TWI657171B - SiC epitaxial wafer and manufacturing method thereof, and method for detecting large pit defects and defect identification method - Google Patents

Abstract

This SiC epitaxial wafer is a SiC epitaxial wafer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate having a deviation angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . The density of large pit defects due to the carbon inclusions on the substrate contained in the epitaxial layer is 0.5 pieces / cm ² or less.

Description

   SiC epitaxial wafer and manufacturing method thereof, large pit defect detection method and defect identification method   

The invention relates to a SiC epitaxial wafer and a manufacturing method thereof, a large pit defect detection method and a defect identification method.

This application claims priority based on Japanese Patent Application No. 2016-170221 filed in Japan on August 31, 2016 and Japanese Patent Application No. 2016-185945 filed in Japan on September 23, 2016, the contents of which are incorporated herein by reference.

Silicon carbide (SiC) is expected to be used in power because it has characteristics such as a single-digit higher dielectric breakdown electric field strength than silicon (Si), an energy gap that is three times larger, and a thermal conductivity that is about three times higher. Equipment, high frequency equipment, high temperature operation equipment, etc.

To promote the practical use of SiC devices, the establishment of high-quality crystal growth technology and high-quality epitaxial growth technology is indispensable.

A SiC device is generally grown on a SiC single crystal substrate obtained by processing a bulk single crystal of SiC grown by a sublimation recrystallization method or the like, and is grown by a chemical vapor growth method (Chemical Vapor Deposition: CVD). SiC epitaxial wafer (film) in the active region is fabricated.

More specifically, SiC epitaxial wafers generally perform a step flow on a SiC single crystal substrate having a growth surface from a (0001) plane having a deviation angle in the <11-20> direction. Growth (horizontal growth from the atomic level) causes the 4H SiC epitaxial layer to grow.

As defects of an epitaxial layer of a SiC epitaxial wafer, there are known defects that inherit defects from a SiC single crystal substrate and newly formed defects in an epitaxial layer. As the former, penetration dislocation, basal plane dislocation, carrot defect, and the like are known, and as the latter, triangular defect and the like are known.

For example, if a carrot defect is viewed from the epitaxial surface side, it is a long rod-shaped defect in the flow growth direction, but it is considered to be a substrate dislocation (through spiral dislocation (TSD) or basal plane dislocation (BPD)). A flaw on the substrate is formed as a starting point (see Non-Patent Document 1).

In addition, the triangle defect is formed along the step growth direction (<11-20> direction) from upstream to downstream, and the triangle vertices are formed in a direction in which the opposite edges (bottom edges) are sequentially arranged. The foreign substance (downfall) existing on the SiC single crystal substrate before the epitaxial growth during the epitaxial wafer or in the epitaxial layer during the epitaxial growth is used as a starting point. From there, a 3C polytype The layer extends along the deviation angle of the substrate and is exposed on the epitaxial surface (see Non-Patent Document 2).

Prior art literature Patent literature

Patent Document 1 JP 2013-023399

Patent Document 2 Japanese Patent Application Publication No. 2016-058499

Non-patent literature

Non-Patent Document 1 J. Hassan et al., Journal of Crystal Growth 312 (2010) 1828-1837

Non-Patent Document 2 C. Hallin et al., Diamond and Related Materials 6 (1997) 1297-1300

As described above, the triangular defect includes a 3C polytype. The electrical characteristics of the 3C polytype are different from the electrical characteristics of the 4H polytype. Therefore, if a triangular defect exists in the 4H-SiC epitaxial layer, this part cannot be used as a device. That is, triangular defects are known as killer defects.

As a defect in a SiC single crystal substrate, carbon inclusions are known (hereinafter, referred to as "substrate carbon inclusions"). When manufacturing silicon carbide single crystal ingots, as the sublimation gas from the silicon carbide raw material (powder), in addition to SiC, there are mainly Si, Si ₂ C, SiC ₂ and the like. Graphite crucibles are made of these sublimation gases and their inner walls. Interaction, the internal wall absorbs such sublimation gases, and the surface of the silicon carbide single crystal ingot gradually deteriorates as the growth of the silicon carbide single crystal ingot is repeated. Due to the deterioration of the surface of the inner wall of the graphite crucible, graphite fine particles fly in the inner space (cavity portion) of the crucible, which causes carbon inclusions to enter the silicon carbide single crystal ingot. The carbon inclusions in the SiC single crystal substrate are the carbon inclusions in the ingot that remain in the SiC single crystal substrate after the ingot is sliced into the SiC single crystal substrate. It is not fully understood how the carbon inclusions in the SiC single crystal substrate will affect the epitaxial layer of the SiC epitaxial wafer.

As described above, the triangular defects are known to be caused by falling objects. As a result of careful study, the inventors found that the triangular defects are caused in the epitaxial layer of the carbon inclusions in the SiC single crystal substrate. The inventors further discovered defects (large pit defects, oblique line defects, bump defects) in three kinds of epitaxial layers other than triangular defects caused by carbon inclusions in a SiC single crystal substrate. That is, the inventors discovered that in an SiC epitaxial wafer, carbon inclusions in a SiC single crystal substrate were converted (transformed) into four types of defects in the epitaxial layer, and the conversion rate was further determined. In addition, the inventors discovered that in addition to the triangular defects caused by carbon inclusions in a SiC single crystal substrate, large pit defects are also fatal defects, and came to the present invention. In addition, as ordinary pits, it is known that they are caused by dislocation of a SiC single crystal substrate (for example, refer to Patent Document 2). In contrast, the ordinary pits are caused by large pits of carbon inclusions on the substrate. Defects were first discovered by the inventors.

The present invention is an invention completed in view of the above-mentioned facts, and an object thereof is to provide a SiC epitaxial wafer with reduced large pit defects caused by carbon inclusions on a substrate, a manufacturing method thereof, and a large pit defect detection method that reduce fatal defects of the device Defect identification method.

In order to solve the above problems, the present invention adopts the following means.

One aspect of the SiC epitaxial wafer of the present invention is a SiC epitaxial layer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate having a deviation angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . In a crystal wafer, the density of large pit defects caused by the substrate carbon inclusions contained in the SiC epitaxial layer is 0.5 pieces / cm ² or less.

The manufacturing method of one aspect of the SiC epitaxial wafer according to the present invention is to form a SiC epitaxial crystal on a 4H-SiC single crystal substrate having a deviation angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . The method of a SiC epitaxial wafer with a single layer includes an epitaxial growth step of growing an epitaxial layer on the SiC single crystal substrate. In the epitaxial growth step, the growth rate is set to 5 to 100 μm / hour, and the growth is performed. The temperature was set to 1500 ° C or higher, and the C / Si ratio was set to 1.25 or lower.

In the method for manufacturing an SiC epitaxial wafer, the C / Si ratio may be 1.10 or less.

In the method for manufacturing an SiC epitaxial wafer, a SiC epitaxial wafer having a density of 0.5 pits / cm ² or less due to large pit defects due to substrate carbon inclusions contained in the SiC epitaxial layer may be selected.

In one aspect of the present invention, a large pit defect detection method uses a confocal microscope with a confocal differential interference optical system to detect large pit defects in a SiC epitaxial layer in a SiC epitaxial wafer.

One aspect of the defect identification method of the present invention is a method for identifying defects in a SiC epitaxial layer in a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate. The position of the substrate carbon inclusions in the SiC single crystal substrate measured by the confocal microscope of the optical system is compared with the position of the large pit defect of the SiC epitaxial layer, so that the other causes the substrate carbon inclusions to be identified from other defects. Large pit defects.

One aspect of the present invention is a method for identifying defects in a SiC epitaxial layer of a SiC epitaxial wafer having a SiC epitaxial layer formed on a SiC single crystal substrate. The method uses a confocal differential interference optical system. The confocal microscope and the photoluminescence device of the present invention identify a large pit defect caused by a SiC epitaxial layer of a substrate carbon inclusion in the aforementioned SiC single crystal substrate and a defect of a SiC epitaxial layer caused by a falling object.

One aspect of the present invention is a method for identifying defects in a SiC epitaxial layer of a SiC epitaxial wafer having a SiC epitaxial layer formed on a SiC single crystal substrate. The method uses a confocal differential interference optical system. Confocal microscope and photoluminescence device to identify large pit defects caused by the SiC epitaxial layer of the substrate carbon inclusions in the aforementioned SiC single crystal substrate and the through-dislocation SiC epitaxial layer caused by the aforementioned SiC single crystal substrate Defects.

According to the SiC epitaxial wafer of the present invention, it is possible to provide an epitaxial wafer in which the fatal defect of the device and the large pit defect caused by the carbon inclusions in the substrate are reduced.

According to the method for manufacturing an SiC epitaxial wafer according to the present invention, it is possible to provide a method for manufacturing a SiC epitaxial wafer in which fatal defects in the device due to large pit defects caused by carbon inclusions in the substrate are reduced.

According to the large pit defect detection method of the present invention, a large pit defect detection method capable of detecting large pit defects in a SiC epitaxial layer in a SiC epitaxial wafer can be provided.

According to the defect identification method of the present invention, it is possible to provide a defect identification method capable of identifying large pit defects in a SiC epitaxial wafer caused by a substrate carbon inclusion in a SiC epitaxial layer.

According to the defect identification method of the present invention, it is possible to provide a defect capable of identifying a large pit defect caused by a SiC epitaxial layer of a substrate carbon inclusion in a SiC single crystal substrate and a defect caused by a fallen SiC epitaxial layer. recognition methods.

According to the defect identification method of the present invention, it is possible to provide a large pit defect capable of identifying a SiC epitaxial layer caused by a substrate carbon inclusion in a SiC single crystal substrate and a SiC caused by a through-dislocation in the SiC single crystal substrate. Defect identification method for defects of epitaxial layer.

Fig. 1 is an image of a substrate carbon inclusion (left side) and an image of four kinds of defects due to the substrate carbon inclusion (right side) obtained by a confocal microscope of a surface inspection device using a confocal differential interference optical system. The images include (a) large pit defects, (b) triangular defects, (c) oblique line defects, and (d) bump image defects.

FIG. 2 is a STEM image of a cross section near a large pit defect caused by a substrate carbon inclusion.

FIG. 3 is an STEM image of a normal pit caused by dislocation of a single crystal substrate.

Fig. 4 is a cross-sectional STEM image of a carbon inclusion itself of a substrate.

Figure 5 is EDX data of carbon inclusions.

Figure 6 is the EDX data of the 4H-SiC portion.

Fig. 7 Confocal microscope image and cross-section STEM image of bump defects after epitaxial layer formation.

FIG. 8 is an enlarged image and EDX data of a carbon inclusion portion of a bump defect converted into a cross-sectional STEM image shown in FIG. 7.

FIG. 9 is a graph showing the results of investigating changes in the conversion rate of large pit defects and triangular defects, which are fatal defects of the device, corresponding to the C / Si ratio.

FIG. 10 is a graph showing the results of investigating changes in the conversion rate of bump defects and oblique line defects which are non-fatal fatal defects corresponding to the C / Si ratio.

FIG. 11 is a graph showing a film thickness dependency of an epitaxial film which is a conversion rate of a device fatal defect and a non-device fatal defect.

The images on the left of FIG. 12 are SICA images near the surface of the SiC epitaxial wafer due to large pit defects caused by carbon inclusions on the substrate, and the images on the right are their PL images.

The images on the left of FIG. 13 are SICA images on the surface of the SiC epitaxial wafer that are caused by the pits of the falling objects on the single crystal substrate, and the images on the right are PL images.

Fig. 14 (a) shows SICA images of large pit defects on the surface of SiC epitaxial wafers due to substrate carbon inclusions (Large-pit) and defects starting from the substrate through dislocation (TD), (b ) Display such PL images.

A form for implementing the invention

Hereinafter, the structure of an SiC epitaxial wafer to which the present invention is applied and a manufacturing method thereof will be described using drawings. In addition, the drawings used in the following description may be enlarged and displayed for easy understanding of the features. The size ratios and the like of the constituent elements are not necessarily the same as the actual ones. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented within the scope of exerting the effects of the present invention.

(SiC Epitaxial Wafer)

An SiC epitaxial wafer according to an embodiment of the present invention is a SiC epitaxial layer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate having a deviation angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . In the wafer, the density of large pit defects due to the substrate carbon inclusions contained in the SiC epitaxial layer is 0.5 pieces / cm ² or less.

The 4H-SiC single crystal substrate used in the SiC epitaxial wafer of the present invention has a deviation angle of, for example, 0.4 ° or more and 8 ° or less. Typically, 4 ° is used.

An SiC epitaxial wafer according to an embodiment of the present invention uses one of the point system characteristics of a 4H-SiC single crystal substrate having a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² .

The reason why the density of large pit defects due to substrate carbon inclusions contained in the SiC epitaxial layer is 0.5 or less / cm ² is because the large pit defects are fatal defects of the device.

That is, a Schottky barrier diode fabricated from an SiC epitaxial wafer containing large pit defects is produced. When a reverse bias current is applied to measure a reverse leakage current, a large Current leakage. From this, it was understood that the large pit defect system may be a defect that may become a fatal defect in the final semiconductor device. Therefore, it is important to reduce the density of large pit defects in the same manner as the triangular defects. On the other hand, Schottky barrier diodes including bump defects and oblique line defects do not cause current leakage.

The inventors discovered a method for reducing the large pit defect, and thought of the SiC epitaxial wafer of the present invention. Hereinafter, this will be described first.

(Types of surface defects due to carbon inclusions on the substrate)

As a result of careful review by the present inventor, a confocal microscope image of the surface of the SiC single crystal substrate was obtained, and after confirming the position and number of carbon inclusions on the substrate surface, a SiC epitaxial layer was formed on the SiC single crystal substrate to prepare a SiC epitaxial crystal. Obtain a confocal microscope image of the surface of the SiC epitaxial layer on the wafer. Compare the confocal microscope image of the surface of the SiC epitaxial layer with the confocal microscope image of the substrate surface to confirm and review whether each carbon inclusion is epitaxial in the SiC What kind of defect appears in the layer. As a result, it was found that the carbon inclusions of the SiC single crystal substrate were almost converted (transformed) into the four defect types in the SiC epitaxial layer, and the conversion rate was determined. Here, the identification of the defect type is difficult, but the present invention is of great significance for identifying the "at least major" defect type in a situation where there is little information about the relationship between the substrate carbon inclusions and the defects caused by the substrate.

FIG. 1 shows an image (hereinafter, referred to as a SICA image) of the four types of defects obtained by a confocal microscope (Lasertec Corporation, SICA6X) using a confocal differential inspection optical system surface inspection apparatus. ). In each of Figs. 1 (a) to (d), the SICA image on the right is the SICA image on the surface of the SiC epitaxial layer, which are sequentially large pit defects, triangular defects, oblique line defects, and bump defects. In each of FIGS. 1 (a) to (d), the SICA image on the left is a SICA image of the substrate surface. In the SICA image on the left, as described later, an image of the substrate carbon inclusions is observed.

The SiC epitaxial wafer shown in FIG. 1 is obtained by using the same manufacturing method as the SiC epitaxial wafer obtained with the data shown in FIGS. 9 to 11 described later, and setting the C / Si ratio to 1.1. . The same is true for SiC epitaxial wafers with images shown in FIGS. 2 to 8 and 12 to 14 below.

The characteristics of carbon inclusions in the SiC single crystal substrate and the four types of defects described above will be described.

Carbon inclusions on SiC single crystal substrates are defects that can be viewed by a confocal microscope as black pits in the SICA image of the substrate surface. The carbon inclusions of the SiC single crystal substrate are generated by the carbon ingots that fly in the middle of crystal formation and are absorbed by the ingot. Even if it is the same ingot, the position varies with the SiC single crystal substrate. As will be described later, a carbon peak is strongly detected at a carbon inclusion of a SiC single crystal substrate, and thus it becomes possible to distinguish a defect caused by a carbon inclusion of a SiC single crystal substrate from other defects.

The large pit defect of the SiC epitaxial layer is a defect that can be viewed by a confocal microscope on the surface of the SiC epitaxial layer (hereinafter referred to as "epitaxial surface" in this specification). The starting point of the large pit defect is the carbon inclusions of the substrate and a part thereof is consumed, and the carbon inclusions extend from the carbon inclusions along the vertical direction of the deviation angle of the substrate to form deep pits. Typically, the size of the large pit defect is 200 to 500 μm ² . Small large pit defects of 100 μm ² or less are difficult to distinguish from ordinary pits, but can be distinguished by comparison with the position of substrate defects. That is, the pits at positions corresponding to the positions of the carbon inclusions on the substrate surface are large pit defects.

The triangular defects of the SiC epitaxial layer are those that can be viewed by a confocal microscope and appear as triangular defects on the epitaxial surface. The starting point is the carbon inclusions of the substrate, and the 3C polytype layer extends from the carbon inclusions in a direction perpendicular to the deviation angle of the substrate and is exposed on the epitaxial surface. In addition, as a triangular defect, there is a triangular defect caused by particles (falling objects) in the furnace, which cannot be distinguished in the confocal microscope image of the SiC epitaxial layer, but if the confocal microscope image of a SiC single crystal substrate is compared Can be distinguished.

That is, the triangular defects caused by the substrate carbon inclusions can be seen at this position in the confocal microscope image of the SiC single crystal substrate, and the falling objects do not exist in the SiC single crystal substrate. It does not exist in the confocal microscope image before it is placed in the growth furnace. That is, when a SiC epitaxial wafer is manufactured, the falling object is a substance that has fallen on a SiC single crystal substrate before the SiC epitaxial layer is grown, or it is dropped on the SiC epitaxial layer during the growth of the SiC epitaxial layer. The substance.

The oblique line defects of the SiC epitaxial layer can be viewed by a confocal microscope. The epitaxial surface looks like oblique line defects, and some of the laminated defects can be seen. The starting point is the carbon inclusions of the substrate, and the oblique line from the carbon inclusions extends along the vertical direction of the deviation angle of the substrate and is exposed on the epitaxial surface. In addition, there are oblique line defects caused by the dislocation of the substrate, which cannot be distinguished in the confocal microscope image of the SiC epitaxial layer, but can be distinguished by comparing the confocal microscope images of the SiC single crystal substrate.

The bump defects of the SiC epitaxial layer are defects that can be seen by the confocal microscope as buried bumps on the epitaxial surface. Substances that extend vertically from the carbon inclusions along the deviation angle of the substrate are those that are buried to a certain extent by forming a SiC epitaxial layer.

Specifically, the conversion rate of the four types of defects due to the substrate carbon inclusions is determined as follows.

As the SiC single crystal substrate, a 6-inch 4H-SiC single crystal substrate having a deviation angle of 4 ° in the <11-20> direction with respect to the (0001) Si plane was used.

After 12 known 4H-SiC single crystal substrates were subjected to a known polishing step, a SICA image was first obtained on the polished substrate using a confocal microscope (Lasertec Corporation, SICA6X), and the position of the carbon inclusions on the surface of the substrate was recorded. Information. The number of carbon inclusions in each SiC single crystal substrate was 6 to 49, with an average of about 29. That is, the density of the substrate carbon inclusions is 0.06 pieces / cm ² to 0.47 pieces / cm ² , and the average is about 0.28 pieces / cm ² .

Thereafter, the single crystal substrate is set in a CVD apparatus, and a cleaning (etching) step of the substrate surface using hydrogen is performed.

Next, while using silane and propane as source gases and supplying hydrogen as a carrier gas, an SiC epitaxial growth step was performed under conditions of a growth temperature of 1600 ° C and a C / Si ratio of 1.22 to form a SiC epitaxial layer with a thickness of 9 μm. On a SiC single crystal substrate, an SiC epitaxial wafer is obtained.

Here, the C / Si ratio refers to the atomic ratio of C and Si.

For this SiC epitaxial wafer, a confocal microscope (Lasertec Co., Ltd., SICA6X) was used to obtain a SICA image again, and the SICA image was used to classify the four defects. The measurement range is set to the entire wafer except for 3 mm from the outer peripheral edge. Based on the number of each defect after classification, the conversion rate of each defect was calculated from the number of each defect with respect to the number of full substrate carbon inclusions.

The conversion rates of large pit defects, triangular defects, oblique defects, and bump defects were 24.4%, 13.6%, 4.3%, and 57.6%, respectively.

Although such a conversion rate varies depending on the manufacturing conditions of the SiC epitaxial wafer, if the growth rate is in a range of 20 μm / hour or more and the growth temperature is 1500 ° C. or more, the manufacturing conditions are the same under the same C / Si ratio. The tendency to get the same conversion ratio. Therefore, for example, when it is desired to set the density of the large pit defect of the fatal defect to a predetermined density or less, it is sufficient to use a SiC single crystal substrate having a predetermined density of carbon inclusions inferred from the conversion rate. .

For example, if the conversion ratios based on the formation of large pit defects and triangular defects are 24.4% and 13.6%, when the substrate carbon inclusion density is 0.06 pcs / cm ² to 0.47 pcs / cm ² as described above, large pits The defect densities of the defects and triangular defects are 0.015 pieces / cm ² to 0.115 pieces / cm ² and 0.008 pieces / cm ² to 0.064 pieces / cm ^{2 respectively} .

When the conversion rate of large pit defects is 24.4%, if a SiC epitaxial wafer with a density of 0.5 pits / cm ² or less due to large pit defects due to substrate carbon inclusions is used, A SiC single crystal substrate having a substrate carbon inclusion density of 2.0 pieces / cm ² or less may be sufficient.

In general expressions, when the conversion rate of large pit defects is p%, and when it is desired to obtain SiC epitaxial wafers with a density of large pit defects of q pieces / cm ² or less, substrate carbon is used. It is sufficient if the SiC single crystal substrate has an inclusion density of (100 × q / p) pieces / cm ² or less.

In the SiC epitaxial wafer of the present invention, the lower the density of large pit defects due to the substrate carbon inclusions, the better. If the lower limit of the substrate carbon inclusion density range is exemplified, the lower limit is 0.01 to 0.03 pieces / cm ² or so.

Next, the characteristics of each defect will be described.

In FIG. 2, a section near a large pit defect caused by a carbon inclusion in a substrate is shown by a scanning transmission electron microscope (STEM: Scanning Transmission Electron Microscope) (manufactured by Hitachi High Technologies, HF-2200). Image (STEM image). For comparison, FIG. 3 shows an STEM image of a normal pit due to dislocation of a single crystal substrate.

The STEM images shown in FIGS. 2 to 4 and 7 are for explaining the characteristics of each defect, and the dimensions are shown in the figure.

The STEM image shown in FIG. 2 is an example. In the STEM image, the substrate carbon inclusions can be seen at the position of the substrate below. In addition, there is a misalignment extending from the substrate carbon inclusions through the abnormal growth portion, and large pit defects are seen on the surface side of the misaligned tip ("deep pits" in FIG. 2). In this way, in the STEM image shown in FIG. 2, the cause of large pit defects on the epitaxial surface is clearly shown as the substrate carbon inclusions. Between the carbon inclusions on the substrate and the large pit defects on the surface, there are cases where dislocations enter the epitaxial layer as shown in FIG. 2, but there are also cases where dislocations do not enter the epitaxial layer. In addition, large deep pits are formed on the epitaxial surface.

On the other hand, it can be seen from FIG. 3 that in the STEM image of the ordinary pits caused by the dislocation of the single crystal substrate, carbon inclusions do not exist in the substrate. Below the pits, inheritance from the dislocation of the substrate was seen. A collection of dislocations to the epitaxial layer. In this case, only extremely small pits are formed on the epitaxial surface.

Thus, the large pit defect caused by the substrate carbon inclusions of the present invention is completely different from the ordinary pit caused by the dislocation of the single crystal substrate.

Fig. 4 is a cross-sectional STEM image of foreign matter inclusions on the substrate, and the presence of foreign matter can be confirmed. The composition of this foreign matter was confirmed by EDX (EDX: Energy Dispersive X-ray Spectroscopy).

FIG. 5 shows the results of EDX for the foreign matter inclusions shown in FIG. 4. The upper right image is the one in which the vicinity of the foreign object inclusion is enlarged in the STEM image of FIG. 4, and the image shows the result of EDX of the portion of the point in the foreign object indicated by the symbol 2.

On the other hand, the image in the upper right of FIG. 6 is a result of enlarging the vicinity of a foreign object inclusion in the STEM image of FIG. 4, and the image shows a result of EDX of a portion other than the foreign object indicated by reference numeral 12.

Compared with FIG. 6, the result of EDX shown in FIG. 5 is that it is confirmed that the foreign matter is carbon (substrate carbon inclusion) because of the peak strength of carbon.

FIG. 7 is a cross-sectional STEM image of a place where a SiC epitaxial layer is formed on a substrate carbon inclusion and becomes a bump defect. It is known that the dislocation (a straight line that appears slightly thicker in the STEM image) extends from the carbon inclusions of the substrate and reaches the epitaxial surface. The upper part of the cross-sectional STEM image shows a confocal microscope image of the bump defect (surface defect) (the scale of the image is displayed on the right side of the image). The dashed arrow indicates the bump defect (surface defect) with the cross-section STEM image. ).

The place where the dislocation indicated by the arrow in FIG. 7 reaches the epitaxial surface corresponds to the end of the bump defect shown in the upper part of FIG. 7.

FIG. 8 is an enlarged image of an inclusion portion corresponding to the bump defect shown in FIG. 7 and an EDX measurement spectrum in the vicinity thereof. In the EDX shown in FIG. 8, it was also confirmed that the foreign substance was carbon because the wave peak of carbon was stronger in the inclusion portion (upper side data) than in the outer portion (lower side data) of the inclusions.

As can be seen from FIGS. 7 and 8, the bump defects shown in FIG. 7 are caused by the substrate carbon inclusions.

(Manufacturing method of SiC epitaxial wafer)

A method for manufacturing an SiC epitaxial wafer according to an embodiment of the present invention is to form a SiC epitaxial crystal on a 4H-SiC single crystal substrate having a deviation angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . The method of a SiC epitaxial wafer with two layers includes an epitaxial growth step of growing an epitaxial layer on the aforementioned SiC single crystal substrate. In the foregoing epitaxial growth step, the growth rate in the thickness direction of the SiC epitaxial layer is increased. It is set to 5 to 100 μm / hour, the growth temperature is set to 1500 ° C. or more, and the C / Si ratio is set to 1.25 or less.

The manufacturing method of the SiC epitaxial wafer of the present invention is based on the premise that a "4H-SiC single crystal substrate having a deviation angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² " is prepared.

One of the characteristics of the method for manufacturing an SiC epitaxial wafer of the present invention is to use a 4H-SiC single crystal substrate having a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . A substrate having a substrate carbon inclusion density of 0.1 to 4.5 substrates / cm ² is preferred, a substrate having a substrate carbon inclusion density of 0.1 to 3.5 substrates / cm ² is more preferred, and a substrate having 0.1 to 2.5 substrates / cm ² is even more preferred. cm ² substrate substrate with carbon inclusion density.

Figures 9 and 10 show that the investigation was conducted using a 6-inch 4H-SiC single crystal substrate having a deviation angle of 4 ° in the <11-20> direction with respect to the (0001) Si plane, and the substrate carbon inclusion density was 0.1. A SiC single crystal substrate of ~ 6.0 pieces / cm ² is subjected to a known polishing step and a substrate surface cleaning (etching) step, and the SiC epitaxial growth is performed while using silane and propane as source gases and supplying hydrogen as a carrier gas. Steps: forming an SiC epitaxial layer with a thickness of 30 μm on a SiC epitaxial wafer obtained on a SiC single crystal substrate, and changing the C / Si ratio to 0.80, 0.95, 1.10, 1.22 for setting the growth temperature to 1600 ° C In the case of each SiC epitaxial wafer, it is the result of changes in the conversion rate of each defect type. Within the range of the growth temperature and growth rate described later, the conversion rate for each defect type is hardly affected.

FIG. 9 is a result of investigating a change in the conversion rate of a large pit defect and a triangular defect that becomes a fatal defect of the device, and FIG. 10 is a result of investigating a change in the conversion rate of a slant line defect and a bump defect.

As shown in FIG. 9, the larger the C / Si ratio is, the larger the conversion rate becomes a large pit defect. Specifically, at C / Si ratios of 0.80, 0.95, 1.10, and 1.22, they are 0%, 0.6%, 4.5%, and 16.1%, respectively. If the C / Si ratio exceeds 1.10, the conversion rate becomes a large pit defect. More than 5%. Therefore, in order to suppress the conversion rate that becomes a large pit defect to 5% or less, it is necessary to suppress the C / Si ratio to 1.10 or less. In FIG. 9, the conversion rate of the combined large pit defect and the triangular defect is shown as the conversion rate of a fatal defect.

In addition, although the conversion rate that becomes a triangular defect is not as good as the conversion rate that becomes a large pit defect, the larger the C / Si ratio, the more it tends to be almost larger. At any C / Si ratio, the conversion rate that becomes a triangular defect is lower than 3%. Specifically, at C / Si ratios of 0.80, 0.95, 1.10, and 1.22, they were 1.7%, 2.6%, 2.2%, and 2.7%, respectively.

The larger the conversion ratio of a fatal defect that merges large pit defects and triangular defects is, the larger the C / Si ratio becomes. Specifically, with C / Si ratios of 0.80, 0.95, 1.10, and 1.22, they are 1.7%, 3.2%, 6.7%, and 18.8%, respectively. If the C / Si ratio exceeds 1.10, the conversion rate of fatal defects exceeds 6 %. Therefore, in order to suppress the conversion rate that becomes a fatal defect to 6% or less, it is necessary to suppress the C / Si ratio to 1.10 or less.

On the other hand, as shown in FIG. 10, the larger the conversion ratio of the bump defect (Bump) is, the smaller the C / Si ratio becomes. Specifically, at C / Si ratios of 0.80, 0.95, 1.10, and 1.22, they are 97.2%, 94.8%, 92.7%, and 79.6%, respectively. When the C / Si ratio is 1.10 or less, the conversion becomes a bump defect. The rate is over 92%. Therefore, in order to increase the conversion rate of bump defects to 92% or more, it is necessary to set the C / Si ratio to 1.10 or less.

In addition, the conversion rate that becomes a oblique defect is different from the conversion rate that becomes a bump defect, and does not change much even if the C / Si ratio is changed. Specifically, at C / Si ratios of 0.80, 0.95, 1.10, and 1.22, they are 1.1%, 1.9%, 0.6%, and 1.6%, respectively. At any C / Si ratio, the conversion rate of oblique defects is Values as small as less than 2%.

The conversion rate of non-killer defects that become a combination of bump defects and oblique defects is larger as the C / Si ratio becomes smaller. Specifically, at a C / Si ratio of 0.80, 0.95, 1.10, and 1.22, respectively, 98.3%, 96.7%, 93.3%, and 81.2%, and at a C / Si ratio of 1.10, the conversion rate of non-fatal defects exceeds 93%. Therefore, in order to increase the conversion rate which is a non-fatal defect to 93% or more, it is necessary to set the C / Si ratio to 1.10 or less.

The relationship between the conversion rate of each defect type and the epitaxial film thickness (thickness of the epitaxial film) was investigated. The C / Si ratio was fixed at 1.22, and the epitaxial film thickness was set to 9 µm, 15 µm, and 30 µm. The conversion rates of the fatal defect of the device and the fatal defect of the non-device are summarized in FIG. 11. The larger the film thickness is, the smaller the conversion rate becomes a fatal defect. Specifically, at a film thickness of 9, 15, and 30 μm, 38.1%, 24.5%, and 18.8%, respectively, and at a C / Si ratio of 1.22, the epitaxial film thickness is 30 μm, which becomes a conversion rate of fatal defects. Suppressed below 20%. That is, it was found that the conversion rate that is the type of each defect is affected by the C / Si ratio and also affected by the epitaxial film thickness. In other words, the conversion rate that becomes each defect can be controlled by two parameters: C / Si ratio and epitaxial film thickness. In general, the larger the C / Si ratio, the better the uniformity of the impurity concentration. When it is desired to increase the C / Si ratio in order to give priority to the uniformity of the impurity concentration, it is possible to suppress the conversion rate that becomes a fatal defect by increasing the thickness of the epitaxial film.

In the method for manufacturing an SiC epitaxial wafer according to an embodiment of the present invention, the C / Si ratio in the epitaxial growth step is 1.25 or less. Based on the results shown in FIG. 9, in order to reduce the conversion rate of large pit defects, the C / Si ratio is preferably 1.22 or less, more preferably 1.15 or less, and even more preferably 1.10 or less. In order to reduce the conversion rate that becomes a large pit defect, it is preferable that the C / Si ratio be a smaller value. If the C / Si ratio is set to 1.22 or less, the conversion rate that becomes a large pit defect can be set to 16% or less. If the C / Si ratio is set to 1.10 or less, the conversion rate that becomes a large pit defect can be set. When it is set to 4.5% or less, if the C / Si ratio is set to 1.05 or less, the conversion rate that becomes a large pit defect can be set to 3.0% or less. If the C / Si ratio is set to 1.0 or less, it can be made large. The conversion rate of pit defects is set to 2.0% or less. If the C / Si ratio is set to 0.95 or less, the conversion rate of large pit defects can be set to 0.6% or less. If the C / Si ratio is set to 0.90 or less, , The conversion rate that becomes a large pit defect can be set to 0% or less.

In the method for manufacturing an SiC epitaxial wafer according to an embodiment of the present invention, the epitaxial film thickness is not particularly limited. When the epitaxial film thickness is thinner than 10 μm, the C / Si ratio is preferably further reduced. When the epitaxial film thickness is thicker than 15 μm, the C / Si ratio can be slightly larger.

The method for manufacturing an SiC epitaxial wafer according to an embodiment of the present invention is not particularly limited, and the growth rate in the epitaxial growth step is 5 to 100 μm / hour.

The faster the growth rate, the higher the productivity. Therefore, the growth rate is preferably 20 μm / hour or more, more preferably 40 μm / hour or more, and even more preferably 60 μm / hour or more.

In the method for manufacturing an SiC epitaxial wafer according to an embodiment of the present invention, the growth temperature in the epitaxial growth step is 1500 ° C. or higher. If the temperature is too low, lamination defects increase, and if the temperature is too high, there is a problem of deterioration of internal components of the furnace. Therefore, the growth temperature is preferably 1500 ° C or higher, more preferably 1550 ° C or higher, and even more preferably 1600 ° C or higher. Moreover, as an upper limit, about 1750 degreeC is mentioned, for example.

In the method for manufacturing an SiC epitaxial wafer according to an embodiment of the present invention, before the epitaxial growth, the density of large pit defects caused by the carbon inclusions in the substrate included in the SiC epitaxial layer can be set to be 0.5. Steps of SiC epitaxial wafers below / cm ² .

(Large pit defect detection method)

A large pit defect detection method according to an embodiment of the present invention uses a confocal microscope with a confocal differential interference optical system to detect large pit defects in a SiC epitaxial layer in a SiC epitaxial wafer.

The large pit defect of the SiC epitaxial layer is based on the carbon inclusions of the substrate, so the confocal microscope image of the SiC single crystal substrate and the confocal microscope image of the SiC epitaxial wafer (ie, the SiC epitaxial layer) can be used A comparison is performed to easily detect large pit defects in the SiC epitaxial layer in the SiC epitaxial wafer. By using the SICA6X device that can output the coordinates of each defect and observe the defect image in detail, it is possible to easily compare the substrate with the epitaxial wafer.

(Defect identification method (first embodiment))

The defect identification method according to the first embodiment of the present invention is a method for identifying defects in a SiC epitaxial layer in a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate. The position of the substrate carbon inclusions in the SiC single crystal substrate measured by the confocal microscope of the interference optical system is compared with the position of the large pit defect of the SiC epitaxial layer, thereby identifying the large size of the substrate carbon inclusions. Defects in pits.

(Defect identification method (second embodiment))

The defect recognition method according to the second embodiment of the present invention is a method for identifying defects in a SiC epitaxial layer in a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate, and uses confocal differential interference optics. The system's confocal microscope and near-infrared photoluminescence device (NIR-PL) identify large pit defects caused by the SiC epitaxial layer of the substrate carbon inclusions in the aforementioned SiC single crystal substrate and SiC epitaxy caused by falling objects Defects in the crystal layer.

The left side (surface) of FIG. 12 shows a SICA image near the surface of the SiC epitaxial wafer due to large pit defects caused by the substrate carbon inclusions, and the right side (NIR) shows the use of a near-infrared photoluminescence device (Lasertec Co., Ltd. (SICA87), a PL image obtained by using a bandpass (630 to 780 nm) light receiving wavelength. For comparison, in FIG. 13, the SICA image and the PL image caused by the pits (defects) of the falling object on the single crystal substrate are displayed on the left (surface) and right (NIR), respectively.

In the SICA image, large pit defects due to carbon inclusions on the substrate and pits due to falling objects are both circular shapes, making it difficult to make a clear distinction. In contrast, in the PL image, the pits caused by the falling objects are circular in shape, and the large pit defects caused by the substrate carbon inclusions are mostly spider nests. In this case, the difference between the two is obvious. of.

In addition, even in the case where the PL image due to large pit defects caused by the carbon inclusions of the substrate is circular, if the positions of the carbon inclusions observed by the SICA image of the SiC single crystal substrate are compared, it can be compared with the position of the carbon inclusions. The pits are distinguished by falling objects. In addition, in near-infrared photoluminescence devices, if the PL image with large pit defects is compared with the band-receiving wavelength of 400 to 678 nm or band pass 370 to 388 nm, the spider nest part looks black, which is equivalent to The core portion looks white, so it can be distinguished from the pits caused by falling objects as in FIG. 13.

(Defect identification method (third embodiment))

A defect recognition method according to a third embodiment of the present invention is a method for identifying defects in a SiC epitaxial layer in a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate, and uses confocal differential interference optics. The system's confocal microscope and near-infrared photoluminescence device identify the large pit defects caused by the SiC epitaxial layer of the substrate carbon inclusions in the aforementioned SiC single crystal substrate and the penetrating dislocations caused by the aforementioned SiC single crystal substrate. Defects in SiC epitaxial layer.

Fig. 14 (a) shows a SICA image near the surface of a SiC epitaxial wafer due to a large pit defect due to substrate carbon inclusions (Large-pit) and a defect due to substrate through dislocation (TD). 14 (b) shows a PL image obtained by using a near-infrared photoluminescence device (Lasertec Co., Ltd., SICA87) at a light receiving wavelength of bandpass (630 to 780 nm).

The large pit defect caused by the substrate carbon inclusions and the defect starting from the through displacement of the substrate appear similar on the SICA image in FIG. 14 (a), but in the PL image in FIG. 14 (b), Defects starting from the through displacement of the substrate do not emit light, and large pit defects look like spider nests and can be clearly distinguished.

Industrial availability

The SiC epitaxial wafer and the manufacturing method thereof of the present invention can be used, for example, as a SiC epitaxial wafer for power semiconductors, and can also be used as a manufacturing method thereof.

Claims (8)

A SiC epitaxial wafer is a SiC epitaxial layer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate having an off angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . The wafer is characterized in that the density of large pit defects in the SiC epitaxial layer caused by carbon inclusions on the substrate is 0.5 pieces / cm ² or less. A method for manufacturing a SiC epitaxial wafer, which is a SiC epitaxial wafer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate having a deviation angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces / cm ² . The wafer method is characterized by having an epitaxial growth step for growing an epitaxial layer on the SiC single crystal substrate. In the epitaxial growth step, a growth rate is set to 5 to 100 μm / hour, and a growth temperature is set. The temperature is set to 1500 ° C or higher, and the C / Si ratio is set to 1.25 or lower. The method for manufacturing an SiC epitaxial wafer according to claim 2, wherein the C / Si ratio is set to 1.10 or less. For example, the method for manufacturing an SiC epitaxial wafer according to claim 2 or 3, wherein the SiC epitaxial layer having a density of 0.5 pits / cm ² or less due to large pit defects contained in the substrate carbon inclusions is selected. Crystal wafer. A large pit defect detection method using a confocal microscope with a confocal differential interference optical system to measure the density of carbon inclusions caused by a substrate in a SiC epitaxial layer in a SiC epitaxial wafer. The density of the object detects the density of large pit defects. A defect identification method for identifying defects in a SiC epitaxial layer in a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate. The method uses a confocal with a confocal differential interference optical system. The position of the substrate carbon inclusions in the SiC single crystal substrate and the position of the large pit defects of the SiC epitaxial layer were compared with each other measured by a microscope, and the large pit defects caused by the substrate carbon inclusions were identified from other defects. . A defect identification method for identifying defects in a SiC epitaxial layer in a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate, using a confocal microscope and light having a confocal differential interference optical system The electroluminescence device recognizes a large pit defect caused by a SiC epitaxial layer of a substrate carbon inclusion in the SiC single crystal substrate and a defect of the SiC epitaxial layer caused by a falling object. A defect identification method for identifying defects in a SiC epitaxial layer in a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC single crystal substrate, using a confocal microscope and light having a confocal differential interference optical system The electroluminescence device recognizes a large pit defect caused by a SiC epitaxial layer of a substrate carbon inclusion in the SiC single crystal substrate and a defect caused by a through-dislocation SiC epitaxial layer in the SiC single crystal substrate.