JP2018188327A - Evaluation method of silicon carbide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method of a silicon carbide substrate capable of easily grasping a state of dislocation of a silicon carbide substrate.SOLUTION: An evaluation method of a silicon carbide substrate 10 includes a step for preparing a silicon carbide substrate 10 having a first principal plane 11 of an off-angle to a Si plane of 0° or more and 4° or less and having a 4H type crystal structure, a step for etching the first principal plane 11 with a first gas containing halogen atoms and then forming a first etch pit 31 corresponding to penetration screw dislocation by oxidizing the first principal plane 11, a step for etching the first principal plane 11 having the first etch pit 31 formed with an etching solution containing a hydroxide to enlarge the first etch pit 31 and forming a second etch pit 32 corresponding to penetration edge dislocation, and a step for evaluating a state of dislocation of the silicon carbide substrate 10 by observing the first principal plane 11 having the first etch pit 31 and the second etch pit 32 formed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for evaluating a silicon carbide substrate.

  As a method for evaluating the crystallinity of a silicon carbide substrate, a method for evaluating the density of crystal defects in a silicon carbide substrate is known. For example, a method is known in which the surface of a silicon carbide substrate is etched with a potassium hydroxide melt to form a recess (etch pit) in a portion having crystal defects on the silicon carbide substrate, and the density of crystal defects is evaluated. Yes. Further, a method has been proposed in which the surface of a silicon carbide substrate is etched with chlorine gas and then oxidized with oxygen gas to form etch pits (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2014-024702

  Examples of crystal defects in the silicon carbide substrate include threading screw dislocations and threading edge dislocations. In evaluating the crystallinity of the silicon carbide substrate, it is preferable to evaluate the state of threading screw dislocations and threading edge dislocations. However, when etch pits are formed on the surface of the silicon carbide substrate by the method using chlorine gas disclosed in Patent Document 1, there are cases where the etch pits of threading edge dislocations are not sufficiently formed. In such a case, it is difficult to evaluate the state of threading edge dislocations.

  When the surface of the silicon carbide substrate is etched using a potassium hydroxide melt, etch pits corresponding to threading screw dislocations and threading edge dislocations are formed. However, it is difficult to distinguish between threading screw dislocations and threading edge dislocations, and it may not be possible to separately evaluate the states of threading screw dislocations and threading edge dislocations.

  Therefore, an object is to provide a method for evaluating a silicon carbide substrate that can easily grasp the dislocation state of the silicon carbide substrate.

  The method for evaluating a silicon carbide substrate of the present application includes a step of preparing a silicon carbide substrate having a first main surface having an off angle with respect to the Si surface of greater than 0 ° and 4 ° or less and having a 4H crystal structure, After the first main surface is etched with the first gas containing atoms, the first main surface is oxidized to form first etch pits corresponding to threading screw dislocations, and an etching solution containing hydroxide Etching the first main surface on which the first etch pits are formed to enlarge the size of the first etch pits and forming the second etch pits corresponding to the threading edge dislocations; Observing the first main surface on which the pits and the second etch pits are formed, and evaluating a dislocation state of the silicon carbide substrate.

  According to the silicon carbide substrate evaluation method, it is possible to provide a silicon carbide substrate evaluation method capable of easily grasping the dislocation state of the silicon carbide substrate.

It is a flowchart which shows the outline of the evaluation method of a silicon carbide substrate. It is a cross-sectional schematic diagram which shows a cross section when a silicon carbide substrate is cut | disconnected in the thickness direction. It is a schematic diagram which shows the silicon carbide substrate in which the 1st etch pit was formed. It is a schematic diagram which shows the state which observes a silicon carbide substrate with an optical microscope. It is a schematic diagram which shows the silicon carbide substrate in which the 2nd etch pit was formed.

[Description of Embodiment of Present Invention]
First, embodiments of the present invention will be listed and described. The method for evaluating a silicon carbide substrate of the present application includes a step of preparing a silicon carbide substrate having a first main surface having an off angle with respect to the Si surface of greater than 0 ° and 4 ° or less and having a 4H crystal structure, After the first main surface is etched with the first gas containing atoms, the first main surface is oxidized to form first etch pits corresponding to threading screw dislocations, and an etching solution containing hydroxide Etching the first main surface on which the first etch pits are formed to enlarge the size of the first etch pits and forming the second etch pits corresponding to the threading edge dislocations; Observing the first main surface on which the pits and the second etch pits are formed, and evaluating a dislocation state of the silicon carbide substrate.

  In the silicon carbide substrate evaluation method of the present application, the first main surface of the silicon carbide substrate is first etched with the first gas, and then the first main surface is oxidized. Thereby, the 1st etch pit corresponding to a threading screw dislocation is formed in the 1st principal surface of a silicon carbide substrate. Next, the 1st main surface in which the 1st etch pit was formed is etched with the etching liquid containing a hydroxide. By doing so, the size of the first etch pit is enlarged and the second etch pit corresponding to the threading edge dislocation is formed. As a result, the etch pit corresponding to the threading screw dislocation is formed as a first etch pit having a large size, and the etch pit corresponding to the threading edge dislocation is formed as a second etch pit having a small size. By observing the first etch pit and the second etch pit having different sizes, it is possible to distinguish and evaluate the threading screw dislocation and the threading edge dislocation. For this reason, in a silicon carbide substrate having a first main surface with an off angle with respect to the Si surface of greater than 0 ° and less than or equal to 4 ° and having a crystal structure of 4H type, it is distinguished between threading screw dislocations and threading edge dislocations. Thus, the dislocation state can be evaluated.

  Thus, according to the silicon carbide substrate evaluation method of the present application, it is possible to provide a silicon carbide substrate evaluation method capable of easily grasping the dislocation state of the silicon carbide substrate.

  In the silicon carbide substrate evaluation method, in the step of forming the second etch pit, a third etch pit corresponding to the basal plane dislocation may be formed by etching with an etchant. In the step of evaluating the dislocation state of the silicon carbide substrate, the first main surface on which the first etch pit, the second etch pit, and the third etch pit are formed may be observed. By etching with the etchant, etch pits due to basal plane dislocations are formed as third etch pits having different shapes from the first and second etch pits. Therefore, the state of the dislocation can be evaluated by discriminating the threading screw dislocation, the threading edge dislocation, and the basal plane dislocation.

  In the silicon carbide substrate evaluation method, in the step of evaluating the dislocation state of the silicon carbide substrate, the first etch pit and the second etch pit are based on the area of the etch pit when the first main surface is viewed in plan. You may make it discriminate | determine from an etch pit. By doing so, it is possible to easily discriminate between threading screw dislocations and threading edge dislocations and evaluate the state of dislocations.

  In the silicon carbide substrate evaluation method, in the step of evaluating the dislocation state of the silicon carbide substrate, the first etch pit and the second etch pit are based on the inner diameter of the etch pit when the first main surface is viewed in plan. You may make it discriminate | determine from an etch pit. By doing so, it is possible to easily discriminate between threading screw dislocations and threading edge dislocations and evaluate the state of dislocations.

  In the silicon carbide substrate evaluation method, the etching with the first gas may be performed by etching the silicon carbide substrate at a temperature of 800 ° C. or higher and 1000 ° C. or lower. By doing in this way, the 1st etch pit corresponding to a threading screw dislocation can be easily formed in the 1st main surface of a silicon carbide substrate.

  In the method for evaluating a silicon carbide substrate, the first gas may be a chlorine gas. Chlorine gas is suitable as a gas for etching the silicon carbide substrate.

  In the silicon carbide substrate evaluation method, the temperature of the etching solution may be 400 ° C. or higher and 600 ° C. or lower. By doing so, the size of the first etch pit can be enlarged and the second etch pit corresponding to the threading edge dislocation can be easily formed.

  In the silicon carbide substrate evaluation method, the etching solution may be a potassium hydroxide melt. A potassium hydroxide melt is suitable as an etchant for etching a silicon carbide substrate.

  In the silicon carbide substrate evaluation method, the dislocation density of the silicon carbide substrate may be evaluated in the step of evaluating the dislocation state of the silicon carbide substrate. By doing in this way, the quality of a silicon carbide substrate can be evaluated.

[Details of the embodiment of the present invention]
Next, an embodiment of a silicon carbide substrate evaluation method of the present application will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  A procedure for evaluating a silicon carbide substrate by the method for evaluating a silicon carbide substrate in the present embodiment will be described. FIG. 1 is a flowchart schematically showing a method for evaluating a silicon carbide substrate. Referring to FIG. 1, in the method for evaluating a silicon carbide substrate in the present embodiment, a step of preparing a silicon carbide substrate is first performed as a step (S10).

  FIG. 2 is a schematic cross-sectional view showing a cross section when the silicon carbide substrate is cut in the thickness direction. An arrow D1 in FIG. 2 indicates the thickness direction. Referring to FIG. 2, silicon carbide substrate 10 is a silicon carbide substrate having a first main surface 11 and a second main surface 12 located on the opposite side to the side on which first main surface 11 is located. . As silicon carbide substrate 10, a silicon carbide substrate having a 4H crystal structure is prepared. As silicon carbide substrate 10, a silicon carbide substrate having first main surface 11 having an off angle greater than 0 ° and 4 ° or less with respect to the Si surface is used. The off orientation with respect to the Si surface of silicon carbide substrate 10 is, for example, the <11-20> direction.

As silicon carbide substrate 10, silicon carbide substrate 10 having an n-type conductivity may be used by including an n-type impurity such as nitrogen. Silicon carbide substrate 10 containing an n-type impurity such as nitrogen at a concentration of 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less, for example, may be used. The thickness in the thickness direction from the first main surface 11 to the second main surface 12 of the silicon carbide substrate 10 is, for example, 300 μm to 500 μm.

  Next, a step of forming a first etch pit is performed as a step (S20). Referring to FIG. 2, first, first main surface 11 of silicon carbide substrate 10 is etched with a first gas containing halogen atoms. By doing in this way, the silicon atom which comprises the silicon carbide in the silicon carbide substrate 10 can be selectively removed. Etching with the first gas is performed, for example, by placing the silicon carbide substrate 10 in an atmosphere containing the first gas and heating. For example, the etching is performed by heating to a temperature of 800 ° C. or higher and 1000 ° C. or lower. Moreover, as time to heat, it is about 15 minutes-30 minutes, for example. The rate at which silicon atoms are removed is increased in the portion where threading screw dislocations exist. Therefore, in the region corresponding to the threading screw dislocation, the depth at which silicon atoms are removed is larger than in other regions. In the present embodiment, chlorine gas can be employed as the first gas. As the first gas, hydrogen chloride gas, fluorine gas, or the like can be used in addition to the chlorine gas of the present embodiment. Among these, chlorine gas is suitable as a gas for etching the silicon carbide substrate 10. As the first gas, one kind may be used alone, or two or more kinds may be mixed and used. Etching may be performed in an atmosphere containing the first gas and the carrier gas. As the carrier gas, for example, nitrogen gas, argon gas, helium gas or the like can be used.

  Next, the first main surface 11 etched with the first gas is oxidized. The first main surface 11 is oxidized by the second gas containing oxygen atoms. By doing in this way, the carbon atom which comprises silicon carbide can further be removed from the etching area | region from which the silicon atom was removed. As described above, the depth at which silicon atoms are removed increases in the threading screw dislocation portion. Therefore, after the first main surface 11 is etched with the first gas, the first main surface 11 is oxidized with the second gas, whereby the first etch pits, which are recesses corresponding to threading screw dislocations, are formed on the first main surface 11. Formed. The oxidation with the second gas is performed, for example, by placing the silicon carbide substrate 10 in an atmosphere containing the second gas and heating it. For example, it is carried out by heating to a temperature of 800 ° C. or higher and 1000 ° C. or lower. In the present embodiment, oxygen gas can be employed as the second gas containing oxygen atoms.

  FIG. 3 is a schematic diagram showing a state of first main surface 11 of silicon carbide substrate 10 on which the first etch pits are formed. 3 is a diagram when silicon carbide substrate 10 is viewed in the direction of the arrow pointing in the direction D1 in FIG. Referring to FIG. 3, first etch pits 31 corresponding to threading screw dislocations are formed on first main surface 11 of silicon carbide substrate 10. The first etch pits 31 corresponding to threading screw dislocations are formed to have a circular shape when the first main surface 11 is viewed in plan.

Next, as a step (S30), a step of evaluating the dislocation state of the silicon carbide substrate 10 is performed by observing the first main surface 11 on which the first etch pits 31 are formed. By doing in this way, the state of the threading screw dislocation can be grasped on the first main surface 11 of the silicon carbide substrate 10. The evaluation of the dislocation state of the silicon carbide substrate 10 is performed, for example, by evaluating the dislocation density of the silicon carbide substrate. Evaluation of the dislocation state of the silicon carbide substrate 10 is performed by observing the first main surface 11 on which the first etch pits are formed with an optical microscope. More specifically, the dislocation density is evaluated using an image taken with an optical microscope. FIG. 4 is a schematic diagram showing a state in which silicon carbide substrate 10 is observed with an optical microscope. Referring to FIG. 4, the entire first main surface 11 of silicon carbide substrate 10 is imaged at an interval of, for example, 5 mm, and the number of first etch pits 31 is calculated from the obtained image to penetrate through silicon carbide substrate 10. The dislocation density of dislocations is evaluated. In FIG. 4, d ₁ and d ₂ are each 5 mm, for example.

  Next, a step of forming second etch pits is performed as a step (S40). Referring to FIGS. 2 and 3, first main surface 11 on which first etch pit 31 is formed is etched with an etchant containing hydroxide. More specifically, first main surface 11 is etched such that first main surface 11 of silicon carbide substrate 10 is immersed in an etchant. In the present embodiment, the etching solution is a potassium hydroxide melt. As the etching solution containing hydroxide, in addition to the melt of potassium hydroxide as in the present embodiment, a melt containing potassium hydroxide and sodium hydroxide, and a melt containing potassium hydroxide and sodium peroxide are used. A liquid or the like can be used. From the viewpoint of handleability, a melt of potassium hydroxide can be suitably used. The temperature of the etching solution is, for example, 400 ° C. or more and 600 ° C. or less. Further, the etching time is, for example, about 2 to 60 minutes. By doing in this way, while the magnitude | size of the 1st etch pit 31 can be expanded, the 2nd etch pit 32 corresponding to a threading edge dislocation can be formed easily.

  The first main surface 11 on which the first etch pits 31 are formed is etched with an etchant containing a hydroxide, so that the size of the first etch pits 31 is enlarged and the first edge corresponding to the threading edge dislocations. Two etch pits are formed. FIG. 5 is a schematic diagram showing the silicon carbide substrate 10 on which the second etch pits are formed. FIG. 5 is a view when silicon carbide substrate 10 is viewed in the direction of the arrow pointing in the direction D1 of FIG. Referring to FIG. 5, first etch pit 31 in which the size of the etch pit is enlarged and second etch pit 32 corresponding to the threading edge dislocation are formed on first main surface 11 of silicon carbide substrate 10. The The size of the second etch pit 32 is formed smaller than the size of the first etch pit. The second etch pits 32 corresponding to the threading edge dislocations are formed to have a circular shape when the first main surface 11 is viewed in plan. On the first main surface 11, etch pits corresponding to threading screw dislocations are formed as large first etch pits 31. Further, the etch pit corresponding to the threading edge dislocation is formed as the second etch pit 32 having a small size.

  Referring to FIG. 5, in the step of forming second etch pit 32, third etch pit 33 corresponding to the basal plane dislocation is formed by etching with an etchant containing hydroxide. The third etch pit 33 corresponding to the basal plane dislocation has a shell shape (elliptical shape). On the first main surface 11, etch pits corresponding to threading screw dislocations and threading edge dislocations are formed as first etch pits 31 and second etch pits 32 having a circular shape. Etch pits corresponding to basal plane dislocations are formed as third etch pits 33 having a shell-like (elliptical) shape.

  Next, as a step (S50), the dislocation state of the silicon carbide substrate 10 is observed by observing the first main surface 11 on which the first etch pit 31, the second etch pit 32, and the third etch pit 33 are formed. An evaluation step is performed. Evaluation of the dislocation state of silicon carbide substrate 10 is performed by evaluating the dislocation density of the silicon carbide substrate. Evaluation of the dislocation state of the silicon carbide substrate 10 is performed by observing the first main surface 11 on which the first etch pit 31, the second etch pit 32, and the third etch pit 33 are formed with an optical microscope. On the first main surface 11, first etch pits 31 and second etch pits 32 that are circular and have different sizes are observed. Further, a third etch pit 33 that is an etch pit having an elliptical shape is observed. The first etch pit 31 and the second etch pit 32 can be discriminated based on the size of the etch pit. Further, the third etch pit 33 can be determined by the shape. In the same manner as in the step (S30), the number of second etch pits 32 and third etch pits 33 is calculated from the obtained image, and the dislocation density of threading edge dislocations of silicon carbide substrate 10 and dislocations of basal plane dislocations. Density is evaluated. The number of first etch pits 31 may also be calculated to check consistency.

  In the present embodiment, the dislocation state of silicon carbide substrate 10 is evaluated by step (S30) and step (S50). By doing in this way, the 1st etch pit 31 and the 2nd etch pit 32 can be discriminate | determined more easily. Note that the dislocation state of silicon carbide substrate 10 may be evaluated only by the step (S50).

  Referring to FIG. 5, in the evaluation of the dislocation state of silicon carbide substrate 10, the first etch pit is based on the area of the etch pit having a circular shape when first main surface 11 is viewed in plan. 31 and the second etch pit 32 may be discriminated. If the area of the etch pit is equal to or larger than a predetermined reference value, it is determined as the first etch pit 31, and if it is smaller than the reference value, it is determined as the second etch pit. By doing so, it is possible to easily discriminate between threading screw dislocations and threading edge dislocations and evaluate the state of dislocations.

  Further, in the evaluation of the dislocation state of the silicon carbide substrate 10, the first etch pit 31 and the second etch pit 31 are based on the inner diameter of the etch pit having a circular shape when the first main surface 11 is viewed in plan. The etch pit 32 may be discriminated. Here, the inner diameter of the etch pit is the diameter of the inscribed circle of the etch pit when the first main surface 11 is viewed in plan. Further, based on the inner diameter includes a case based on an equivalent such as a radius. If the inner diameter of the etch pit is equal to or greater than a predetermined reference value, the first etch pit 31 is determined, and if the inner diameter is smaller than the reference value, the second etch pit 32 is determined. By doing so, it is possible to easily discriminate between threading screw dislocations and threading edge dislocations and evaluate the state of dislocations.

  In the evaluation method for silicon carbide substrate 10 of the present embodiment, first main surface 11 of silicon carbide substrate 10 is first etched with a first gas, and then the first main surface is oxidized. Thereby, first etch pits 31 corresponding to threading screw dislocations are formed on first main surface 11 of silicon carbide substrate 10. Next, the 1st main surface 11 in which the 1st etch pit 31 was formed is etched with the etching liquid containing a hydroxide. By doing so, the size of the first etch pit 31 is enlarged and the second etch pit 32 corresponding to the threading edge dislocation is formed. As a result, etch pits corresponding to threading screw dislocations are formed as first etch pits 31 having a large size, and etch pits corresponding to threading edge dislocations are formed as second etch pits 32 having a small size. By observing the first etch pit 31 and the second etch pit 32 having different sizes, it is possible to distinguish and evaluate the threading screw dislocation and the threading edge dislocation. For this reason, in silicon carbide substrate 10 having first main surface 11 having an off angle with respect to the Si surface of greater than 0 ° and 4 ° or less and having a crystal structure of 4H type, threading screw dislocation, threading edge dislocation, And the state of dislocation can be evaluated. Thus, the silicon carbide substrate evaluation method of the present embodiment is a silicon carbide substrate evaluation method by which the dislocation state of silicon carbide substrate 10 can be easily grasped.

  It should be understood that the embodiments disclosed herein are illustrative in all respects and are not restrictive in any aspect. The scope of the present invention is defined by the terms of the claims, rather than the meaning described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The silicon carbide substrate evaluation method of the present application is particularly advantageously applied to a silicon carbide substrate evaluation method in which it is required to easily grasp the dislocation state of the silicon carbide substrate.

DESCRIPTION OF SYMBOLS 10 Silicon carbide substrate 11 1st main surface 12 2nd main surface 31 1st etch pit 32 2nd etch pit 33 3rd etch pit

Claims (9)

Providing a silicon carbide substrate having a first main surface having an off angle with respect to the Si surface of greater than 0 ° and 4 ° or less and having a crystal structure of 4H type;
Forming a first etch pit corresponding to a threading screw dislocation by etching the first main surface with a first gas containing a halogen atom and then oxidizing the first main surface;
The first main surface on which the first etch pits are formed is etched with an etchant containing hydroxide to increase the size of the first etch pits, and the second corresponding to penetrating edge dislocations. Forming etch pits;
Evaluating the dislocation state of the silicon carbide substrate by observing the first main surface on which the first etch pit and the second etch pit are formed. In the step of forming the second etch pit, a third etch pit corresponding to a basal plane dislocation is formed by etching with the etchant,
2. The step of evaluating the dislocation state of the silicon carbide substrate, wherein the first main surface on which the first etch pit, the second etch pit, and the third etch pit are formed is observed. Evaluation method of silicon carbide substrate.   In the step of evaluating the dislocation state of the silicon carbide substrate, the first etch pit and the second etch pit are discriminated based on the area of the etch pit when the first main surface is viewed in plan. A method for evaluating a silicon carbide substrate according to claim 1 or 2.   In the step of evaluating the dislocation state of the silicon carbide substrate, the first etch pit and the second etch pit are discriminated based on the inner diameter of the etch pit when the first main surface is viewed in plan. The method for evaluating a silicon carbide substrate according to any one of claims 1 to 3.   5. The method for evaluating a silicon carbide substrate according to claim 1, wherein the etching with the first gas is performed by etching the silicon carbide substrate at a temperature of 800 ° C. or higher and 1000 ° C. or lower. .   The method for evaluating a silicon carbide substrate according to claim 1, wherein the first gas is chlorine gas.   The method for evaluating a silicon carbide substrate according to claim 1, wherein a temperature of the etching solution is 400 ° C. or more and 600 ° C. or less.   The method for evaluating a silicon carbide substrate according to claim 1, wherein the etching solution is a melt of potassium hydroxide.   The method for evaluating a silicon carbide substrate according to claim 1, wherein the dislocation density of the silicon carbide substrate is evaluated in the step of evaluating the dislocation state of the silicon carbide substrate.

Images