2. Here, the etching and heating step S32 preferably includes heating the crucible 2 while evacuating the inside of the crucible 2, and generating a source gas from the crucible 2 into the inside of the crucible 2, thereby maintaining the inside of the crucible 2 in a SiC-C equilibrium vapor pressure environment.

[0185] When the inside of the crucible 2 is maintained in a SiC-C equilibrium vapor pressure environment, the etching heating step S32 includes heating the crucible 2 and maintaining the temperature inside the crucible 2 at 1600°C or higher (or above 1600°C). This temperature is preferably 1700°C or higher (or above 1700°C). This temperature is preferably 2000°C or lower (or lower than 2000°C). This temperature is preferably 1900°C or lower (or lower than 1900°C). This temperature is preferably lower than the temperature inside the crucible 2 in the heating step S22.

[0186] The etching and heating step S32 preferably includes maintaining a SiC-Si equilibrium vapor pressure environment inside the crucible 2. Here, the etching and heating step S32 preferably includes heating the crucible 2 while evacuating the inside of the crucible 2, generating a source gas from the crucible 2 into the inside of the crucible 2, and generating Si gas from the Si gas source 5 into the inside of the crucible 2, thereby maintaining the inside of the crucible 2 in a SiC-Si equilibrium vapor pressure environment.

[0187] When the inside of the crucible 2 is maintained in a SiC-Si equilibrium vapor pressure environment, the etching heating step S32 includes heating the crucible 2 and maintaining the temperature inside the crucible 2 at 1800°C or higher (or higher than 1800°C). This temperature is preferably 1900°C or higher (or higher than 1900°C). This temperature is 2000°C or lower (or lower than 2000°C). This temperature is preferably lower than the temperature inside the crucible 2 in the heating step S22.

[0188] The etching heating step S32 involves forming a temperature gradient inside the crucible 2 in a direction penetrating the SiC substrate 1, thereby forming a macroscopic flow of the source gas inside the crucible 2. Here, the etching heating step S32 involves creating a temperature difference such that the base 21 is at a high temperature and the lid 22 is at a low temperature. This creates a temperature gradient in which the temperature decreases from the C-face 112 side toward the Si-face 111 side, and as a result, the Si-face 111 can be precisely etched.

[0189] The etching heating step S32 includes heating the crucible 2 using a heating furnace as a heat source. This allows the inside of the crucible 2 to be heated from the outside of the crucible 2. In addition, by providing a difference in heating output between the upper and lower parts of the heating furnace, a desired temperature gradient can be formed inside the crucible 2.

[0190] The flow of processing method Y is as shown in FIG. 10. Processing method Y includes a preparation step S1, an annealing step S2, and an etching step S3. The annealing step S2 includes a storage step S21 and a heating step S22. The etching step S3 includes an etching storage step S31 and an etching heating step S32. Processing method Y may include a step of performing an optional treatment after etching step S3. Here, processing method Y preferably does not include a step of performing a mechanical treatment after etching step S3.

[0191] <Processing Method Z> A third preferred embodiment of the present processing method will be described in detail with reference to Fig. 11. In Fig. 11, the same components as those shown in Figs. 1 to 10 are designated by the same reference numerals. Hereinafter, this third preferred embodiment of the present processing method will be referred to as Processing Method Z.

[0192] <Preparation Step S1> Processing method Z includes a preparation step S1 of preparing a SiC substrate 1. Since preparation step S1 is similar to preparation step S1 of processing method Y, a description thereof will be omitted.

[0193] <Annealing Step S2> Processing method Z includes an annealing step S2 in which the SiC substrate 1 is annealed inside a crucible 2 made of SiC. The annealing step S2 is similar to the annealing step S2 of processing method Y, and therefore a description thereof will be omitted.

[0194] <First Etching Step S4> Processing method Z includes a first etching step S4 of etching the SiC substrate 1 that has been subjected to the annealing step S2. The first etching step S4 is substantially the same as the etching step S3 of processing method Y, except that the inside of the crucible 2 is maintained in a SiC-C equilibrium vapor pressure environment.

[0195] <First Etching Accommodation Step S41> The first etching step S4 includes a first etching accommodation step S41 in which the SiC substrate 1 is accommodated inside the crucible 2. The first etching accommodation step S41 is substantially similar to the etching accommodation step S31 of the processing method Y, but includes the fact that the Si gas source 5 is not disposed inside the crucible 2, as shown in FIG.

[0196] <First Etching Heating Step S42> The first etching step S4 includes a first etching heating step S42, which is performed after the first etching accommodation step S41, to heat the crucible 2. The first etching heating step S42 is substantially similar to the etching heating step S32 of the processing method Y, but includes maintaining the inside of the crucible 2 in a SiC—C equilibrium vapor pressure environment.

[0197] <Second Etching Step S5> Processing method Z includes a second etching step S5 in which the SiC substrate 1 that has been subjected to the first etching step S4 is further etched. The second etching step S5 is substantially the same as the etching step S3 of processing method Y, but the inside of the crucible 2 is maintained in a SiC-Si equilibrium vapor pressure environment.

[0198] <Second Etching Accommodation Step S51> The second etching step S5 includes a second etching accommodation step S51 of accommodating the SiC substrate 1 inside the crucible 2. The second etching accommodation step S51 is substantially similar to the etching accommodation step S31 of the processing method Y, but includes disposing a Si gas source 5 inside the crucible 2, as shown in FIG.

[0199] <Second Etching Heating Step S52> The second etching step S5 includes, after the second etching accommodation step S51, a second etching heating step S52 of heating the crucible 2. The second etching heating step S52 is substantially similar to the etching heating step S32 of the processing method Y, but includes maintaining the inside of the crucible 2 in a SiC-Si equilibrium vapor pressure environment.

[0200] In the processing method Z, as described above, the SiC substrate 1 is etched in a SiC-C equilibrium vapor pressure environment in the first etching step S4, and then the SiC substrate 1 is etched in a SiC-Si equilibrium vapor pressure environment in the second etching step S5, thereby etching the Si surface 111 more precisely and further reducing the surface roughness of the Si surface (in particular, the macrostep bunching on the Si surface can be resolved).

[0201] The flow of processing method Z is as shown in FIG. 11 . Processing method Z includes a preparation step S1, an annealing step S2, a first etching step S4, and a second etching step S5. The annealing step S2 includes a storage step S21 and a heating step S22. The first etching step S4 includes a first etching storage step S41 and a first etching heating step S42. The second etching step S5 includes a second etching storage step S51 and a second etching heating step S52. Processing method Z may include a step of performing an optional treatment after the second etching step S5. Here, processing method Z preferably does not include a step of performing a mechanical treatment after the second etching step S5.

[0202] <Processing Method V> A fourth preferred embodiment of the present processing method will be described in detail with reference to Fig. 12. In Fig. 12, the same components as those shown in Figs. 1 to 11 are designated by the same reference numerals. Hereinafter, this fourth preferred embodiment of the present processing method will be referred to as Processing Method V.

[0203] <Preparation Step S1> Processing method V includes a preparation step S1 of preparing a SiC substrate 1. Since preparation step S1 is similar to preparation step S1 of processing method Z, a description thereof will be omitted.

[0204] <Annealing Step S2> Processing method V includes an annealing step S2 in which the SiC substrate 1 is annealed inside a crucible 2 made of SiC. The annealing step S2 is similar to the annealing step S2 of processing method Z, and therefore a description thereof will be omitted.

[0205] <Etching Step S3> Processing method V includes an etching step S3 of etching the SiC substrate 1 that has been subjected to the annealing step S2. Since the etching step S3 is similar to the etching step S3 of processing method Y, a description thereof will be omitted.

[0206] The processing method V preferably includes a first etching step S4 and a second etching step S5 in this order as the etching step S3. The first etching step S4 and the second etching step S5 are similar to the first etching step S4 and the second etching step S5 of the processing method Z, and therefore a description thereof will be omitted.

[0207] <Growth Step S6> Processing method V includes a growth step S6 in which a SiC substrate 1 that has been subjected to the etching step S3 is grown.

[0208] The growth in the growth step S6 is similar to conventional growth in that a macroscopic increase in atoms occurs as a result of repeated microscopic increases in atoms. That is, it differs from the growth in the annealing step S2. At this time, the surface 11 of the SiC substrate 1 grows precisely, resulting in a SiC substrate 1 with significantly reduced surface roughness.

[0209] The arrangement of the components is the same as that in the etching step S3.

[0210] The interior of the crucible 2 is maintained in a source gas phase equilibrium environment. That is, the growth step of this processing method can be said to be a step of growing a SiC substrate in a source gas phase equilibrium environment.

[0211] The temperature inside the crucible 2 maintained in the SiC-C equilibrium vapor pressure environment is preferably 1600°C or higher (or higher than 1600°C), and preferably 1700°C or higher (or higher than 1700°C). This temperature is preferably 2000°C or lower (or lower than 2000°C), and preferably 1900°C or lower (or lower than 1900°C). This temperature is preferably lower than the temperature inside the crucible 2 in the annealing step S2.

[0212] The temperature inside the crucible 2 maintained in the SiC-Si equilibrium vapor pressure environment is preferably 1800°C or higher (or higher than 1800°C), and more preferably 1900°C or higher (or higher than 1900°C). This temperature is preferably 2000°C or lower (or lower than 2000°C). This temperature is preferably lower than the temperature inside the crucible 2 in the annealing step S2.

[0213] A temperature gradient is formed inside the crucible 2. The magnitude of this temperature gradient is 0.1 mm / K or more and 5 mm / K or less. This temperature gradient is formed in a direction penetrating the SiC substrate 1. This temperature gradient is formed in a direction in which the temperature decreases from the Si face 111 toward the C face 112.

[0214] In the processing method V, the inside of the crucible 2 is maintained in a source gas phase equilibrium environment in the above-described manner, so that the growth of the Si surface 111 can be carried out under suitable conditions.

[0215] By maintaining the interior of the crucible 2 in a source gas phase equilibrium environment as described above, the sublimation reaction and the recrystallization reaction are gently balanced with a slight bias toward the recrystallization reaction, and the source gas gradually recrystallizes on the Si surface 111. As a result, the Si surface 111 can be grown precisely, and an increase in the surface roughness of the Si surface 111 can be significantly suppressed.

[0216] The steps included in the growth step S6 will be described in detail below.

[0217] <Growth Accommodation Step S61> The growth step S6 includes a growth accommodation step S61 in which the SiC substrate 1 is accommodated in the crucible 2. The growth accommodation step S61 is similar to the etching accommodation step S31 of the processing method Y. In the growth accommodation step S61, the crucible 2 may be the same as that used in the accommodation step S21, the same as that used in the etching accommodation step S31, or a different crucible. Here, the growth accommodation step S61 may include preparing the crucible 2 that has been subjected to the etching step S3, with the SiC substrate 1 still accommodated in it, instead of accommodating the SiC substrate 1 in the crucible 2.

[0218] <Growth Heating Step S62> The growth step S6 includes, after the growth accommodation step S61, a growth heating step S62 of heating the crucible 2. The growth heating step S62 includes heating the crucible 2 to heat the SiC substrate 1 accommodated inside the crucible 2.

[0219] The growth heating step S62 preferably includes maintaining a SiC-C equilibrium vapor pressure environment inside the crucible 2. Here, the growth heating step S62 preferably includes heating the crucible 2 while evacuating the inside of the crucible 2, and generating a source gas from the crucible 2 into the crucible 2, thereby maintaining the inside of the crucible 2 in a SiC-C equilibrium vapor pressure environment.

[0220] When the inside of the crucible 2 is maintained in a SiC-C equilibrium vapor pressure environment, the growth heating step S62 includes heating the crucible 2 and maintaining the temperature inside the crucible 2 at 1600°C or higher (or above 1600°C). This temperature is preferably 1700°C or higher (or above 1700°C). This temperature is 2000°C or lower (or lower than 2000°C). This temperature is preferably 1900°C or lower (or lower than 1900°C). This temperature is preferably lower than the temperature inside the crucible 2 in the heating step S22.

[0221] The growth heating step S62 also preferably includes maintaining a SiC-Si equilibrium vapor pressure environment inside the crucible 2. Here, the growth heating step S62 preferably includes heating the crucible 2 while evacuating the inside of the crucible 2, generating source gas from the crucible 2 into the inside of the crucible 2, and generating Si gas from the Si gas source 5 into the inside of the crucible 2, thereby maintaining the inside of the crucible 2 in a SiC-Si equilibrium vapor pressure environment.

[0222] When the inside of the crucible 2 is maintained in a SiC-Si equilibrium vapor pressure environment, the growth heating step S62 includes heating the crucible 2 and maintaining the temperature inside the crucible 2 at 1800°C or higher (or higher than 1800°C). This temperature is preferably 1900°C or higher (or higher than 1900°C). This temperature is 2000°C or lower (or lower than 2000°C). This temperature is preferably lower than the temperature inside the crucible 2 in the heating step S22.

[0223] The growth heating step S62 includes forming a temperature gradient inside the crucible 2 in a direction penetrating the SiC substrate 1, thereby forming a macroscopic flow of the source gas inside the crucible 2. Here, the growth heating step S62 includes creating a temperature difference so that the base 21 is at a low temperature and the lid 22 is at a high temperature. This creates a temperature gradient in which the temperature decreases from the Si face 111 side toward the C face 112 side, and as a result, the Si face 111 can be grown precisely.

[0224] The growth heating step S62 includes heating the crucible 2 using a heating furnace as a heat source. This allows the inside of the crucible 2 to be heated from the outside of the crucible 2. In addition, by providing a difference in heating output between the upper and lower parts of the heating furnace, a desired temperature gradient can be formed inside the crucible 2.

[0225] The flow of processing method V is as shown in FIG. 12 . Processing method V includes a preparation step S1, an annealing step S2, an etching step S3, and a growth step S6. The annealing step S2 includes a storage step S21 and a heating step S22. The etching step S3 includes an etching storage step S31 and an etching heating step S32. The growth step S6 includes a growth storage step S61 and a growth heating step S62. Processing method V may include a step of performing an optional treatment after the growth step S6. Here, processing method V preferably does not include a step of performing a mechanical treatment after the growth step S6.

[0226] <Processing Method W> A fifth preferred embodiment of the present processing method will be described in detail with reference to Fig. 13. In Fig. 13, the same components as those shown in Figs. 1 to 12 are designated by the same reference numerals. Hereinafter, this fifth preferred embodiment of the present processing method will be referred to as Processing Method W.

[0227] <Preparation Step S1> Processing method W includes a preparation step S1 of preparing a SiC substrate 1. Since preparation step S1 is similar to preparation step S1 of processing method V, a description thereof will be omitted.

[0228] <Annealing Step S2> Processing method W includes an annealing step S2 in which the SiC substrate 1 is annealed inside a crucible 2 made of SiC. The annealing step S2 is similar to the annealing step S2 of processing method V, and therefore a description thereof will be omitted.

[0229] <First Etching Step S4> Processing method W includes a first etching step S4 of etching the SiC substrate 1 that has been subjected to the annealing step S2. The first etching step S4 is similar to the first etching step S4 of processing method Z, and therefore a description thereof will be omitted.

[0230] <Second Etching Step S5> Processing method W includes a second etching step S5 in which the SiC substrate 1 that has been subjected to the first etching step S4 is further etched. The second etching step S5 is similar to the second etching step S5 of processing method Z, and therefore a description thereof will be omitted.

[0231] <First Growth Step S7> Processing method W includes a first growth step S7 in which the SiC substrate 1 that has been subjected to the second etching step S5 is grown. The first growth step S7 is substantially the same as the growth step S6 of processing method V, but the inside of the crucible 2 is maintained in a SiC-C equilibrium vapor pressure environment.

[0232] <First Growth Accommodation Step S71> The first growth step S7 includes a first growth accommodation step S71 in which the SiC substrate 1 is accommodated inside the crucible 2. The first growth accommodation step S71 is substantially similar to the growth accommodation step S61 of the processing method V, but includes the difference that the Si gas source 5 is not disposed inside the crucible 2, as shown in FIG.

[0233] <First Growth Heating Step S72> The first growth step S7 includes a first growth heating step S72, which is performed after the first growth accommodation step S71, to heat the crucible 2. The first growth heating step S72 is substantially similar to the growth heating step S62 of the processing method V, but includes maintaining the inside of the crucible 2 in a SiC—C equilibrium vapor pressure environment.

[0234] <Second Growth Step S8> Processing method W includes a second growth step S8 in which the SiC substrate 1 that has been subjected to the first growth step S7 is further grown. The second growth step S8 is substantially the same as the growth step S6 of processing method V, but the inside of the crucible 2 is maintained in a SiC-Si equilibrium vapor pressure environment.

[0235] <Second Growth Accommodation Step S81> The second growth step S8 includes a second growth accommodation step S81 in which the SiC substrate 1 is accommodated inside the crucible 2. The second growth accommodation step S81 is substantially similar to the growth accommodation step S61 of the processing method V, but includes disposing a Si gas source 5 inside the crucible 2, as shown in FIG.

[0236] <Second Growth Heating Step S82> The second growth step S8 includes a second growth heating step S82, which is performed after the second growth accommodation step S81, to heat the crucible 2. The second growth heating step S82 is substantially similar to the growth heating step S62 of the processing method V, but includes maintaining the inside of the crucible 2 in a SiC-Si equilibrium vapor pressure environment.

[0237] In the processing method W, in the above-described manner, the SiC substrate 1 is etched in a SiC-Si equilibrium vapor pressure environment in the second etching step S5, and then the SiC substrate 1 is grown in a SiC-C equilibrium vapor pressure environment in the first growth step S7, thereby significantly suppressing the inheritance of basal plane dislocations (BPDs) in the growth layer.

[0238] Furthermore, in the processing method W, in the above-described manner, the SiC substrate 1 is grown in a SiC-C equilibrium vapor pressure environment in the first growth step S7, and then the SiC substrate 1 is grown in a SiC-Si equilibrium vapor pressure environment in the second growth step S8, thereby significantly reducing the surface roughness of the Si surface (in particular, the macrostep bunching on the Si surface can be resolved).

[0239] In general, processing method W can process a SiC substrate in any state into a SiC substrate suitable for manufacturing SiC semiconductor devices, in which the surface roughness is significantly suppressed, BPDs are significantly suppressed, and the process-affected layer that causes in-grown stacking faults (IGSFs) is significantly removed.

[0240] The flow of processing method W is as shown in FIG. 13 . Processing method Z includes a preparation step S1, an annealing step S2, a first etching step S4, a second etching step S5, a first growth step S7, and a second growth step S8. The annealing step S2 includes a storage step S21 and a heating step S22. The first etching step S4 includes a first etching storage step S41 and a first etching heating step S42. The second etching step S5 includes a second etching storage step S51 and a second etching heating step S52. The first growth step S7 includes a first growth storage step S71 and a first growth heating step S72. The second growth step S8 includes a second growth storage step S81 and a second growth heating step S82. Note that processing method W may include a step of performing an optional treatment after the second growth step S8. Here, it is preferable that the processing method W does not include a step of performing a mechanical treatment after the second growth step S8.

[0241] Treatment method X was carried out according to the following steps.

[0242] <Preparation Step S1> A substrate for which the following characteristics were measured was prepared as a SiC substrate 1. In order to eliminate the influence of the measurement of the SiC substrate 1 on the surface 11, the SiC substrate 1 was cleaned with a chemical solution.

[0243] Material: 4H-SiC Offset angle: 4° Offset direction: [11-20] direction Size: 6 inches Arithmetic mean roughness Ra of Si surface 111: 46.2 nm Substrate thickness: 400.0 μm

[0244] <Annealing Step S2> The SiC substrate 1 was annealed in accordance with the following steps.

[0245] <Accommodating Step S21> As shown in FIG. 6, the SiC substrate 1 was accommodated in a crucible 2 made of polycrystalline SiC.

[0246] <Heating Step S22> The SiC substrate 1 was heated under the following conditions.

[0247] Introduced gas: Ar gas Pressure: 1 kPa or more and 300 kPa or less Temperature: 1800°C or more and 2300°C or less Temperature difference: base 21 is high temperature, lid 22 is low temperature Time: 1 hour

[0248] Figure 14 shows contour lines based on AFM images (10 μm × 10 μm). In Figure 12, (a) is the SiC substrate 1 prepared in the preparation step S1, and (b) is the SiC substrate 1 that has undergone the annealing step S2. Comparing the contour line shapes reveals that the surface roughness of the Si surface 111 has been reduced.

[0249] FIG. 15 shows the relationship between the arithmetic mean roughness Ra of the Si surface 111 and the substrate thickness. The arithmetic mean roughness Ra of the Si surface 111 was reduced from 46.2 nm to 13.7 nm after the annealing step S2. Furthermore, the substrate thickness of the SiC substrate 1 increased from 400.0 μm to 409.8 μm after the annealing step S2. This indicates that the surface roughness of the Si surface 111 was reduced while the substrate thickness of the SiC substrate 1 was almost maintained. Due to the temperature difference, it is believed that the Si surface 111 was etched and, at the same time, the C surface 112 grew. Furthermore, it is believed that the amount of etching of the Si surface 111 was approximately the same as or smaller than the amount of growth of the C surface 112.

[0250] Treatment method X was carried out according to the following steps.

[0251] <Preparation Step S1> A substrate for which the following characteristics were measured was prepared as a SiC substrate 1. In order to eliminate the influence of the measurement of the SiC substrate 1 on the surface 11, the SiC substrate 1 was cleaned with a chemical solution.

[0252] Material: 4H-SiC Offset angle: 4° Offset direction: [11-20] direction Size: 6 inches Arithmetic mean roughness Ra of Si surface 111: 46.2 nm Substrate thickness: 400.0 μm

[0253] <Annealing Step S2> The SiC substrate 1 was annealed in accordance with the following steps.

[0254] <Accommodating Step S21> As shown in FIG. 6, the SiC substrate 1 was accommodated in a crucible 2 made of polycrystalline SiC.

[0255] <Heating Step S22> The SiC substrate 1 was heated under the following conditions.

[0256] Introduced gas: Ar gas Pressure: Vacuum (up to 10 -4 kPa), 5 kPa, or 10 kPa Temperature: 1800°C, 2000°C, or 2200°C Temperature difference: base 21 is high temperature, lid 22 is low temperature Time: 1 hour

[0257] Figure 16 shows laser microscope images of the Si surface 111 of the SiC substrates processed under each condition. It was found that the surface irregularities were smaller when the pressure was 5 kPa or higher than when the pressure was vacuum. Additionally, it was found that a step-terrace structure appeared on the surface when the temperature was 2200°C or higher, i.e., the surface shape was regularized.

[0258] The arithmetic mean height Sa was 70 nm when the pressure was vacuum and 153 nm when the pressure was 10 kPa at a temperature of 1800°C. At a temperature of 2000°C, it was 174 nm when the pressure was vacuum, 71 nm when the pressure was 5 kPa, and 86 nm when the pressure was 10 kPa. At a temperature of 2200°C, it was 242 nm when the pressure was vacuum, 56 nm when the pressure was 5 kPa, and 54 nm when the pressure was 10 kPa. Comparison of the arithmetic mean height Sa revealed that the surface roughness of the Si surface 111 was significantly reduced when the pressure was 5 kPa or higher. Furthermore, it was found that the surface roughness of the Si surface 111 was significantly reduced when the temperature was 2000°C or higher, and even more significantly reduced when the temperature was 2200°C or higher.

[0259] Following Example 1, processing method Y was carried out according to the following steps: In order to eliminate the influence of the measurement of SiC substrate 1 on surface 11, SiC substrate 1 was washed with a chemical solution.

[0260] <Etching Step S3> The SiC substrate 1 was etched according to the following steps.

[0261] <Etching and Accommodation Step S31> As shown in FIG. 7, the SiC substrate 1 was accommodated in the crucible 2.

[0262] <Etching and Heating Step S32> The SiC substrate 1 was heated under the following conditions: At this time, the inside of the crucible 2 was in a SiC-C equilibrium vapor pressure environment.

[0263] Introduced gas: None Pressure: Vacuum (raw material gas pressure) Temperature: 1600°C or higher and 2000°C or lower (lower than the temperature in the heating step S22) Temperature difference: base 21 is high temperature, lid 22 is low temperature Time: 1 hour

[0264] 14, (c) is the SiC substrate 1 that has been subjected to the etching step S3. A comparison of the contour line shapes reveals that the surface roughness of the Si surface 111 has been further reduced.

[0265] The arithmetic mean roughness Ra of the Si surface 111 was reduced from 13.7 nm to 6.1 nm after the etching step S3. Furthermore, the substrate thickness of the SiC substrate 1 increased from 409.8 μm to 414.0 μm after the etching step S3. This indicates that the surface roughness of the Si surface 111 was reduced while the substrate thickness of the SiC substrate 1 was almost maintained. Due to the temperature difference conditions, it is believed that the Si surface 111 was etched and, at the same time, the C surface 112 grew. Furthermore, it is believed that the amount of etching of the Si surface 111 was approximately the same as or smaller than the amount of growth of the C surface 112.

[0266] Following Example 3, Processing Method Z was performed according to the following steps. However, the first etching step S4 of Processing Method Z was the same as the etching step S3 of Example 2. In order to eliminate the influence of the measurement of SiC substrate 1 on surface 11, SiC substrate 1 was washed with a chemical solution.

[0267] <Second Etching Step S5> The SiC substrate 1 was etched according to the following steps.

[0268] <Second Etching Accommodation Step S51> As shown in FIG. 9, the SiC substrate 1 was accommodated in the crucible 2 together with the Si gas source 5.

[0269] <Second Etching and Heating Step S52> The SiC substrate 1 was heated under the following conditions: At this time, the inside of the crucible 2 was in a SiC-Si equilibrium vapor pressure environment.

[0270] Introduced gas: None Pressure: Vacuum (raw material gas pressure) Temperature: 1800°C to 2000°C (lower than the temperature in the heating step S22 and higher than the temperature in the first etching heating step S42) Temperature difference: base 21 is high temperature, lid 22 is low temperature Time: 1 hour

[0271] 14, (d) shows the SiC substrate 1 after the second etching step S5. A comparison of the contour line shapes reveals that the surface roughness of the Si surface 111 has been further reduced.

[0272] The arithmetic mean roughness Ra of the Si surface 111 was reduced from 6.1 nm to 0.7 nm after the second etching step S5. Furthermore, the substrate thickness of the SiC substrate 1 increased from 414.0 μm to 426.1 μm after the second etching step S5. This indicates that the surface roughness of the Si surface 111 was reduced while the substrate thickness of the SiC substrate 1 was almost maintained. Due to the temperature difference conditions, it is believed that the Si surface 111 was etched and, at the same time, the C surface 112 grew. Furthermore, it is believed that the amount of etching of the Si surface 111 was approximately the same as or smaller than the amount of growth of the C surface 112.

[0273] Treatment method V was carried out according to the following steps.

[0274] <Preparation Step S1> A substrate for which the following characteristics were measured was prepared as a SiC substrate 1. In order to eliminate the influence of the measurement of the SiC substrate 1 on the surface 11, the SiC substrate 1 was cleaned with a chemical solution.

[0275] Material: 4H-SiC Off-angle: 4° Off-axis direction: [11-20] direction Size: 3 inches Arithmetic mean roughness Ra of Si surface 111: 60 nm or more Photoluminescence image of Si surface 111: Figure 17 (left)

[0276] <Annealing Step S2> The SiC substrate 1 was annealed in accordance with the following steps.

[0277] <Accommodating Step S21> As shown in FIG. 6, the SiC substrate 1 was accommodated in a crucible 2 made of polycrystalline SiC.

[0278] <Heating Step S22> The SiC substrate 1 was heated under the following conditions.

[0279] Introduced gas: Ar gas Pressure: 10 kPa Temperature: 2200°C Temperature difference: base 21 is high temperature, lid 22 is low temperature Time: 1 hour

[0280] <First Etching Step S4> The SiC substrate 1 was etched according to the following steps.

[0281] <First Etching Accommodation Step S41> As shown in FIG. 7, the SiC substrate 1 was accommodated in the crucible 2.

[0282] <First Etching and Heating Step S42> The SiC substrate 1 was heated under the following conditions: At this time, the inside of the crucible 2 was in a SiC-C equilibrium vapor pressure environment.

[0283] Introduced gas: None Pressure: Vacuum (raw material gas pressure) Temperature: 1800°C Temperature difference: Base 21 is high temperature, lid 22 is low temperature Time: 1 hour

[0284] <Second Etching Step S5> The SiC substrate 1 was etched according to the following steps.

[0285] <Second Etching Accommodation Step S51> As shown in FIG. 9, the SiC substrate 1 was accommodated in the crucible 2.

[0286] <Second Etching and Heating Step S52> The SiC substrate 1 was heated under the following conditions: At this time, the inside of the crucible 2 was in a SiC-Si equilibrium vapor pressure environment.

[0287] Introduced gas: None Pressure: Vacuum (raw material gas pressure) Temperature: 1800°C Temperature difference: Base 21 is high temperature, lid 22 is low temperature Time: 1 hour

[0288] <Growth Step S6> The SiC substrate 1 was grown according to the following steps.

[0289] <Growth Accommodation Step S61> As shown in FIG. 7, the SiC substrate 1 was accommodated in the crucible 2.

[0290] <Growth Heating Step S62> The SiC substrate 1 was heated under the following conditions: At this time, the inside of the crucible 2 was in a SiC-C equilibrium vapor pressure environment.

[0291] Introduced gas: None Pressure: Vacuum (raw material gas pressure) Temperature: 1800°C Temperature difference: Base 21 is high temperature, lid 22 is low temperature Time: 2 hours

[0292] The arithmetic mean roughness Ra of the Si surface 111 was less than 5 nm. The photoluminescence image of the Si surface 111 was as shown on the right in Figure 17. Note that there were three BPDs (number density 0.07 cm) on the entire surface of the SiC substrate 1. -2 ), 12 IGSFs (number density 0.27 cm -2) That is, it was found that the surface roughness of the Si surface 111 was reduced and the BPD and IGSF were almost completely removed.

[0293] X: Processing method S2: Annealing process S21: Housing process S22: Heating process 1: SiC substrate 11: Surface 111: Si surface 112: C surface 12: Process-affected layer 2: Crucible 21: Substrate 22: Lid 3: Substrate support d: Depth

Claims

1. A method for treating a SiC substrate, comprising: an annealing step of heating a SiC substrate in an inert gas environment; and an etching step of etching the SiC substrate that has undergone the annealing step in an environment containing a gas composed of one or both of Si and C elements.

2. The method for processing a SiC substrate according to claim 1, wherein the annealing step includes heating the SiC substrate inside a crucible made of SiC, and during the annealing step, the inside of the crucible is maintained in the inert gas environment.

3. The method for treating a SiC substrate according to claim 1 or 2, wherein the annealing step includes etching one surface of the SiC substrate and simultaneously growing the other surface of the SiC substrate.

4. The method for processing a SiC substrate according to claim 3, wherein the annealing step includes making an amount of etching on the one surface approximately equal to an amount of growth on the other surface, thereby making the thickness of the SiC substrate approximately equal before and after the annealing step.

5. A method for treating a SiC substrate as described in claim 3 or 4, wherein the annealing step includes increasing a thickness of the SiC substrate before and after the annealing step by making an amount of etching on the one surface smaller than an amount of growth on the other surface.

6. The method for treating a SiC substrate according to any one of claims 2 to 5, wherein in the annealing step, the pressure inside the crucible is 5 kPa or more.

7. The method for treating a SiC substrate according to any one of claims 2 to 5, wherein in the annealing step, the pressure inside the crucible is 10 kPa or more.

8. The method for treating a SiC substrate according to any one of claims 2 to 7, wherein in the annealing step, the temperature inside the crucible is 2000°C or higher.

9. The method for treating a SiC substrate according to any one of claims 2 to 7, wherein in the annealing step, the temperature inside the crucible is 2200°C or higher.

10. The method for treating a SiC substrate according to any one of claims 2 to 9, wherein in the annealing step, a combination of pressure and temperature inside the crucible is 5 kPa or more and 2000°C or more.

11. The method for treating a SiC substrate according to any one of claims 2 to 9, wherein in the annealing step, a combination of pressure and temperature inside the crucible is 5 kPa or more and 2200°C or more.

12. The method for treating a SiC substrate according to any one of claims 1 to 11, wherein in the annealing step, no protective film is formed on the surface of the SiC substrate.

13. A method for treating a SiC substrate according to any one of claims 1 to 12, wherein the etching step includes heating the SiC substrate inside a crucible made of SiC, and during the etching step, the inside of the crucible is maintained in the environment containing a gas consisting of one or both of Si and C elements.

14. The SiC substrate processing method according to claim 13, wherein in the etching step, the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment.

15. The SiC substrate processing method according to claim 13, wherein in the etching step, the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment.

16. A method for treating a SiC substrate according to any one of claims 13 to 15, wherein in the etching step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases from the C-face side to the Si-face side of the SiC substrate.

17. The method for treating a SiC substrate according to any one of claims 13 to 16, which does not include a step of performing a mechanical treatment on the SiC substrate after the etching step.

18. The method for treating a SiC substrate according to any one of claims 13 to 17, wherein the etching step is performed at least twice, a first etching step and a second etching step, the first etching step includes etching the SiC substrate that has been subjected to the annealing step, and the second etching step includes etching the SiC substrate that has been subjected to the first etching step, the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment in the first etching step, and the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment in the second etching step.

19. A method for treating a SiC substrate according to any one of claims 1 to 18, further comprising a growing step of growing the SiC substrate that has been subjected to the etching step in an environment containing a gas composed of one or both of Si and C elements.

20. A method for treating a SiC substrate according to any one of claims 1 to 19, wherein the growth step includes heating the SiC substrate inside a crucible made of SiC, and during the growth step, the inside of the crucible is maintained in an environment containing a gas consisting of one or both of Si and C elements.

21. The SiC substrate processing method according to claim 20, wherein in the growing step, the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment.

22. The method for treating a SiC substrate according to claim 20, wherein, in the growing step, the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment.

23. A method for treating a SiC substrate according to any one of claims 20 to 22, wherein, in the growth step, a temperature gradient is formed inside the crucible in a direction penetrating the SiC substrate and in a direction in which the temperature decreases from the Si face side to the C face side of the SiC substrate.

24. The method for treating a SiC substrate according to any one of claims 20 to 23, wherein the growing step is performed at least twice, a first growing step and a second growing step, the first growing step includes growing a SiC substrate that has been subjected to the etching step, the second growing step includes growing a SiC substrate that has been subjected to the first growing step, the inside of the crucible is maintained in a SiC-C equilibrium vapor pressure environment in the first growing step, and the inside of the crucible is maintained in a SiC-Si equilibrium vapor pressure environment in the second growing step.

25. A method for removing a processed-damaged layer from a SiC substrate, comprising subjecting a SiC substrate having a processed-damaged layer to the SiC substrate processing method recited in any one of claims 1 to 24, thereby removing the processed-damaged layer.

26. A method for removing a process-damaged layer of a SiC substrate as set forth in claim 25, comprising carrying out the processing method on the SiC substrate on which the process-damaged layer has been formed by mechanical processing.

27. A method for removing a process-damaged layer of a SiC substrate as described in claim 25 or 26, wherein the annealing step includes exchanging atoms between a surface layer of the SiC substrate and the inert gas environment to remove the process-damaged layer.

28. A method for reducing the surface roughness of a SiC substrate, comprising subjecting a SiC substrate having an arithmetic mean roughness Ra of a Si surface of 15 nm or more to a SiC substrate processing method according to any one of claims 1 to 24, thereby reducing the arithmetic mean roughness Ra.

29. A method for reducing surface roughness of a SiC substrate as recited in claim 28, comprising subjecting the processing method to a SiC substrate that has been subjected to mechanical processing.

30. A method for reducing surface roughness of a SiC substrate as described in claim 28 or 29, wherein the annealing step includes exchanging atoms between the surface layer of the SiC substrate and the inert gas environment to smooth the surface layer.

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