The present disclosure relates to a silicon carbide epitaxial substrate. This application claims priority based on Japanese Patent Application No. 2020-125075 filed on Jul. 22, 2020. The entire contents of the Japanese patent application are incorporated herein by reference.
Japanese Unexamined Patent Application Publication No. 2019-46855 (PTL1) describes a method of forming a silicon carbide epitaxial film using CVD (Chemical Vapor Deposition).
A silicon carbide epitaxial substrate according to the present disclosure includes a silicon carbide substrate, a silicon carbide epitaxial layer and a backside surface. The silicon carbide epitaxial layer is disposed on the silicon carbide substrate. The backside surface is disposed opposite to the silicon carbide epitaxial layer with respect to the silicon carbide substrate. The backside surface includes a central region having a radius equal to ⅔ of a radius of the backside surface and surrounded by a circle centered at a center of the backside surface and an outer circumferential region surrounding the central region. When an area density of a first protrusion present in the central region is denoted by Xa, an area density of a second protrusion present in the central region is denoted by Xb, an area density of a third protrusion present in the central region is denoted by Xc, an area density of a fourth protrusion present in the outer circumferential region is denoted by Ya, an area density of a fifth protrusion present in the outer circumferential region is denoted by Yb, and an area density of a sixth protrusion present in the outer circumferential region is denoted by Yc, as viewed in a thickness direction of the silicon carbide substrate, the first protrusion and the fourth protrusion each have an area of 100 μm2 or more and less than 1,000 μm2, the second protrusion and the fifth protrusion each have an area of 1,000 μm2 or more and less than 5,000 μm2, and the third protrusion and the sixth protrusion each have an area of 5,000 μm2 or more. The backside surface has a diameter of 100 mm or more, a value determined by dividing Xa by (Xa+Ya) is 0.3 or more and 0.5 or less, Xc is 10.0/cm2 or less, and Yc is 12.0/cm2 or less.
An object of the present disclosure is to provide a silicon carbide epitaxial substrate capable of suppressing adsorption failure.
According to the present disclosure, it is possible to provide a silicon carbide epitaxial substrate capable of suppressing adsorption failure.
First, an outline of embodiments of the present disclosure will be described. Regarding crystallographic indications in the present specification, an individual orientation is represented by [ ], a group orientation is represented by < >, an individual plane is represented by ( ), and a group plane is represented by { }. A negative crystallographic index is usually indicated by putting “−” (bar) above a numeral but is indicated by putting the negative sign before the numeral in the present specification.
When there are a plurality of first protrusions 1 and a plurality of fourth protrusions 4, the area of each of first protrusions 1 and fourth protrusions 4 being 100 μm2 or more and less than 1,000 μm2 means that the area of each of the plurality of first protrusions 1 is 100 μm2 or more and less than 1,000 μm2, and the area of each of the plurality of fourth protrusions 4 is 100 μm2 or more and less than 1,000 μm2. Similarly, when there are a plurality of second protrusions 2 and a plurality of fifth protrusions 5, the area of each of second protrusions 2 and fifth protrusions 5 being 1,000 μm2 or more and less than 5,000 μm2 means that the area of each of the plurality of second protrusions 2 is 1,000 μm2 or more and less than 5,000 μm2 and the area of each of the plurality of fifth protrusions 5 is 1,000 μm2 or more and less than 5,000 μm2. Similarly, when there are a plurality of third protrusions 3 and a plurality of sixth protrusions 6, the area of each of third protrusions 3 and sixth protrusions 6 being 5,000 μm2 or more means that the area of each of the plurality of third protrusions 3 is 5,000 μm2 or more and the area of each of the plurality of sixth protrusions 6 is 5,000 μm2 or more.
Hereinafter, embodiments of the present disclosure will be described in detail. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.
(Silicon Carbide Epitaxial Substrate)
First silicon carbide epitaxial layer 20 is disposed on silicon carbide substrate 10. First silicon carbide epitaxial layer 20 is in contact with silicon carbide substrate 10 at first main surface 17. First main surface 17 is an interface between silicon carbide substrate and first silicon carbide epitaxial layer 20. First silicon carbide epitaxial layer 20 forms a surface of silicon carbide epitaxial substrate 100 (third main surface 21). When a silicon carbide semiconductor device (not shown) is manufactured using silicon carbide epitaxial substrate 100, a drift region (not shown), a base region (not shown), a source region (not shown), a gate electrode (not shown), or a gate insulating film (not shown) may be formed on third main surface 21.
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Outer circumferential edge 15 has, for example, an orientation flat 13 and an arc-shaped portion 14. Orientation flat 13 extends along a first direction 101. As shown in
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First direction 101 is, for example, a <11-20> direction. First direction 101 may be, for example, a [11-20] direction. First direction 101 may be a direction obtained by projecting the <11-20> direction onto first main surface 17. In other words, first direction 101 may be, for example, a direction including a <11-20> direction component.
Second direction 102 is, for example, a <1-100> direction. Second direction 102 may be, for example, a [1-100] direction. Second direction 102 may be, for example, a direction obtained by projecting the <1-100> direction onto first main surface 17. In other words, second direction 102 may be, for example, a direction including a <1-100> direction component.
First main surface 17 may be a {0001} plane or a surface inclined with respect to the {0001} plane. When first main surface 17 is inclined with respect to the {0001} plane, an angle of inclination (off angle) with respect to the {0001} plane is from 2° to 6°, for example. When first main surface 17 is inclined with respect to the {0001} plane, the inclination direction (off direction) of first main surface 17 is, for example, the <11-20>direction.
The diameter (maximum diameter) of backside surface 30 is 100 mm (4 inches) or more. The diameter of backside surface 30 may be 125 mm (5 inches) or more, or 150 mm (6 inches) or more. The upper limit of the diameter of backside surface 30 is not particularly limited, but may be, for example, 200 mm (8 inches) or less. The diameter (maximum diameter) of backside surface 30 is the longest linear distance between two different points on outer circumferential edge 15. The diameter of backside surface 30 may be a diameter of outer circumferential edge 15 (i.e., arc-shaped portion 14) excluding orientation flat 13.
As used herein, 4 inches refers to 100 mm or 101.6 mm (4 inches×25.4 mm/inch). Five inches refers to 125 mm or 127.0 mm (5 inches×25.4 mm/inch). 6 inches refers to 150 mm or 152.4 mm (6 inches×25.4 mm/inch). 8 inches refers to 200 mm or 203.2 mm (8 inches×25.4 mm/inch).
The polytype of silicon carbide constituting silicon carbide substrate 10 is, for example, 4H. Similarly, the polytype of silicon carbide constituting first silicon carbide epitaxial layer 20 is, for example, 4H. Similarly, the polytype of silicon carbide constituting second silicon carbide epitaxial layer 40 is, for example, 4H. The thickness of silicon carbide substrate 10 is, for example, from 350 μm to 500 μm. The thickness of first silicon carbide epitaxial layer 20 may be less than the thickness of silicon carbide substrate 10. The thickness of second silicon carbide epitaxial layer 40 may be less than the thickness of silicon carbide substrate 10.
Silicon carbide substrate 10 contains an n-type impurity, for example, such as nitrogen (N). The conductivity type of silicon carbide substrate 10 is, for example, n-type. First silicon carbide epitaxial layer 20 contains an n-type impurity, for example, such as nitrogen. The conductivity type of first silicon carbide epitaxial layer 20 is, for example, n-type. The concentration of the n-type impurity included in first silicon carbide epitaxial layer 20 may be lower than the concentration of the n-type impurity included in silicon carbide substrate 10. Second silicon carbide epitaxial layer 40 contains an n-type impurity such as nitrogen. The conductivity type of second silicon carbide epitaxial layer 40 is, for example, n-type. The concentration of the n-type impurity included in second silicon carbide epitaxial layer 40 may be lower than the concentration of the n-type impurity included in silicon carbide substrate 10.
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In silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, when the area density of first protrusion 1 present in central region 32 is denoted by Xa, the area density of second protrusion 2 present in central region 32 is denoted by Xb, the area density of third protrusion 3 present in central region 32 is denoted by Xc, the area density of fourth protrusion 4 present in outer circumferential region 31 is denoted by Ya, the area density of fifth protrusion 5 present in outer circumferential region 31 is denoted by Yb, and the area density of sixth protrusion 6 present in outer circumferential region 31 is denoted by Yc, a value determined by dividing Xa by (Xa+Ya) is 0.3 or more and 0.5 or less, Xc is 10.0/cm2 or less, and Yc is 12.0/cm2 or less.
In silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, Yb may be, for example, 30.0/cm2 or less. Yb may be, for example, 20.0/cm2 or less, or 10.0/cm2 or less. The lower limit of Yb is not particularly limited, and may be, for example, 0.1/cm2 or more, or 0.5/cm2 or more.
According to silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, Xc may be, for example, 3.0/cm2 or less. Xc may be, for example, 2.0/cm2 or less, or 1.0/cm2 or less. The lower limit of Xc is not particularly limited, and may be, for example, 0.01/cm2 or more, or 0.05/cm2 or more.
According to silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, Xb may be, for example, 20.0/cm2 or less. Xb may be, for example, 16.0/cm2 or less, or 8.0/cm2 or less. The lower limit of Xb is not particularly limited, and may be, for example, 0.1/cm2 or more, or 0.5/cm2 or more.
According to silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, Yc may be 4.0/cm2 or less. Yc may be, for example, 3.0/cm2 or less, or 2.0/cm2 or less. The lower limit of Yc is not particularly limited, and may be, for example, 0.01/cm2 or more, or 0.05/cm2 or more.
According to silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, Xa may be, for example, 800.0/cm2 or less or 400.0/cm2 or less. The lower limit of Xa is not particularly limited, and may be, for example, 0.1/cm2 or more, or 1/cm2 or more.
According to silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, Ya may be, for example, 600.0/cm2 or less or 400.0/cm2 or less. The lower limit of Ya is not particularly limited, and may be, for example, 0.1/cm2 or more, or 1/cm2 or more.
According to silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, a value determined by dividing Xa by (Xa+Ya) may be 0.45 or less or 0.4 or less.
(Method of Measuring Protrusion)
Next, a method of measuring the protrusion will be described. The protrusion can be identified by observing backside surface 30 of silicon carbide epitaxial substrate 100 using, for example, a defect inspection apparatus equipped with a confocal differential interference microscope. For example, WASAVI series “SICA 6X” manufactured by Lasertec Corporation can be used as a defect inspection apparatus including a confocal differential interference microscope. The magnification of the objective lens is 10 times, for example.
The protrusion is detected as a defect by SICA. The area of the detected defect is the area of the protrusion. In the case where a triangular defect or the like connected to the projection portion is involved, the area of the triangular defect is also included. When the protrusion is specified from the defect detected by the SICA, the measurement sensitivity of the SICA is adjusted in advance so that the protrusion can be detected. The protrusion is defined in consideration of typical planar shape, dimension, and the like of the protrusion. Based on the observed image, the protrusion is identified. “Thresh S” which is an index of the measurement sensitivity of the SICA is set to 40, for example.
A confocal differential interference microscope image of entire backside surface 30 is taken while moving silicon carbide epitaxial substrate 100 in a direction parallel to the surface of silicon carbide epitaxial substrate 100. In the acquired confocal differential interference microscope image, first protrusion 1, second protrusion 2, third protrusion 3, fourth protrusion 4, fifth protrusion 5, and sixth protrusion 6 are observed. In the acquired confocal differential interference contrast microscope image, the number of each of first protrusion 1, second protrusion 2, third protrusion 3, fourth protrusion 4, fifth protrusion 5, and sixth protrusion 6 is obtained. The values obtained by dividing the numbers of first protrusion 1, second protrusion 2, and third protrusion 3 by the measurement area in central region 32 are taken as the area densities of first protrusion 1, second protrusion 2, and third protrusion 3, respectively. Values obtained by dividing the numbers of fourth protrusion 4, fifth protrusion 5, and sixth protrusion 6 by the measurement area in outer circumferential region 31 are defined as the area densities of fourth protrusion 4, fifth protrusion 5, and sixth protrusion 6, respectively. Note that edge region 33 within 3 mm from outer circumferential edge 15 is excluded from the measurement region of the protrusion (edge exclusion).
(Method of Manufacturing Silicon Carbide Epitaxial Substrate)
Next, a method of manufacturing silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure will be described.
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Next, silicon carbide substrate 10 is prepared. For example, a silicon carbide single crystal having a polytype 4H is produced by a sublimation method. Next, the silicon carbide single crystal is sliced by, for example, a wire saw. Silicon carbide substrate 10 contains an n-type impurity such as nitrogen. The conductivity type of silicon carbide substrate 10 is, for example, n-type. Next, mechanical polishing, chemical mechanical polishing, and cleaning are performed on silicon carbide substrate 10. Thus, silicon carbide substrate 10 is prepared.
Next, silicon carbide substrate 10 is placed on susceptor 50.
By repeating the rise and fall of the temperature in the CVD furnace, deflection occurs in the carbon member constituting the inner wall. As a result, the deposition material adhering to the inner wall falls onto susceptor 50. The deposition material falling on susceptor 50 is referred to as a downfall. The downfall is generally particulate. The downfall is, for example, polycrystalline silicon carbide or carbon. The diameter of the downfall is, for example, in the range of 0.1 μm to 1 mm.
The downfall falls, for example, onto top surface 59 of susceptor 50. The downfall that has fallen onto top surface 59 of susceptor 50 moves to bottom surface 61 of silicon carbide substrate placing member 60 of susceptor 50. If there is a downfall on bottom surface 61 of susceptor 50, the downfall will adhere to backside surface 30 of silicon carbide substrate 10 when silicon carbide substrate 10 is placed on bottom surface 61 of silicon carbide substrate placing member 60.
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Next, effects of silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure will be described.
A process of manufacturing a silicon carbide semiconductor device using silicon carbide epitaxial substrate 100 generally includes an exposure step and an inspection step. During these steps, backside surface 30 of silicon carbide epitaxial substrate 100 is adsorbed to a chuck. As the chuck, a vacuum chuck, an electrostatic chuck or the like is generally used. For example, adsorption failure of silicon carbide epitaxial substrate 100 to the chuck in the exposure step causes exposure failure. As a result of diligent studies on the cause of adsorption failure of silicon carbide epitaxial substrate 100 to the chuck, the inventors have obtained the following findings.
First, the inventors focused on the size and position of the protrusions present on backside surface 30 of silicon carbide epitaxial substrate 100. Specifically, the protrusions were classified into six types (first protrusion 1, second protrusion 2, third protrusion 3, fourth protrusion 4, fifth protrusion 5, and sixth protrusion 6) by focusing on the areas of the protrusions viewed in a direction perpendicular to backside surface 30 and the regions (central region or outer circumferential region) of the backside surface in which the protrusions were present, and the relationship between the area density of the six types of protrusions and the adsorption failure was investigated. As a result, it has been found that the occurrence of adsorption failure is significantly suppressed by controlling the relationship between the six types of protrusions as follows.
In silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, when the area density of first protrusion 1 in central region 32 is denoted by Xa, the area density of second protrusion 2 in central region 32 is denoted by Xb, the area density of third protrusion 3 in central region 32 is denoted by Xc, the area density of fourth protrusion 4 in outer circumferential region 31 is denoted by Ya, the area density of fifth protrusion 5 in outer circumferential region 31 is denoted by Yb, and the area density of sixth protrusion 6 in outer circumferential region 31 is denoted by Yc, as viewed in the thickness direction of silicon carbide substrate 10, first protrusion 1 and fourth protrusion 4 each have an area of 100 μm2 or more and less than 1,000 μm2, second protrusion 2 and fifth protrusion 5 each have an area of 1,000 μm2 or more and less than 5,000 μm2, and third protrusion 3 and sixth protrusion 6 each have an area of 5,000 μm2 or more. Backside surface 30 has a diameter of 100 mm or more, a value determined by dividing Xa by (Xa+Ya) is 0.3 or more and 0.5 or less, Xc is 10.0/cm2 or less, and Yc is 12.0/cm2 or less. Accordingly, adsorption failure of silicon carbide epitaxial substrate 100 can be suppressed.
In silicon carbide epitaxial substrate 100 according to the embodiment of the present disclosure, a value determined by dividing Xa by (Xa+Ya) may be 0.4 or less. Accordingly, the adsorption failure of silicon carbide epitaxial substrate 100 can be further suppressed.
(Sample Preparation)
First, seven silicon carbide epitaxial substrates 100 having different values determined by dividing Xa by (Xa+Ya) were prepared. Silicon carbide epitaxial substrates 100 of samples 1 to 5 are examples. Silicon carbide epitaxial substrates 100 of samples 6 and 7 are comparative examples. In silicon carbide epitaxial substrates 100 of Samples 1 to 5, the value determined by dividing Xa by (Xa+Ya) was set to 0.3 or more and 0.5 or less. In silicon carbide epitaxial substrates 100 of Samples 6 and 7, the value determined by dividing Xa by (Xa+Ya) was set to be more than 0.5.
(Experimental Method)
Next, backside surface 30 of silicon carbide epitaxial substrate 100 of Samples 1 to 7 was adsorbed to a vacuum chuck (adsorption step). In the adsorption step, it was confirmed whether or not an adsorption error occurred. Next, the exposure step was performed on the samples in which no adsorption error occurred. In the exposure step, it was confirmed whether or not exposure failure occurred. It is considered that the exposure failure occurs when the adsorption is not sufficiently good although the adsorption error does not occur in the adsorption step.
(Experimental Results)
Table 1 shows the evaluation results of silicon carbide substrate 10 of Samples 1 to 7. When no adsorption error occurred in the adsorption step and no exposure failure occurred in the exposure step, the evaluation result was evaluated as “A”. When no adsorption error occurred but exposure failure occurred in the exposure step, the evaluation result was “B”. When an adsorption error occurred in the adsorption step and the exposure step could not be performed, the evaluation result was “C”.
As shown in Table 1, when the value determined by dividing Xa by (Xa+Ya) was 0.3 or more and 0.5 or less, the evaluation result was “A” or “B”. When the value determined by dividing Xa by (Xa+Ya) was 0.3 to 0.4, the evaluation result was “A”. On the other hand, when the value determined by dividing Xa by (Xa+Ya) was more than 0.5, the evaluation result was “C”. From the above results, it was confirmed that the occurrence of the adsorption failure can be suppressed by setting the value determined by dividing Xa by (Xa+Ya) to 0.3 or more and 0.5 or less.
It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is defined not by the above-described embodiments and examples but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.
Number | Date | Country | Kind |
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2020-125075 | Jul 2020 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2021/024523 | 6/29/2021 | WO |