JP6635579B2 - SiC epitaxial wafer - Google Patents

Description

The present invention also relates to the SiC epitaxial web leaves.

  Silicon carbide (SiC) has properties such as a dielectric breakdown electric field that is one digit larger than silicon (Si), a band gap three times larger, and a thermal conductivity about three times higher than that of silicon (Si). Applications to devices, high-frequency devices, high-temperature operating devices, and the like are expected.

  In order to promote the practical use of SiC devices, it is essential to establish a high-quality crystal growth technology and a high-quality epitaxial growth technology.

  An SiC device is formed by subjecting a device to a SiC single crystal substrate obtained by processing a bulk single crystal of SiC grown by a sublimation recrystallization method or the like by a chemical vapor deposition (CVD) method or the like. It is generally manufactured using a SiC epitaxial wafer on which a SiC epitaxial film (layer) serving as a region is grown.

  More specifically, 4H is grown by step flow growth (lateral growth from atomic steps) on a SiC single crystal substrate whose growth surface is a plane having an off angle in the <11-20> direction from the (0001) plane. It is common to grow an SiC epitaxial film.

In a SiC epitaxial wafer, a defect (triangular defect) that looks like a triangle when viewed from the epi surface side is known.
The triangular defects are formed in a direction such that the vertices of the triangle and the opposite side (bottom side) are arranged in order from upstream to downstream along the step flow growth direction (<11-20> direction).
The triangular defect originates from a foreign substance (particle) existing on the SiC single crystal substrate before the epitaxial growth, from which a 3C polymorph layer extends along the off-angle of the substrate and is exposed to the epi surface (non-crystal). Patent Document 1).

  Further, in the SiC epitaxial wafer, a rod-like defect (a carrot-like defect) that is long in the step flow growth direction when viewed from the epi surface side is known. In a carrot-like defect, it is said that the starting point is not a foreign substance (particle) but a substrate dislocation (a threading screw dislocation (TSD) or a basal plane dislocation (BPD)) or a scratch on the substrate (see Non-Patent Document 2). ). In the confocal microscope image, there is a long dent at the center from the upstream side to the downstream side of the step flow.

JP 2013-023399 A

C. Hallin et al., Diamond and Related Materials 6 (1997) 1297-1300 J. Hassan et al., Journal of Crystal Growth 312 (2010) 1828-1837

  As described above, the triangular defect is composed of a 3C polymorph. Since the electrical characteristics of the 3C polymorph are different from those of the 4H polymorph, if a triangular defect is present in the 4H-SiC epitaxial film, that portion cannot be used as a device. Therefore, the triangular defect is known as a killer defect, and it is desirable that the area occupied by the triangular defect as the killer defect (hereinafter, sometimes referred to as a device killer region) is as small as possible.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a SiC epitaxial web Ha device killer region is reduced.

  The present inventor has conducted intensive studies in order to solve the above-described problems. As a result, under specific epitaxial growth conditions, the present inventors have found that the area expansion of triangular defects exposed on the epi surface can be suppressed. , A linear defect). As a result, the device killer region on the epi surface can be significantly reduced.

  The present invention employs the following means in order to solve the above problems.

  An SiC epitaxial wafer according to one embodiment of the present invention is a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate having an off-angle, and is a linear type with respect to the number of triangular defects included in the SiC epitaxial layer. The ratio of the number of defects is 0.2 to 2.

  In the SiC epitaxial wafer, a ratio of the number of linear defects to the number of triangular defects may be 0.7 to 1.5.

In the SiC epitaxial wafer, the triangular defect density may be 0.8 defects / cm ² or less.

  A method for manufacturing a SiC epitaxial wafer according to one embodiment of the present invention is a method for manufacturing a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate having an off-angle. The method includes an epitaxial growth step of growing an epitaxial layer. In the epitaxial growth step, a growth temperature is set to 1640 ° C. or more and a C / Si ratio is set to 1 or less.

  In the method for manufacturing a SiC epitaxial wafer, the C / Si ratio may be 0.96 or less.

According to the SiC epitaxial wafer of the present invention, an SiC epitaxial wafer having a reduced device killer region can be provided.
ADVANTAGE OF THE INVENTION According to the manufacturing method of the SiC epitaxial wafer of this invention, the manufacturing method of the SiC epitaxial wafer in which the device killer area | region was reduced can be provided.

(A) is a SICA image of a linear defect obtained by the surface inspection apparatus, and (b) is a SICA image of a carrot-like defect. 5 is a STEM image of a linear defect obtained by a scanning transmission electron microscope. (A) is a schematic diagram of a cross section of the SiC epitaxial wafer near a linear defect, and (b) is a schematic diagram of a cross section of the SiC epitaxial wafer near a carrot-like defect. 5A and 5B are a STEM image and a diffraction image of a cross section near a tail portion of a linear defect.

  Hereinafter, the configuration of a SiC epitaxial wafer to which the present invention is applied and a method of manufacturing the same will be described with reference to the drawings. In the drawings used in the following description, a characteristic part may be enlarged for convenience in order to make the characteristic easy to understand, and the dimensional ratio of each component is not necessarily the same as the actual one. . Further, the materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately modified and implemented within a range in which the effects of the present invention are exhibited. .

(Linear defect)
FIG. 1A shows an image of a linear defect (hereinafter, referred to as a SICA image) obtained by a confocal microscope (SICA6X, manufactured by Lasertec Inc.) which is a surface inspection apparatus using a confocal differential interference optical system. . FIG. 1B shows an SICA image of a carrot-like defect for comparison.
The SICA image of a linear defect is similar to the SICA image of a carrot-like defect in that it has an elongated shape, but the SICA image of a carrot-like defect has a long groove extending from the upstream side to the downstream side at the center in the longitudinal direction. On the other hand, they differ in that they do not have a similar long groove. However, the SICA image of the linear defect also has a recess at the downstream end of the step flow (hereinafter, sometimes referred to as a tail).

  The confocal microscope that obtained the SICA image shown in FIG. 1 has less luminance unevenness than the currently used confocal microscope, and has a performance in which the depth sensitivity has been improved from several nm to 1 nm or less from the conventional one. As a result of detailed observation at high magnification using such high resolution, the existence of a linear defect different from the SICA image of the carrot-like defect as shown in FIG. 1 was found. Conventionally, defects that have been recognized as carrot-shaped defects are considered to include those found to be linear defects that we have found this time.

In the SICA image of the linear defect shown in FIG. 1A, the dent that appears in the tail portion has a width of about 1 μm and a length of about 6 μm. The depth is about 25 nm from the measurement by AFM (atomic force microscope) (Nanoscope D3100, manufactured by Veeco).
On the other hand, in the SICA image of the carrot-like defect in FIG. 1B, the width of the groove at the center was 0.5 μm or less. The depth is about 20 nm from the measurement by AFM.

Electrical properties of linear defects and carrot-like defects were evaluated using Conductive AFM (Agilent Technologies, Agilent 5500).
In the case of the carrot-like defect, no current was measured in the tail portion, the head portion (upstream end of the step flow), and neither the tail portion nor the head portion.
On the other hand, in the case of the linear defect, the current was not measured in the head portion in both the forward direction and the backward direction, but the current was measured in the tail portion in the reverse direction.
As described above, the electrical characteristics of a linear defect are completely different from those of a carrot-like defect.

FIG. 2 shows a STEM image of a linear defect obtained by using a scanning transmission electron microscope (STEM: HF-2200, manufactured by Hitachi High-Technologies Corporation).
FIG. 2A is a STEM image viewed from above, and FIG. 2B is a STEM image of a cross section of the wafer near the head.
In each of the STEM images of FIG. 2A and FIG. 2B, a foreign substance (particle) is visible.
In the STEM image shown in FIG. 2B, the position of the foreign matter in the depth direction (the deepest position) is 10.9 μm from the epi surface, which substantially matches the average thickness of the SiC epitaxial film of 10.1 μm. Therefore, it can be said that the foreign matter exists at the interface between the SiC single crystal substrate and the SiC epitaxial film.
In the STEM image shown in FIG. 2B, dislocations extending from the foreign matter toward the epi surface are visible.

  From the STEM image of the linear defect in FIG. 2, it can be seen that the linear defect is a defect originating from a foreign substance. This point is a point common to the triangular defect, whereas the starting point is different from a dislocation of the substrate (a threading screw dislocation (TSD) or a basal plane dislocation (BPD) or a carrot-like defect which is a scratch on the substrate). is there.

  Based on the above STEM image, FIG. 3A shows a schematic diagram of a cross section of the SiC epitaxial wafer near a linear defect. FIG. 3B is a schematic view of a cross section of the SiC epitaxial wafer near the carrot-like defect.

FIG. 4 shows a STEM image of a cross section near the tail portion of the linear defect.
4A to 4C show three regions divided from the epi surface in the depth direction in the tail portion, and show diffraction images obtained for each region. On the other hand, D shown in FIG. 4 indicates a normal region, and indicates a diffraction image obtained for this region.

From the diffraction image of the region D, it can be seen that the portion having no defect is made of 4H—SiC.
On the other hand, it can be seen from the diffraction images of the three regions A to C of the tail portion that the tail portion is made of 3C-SiC. This point is also common with the triangular defect.

  As described above, a linear defect is one in which a 3C polymorph layer extends from the starting point of a foreign substance (particle) along the off-angle of the substrate and is exposed on the epi surface. This point is common to the triangular defect. However, the linear defects extend straight and are exposed on the epi surface without increasing the area together with the epitaxial growth unlike the triangular defects.

(SiC epitaxial wafer)
An SiC epitaxial wafer according to one embodiment of the present invention is a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate having an off angle, and includes a straight line corresponding to the number of triangular defects included in the SiC epitaxial layer. The ratio of the number of mold defects is 0.2 to 2.

  The ratio of the number of linear defects to the number of triangular defects may be 0.7 to 1.5.

The triangular defect density is preferably 0.8 / cm ² or less, more preferably 0.6 / cm ² or less, and even more preferably 0.4 / cm ² or less.

(Method of manufacturing SiC epitaxial wafer)
The method for manufacturing a SiC epitaxial wafer according to one embodiment of the present invention is a method for manufacturing a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate having an off-angle. An epitaxial growth step of growing an epitaxial layer is performed, wherein the growth temperature is set to 1640 ° C. or more and the C / Si ratio is set to 1 or less in the epitaxial growth step.

  If a foreign substance is present on the SiC single crystal substrate before the epitaxial growth, a triangular defect may grow with the foreign substance as a starting point along with the epitaxial growth. Since the triangular defect has a polymorphism of 3C and a different electrical characteristic from a normal SiC epitaxial film having a polymorph of 4H, a device including the triangular defect is a defective product. The larger the 3C polymorphic region, the higher the percentage of the device containing the 3C polymorphic region. Therefore, it is desirable to reduce this region. Reduction of this region contributes to improvement of the effective area and the yield of the device.

The present inventor has found that by combining the growth temperature condition and the C / Si ratio condition within a predetermined range, the area expansion of the 3C polymorphic region can be suppressed. That is, the epitaxial growth conditions that can reduce the rate at which the 3C polymorph becomes a triangular defect, in other words, the epitaxial growth conditions that increase the rate at which the 3C polymorph does not expand to a triangular defect but remains a linear defect. I found it. The ratio between the number of linear defects and the number of triangular defects is used as a new index.
According to the present invention, it can be said that the device-killer region is reduced by minimizing a triangular defect depending on the growth condition to a linear shape, that is, by changing the triangular defect shape to a linear shape. Therefore, the area of the polymorph (3C) exposed on the epi surface which deteriorates the device characteristics can be minimized, and the yield of SiC semiconductor devices can be improved.

The found epitaxial growth conditions are that the growth temperature is 1640 ° C. or more and 1680 ° C. or less, and the C / Si ratio is 0.90 or more and 1 or less.
By performing the epitaxial growth process under these conditions, a SiC epitaxial wafer having a ratio of the number of linear defects to the number of triangular defects in the SiC epitaxial layer of 0.2 to 2 can be manufactured.
When the C / Si ratio is less than 0.9, the growth surface is in a condition of excessive Si, which makes it difficult to obtain the flatness of the surface, and the distribution of the carrier concentration is deteriorated. Is not desirable for large wafers.
At this time, the triangular defect density is 0.8 / cm ² or less.
The growth temperature can be 1640 ° C. or higher and 1660 ° C. or lower.

When the growth temperature is 1640 ° C. or more and 1680 ° C. or less and the C / Si ratio is 0.90 or more and 0.96 or less, SiC having a ratio of the number of linear defects to the number of triangular defects of 0.7 to 2 is used. Epitaxial wafers can be manufactured.
At this time, the triangular defect density is 0.6 / cm ² or less.
The growth temperature can be 1640 ° C. or higher and 1660 ° C. or lower.

When the growth temperature is 1640 ° C. or more and 1680 ° C. or less and the C / Si ratio is 0.90 or more and 0.93 or less, the ratio of the number of linear defects to the number of triangular defects is 1.0 to 2.0. A certain SiC epitaxial wafer can be manufactured.
At this time, the triangular defect density is 0.4 / cm ² or less.
The growth temperature can be 1640 ° C. or higher and 1660 ° C. or lower.

  Hereinafter, examples of the present invention will be described, but the present invention is not limited to these examples.

(Example 1)
As the SiC single crystal substrate, a 4 inch 4H-SiC single crystal substrate having an off angle of 4 degrees in the <11-20> direction with respect to the (0001) Si plane was used.
After performing a known polishing process on the SiC single crystal substrate, the substrate was set in a hot-wall planetary-type wafer self-revolution type CVD apparatus, and a substrate surface cleaning (etching) process using hydrogen gas was performed.
Next, while using silane and propane as source gases and supplying hydrogen as a carrier gas, a SiC epitaxial growth step was performed under the conditions of a growth temperature of 1650 ° C. and a C / Si ratio of 0.93, and a 9 μm-thick SiC epitaxial growth step was performed. An epitaxial layer was formed on a SiC single crystal substrate to obtain a SiC epitaxial wafer.

For this SiC epitaxial wafer, an SICA image was obtained using a confocal microscope (manufactured by Lasertec Corporation, SICA6X), and the number of linear defects and triangular defects was counted. The measurement range was the entire wafer except for 3 mm from the outer peripheral edge. The ratio of the number of linear defects to the number of triangular defects was calculated based on the measured numbers of linear defects and triangular defects.
The number of linear defects was 38 and the number of triangular defects was 28. Therefore, the ratio of the number of linear defects to the number of triangular defects was 1.36.

Here, in the SICA image, those that extend linearly and whose width of the tail portion is about the same as the width of the head portion but smaller than that are classified as linear defects. On the other hand, in the SICA image, an image in which the vertex and the base can be identified as being sequentially arranged in the step flow direction is classified as a triangular defect.
In the SICA image, the linear defect and the carrot-like defect are similar in that they are linear, but as described above, the carrot-like defect differs from the linear defect in that a groove is visible at the center in the longitudinal direction. . Therefore, even for a linear defect, an SICA image having a groove at the center in the longitudinal direction is not counted as a linear defect.

(Example 2)
An SiC epitaxial wafer was manufactured under the same conditions as in Example 1 except that the C / Si ratio was set to 0.96.
The number of linear defects was 28 and the number of triangular defects was 39. Therefore, the ratio of the number of linear defects to the number of triangular defects was 0.72.

(Example 3)
An SiC epitaxial wafer was manufactured under the same conditions as in Example 1 except that the C / Si ratio was set to 0.99.
The number of linear defects was 19 and the number of triangular defects was 50. Therefore, the ratio of the number of linear defects to the number of triangular defects was 0.38.

(Example 4)
An SiC epitaxial wafer was manufactured under the same conditions as in Example 1 except that the C / Si ratio was set to 0.90.
The number of linear defects was 44 and the number of triangular defects was 22. Therefore, the ratio of the number of linear defects to the number of triangular defects was 2.00.

(Comparative Example 1)
An SiC epitaxial wafer was manufactured under the same conditions as in Example 1 except that the C / Si ratio was changed to 1.03.
The number of linear defects was 9 and the number of triangular defects was 63. Therefore, the ratio of the number of linear defects to the number of triangular defects was 0.14.

(Comparative Example 2)
An SiC epitaxial wafer was manufactured under the same conditions as in Example 1 except that the C / Si ratio was 1.13.
The number of linear defects was 0 and the number of triangular defects was 82. Therefore, the ratio of the number of linear defects to the number of triangular defects was 0.

  INDUSTRIAL APPLICABILITY The SiC epitaxial wafer and the method of manufacturing the same of the present invention can be used as a SiC epitaxial wafer for power semiconductors and as a method of manufacturing the same.

Claims (3)

An SiC epitaxial wafer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate having an off angle,
An SiC epitaxial wafer, wherein the ratio of the number of linear defects to the number of triangular defects contained in the SiC epitaxial layer is 0.2 to 2.   The said ratio is 0.7-1.5, The SiC epitaxial wafer of Claim 1 characterized by the above-mentioned. 3. The SiC epitaxial wafer according to claim 1, wherein the density of triangular defects is 0.8 / cm ² or less.