CN109642343B - SiC epitaxial wafer, method for manufacturing same, method for detecting large pit defect, and method for identifying defect - Google Patents

SiC epitaxial wafer, method for manufacturing same, method for detecting large pit defect, and method for identifying defect Download PDF

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CN109642343B
CN109642343B CN201780052334.5A CN201780052334A CN109642343B CN 109642343 B CN109642343 B CN 109642343B CN 201780052334 A CN201780052334 A CN 201780052334A CN 109642343 B CN109642343 B CN 109642343B
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郭玲
龟井宏二
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Lishennoco Co ltd
Resonac Holdings Corp
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Showa Denko KK
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Abstract

A SiC epitaxial wafer is provided, which has a bias angle and a substrate carbon inclusion density of 0.1-6.0 pieces/cm2The SiC epitaxial wafer having an SiC epitaxial layer formed on the 4H-SiC single crystal substrate, wherein the density of large pit defects caused by substrate carbon inclusions contained in the SiC epitaxial layer is 0.5 pieces/cm2The following.

Description

SiC epitaxial wafer, method for manufacturing same, method for detecting large pit defect, and method for identifying defect
Technical Field
The present invention relates to a SiC epitaxial wafer and a method for manufacturing the same, and a Large-pit (Large-pit) defect detection method and a defect identification method.
The present application claims priority based on the application 2016-170221 in Japanese at 2016, 8, 31 and 2016-185945 in Japanese at 2016, 9, 23, which are hereby incorporated by reference.
Background
Silicon carbide (SiC) has characteristics such as an insulation breakdown electric field larger by 1 order of magnitude, a band gap larger by 3 times, and thermal conductivity higher by about 3 times than that of silicon (Si), and is expected to be applied to power devices, high-frequency devices, high-temperature operating devices, and the like.
In order to promote the practical use of SiC devices, the establishment of high-quality crystal growth techniques and high-quality epitaxial growth techniques is indispensable.
Generally, a SiC device is manufactured using a SiC epitaxial wafer in which a SiC epitaxial layer (film) to be an active region of the device is grown by a Chemical Vapor Deposition method (CVD) or the like on a SiC single crystal substrate obtained by processing a SiC bulk single crystal grown by a sublimation recrystallization method or the like.
More specifically, the SiC epitaxial wafer is generally grown by performing step flow growth (lateral growth from an atomic step) on a SiC single crystal substrate having a growth plane as a plane having an off-angle from the (0001) plane to the <11-20> direction, thereby growing a 4H SiC epitaxial layer.
As defects of the epitaxial layer of the SiC epitaxial wafer, there are known: a defect that inherits the defect of the SiC single crystal substrate and a defect that is newly formed in the epitaxial layer. As the former, threading dislocations, basal plane dislocations, carrot defects, and the like are known, and as the latter, triangular defects, and the like are known.
For example, although a carrot-type defect is a rod-like defect that is long in the direction of step flow growth when viewed from the epitaxial surface side, it is generally considered that dislocations (threading dislocations (TSDs) or Basal Plane Dislocations (BPDs)) on a substrate and scratches on the substrate are formed as starting points (see non-patent document 1).
Further, the triangular defects are formed in a direction in which the apexes of the triangles and the opposite sides (bases) thereof are arranged in order from the upstream side to the downstream side along the direction of the step flow growth (<11-20> direction), but it is generally considered that the 3C polycrystalline layer extends from there along the off angle of the substrate and is exposed on the epitaxial surface, starting from foreign matter (falling matter) present on the SiC single crystal substrate before epitaxial growth or in the epitaxial growth at the time of manufacturing the SiC epitaxial wafer (see non-patent document 2).
Prior art documents
Patent document
Patent document 1: japanese patent laid-open publication No. 2013-023399
Patent document 2: japanese patent laid-open publication No. 2016-058499
Non-patent document
Non-patent document 1: hassan et al, Journal of Crystal Growth 312(2010)1828-1837
Non-patent document 2: hallin et al, Diamond and Related Materials 6(1997)1297-1300
Disclosure of Invention
As described above, the triangular defect is constituted by 3C polycrystals (polytypes). Since the electrical characteristics of the 3C polycrystal are different from those of the 4H polycrystal, if a triangular defect exists in the 4H-SiC epitaxial layer, the portion cannot be used as a device. That is, the triangular defect is known as a fatal defect.
As a defect in the SiC single crystal substrate, a carbon inclusion (hereinafter, sometimes referred to as "substrate carbon inclusion") is known. In the production of a silicon carbide single crystal ingot, as a sublimation gas derived from a silicon carbide raw material (powder), mainly Si and Si are contained in addition to SiC2C、SiC2For example, the graphite crucible is repeatedly grown by interaction of the sublimation gas with the inner wall thereof, entry of the sublimation gas into the inner wall, and the like, and the surface thereof is degraded. The deterioration of the inner wall surface of the graphite crucible causes graphite particles to fly into the inner space (cavity) of the crucible, which causes carbon inclusions in the silicon carbide single crystal ingot. The carbon inclusion in the SiC single crystal substrate is caused by the carbon inclusion in the ingot remaining in the SiC single crystal substrate even after the ingot is sliced into the substrate. How the carbon inclusions in the SiC single crystal substrate affect the epitaxial layer of the SiC epitaxial wafer is not fully understood.
As for the triangular defect, the triangular defect due to the falling object as described above is known, but the present inventors have conducted extensive studies and found the triangular defect in the epitaxial layer due to the carbon inclusion in the SiC single crystal substrate. The present inventors further found defects (large pit defects, diagonal defects, bump defects) in 3 types of epitaxial layers other than the triangular defects caused by carbon inclusions in the SiC single crystal substrate. Namely, the present inventors found that: in the SiC epitaxial wafer, carbon inclusions in the SiC single crystal substrate are converted (transformed) into 4 kinds of defects in the epitaxial layer, and moreover, the conversion rate thereof is determined. Further, the present inventors found that a large pit defect is a fatal defect in addition to a triangular defect caused by carbon inclusions in the SiC single crystal substrate, and have made the present invention. Further, pits generated due to dislocations of the SiC single crystal substrate are known as normal pits (for example, see patent document 2), and a large pit defect due to substrate carbon inclusions is a pit defect first discovered by the present inventors with respect to the normal pits.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a SiC epitaxial wafer in which large pit defects caused by substrate carbon inclusions, which are fatal defects of devices, are reduced, a method for manufacturing the same, a large pit defect detection method, and a defect identification method.
In order to solve the above problems, the present invention adopts the following technical means.
An aspect of the present invention relates to a SiC epitaxial wafer having an off-angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces/cm2The SiC epitaxial wafer having an SiC epitaxial layer formed on the 4H-SiC single crystal substrate, wherein the density of large pit defects caused by substrate carbon inclusions contained in the SiC epitaxial layer is 0.5 pieces/cm2The following.
A method for manufacturing a SiC epitaxial wafer according to one aspect of the present invention is a method for manufacturing a SiC epitaxial wafer having an off-angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces/cm2The method for producing a SiC epitaxial wafer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate according to (1), comprising an epitaxial growth step of growing an epitaxial layer on the SiC single crystal substrate, wherein in the epitaxial growth step, the growth rate is set to 5 to 100 μm/hr, the growth temperature is set to 1500 ℃ or higher, and the C/Si ratio is set to 1.25 or lower.
In the method for producing a SiC epitaxial wafer, the C/Si ratio may be 1.10 or less.
In the method for manufacturing a SiC epitaxial wafer, the density of large pit defects caused by substrate carbon inclusions contained in the SiC epitaxial layer can be sorted to0.5 pieces/cm2The following SiC epitaxial wafers.
In a method for detecting a large pit defect according to an aspect of the present invention, a confocal microscope having a confocal differential interference optical system is used to detect a large pit defect in an SiC epitaxial layer of an SiC epitaxial wafer.
A defect recognition method according to an aspect of the present invention is a method for recognizing a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate, and recognizes a large pit defect caused by substrate carbon inclusions from other defects by comparing a position of the substrate carbon inclusions in the SiC single crystal substrate measured by a confocal microscope having a confocal differential interference optical system with a position of the large pit defect in the SiC epitaxial layer.
A defect recognition method according to an aspect of the present invention is a method for recognizing a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate, and recognizes a large pit defect in the SiC epitaxial layer caused by substrate carbon inclusions in the SiC single crystal substrate and a defect in the SiC epitaxial layer caused by a falling object, using a confocal microscope and a photoluminescence device having a confocal differential interference optical system.
A defect recognition method according to an aspect of the present invention is a method for recognizing a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate, and recognizes a large pit defect in the SiC epitaxial layer caused by substrate carbon inclusion in the SiC single crystal substrate and a defect in the SiC epitaxial layer caused by threading dislocation in the SiC single crystal substrate using a confocal microscope and a photoluminescence device having a confocal differential interference optical system.
According to the SiC epitaxial wafer of the present invention, it is possible to provide an epitaxial wafer in which large pit defects caused by substrate carbon inclusions, which are fatal defects of devices, are reduced.
According to the method for manufacturing a SiC epitaxial wafer of the present invention, it is possible to provide a method for manufacturing a SiC epitaxial wafer in which large pit defects caused by substrate carbon inclusions, which are fatal defects of devices, are reduced.
According to the large pit defect detection method of the present invention, it is possible to provide a large pit defect detection method capable of detecting a large pit defect in a SiC epitaxial layer of a SiC epitaxial wafer.
According to the defect identifying method of the present invention, it is possible to provide a defect identifying method capable of identifying a large pit defect caused by substrate carbon inclusions in a SiC epitaxial layer of a SiC epitaxial wafer.
According to the defect identifying method of the present invention, it is possible to provide a defect identifying method capable of identifying a large pit defect of a SiC epitaxial layer caused by substrate carbon inclusions in a SiC single crystal substrate and a defect of the SiC epitaxial layer caused by a falling object.
According to the defect identifying method of the present invention, it is possible to provide a defect identifying method capable of identifying a large pit defect of a SiC epitaxial layer caused by substrate carbon inclusions in a SiC single crystal substrate and a defect of the SiC epitaxial layer caused by threading dislocations in the SiC single crystal substrate.
Drawings
Fig. 1 shows an image of a substrate carbon inclusion (left side) and 4 types of defects caused by the substrate carbon inclusion (right side) obtained by a confocal microscope as a surface inspection apparatus using a confocal differential interference optical system, wherein (a) is an image including a large pit defect, (b) is an image including a triangular defect, (c) is an image including an oblique line defect, and (d) is an image including a convex defect.
Fig. 2 is a STEM image of a cross section near a large pit defect due to substrate carbon inclusions.
Fig. 3 is a STEM image of a normal pit caused by a dislocation of a single crystal substrate.
Fig. 4 is a cross-sectional STEM image of the carbon inclusion itself of the substrate.
Fig. 5 is EDX data of the carbon inclusion fraction.
FIG. 6 is EDX data of 4H-SiC parts.
Fig. 7 is a confocal microscope image and a cross-sectional STEM image of a convex defect after epitaxial layer formation.
Fig. 8 is an enlarged image of a carbon inclusion portion of a protrusion defect converted into the cross-sectional STEM image shown in fig. 7 and EDX data.
Fig. 9 is a graph showing the results of examining the change in conversion rate to a large pit defect and a triangular defect, which are critical defects of a device, according to the C/Si ratio.
Fig. 10 is a graph showing the results of examining the change in conversion rate to the bump defect and the oblique line defect, which are non-device-fatal defects, according to the C/Si ratio.
Fig. 11 is a graph showing the dependence of the conversion rate to the device critical defect and the non-device critical defect on the film thickness of the epitaxial film.
The left image in fig. 12 is a SICA image in the vicinity of a large pit defect caused by substrate carbon inclusions on the SiC epitaxial wafer surface, and the right image is a PL image thereof.
The left image in fig. 13 is a SICA image in the vicinity of a pit due to a falling object on the single crystal substrate on the SiC epitaxial wafer surface, and the right image is a PL image thereof.
Fig. 14(a) shows a Large pit defect (Large-pit) caused by substrate carbon inclusions on the surface of the SiC epitaxial wafer and SICA images in the vicinity of the defect starting from a Threading Dislocation (TD) of the substrate, and (b) shows PL images thereof.
Detailed Description
Hereinafter, the structure of the SiC epitaxial wafer and the method for manufacturing the same to which the present invention is applied will be described with reference to the drawings. In the drawings used in the following description, for the sake of easy understanding of the features, the portions that become the features may be shown enlarged for convenience, and the dimensional ratios of the respective components 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 these examples, and can be implemented by being appropriately changed within a range in which the effects of the present invention are exhibited.
(SiC epitaxial wafer)
An SiC epitaxial wafer according to an embodiment of the present invention has an off-angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces/cm2A SiC epitaxial wafer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate, wherein a large pit defect caused by substrate carbon inclusion contained in the SiC epitaxial layerHas a density of 0.5 pieces/cm2The following.
The 4H — SiC single crystal substrate used for the SiC epitaxial wafer of the present invention is a substrate having an off angle of, for example, 0.4 ° or more and 8 ° or less. Typically, a 4H-SiC single crystal substrate having an off-angle of 4 degrees is used.
An SiC epitaxial wafer according to an embodiment of the present invention is characterized in that: the density of the carbon inclusion of the substrate is 0.1-6.0/cm2The 4H-SiC single crystal substrate of (1).
The density of large pit defects caused by substrate carbon inclusions contained in the SiC epitaxial layer was set to 0.5 pieces/cm2The reason for this is that a large pit defect is a critical defect of the device.
That is, a schottky barrier diode manufactured using a SiC epitaxial wafer including a large pit defect was manufactured, and a reverse bias voltage was applied to measure a reverse leakage current, and as a result, a large current leakage occurred at a low reverse bias voltage. Therefore, it is known that the large pit defect is a defect which can become a fatal defect of the final semiconductor device. Therefore, it is important to reduce the density of large pit defects, as in the case of the triangular defects. On the other hand, the schottky barrier diode including the bump defect and the inclined line defect does not leak the current.
The present inventors found a method for reducing such large pit defects, and created SiC epitaxial wafers of the present invention. Hereinafter, this will be explained first.
(kind of surface defects caused by carbon inclusions of the substrate)
As a result of intensive studies, the present inventors have obtained a confocal microscopic image of the surface of a SiC single crystal substrate, confirmed the position and number of carbon inclusions in the surface of the substrate, then formed a SiC epitaxial wafer by forming a SiC epitaxial layer on the SiC single crystal substrate, obtained a confocal microscopic image of the surface of the SiC epitaxial layer, and butted the confocal microscopic image of the surface of the SiC epitaxial layer with the confocal microscopic image of the surface of the substrate, thereby confirming and studying what kind of defect each carbon inclusion is in the SiC epitaxial layer and appears. It was thus found that the carbon inclusions of the SiC single crystal substrate were converted (transformed) into approximately 4 kinds of defects in the SiC epitaxial layer, and the conversion rate thereof was determined. Here, although it is difficult to identify the defect type, the present invention has a great significance in determining the "at least main" defect type in the present situation where information on the relationship between the substrate carbon inclusion and the defect caused thereby is small.
Fig. 1 shows images of the 4 types of defects (hereinafter, also referred to as SICA images) obtained by a confocal microscope (SICA 6X, manufactured by レーザーテック co.) as a surface inspection apparatus using a confocal differential interference optical system. In each of fig. 1(a) to (d), the SICA image on the right side is a SICA image on the surface of the SiC epitaxial layer, and is a large pit defect, a triangular defect, a diagonal defect, and a bump defect, respectively, in this order. In each of fig. 1(a) to (d), the SICA image on the left side is an SICA image of the substrate surface. In the SICA image on the left side, an image of a substrate carbon inclusion was observed as described later.
The SiC epitaxial wafer shown in fig. 1 was obtained by using the same production method as the SiC epitaxial wafer from which the data shown in fig. 9 to 11 described later were obtained, with the C/Si ratio being 1.1. The same applies to the SiC epitaxial wafers shown in fig. 2 to 8 and fig. 12 to 14 below.
The carbon inclusion of the SiC single crystal substrate and the characteristics of the 4 defects described above will be described.
The carbon inclusions of the SiC single crystal substrate were observed by a confocal microscope, and were defects of black pits in the SICA image on the substrate surface. Carbon inclusions of the SiC single crystal substrate are generated by carbon blocks flying during crystal formation entering the ingot. Even in the same ingot, the position thereof varies depending on the SiC single crystal substrate. As described later, since the peak of carbon is strongly detected with respect to the carbon inclusion of the SiC single crystal substrate, it becomes possible to distinguish a defect caused by the carbon inclusion of the SiC single crystal substrate from other defects.
A large pit defect in the SiC epitaxial layer is a defect that can be observed by a confocal microscope and appears as a pit on the surface of the SiC epitaxial layer (in this specification, sometimes referred to as an "epitaxial surface"). Carbon inclusions of the substrate with respect to the starting points of the large pit defects, anda part of the carbon inclusions is depleted, and the carbon inclusions extend in a direction perpendicular to the off-angle of the substrate, thereby forming deep pits. Regarding the size of the large pit defect, the typical size is 200 to 500 μm2。100μm2The following small and large pit defects are difficult to distinguish from normal pits, but can be distinguished by comparing the positions of the defects with those of the substrate. That is, the pits at the positions corresponding to the positions of the carbon inclusions on the substrate surface are large pit defects.
The triangular defect of the SiC epitaxial layer is observable by a confocal microscope, and is a defect that appears triangular on the epitaxial surface. The starting point is the carbon inclusion of the substrate, and the 3C polycrystalline layer extends from the carbon inclusion along the direction perpendicular to the off-angle of the substrate, and is exposed at the epitaxial surface. The triangular defects include triangular defects caused by furnace particles (falling objects), and are not distinguished from confocal microscopic images of SiC epitaxial layers, but can be distinguished from confocal microscopic images of SiC single crystal substrates by comparison.
That is, since the substrate carbon inclusion is observed at the position of the triangular defect due to the substrate carbon inclusion in the confocal microscopic image of the SiC single crystal substrate, the falling object does not exist in the SiC single crystal substrate, and therefore, the falling object does not exist in the confocal microscopic image before being placed in the growth furnace. That is, the falling object falls on the SiC single crystal substrate before the SiC epitaxial layer is grown or falls on the SiC epitaxial layer during the SiC epitaxial layer growth in manufacturing the SiC epitaxial wafer.
The oblique line defects of the SiC epitaxial layer were observed by a confocal microscope, and were seen as oblique lines on the epitaxial surface, and some of the stacking faults were observed. The starting point is the carbon inclusion of the substrate, and the oblique line extends from the carbon inclusion along the vertical direction of the deflection angle of the substrate and is exposed on the epitaxial surface. In addition, although the oblique line defects caused by the substrate dislocation are not distinguished from the confocal microscopic image of the SiC epitaxial layer, they can be distinguished from the confocal microscopic image of the SiC single crystal substrate by comparison.
The protrusion defect of the SiC epitaxial layer is observable by a confocal microscope, and is a defect that appears to be a buried protrusion on the epitaxial surface. The projections extend from the carbon inclusions in the direction perpendicular to the off-angle of the substrate, and the defects are buried to some extent by the deposition of the SiC epitaxial layer.
The conversion rate to 4 defects caused by substrate carbon inclusions is specifically determined as follows.
As the SiC single crystal substrate, a 6-inch 4H — SiC single crystal substrate having an off-angle of 4 ° with respect to the (0001) Si face in the <11-20> direction was used.
After a known polishing process was performed on each of 12 pieces of 4H-SiC single crystal substrates, a SICA image was obtained using a confocal microscope (SICA 6X, manufactured by レーザーテック) for the polished substrate, and positional information of carbon inclusions on the substrate surface was recorded. The number of carbon inclusions in each SiC single crystal substrate is 6 to 49, and the average number is about 29. That is, the density of the carbon inclusions in the substrate was 0.06/cm2About 0.47 pieces/cm2Average of about 0.28 pieces/cm2。
Then, the single crystal substrate was set in a CVD apparatus, and a cleaning (etching) step of the substrate surface using hydrogen gas was performed.
Subsequently, an SiC epitaxial growth step was performed using silane and propane as raw material gases while supplying hydrogen gas as a carrier gas at a growth temperature of 1600 ℃ and a C/Si ratio of 1.22, and an SiC epitaxial layer having a film thickness of 9 μm was formed on the SiC single crystal substrate to obtain an SiC epitaxial wafer.
Here, the C/Si ratio is an atomic ratio of C to Si.
The SiC epitaxial wafer was again subjected to confocal microscopy (SICA 6X, manufactured by レーザーテック corporation) to obtain an SICA image, and the SICA image was classified into the above 4 types of defects. The measurement range was set so that the entire wafer of 3mm was excluded from the outer peripheral edge. Based on the number of each defect classified, the conversion ratio of each defect is calculated from the number of each defect relative to the total number of carbon inclusions of the substrate.
The conversion rates to the large pit defect, the triangular defect, the diagonal defect, and the convex defect were 24.4%, 13.6%, 4.3%, and 57.6%, respectively.
Although this conversion ratio varies depending on the production conditions of the SiC epitaxial wafer, if the growth rate is 20 μm/hour or more and the growth temperature is 1500 ℃ or more, the same conversion ratio tends to be obtained under the same production conditions of the C/Si ratio. Therefore, for example, when the density of large pit defects, which are fatal defects, is to be equal to or less than a predetermined density, a SiC single crystal substrate having a predetermined carbon inclusion density or less, which is inversely calculated from the conversion ratio, may be used.
For example, when the conversion rates based on the large pit defect and the triangular defect are 24.4% and 13.6%, the carbon inclusion density in the substrate is 0.06 pieces/cm as described above2About 0.47 pieces/cm2In the case of (2), the defect density of each of the large pit defect and the triangular defect was 0.015 piece/cm20.115 pieces/cm20.008 pieces/cm20.064 pieces/cm2。
When the conversion rate to the large pit defect was 24.4%, the density of the large pit defect due to the carbon inclusion of the substrate was 0.5 pieces/cm2In the case of the following SiC epitaxial wafer, the substrate carbon inclusion density was 2.0 pieces/cm2The following SiC single crystal substrate may be used.
When the conversion rate to the large pit defect is p%, the density of the large pit defect to be obtained is q/cm by general expression2In the case of the following SiC epitaxial wafer, the substrate carbon inclusion density is (100 Xq/p) pieces/cm2The following SiC single crystal substrate may be used.
In the SiC epitaxial wafer of the present invention, the lower the density of large pit defects caused by substrate carbon inclusion, the better, but the lower limit is 0.01 to 0.03 pieces/cm when the density of substrate carbon inclusion is in the range of the lower limit2Left and right.
Next, the characteristics of each defect will be described.
FIG. 2 shows an image (STEM image) of a cross section near a large pit defect due to a carbon inclusion in a substrate, which is obtained by a Scanning Transmission Electron Microscope (STEM) (HF-2200, a product of Hitachi Kagaku K.K.). For comparison, fig. 3 shows a STEM image of a normal pit caused by a dislocation of a single crystal substrate.
The STEM images shown in fig. 2 to 4 and 7 are for explaining the characteristics of each defect, and the dimensions thereof are as shown in the drawings.
The STEM image shown in fig. 2 is an example, but in the STEM image, carbon inclusions are observed in the substrate at the lower position. In addition, there are dislocations extending from the substrate carbon inclusions via the abnormal growth portion, and a large pit defect ("deep pit" in fig. 2) is observed on the front surface side of the dislocation. As described above, the STEM image shown in fig. 2 clearly shows: the cause of large pit defects on the epitaxial surface is substrate carbon inclusions. As shown in fig. 2, dislocations may or may not penetrate into the epitaxial layer between the substrate carbon inclusions and the large pits on the surface. In addition, large and deep pits are formed in the epitaxial surface.
On the other hand, as is clear from fig. 3, in a STEM image of a normal pit caused by a dislocation of a single crystal substrate, no carbon inclusion exists in the substrate, and a set of dislocations inherited from the substrate to an epitaxial layer is observed below the pit. In this case, only extremely small pits are formed in the epitaxial surface.
Therefore, the large pit defect caused by the substrate carbon inclusion described in the present invention is completely different from the usual pit caused by the dislocation of the single crystal substrate.
Fig. 4 is a cross-sectional STEM image of a foreign impurity on a substrate, and the presence of foreign matter can be confirmed. The composition of the foreign matter was confirmed by EDX (Energy Dispersive X-ray Spectroscopy).
Fig. 5 shows the results of EDX with respect to the foreign inclusions shown in fig. 4. The upper right image is an enlarged image of the vicinity of the foreign object inclusion in the STEM image of fig. 4, and the curve shows the result of EDX of the portion of the point in the foreign object indicated by the reference numeral 2.
On the other hand, the upper right image of fig. 6 is an enlarged image of the STEM image of fig. 4 in the vicinity of the foreign object inclusion, and the curve shows the result of EDX of the portion of the point other than the foreign object indicated by the mark 12.
As a result of EDX shown in fig. 5, since the peak of carbon was stronger than that of fig. 6, it was confirmed that the foreign matter was carbon (substrate carbon inclusion).
Fig. 7 is a cross-sectional STEM image of a portion where a SiC epitaxial layer is formed on a substrate carbon inclusion to become a protrusion defect. It is known that dislocations (observed as slightly dense straight lines in the STEM image) extend from the carbon inclusions of the substrate to reach the epitaxial surface. Shown in the upper part of the cross-sectional STEM image is a confocal microscopic image of the convex defect (surface defect) (the scale of the image is shown on the right side of the image), the correspondence with the convex defect (surface defect) of the cross-sectional STEM image is shown by the dashed arrow.
In fig. 7, the portion where the dislocations shown by the arrows reach the epitaxial surface corresponds to the end of the convex defect shown in the upper part of fig. 7.
FIG. 8 is an EDX measurement spectrum of an enlarged image of an inclusion portion corresponding to the bulge defect shown in FIG. 7 and its vicinity. In EDX shown in fig. 8, the peak of carbon was stronger in the portion of the inclusion (upper data) than in the portion other than the inclusion (lower data), and therefore it was confirmed that the foreign matter was carbon.
As can be seen from fig. 7 and 8, the protrusion defect shown in fig. 7 is caused by carbon inclusions in the substrate.
(method for producing SiC epitaxial wafer)
A method for manufacturing a SiC epitaxial wafer according to an embodiment of the present invention is a method for manufacturing a SiC epitaxial wafer having an off-angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces/cm2The method for producing a SiC epitaxial wafer having a SiC epitaxial layer formed on a 4H-SiC single crystal substrate according to (1), comprising an epitaxial growth step of growing an epitaxial layer on the SiC single crystal substrate, wherein in the epitaxial growth step, the growth rate of the SiC epitaxial layer in the thickness direction is set to 5 to 100 μm/H, the growth temperature is set to 1500 ℃ or higher, and the C/Si ratio is set to 1.25 or lower.
In the method for manufacturing a SiC epitaxial wafer of the present invention, "having an off-angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces/cm2The 4H-SiC single crystal substrate "mentioned above is a prerequisite.
According to the inventionOne of the characteristics of the method for manufacturing SiC epitaxial wafer is that the density of carbon inclusion in the substrate is 0.1-6.0 pieces/cm2The 4H-SiC single crystal substrate of (1). The substrate preferably has a carbon inclusion density of 0.1 to 4.5/cm2More preferably, the substrate has a carbon inclusion density of 0.1 to 3.5 particles/cm2The substrate (2) is more preferably a substrate having a carbon inclusion density of 0.1 to 2.5 particles/cm2The substrate of (1).
Fig. 9 and 10 are graphs showing the results of examining the change in the conversion rate to each defect type for each SiC epitaxial wafer in which the growth temperature was 1600 ℃ and the C/Si ratio was changed to 0.80, 0.95, 1.10, and 1.22, and the SiC epitaxial wafer in which the (0001) Si face was used<11-20>The direction has a deflection angle of 4 degrees, and the density of the carbon inclusion on the substrate is 0.1-6.0/cm2The 6-inch 4H-SiC single crystal substrate was subjected to a known polishing step and a cleaning (etching) step of the substrate surface, and then a SiC epitaxial growth step was performed using silane and propane as raw material gases while supplying hydrogen gas as a carrier gas, thereby forming a SiC epitaxial layer having a film thickness of 30 μm on the SiC single crystal substrate. The conversion rate to each defect type is hardly affected in the range of the growth temperature and growth rate described later.
Fig. 9 shows the results of examining the change in conversion rate to a large pit defect and a triangular defect, which are fatal defects of a device, and fig. 10 shows the results of examining the change in conversion rate to a diagonal defect and a bump defect.
As shown in fig. 9, the larger the C/Si ratio, the larger the conversion ratio to the large pit defect. Specifically, the C/Si ratios are 0.80, 0.95, 1.10, and 1.22, respectively, which are 0%, 0.6%, 4.5%, and 16.1%, respectively, and when the C/Si ratio exceeds 1.10, the conversion rate to the large pit defect exceeds 5%. Therefore, in order to suppress the conversion rate to the 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 large pit defect and the triangular defect in total is shown as the conversion rate to the fatal defect.
The conversion rate to the triangular defect is also inferior to that to the large pit defect, but the larger the C/Si ratio, the larger the conversion rate. The conversion rate to triangular defects was as low as 3% or less at any C/Si ratio. Specifically, the C/Si ratios are 1.7%, 2.6%, 2.2%, and 2.7% when they are 0.80, 0.95, 1.10, and 1.22, respectively.
The larger the C/Si ratio, the larger the conversion rate to the fatal defect that sums together the large pit defect and the triangular defect. Specifically, the C/Si ratios are 1.7%, 3.2%, 6.7%, and 18.8% when the C/Si ratios are 0.80, 0.95, 1.10, and 1.22, respectively, and the conversion rate to the fatal defect exceeds 6% when the C/Si ratio is 1.10. Therefore, in order to suppress the conversion rate to the killer defect to 6% or less, it is necessary to suppress the C/Si ratio to 1.10 or less.
In contrast, as shown in fig. 10, the larger the C/Si ratio, the smaller the conversion rate to Bump defects (Bump). Specifically, the C/Si ratios were 97.2%, 94.8%, 92.7%, and 79.6% for 0.80, 0.95, 1.10, and 1.22, respectively, and the conversion rate to the protrusion defect exceeded 92% for 1.10 or less. Therefore, in order to increase the conversion rate to the bump defect to 92% or more, it is necessary to make the C/Si ratio 1.10 or less.
In addition, the conversion rate to the syncline defect is different from that to the bump defect, and even if the C/Si ratio is changed, it does not change greatly. Specifically, when the C/Si ratios are 0.80, 0.95, 1.10, and 1.22, respectively, the C/Si ratios are 1.1%, 1.9%, 0.6%, and 1.6%, respectively, and the conversion rate to the splay defects is as small as less than 2% in any of the C/Si ratios.
The larger the C/Si ratio, the smaller the conversion rate to non-fatal defects that sum up protrusion defects and diagonal defects. Specifically, the C/Si ratios are 98.3%, 96.7%, 93.3%, and 81.2% for 0.80, 0.95, 1.10, and 1.22, respectively, and the conversion rate to non-fatal defects exceeds 93% for 1.10. Therefore, in order to increase the conversion rate to non-fatal defects to 93% or more, it is necessary to make the C/Si ratio 1.10 or less.
The relationship between the conversion ratio of each defect type and the epitaxial film thickness (epitaxial film thickness) was examined. The conversion rates to device-critical defects and non-device-critical defects were summarized in fig. 11, with the C/Si ratio fixed at 1.22 and the epitaxial film thicknesses set at 9 μm, 15 μm, and 30 μm. The larger the film thickness, the smaller the conversion rate to the fatal defect. Specifically, when the film thickness is 9, 15, and 30 μm, respectively, it is 38.1%, 24.5%, and 18.8%, respectively, and when the C/Si ratio is 1.22, when the epitaxial film thickness is 30 μm, the conversion rate to the fatal defect is suppressed to 20% or less. That is, it was found that the conversion rate to each defect type is affected by the C/Si ratio and also by the epitaxial film thickness. In other words, the conversion rate to each defect can be controlled by using 2 parameters of the C/Si ratio and the epitaxial film thickness. Generally, when the C/Si ratio is large, uniformity of impurity concentration becomes good. When the C/Si ratio is to be increased in order to give priority to the uniformity of the impurity concentration, the conversion rate to a fatal defect can be suppressed by increasing the epitaxial film thickness.
In the method for manufacturing a 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 to large pit defects, the C/Si ratio is preferably 1.22 or less, more preferably 1.15 or less, and still more preferably 1.10 or less. In order to reduce the conversion rate to large pit defects, the C/Si ratio is preferably a smaller value. When the C/Si ratio is 1.22 or less, the conversion rate to the large pit defect can be 16% or less, when the C/Si ratio is 1.10 or less, the conversion rate to the large pit defect can be 4.5% or less, when the C/Si ratio is 1.05 or less, the conversion rate to the large pit defect can be 3.0% or less, when the C/Si ratio is 1.0 or less, the conversion rate to the large pit defect can be 2.0% or less, when the C/Si ratio is 0.95 or less, the conversion rate to the large pit defect can be 0.6% or less, and when the C/Si ratio is 0.90 or less, the conversion rate to the large pit defect can be 0%.
In the method for manufacturing a 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 made smaller. In the case where the epitaxial film thickness is thicker than 15 μm, the C/Si ratio may be slightly larger.
In the method for manufacturing a SiC epitaxial wafer according to an embodiment of the present invention, the growth rate in the epitaxial growth step is 5 to 100 μm/hr, although not particularly limited.
Since productivity is improved when the growth rate is high, the growth rate is preferably 20 μm/hr or more, more preferably 40 μm/hr or more, and still more preferably 60 μm/hr or more.
In the method for manufacturing a SiC epitaxial wafer according to an embodiment of the present invention, the growth temperature in the epitaxial growth step is 1500 ℃. If the temperature is too low, stacking faults increase, and if the temperature is too high, there is a problem of deterioration of the furnace member, so the growth temperature is preferably 1500 ℃ or more, more preferably 1550 ℃ or more, and further preferably 1600 ℃ or more. The upper limit is, for example, about 1750 ℃.
In the method for manufacturing a SiC epitaxial wafer according to one embodiment of the present invention, the density of the large pit defects caused by substrate carbon inclusions, which are sorted in the SiC epitaxial layer before epitaxial growth, may be set to 0.5 pieces/cm2The following steps of the SiC epitaxial wafer.
(method of detecting Large pit Defect)
A method for detecting a large pit defect according to an embodiment of the present invention detects a large pit defect in an SiC epitaxial layer of an SiC epitaxial wafer using a confocal microscope having a confocal differential interference optical system.
Since the large pit defect in the SiC epitaxial layer starts from the substrate carbon inclusion, the large pit defect in the SiC epitaxial layer of the SiC epitaxial wafer can be easily detected by comparing the confocal microscopic image of the SiC single crystal substrate with the confocal microscopic image of the SiC epitaxial wafer (i.e., the SiC epitaxial layer). By using the SICA6X apparatus capable of outputting coordinates of each defect and observing a defect image in detail, the substrate and the epitaxial wafer can be easily compared.
(Defect identifying method (embodiment 1))
A defect recognition method according to embodiment 1 of the present invention is a method for recognizing a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate, and recognizes a large pit defect caused by substrate carbon inclusion by comparing a position of the substrate carbon inclusion in the SiC single crystal substrate measured by a confocal microscope having a confocal differential interference optical system with a position of the large pit defect in the SiC epitaxial layer.
(Defect identifying method (embodiment 2))
A defect recognition method according to embodiment 2 of the present invention is a method for recognizing a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate, and recognizes a large pit defect in the SiC epitaxial layer caused by substrate carbon inclusions in the SiC single crystal substrate and a defect in the SiC epitaxial layer caused by a falling object using a confocal microscope and a near infrared photoluminescence device (NIR-PL) having a confocal differential interference optical system.
The left side (front side) of fig. 12 shows an SICA image of the surface of the SiC epitaxial wafer near a large pit defect caused by substrate carbon inclusions, and the right side (NIR) shows a PL image thereof obtained by using a near-infrared photoluminescence device (SICA 87, manufactured by レーザーテック corporation) at a light receiving wavelength of band pass (630 to 780 nm). In fig. 13, in comparison, SICA and PL images of a pit (defect) due to a falling object on the single crystal substrate are shown on the left side (front surface) and the right side (NIR), respectively.
In the SICA image, a large pit defect due to a substrate carbon inclusion and a pit due to a falling object are both circular in shape, and it is difficult to clearly distinguish them. In contrast, in the PL image, the pits due to the falling objects are circular in shape, while the large pit defects due to the substrate carbon inclusions are mostly spider-nest shaped, and in this case, the difference between the two is clear.
Even when the PL image of a large pit defect due to a carbon inclusion in the substrate has a circular shape, the PL image can be distinguished from a pit starting from a falling object if the position of the carbon inclusion observed in the SICA image of the SiC single crystal substrate is compared. In the near-infrared photoluminescence device, when the PL image of a large pit defect is compared with a light receiving wavelength of a band pass of 400 to 678nm or a band pass of 370 to 388nm, the spider-nest portion looks black, and the portion corresponding to the nucleus looks white, so that the near-infrared photoluminescence device can be distinguished from a pit due to a falling object as seen in the same manner as in fig. 13.
(Defect identifying method (embodiment 3))
A defect recognition method according to embodiment 3 of the present invention is a method for recognizing a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate, and recognizes a large pit defect in the SiC epitaxial layer caused by substrate carbon inclusions in the SiC single crystal substrate and a defect in the SiC epitaxial layer caused by through dislocations in the SiC single crystal substrate using a confocal microscope and a near-infrared photoluminescence device having a confocal differential interference optical system.
FIG. 14(a) shows Large pit defects (Large-pit) on the surface of a SiC epitaxial wafer caused by substrate carbon inclusions and SICA images in the vicinity of the defects caused by substrate Threading Dislocations (TD), and FIG. 14(b) shows PL images of these defects obtained at light receiving wavelengths of band-pass wavelengths (630 to 780nm) using a near-infrared photoluminescence device (SICA 87, manufactured by レーザーテック Co., Ltd.).
While a large pit defect caused by a substrate carbon inclusion and a defect starting from a threading dislocation of the substrate appear similar in the SICA image in fig. 14(a), in the PL image in fig. 14(b), the defect starting from a threading dislocation of the substrate does not emit light, and the large pit defect appears to be in a spider-nest shape, and can be clearly distinguished.
Industrial applicability
The SiC epitaxial wafer and the method for producing the same according to the present invention can be used, for example, as a SiC epitaxial wafer for a power semiconductor and a method for producing the same.

Claims (8)

1. A SiC epitaxial wafer characterized in that it has a bias angle and a substrate carbon inclusion density of 0.1 to 6.0 pieces/cm2A SiC epitaxial wafer having a SiC epitaxial layer formed on the 4H-SiC single crystal substrate,
the density of large pit defects caused by substrate carbon inclusions contained in the SiC epitaxial layer was 0.5 pieces/cm2The following.
2. A method for producing a SiC epitaxial wafer, characterized in that the SiC epitaxial wafer is produced at an off-angle with a substrate carbon inclusion density of 0.1 to 6.0 pieces/cm2A SiC epitaxial wafer having a SiC epitaxial layer formed on the 4H-SiC single crystal substrate of (1),
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/hr, the growth temperature is set to 1500 ℃ or higher, and the C/Si ratio is set to 1.25 or lower.
3. The method of manufacturing a SiC epitaxial wafer according to claim 2, wherein,
the C/Si ratio is set to 1.10 or less.
4. The method of manufacturing a SiC epitaxial wafer according to claim 2 or 3, wherein,
the density of large pit defects caused by substrate carbon inclusions contained in the SiC epitaxial layer was sorted to 0.5 pieces/cm2The following SiC epitaxial wafers.
5. A method for detecting the defect of big pit,
detecting a large pit defect in a SiC epitaxial layer of the SiC epitaxial wafer using a confocal microscope having a confocal differential interference optical system,
the large pit defect is a defect caused by substrate carbon inclusions contained in the SiC epitaxial layer.
6. A defect identifying method for identifying a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate,
the position of the substrate carbon inclusion in the SiC single crystal substrate measured by a confocal microscope having a confocal differential interference optical system is compared with the position of the large pit defect in the SiC epitaxial layer, and thereby the large pit defect caused by the substrate carbon inclusion is identified from the other defects.
7. A defect identifying method for identifying a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate,
a confocal microscope and a photoluminescence device having a confocal differential interference optical system are used to identify a large pit defect of a SiC epitaxial layer caused by substrate carbon inclusions in the SiC single crystal substrate and a defect of the SiC epitaxial layer caused by a falling object.
8. A defect identifying method for identifying a defect in a SiC epitaxial layer of a SiC epitaxial wafer having the SiC epitaxial layer formed on a SiC single crystal substrate,
a confocal microscope and a photoluminescence device having a confocal differential interference optical system are used to identify a large pit defect of a SiC epitaxial layer caused by substrate carbon inclusions in the SiC single crystal substrate and a defect of the SiC epitaxial layer caused by threading dislocations in the SiC single crystal substrate.
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