阅读说明：本技术 SiC外延晶片及其制造方法 (SiC epitaxial wafer and method for producing same ) 是由 龟井宏二 于 2018-05-14 设计创作，主要内容包括：本发明的SiC外延晶片具备4H-SiC单晶基板和形成于所述4H-SiC单晶基板上的SiC外延层,所述4H-SiC单晶基板以相对于c面具有偏离角的面为主面,且在周缘部具有斜角部,所述SiC外延层的膜厚为20μm以上,所述SiC外延层的从外周端延伸存在的界面位错的密度为10根/cm以下。(The SiC epitaxial wafer of the present invention comprises a 4H-SiC single crystal substrate and a SiC epitaxial layer formed on the 4H-SiC single crystal substrate, wherein the 4H-SiC single crystal substrate has a surface having an off angle with respect to the c-surface as a main surface and a beveled portion at a peripheral portion, the thickness of the SiC epitaxial layer is 20 [ mu ] m or more, and the density of interface dislocations extending from the outer peripheral end of the SiC epitaxial layer is 10 roots/cm or less.)

1. A SiC epitaxial wafer comprising a 4H-SiC single crystal substrate and a SiC epitaxial film formed on the 4H-SiC single crystal substrate,

the 4H-SiC single crystal substrate has a surface having an off angle with respect to the c-surface as a main surface and a bevel portion at a peripheral portion,

the thickness of the SiC epitaxial film is 20 [ mu ] m or more,

the SiC epitaxial layer has an interface dislocation density of 10 or less atoms/cm extending from the outer peripheral end.

2. A SiC epitaxial wafer comprising a 4H-SiC single crystal substrate and a SiC epitaxial film formed on the 4H-SiC single crystal substrate,

the 4H-SiC single crystal substrate has a surface having an off angle with respect to the c-surface as a main surface and a bevel portion at a peripheral portion,

the thickness of the SiC epitaxial film is 20 [ mu ] m or more,

the beveled portion includes a beveled portion continuous from the major surface and an outer peripheral end portion,

the width of the inclined plane part is more than 150 mu m.

3. The SiC epitaxial wafer of claim 1,

the interface dislocation density in the central angle ranges of 25 DEG to 155 DEG and 205 DEG to 335 DEG is 10 roots/cm or less, with the central line of the <11-20> direction as the center.

4. The SiC epitaxial wafer of claim 1,

the beveled portion includes a beveled portion continuous from the major surface and an outer peripheral end portion,

the width of the inclined plane part is more than 150 mu m.

5. The SiC epitaxial wafer of claim 2,

the interface dislocation density in the central angle ranges of 25 DEG to 155 DEG and 205 DEG to 335 DEG is 10 roots/cm or less, with the central line of the <11-20> direction as the center.

6. The SiC epitaxial wafer of claim 2,

the SiC epitaxial layer has an interface dislocation density of 10 or less atoms/cm extending from the outer peripheral end.

7. A method for manufacturing a SiC epitaxial wafer uses a 4H-SiC single crystal substrate having a bevel portion at a peripheral edge portion, the bevel portion including a bevel portion continuous from the main surface and an outer peripheral end portion, the bevel portion having a width of 150 [ mu ] m or more.

8. The method for manufacturing a SiC epitaxial wafer according to claim 7, comprising:

preparing the H-SiC single crystal substrate; and

a step of forming a SiC epitaxial film having a film thickness of 20 μm or more on the H-SiC single crystal substrate,

the obtained SiC epitaxial wafer comprises a 4H-SiC single crystal substrate and a SiC epitaxial film formed on the 4H-SiC single crystal substrate,

the 4H-SiC single crystal substrate has a surface having an off angle with respect to the c-surface as a main surface and a bevel portion at a peripheral portion,

the thickness of the SiC epitaxial film is 20 [ mu ] m or more,

the SiC epitaxial layer has an interface dislocation density of 10 or less atoms/cm extending from the outer peripheral end.

9. The method for manufacturing an SiC epitaxial wafer according to claim 7,

the step of forming the SiC epitaxial film having a film thickness of 20 μm or more includes:

a sub-step of obtaining the thickness of the epitaxial film satisfying the formula (1) by using the width of the inclined surface portion of the substrate,

Y＝20X-400···(1)

wherein Y represents a width of the tilt, X represents a thickness of the epitaxial film, and the width Y and the thickness X are each in units of μm; and

and a sub-step of forming the SiC epitaxial film so that the thickness of the SiC epitaxial film is equal to or less than the thickness of the epitaxial film satisfying the formula (1) obtained by the above formula.

Technical Field

The present invention relates to a SiC epitaxial wafer and a method for manufacturing the same.

The present application claims priority based on patent application No. 2017-126744, filed in japan on 28.6.2017, the contents of which are incorporated herein by reference.

Background

Silicon carbide (SiC) has characteristics of 1 order of magnitude larger in dielectric breakdown electric field, 3 times larger in band gap, about 3 times higher in thermal conductivity, and the like, as compared with silicon (Si). Since silicon carbide has these characteristics, it is expected to be applied to power devices, high-frequency devices, high-temperature operating devices, and the like. Therefore, in recent years, SiC epitaxial wafers are used in the semiconductor devices as described above.

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

SiC devices are generally manufactured using SiC epitaxial wafers obtained by growing an SiC epitaxial layer (film) to be a device active region on a SiC single crystal substrate (also referred to simply as a SiC substrate) by Chemical Vapor Deposition (CVD) or the like, which is obtained by bulk single crystal processing of SiC grown by sublimation recrystallization or the like.

More specifically, the SiC epitaxial wafer generally performs step flow growth (lateral growth from an atomic step) of growing a 4H SiC epitaxial layer on a SiC single crystal substrate having a growth plane as a plane having an off angle from the (0001) plane in the <11-20> direction.

Generally, a SiC single crystal substrate has crystal defects called Threading Dislocation (TSD), Threading Edge Dislocation (TED), or Basal Plane Dislocation (BPD) therein, and device characteristics are sometimes deteriorated due to these crystal defects. These dislocations substantially propagate from the SiC single crystal substrate to the SiC epitaxial film.

On the other hand, it is known that dislocations called interface dislocations are generated in the SiC epitaxial film. The interface dislocation is one of basal plane dislocations, and is elongated in a direction orthogonal to a cutting direction of the SiC substrate (a <1-100> direction in the case where the cutting direction is <11-20 >) in the vicinity of an interface between the SiC substrate and the SiC epitaxial film.

The interface dislocation is generated to relax the elongation of the stress near the interface.

Further, not only threading edge dislocations propagating from the SiC single crystal substrate but also threading edge dislocation arrays ("TED pairs 9" in fig. 8) may be formed in the SiC epitaxial film. Specifically, 2 threading edge dislocations newly generated during epitaxial growth form pairs, and when the cutting direction is <11-20>, the 2 dislocation pairs are arranged in a row and continuous in the <1-100> direction, thereby forming threading edge dislocation arrays. As a result of occurrence of threading edge dislocation arrays, the dislocation density of the epitaxial film becomes higher than that of the SiC single crystal substrate, and crystallinity is deteriorated during epitaxial growth. The pair of threading edge dislocations are connected in a half-loop (half-loop) shape at the bottom thereof by basal plane dislocations.

Disclosure of Invention

Non-patent document 1 describes the relationship between the occurrence of threading edge dislocation arrays and the above-described interface dislocations, which is clearly known from observation by X-ray topography, Photoluminescence (PL), and the like, and the characteristics of X-ray topography images and PL images, with reference to fig. 8.

Fig. 8 is a perspective view schematically showing a SiC epitaxial wafer in which a SiC epitaxial film is formed on a SiC single crystal substrate. For easy and clear explanation, points a, B, and C, and AB and BC portions connecting them are shown.

In the X-ray topography images, L-shaped dislocations are observed. The L-shaped dislocations are dislocations in which the AB portion (interface dislocation 14) and the BC portion (basal plane dislocation 15) are observed in fig. 8. The BC portion crosses the SiC epitaxial film 5 with the (0001) basal plane 16 held, and terminates at a point C on the surface of the SiC epitaxial film 5. In the L-shaped dislocation, the BC portion (basal plane dislocation 15) moves to the right during epitaxial growth, and the AB portion (interface dislocation 14) extends to the right. When the AB portion (interface dislocation 14) extends rightward in this way, the threading edge dislocation arrays ("TED pairs 9" in fig. 8) are formed in order at the portion C, and a series of threading edge dislocation arrays is formed (hereinafter, a structure in which the threading edge dislocation arrays are arranged in a direction orthogonal to the step flow direction is referred to as a pair series (pair series 11 in fig. 8)). Thus, the occurrence of threading edge dislocation arrays is closely related to interface dislocations.

In the X-ray topography image, the image of the through-edge dislocation array exists at a position shallower from the surface as it goes to the right side, and thus the contrast becomes weaker.

In the X-ray topography image, most of the AB portion (interface dislocation), BC portion (basal plane dislocation), and through edge dislocation arrays were observed.

In the Photoluminescence (PL) image, a sequence of threading edge dislocations is observed as a dot sequence, and a BC portion (basal plane dislocation) is observed as a line. On the other hand, it is difficult to observe the AB portion (interface dislocation).

Therefore, in the PL image, the presence of the interface dislocation can be known by observing the line pattern corresponding to the dot sequence and the BC portion (basal plane dislocation).

The series of threading edge dislocations extend perpendicularly to the direction of the step flow, and the series of 1 threading edge dislocation and 1 interface dislocation caused by the formation of the threading edge dislocation extend parallel to each other. Therefore, by finding 1 dot sequence, the presence of 1 interface dislocation extending orthogonally to the step flow direction can be confirmed. Further, BC segments (basal plane dislocations) extend in parallel to the direction of the step flow, and 1 BC segment (basal plane dislocation) and 1 interface dislocation resulting therefrom extend orthogonally to each other, so that by finding a linear pattern corresponding to 1 BC segment (basal plane dislocation), it is possible to confirm the presence of 1 interface dislocation extending orthogonally to the direction of the step flow.

The above-described conventionally known interface dislocation occurs in a portion of the SiC substrate where Basal Plane Dislocations (BPDs) exist.

In contrast, the present inventors have found a novel interface dislocation (hereinafter referred to as "outer end interface dislocation") extending from the outer peripheral end of the SiC substrate when the SiC epitaxial film is grown on the SiC substrate. The present inventors have conducted extensive studies on the outer-end interface dislocation and found that the dislocation is generated by thickening the SiC epitaxial film. The conventional interface dislocation starts from a portion of the SiC substrate where BPD exists, but the interface dislocation (outer end interface dislocation) found by the present inventors starts from the outer peripheral edge of the SiC substrate, unlike the conventional interface dislocation. This interface dislocation also lowers the reliability of the device, similarly to the conventional interface dislocation, and therefore should be lowered.

It is considered that the reason why the dislocations in the outer end interface have not been found so far is that the SiC epitaxial film is used only in a small number of cases in which the film is so thick that the dislocations in the outer end interface occur.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a SiC epitaxial wafer having a SiC epitaxial film with a film thickness of 20 μm or more and a low density of dislocations at the interface at the outer end, and a method for manufacturing the same.

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

(1) A SiC epitaxial wafer according to a first aspect of the present invention includes a 4H-SiC single crystal substrate and a SiC epitaxial film formed on the 4H-SiC single crystal substrate, the 4H-SiC single crystal substrate having a plane having a departure angle from a c-plane as a main surface and a bevel portion (bevel portion) in a peripheral portion, the SiC epitaxial film having a film thickness of 20 μm or more, and the SiC epitaxial layer having an interface dislocation density extending from an outer peripheral end of 10 roots/cm or less.

(2) A SiC epitaxial wafer according to a second aspect of the present invention includes a 4H-SiC single crystal substrate and a SiC epitaxial film formed on the 4H-SiC single crystal substrate, the 4H-SiC single crystal substrate having a surface having an off angle with respect to a c surface as a main surface and a bevel portion at a peripheral edge portion, the SiC epitaxial film having a film thickness of 20 μm or more, the bevel portion including a bevel portion continuous from the main surface and an outer peripheral end portion, the bevel portion having a width of 150 μm or more.

(3) The SiC epitaxial wafer according to any one of (1) and (2) above may be: the interface dislocation density in the central angle ranges of 25 DEG to 155 DEG and 205 DEG to 335 DEG is 10 roots/cm or less, with the central line of the <11-20> direction as the center.

(4) The SiC epitaxial wafer according to any one of (1) to (3) above, wherein: the bevel portion includes a bevel portion continuous from the main surface and an outer peripheral end portion, and the bevel portion has a width of 150 μm or more.

(5) The SiC epitaxial wafer according to any one of (2) and (3) above may be: the SiC epitaxial layer has an interface dislocation density of 10 or less atoms/cm extending from the outer peripheral end.

(6) A method for producing a SiC epitaxial wafer according to a third aspect of the present invention uses a 4H-SiC single crystal substrate having a bevel portion at a peripheral edge portion, the bevel portion including a bevel portion continuous from the main surface and an outer peripheral end portion, the bevel portion having a width of 150 μm or more.

(7) The method for producing a SiC epitaxial wafer according to the third aspect of the present invention preferably includes:

preparing the H-SiC single crystal substrate; and

a step of forming a SiC epitaxial film having a film thickness of 20 μm or more on the H-SiC single crystal substrate,

the obtained SiC epitaxial wafer comprises a 4H-SiC single crystal substrate and a SiC epitaxial film formed on the 4H-SiC single crystal substrate,

the 4H-SiC single crystal substrate has a surface having an off angle with respect to the c-surface as a main surface and a bevel portion at a peripheral portion,

the thickness of the SiC epitaxial film is 20 [ mu ] m or more,

the SiC epitaxial layer has an interface dislocation density of 10 or less atoms/cm extending from the outer peripheral end.

In the method for producing a SiC epitaxial wafer according to any one of (6) and (7), the step of forming a SiC epitaxial film having a film thickness of 20 μm or more preferably includes:

a sub-step of obtaining the thickness of the epitaxial film satisfying the formula (1) by using the width of the inclined surface portion of the substrate,

Y＝20X-400···(1)

(wherein Y represents a width (μm) of the tilt, and X represents a thickness (μm) of the epitaxial film); and

and a sub-step of forming the SiC epitaxial film so that the thickness of the SiC epitaxial film is equal to or less than the thickness of the epitaxial film satisfying the formula (1) obtained by the above formula.

According to the SiC epitaxial wafer of the present invention, it is possible to provide a SiC epitaxial wafer having a SiC epitaxial film with a film thickness of 20 μm or more and a low dislocation density at the outer end interface.

Drawings

FIG. 1 is a schematic cross-sectional view of a SiC single crystal substrate in the vicinity of the peripheral edge thereof.

Fig. 2 is a schematic cross-sectional view of the vicinity of the peripheral edge of the SiC epitaxial wafer.

Fig. 3 is a schematic diagram showing a PL image and an observation site obtained for the SiC epitaxial wafer, fig. 3(a) is a PL image at the position of the orientation flat, fig. 3(b) is a PL image at the position opposite to the orientation flat, and fig. 3(c) is a schematic diagram showing the relationship between the position of the orientation flat and the step flow direction in the SiC epitaxial wafer.

Fig. 4A is a schematic cross-sectional view showing 2 stages of growth of the SiC substrate and the SiC epitaxial film grown thereon when the width of the bevel portion is large.

Fig. 4B is a schematic cross-sectional view showing 2 stages of growth of the SiC substrate and the SiC epitaxial film grown thereon when the width of the bevel portion is small.

Fig. 5 is a view showing the results of examining the relationship between the film thickness of the epitaxial film and the presence or absence of the occurrence of dislocations at the interface of the outer ends.

FIG. 6A is a confocal microscopic image shown in FIG. 5 with an inclined portion of 170 μm and a film thickness of the SiC epitaxial film of 28 μm.

FIG. 6B is the PL image shown in FIG. 5, with the inclined portion at 170 μm and the SiC epitaxial film at 28 μm thick.

FIG. 7A is the PL image shown in FIG. 5, with the inclined portion being 150 μm and the SiC epitaxial film having a thickness of 33 μm.

FIG. 7B is the PL image shown in FIG. 5, with the inclined portion being 0 μm and the SiC epitaxial film having a thickness of 33 μm.

Fig. 8 is a perspective view schematically showing a SiC epitaxial wafer in which a SiC epitaxial film is formed on a SiC single crystal substrate for explaining the relationship between the occurrence of threading edge dislocation arrays and interface dislocations.

Detailed Description

Preferred examples of the present invention will be described below. Specifically, a SiC epitaxial wafer and a method for manufacturing the same according to preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings used in the following description, for the sake of easy understanding of the features, a portion to be a feature may be enlarged for convenience, and the dimensional ratio of each component may be different from the actual one. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited thereto, and can be implemented with appropriate modifications within the scope of exhibiting the effects thereof. That is, the present invention is not limited to the following examples, and the position, number, shape, material, configuration, and the like may be added, omitted, replaced, and modified without departing from the scope of the present invention.

(SiC epitaxial wafer)

An SiC epitaxial wafer according to an embodiment of the present invention includes: a 4H-SiC single crystal substrate having a surface having an off-angle with respect to the c-surface as a main surface and a beveled portion at a peripheral portion; and a SiC epitaxial layer formed on the 4H-SiC single crystal substrate and having a film thickness of 20 [ mu ] m or more, wherein the density of interface dislocations extending from the outer peripheral end of the SiC epitaxial layer is 10 roots/cm or less.

"interface dislocations extending from the outer peripheral end" means "outer end interface dislocations".

The c plane represents a 0001 plane. The (0001) plane in the c plane is referred to as a (0001) Si plane.

The density of interface dislocations extending from the outer peripheral end can be measured, for example, by a Photoluminescence (PL) image. As the PL image, for example, a PL image obtained by using a photoluminescence device (SICA 88, manufactured by Lasertec ltd) at a Near-infrared (NIR) light receiving wavelength can be used.

The SiC epitaxial wafer of the present invention includes a wafer in which the thickness of the SiC epitaxial layer is 20 μm or more and the interface dislocation density of the outer end interface dislocation is zero/cm.

The SiC epitaxial wafer of the present invention includes a wafer in which the thickness of the SiC epitaxial layer is 22 μm or more and the interface dislocation density of the outer end interface dislocation is zero root/cm.

The SiC epitaxial wafer of the present invention includes a wafer in which the thickness of the SiC epitaxial layer is 24 μm or more and the interface dislocation density of the outer end interface dislocation is zero root/cm.

The SiC epitaxial wafer of the present invention includes a wafer in which the thickness of the SiC epitaxial layer is 27 μm or more and the interface dislocation density of the outer end interface dislocation is zero root/cm.

The SiC epitaxial wafer of the present invention includes a wafer in which the thickness of the SiC epitaxial layer is 29 μm or more and the interface dislocation density of the outer end interface dislocation is zero root/cm.

FIG. 1 is a schematic cross-sectional view of a SiC single crystal substrate in the vicinity of the peripheral edge thereof.

The shape of the "beveled portion" referred to in the present description will be described with reference to fig. 1. In the present specification, the "chamfered portion" is a portion which is chamfered at the peripheral edge portion of the substrate and is thinner than the substrate in order to prevent generation of fragments and particles of the substrate.

The SiC single crystal substrate 1 has a principal surface (flat portion) 1A and a beveled portion 1A at its peripheral edge, and the beveled portion 1A includes a beveled portion 1Aa and an outer peripheral end portion 1 Ab. The beveled corner 1A can also be understood as follows.

"beveled portion 1A" + "beveled portion 1 Aa" + "outer peripheral end portion 1 Ab"

The "inclined surface portion" is a portion continuing from the flat portion 1a of the SiC single crystal substrate, and has an inclined surface inclined toward the outer periphery at a predetermined angle (angle facing a plane including the main surface) of 60 ° or less with respect to the flat portion. The inclined surface is not limited to an inclined surface having only one angle, and may be an inclined surface having a plurality of angles and/or an inclined surface having a curved surface with a curvature (a curvature smaller than that of the "outer peripheral end portion"). In the case of an inclined surface having a curvature, the angle of the inclined surface means the angle of the tangent plane. As the angle of the inclined surface (angle facing the plane including the principal surface) of the "inclined surface portion", a SiC single crystal substrate of 50 ° or less, 40 ° or less, 30 ° or less, or 20 ° or less can be used. The data shown in fig. 5 described later uses a SiC single crystal substrate of 30 ° or less.

The "outer peripheral end portion" is a portion of the SiC single crystal substrate disposed on the outermost side in the radial direction, and includes a curved surface having a predetermined curvature. The curved surface is not limited to a curved surface having only one curvature, and may have a plurality of curvatures, and/or a portion that is not continuous with the "inclined surface portion" among portions constituting the "outer peripheral end portion" may be a flat surface (for example, a vertical surface). Further, based on the mechanism of occurrence of the outer end interface dislocation estimated later, it is considered that if there is no "outer end portion" and a structure in which the outer side is vertically inclined from the "inclined surface portion", a portion which becomes a nucleus which is a random growth origin may not be formed.

Fig. 2 is a schematic cross-sectional view of the vicinity of the peripheral edge of the SiC epitaxial wafer.

In the SiC epitaxial wafer 10, the outer peripheral end 2a of the SiC epitaxial layer 2 is the radially outermost side of the SiC epitaxial layer 2 formed on the main surface (flat portion) 1a of the SiC single crystal substrate 1.

Fig. 3(a) and (b) show PL images obtained at different positions on the SiC epitaxial wafer. Fig. 3(c) is a schematic diagram showing the relationship between the position of the orientation flat and the step flow direction in the SiC epitaxial wafer.

Fig. 3(a) is a PL image at the position of the orientation plane, and fig. 3(b) is a PL image at the position on the opposite side of the orientation plane.

In both fig. 3(a) and 3(b), a line pattern corresponding to a dot sequence and a BC portion (basal plane dislocation) can be observed. In fig. 3(a), 1 line pattern corresponding to the dot sequence and BC portion (basal plane dislocation) is observed, and therefore, it can be seen that 1 external end interface dislocation exists. In fig. 3(b), since 2 lines are observed for each of the dot sequence and the line pattern corresponding to the BC portion (basal plane dislocation), it can be seen that 2 outer end interface dislocations exist.

Based on the PL observations made by the inventors, the outmost interface dislocations are most near the orientation plane, and secondly the outmost interface dislocations are at locations on the opposite side of the orientation plane. On the other hand, at a position between the orientation flat and the opposite side of the orientation flat, the direction perpendicular to the outer periphery of the connection line, that is, the inclination direction of the inclined surface portion of the inclined corner portion and the step flow direction are nearly parallel, and therefore, outer end interface dislocation is not substantially generated. The outer end interface dislocations are mostly generated at 25 deg. -155 deg. and 205 deg. -335 deg. to the central angle of the center of the wafer.

A SiC epitaxial wafer according to another embodiment of the present invention includes a 4H-SiC single crystal substrate and a SiC epitaxial layer formed on the 4H-SiC single crystal substrate, the 4H-SiC single crystal substrate having a surface having an off angle with respect to a c surface as a main surface and a bevel portion at a peripheral edge portion, the SiC epitaxial layer having a film thickness of 20 μm or more, the bevel portion including a bevel portion and an outer peripheral end portion continuous from the main surface, the bevel portion having a width of 150 μm or more.

Here, the "width of the inclined surface portion" refers to a radial length of the inclined surface portion when viewed from a direction orthogonal to the main surface in a plan view.

The mechanism of generation of the estimated outer end interface dislocation will be described with reference to fig. 4.

Fig. 4A and 4B are schematic cross-sectional views showing 2 stages of growth of the SiC substrate and the SiC epitaxial film grown thereon, respectively (the upper view is at the initial stage of growth, and the lower view is at the completion of growth). Fig. 4A shows a case where the width of the inclined surface portion is large, and fig. 4B shows a case where the width of the inclined surface portion is small.

It is considered that at the initial stage of the epitaxial growth, nuclei 7 which become random growth sources are formed at the peripheral end portion 1 Ab. The reason for this is as follows.

The epitaxial film 5 is formed by step flow growth on the flat portion 1a of the main surface, and the step flow growth is maintained if the c-plane is dominant on the inclined surface portion 1 Aa. In fact, since a SiC substrate with an off-angle is generally used, it is considered that the probability of forming nuclei 7 as random growth sources is low while maintaining the step flow growth. On the other hand, the surfaces (r-plane or m-plane) other than the c-plane are dominant at the outer peripheral end 1 Ab. Therefore, it is considered that the step flow growth is hardly caused at the outer peripheral end portion 1Ab, and the random growth is caused.

Referring to fig. 4A, based on the estimated generation mechanism of the external end interface dislocation, the following can be considered for the reason why the external end interface dislocation has not been found so far.

Epitaxial growth is performed until the thickness of the epitaxial film 5 becomes thicker and becomes a desired film thickness, and even if the polymorphic epitaxial film is extended from the nucleus 7 serving as a random growth source formed in the outer peripheral end portion 1Ab, the interface dislocation of the outer end found by the present inventors does not occur when the interface dislocation does not reach the flat portion. Conventionally, the expected thickness of the epitaxial film is thin, and therefore it is considered that the interface dislocation does not reach the flat portion.

In contrast, among the trends of requiring a high-quality thick epitaxial film, the present inventors have found out a dislocation of the outer end interface in the thick epitaxial film.

On the other hand, as shown in fig. 4B, in a substrate having a small width of the bevel portion (a short distance from the outer peripheral end portion to the flat portion), even when the film thickness of the epitaxial film is thin, it is considered that outer end interface dislocation occurs in the flat portion.

Fig. 5 shows the results of an investigation of the relationship between the film thickness of the epitaxial film and the presence or absence of the occurrence of the interface dislocation at the outer end at a predetermined bevel width.

In the graph shown in fig. 5, the symbol "good" indicates no external end interface dislocation, and the symbol "x" indicates the presence of external end interface dislocation. In the table, the broken line indicates a boundary line where the outer-end interface dislocation density becomes zero.

Samples for which data were obtained as follows.

A4H-SiC single crystal substrate of 4 or 6 inches having an off angle of 4 DEG in the <11-20> direction with respect to the (0001) Si plane was used to carry out a known polishing step and a cleaning (etching) step of the substrate surface. Thereafter, a SiC epitaxial growth step (growth temperature 1600 ℃, C/Si ratio 1.22) was carried out by using silane and propane as raw material gases and supplying hydrogen as a carrier gas, and a SiC epitaxial wafer was obtained by forming a SiC epitaxial layer having a predetermined film thickness on a SiC single crystal substrate.

In fig. 5, "the bevel portion 0 μm" is a bevel in which only the SiC single crystal substrate is chamfered, and the angle of the chamfered portion exceeds 60 °, and therefore, under the above definition of the bevel portion, the portion is not included in the bevel portion (therefore, the bevel portion in the SiC single crystal substrate is constituted only by the outer peripheral end portion).

When the SiC single crystal substrate having the "bevel portion 0 μm" was used, the outer end interface dislocation was not present when the thickness of the SiC epitaxial film was 6 μm, 9 μm, and 18 μm, but was generated at 24 μm and 33 μm. In the case of 24 μm and 33 μm, the dislocation density of the outer end interface dislocations is 50 roots/cm or more.

When a SiC single crystal substrate having "inclined surface portion 60 μm" was used (inclination angle of inclined surface portion 25 °), although the outer end interface dislocation was not present when the thickness of the SiC epitaxial film was 12 μm or 16 μm, the outer end interface dislocation occurred at 33 μm. In the case of 33 μm, the dislocation density of the outer end interface dislocations was 24 roots/cm.

When a SiC single crystal substrate having "inclined plane portion 150 μm" was used (inclined plane portion inclination angle 23 °), although the outer end interface dislocation was not present when the thickness of the SiC epitaxial film was 6 μm, 11 μm, 15 μm, and 18 μm, the outer end interface dislocation occurred at 33 μm and 38 μm. The dislocation densities of the outer end interface dislocations were 20 dislocations/cm and 41 dislocations/cm at 33 μm and 38 μm, respectively.

When a SiC single crystal substrate having "slope portion 170 μm" was used (the inclination angle of the slope portion was 23 °), there was no outer end interface dislocation when the thickness of the SiC epitaxial film was 28 μm.

For this sample, a microscope image obtained by a surface inspection apparatus using a confocal differential interference optical system, i.e., a confocal microscope (SICA 88, manufactured by Lasertec ltd.) is shown in fig. 6A, and a PL image thereof is shown in fig. 6B.

When a SiC single crystal substrate having "inclined surface portion 200 μm" was used (inclination angle of inclined surface portion 11 °), although the outer end interface dislocation was not present when the film thickness of the SiC epitaxial film was 13 μm and 27.5 μm, the outer end interface dislocation occurred at 32 μm. In the case of 32 μm, the dislocation density of the outmost interface dislocations is 18 dislocations/cm.

In fig. 5, when the horizontal axis (X axis) is taken as the thickness of the SiC epitaxial film and the vertical axis (Y axis) is taken as the width of the inclined portion, the estimated boundary line of the presence or absence of the occurrence of the outer end interface dislocation is expressed as a linear equation, and it can be expressed as:

Y＝20X-400···(1)。

by processing the width of the inclined portion so as to satisfy the inequality Y >20X-400 based on the formula (1) and selecting the film thickness of the SiC epitaxial film, a SiC epitaxial wafer free from or having a low density of outer-end interface dislocations can be obtained.

The width of the inclined portion can be processed by a known method. For example, contour machining or the like can be employed (see patent document 1).

Based on fig. 5 and equation (1), when a SiC single crystal substrate having a bevel portion with a width of 50 μm was used, a SiC epitaxial wafer having no outer end interface dislocation density could be obtained until the thickness of the SiC epitaxial film became 22 μm. In addition, when a SiC single crystal substrate having a bevel portion with a width of 100 μm was used, a SiC epitaxial wafer having no outer end interface dislocation density could be obtained until the thickness of the SiC epitaxial film became 24 μm. In addition, when a SiC single crystal substrate having a bevel portion with a width of 150 μm was used, a SiC epitaxial wafer having no outer end interface dislocation density could be obtained until the thickness of the SiC epitaxial film became 27 μm. In the case of using a SiC single crystal substrate having a bevel portion with a width of 200 μm, a SiC epitaxial wafer having no outer end interface dislocation density can be obtained until the thickness of the SiC epitaxial film becomes 29 μm.

FIGS. 7A and 7B are the PL images of the sample shown in FIG. 5, when the inclined portion was 150 μm and the thickness of the SiC epitaxial film was 33 μm, and when the inclined portion was 0 μm and the thickness of the SiC epitaxial film was 33 μm, respectively.

In the PL image of fig. 7A, the presence of 7 interface dislocations can be confirmed from the number of L-shaped dislocations schematically shown in fig. 8.

In the PL image of fig. 7B, the presence of 50 or more interfacial dislocations can be confirmed from the number of L-shaped dislocations schematically shown in fig. 8.

The off angle of the 4H — SiC single crystal substrate used in the SiC epitaxial wafer of the present invention is, for example, 0.4 ° or more and 8 ° or less. Typically 4 may be mentioned.

Method for manufacturing SiC epitaxial wafer "

A method for manufacturing a SiC epitaxial wafer according to an embodiment of the present invention uses a 4H-SiC single crystal substrate having a bevel portion at a peripheral edge portion, the bevel portion including a bevel portion continuous from the main surface and an outer peripheral end portion, the bevel portion having a width of 150 μm or more.

The method may have: preparing the H-SiC single crystal substrate; and

and a step of forming a SiC epitaxial film having a film thickness of 20 μm or more on the H-SiC single crystal substrate. The step of forming the SiC epitaxial film having a film thickness of 20 μm or more may include: a sub-step of determining the thickness of the epitaxial film satisfying the formula (1) by using the width of the inclined surface portion of the substrate to be used; and a sub-step of forming the SiC epitaxial film by setting the thickness of the SiC epitaxial film to be equal to or less than the thickness of the epitaxial film satisfying the formula (1) obtained by the formula.

Y＝20X-400···(1)

(wherein Y represents the width of the tilt (. mu.m) and X represents the thickness of the epitaxial film (. mu.m))

In the method for producing a SiC epitaxial wafer according to the present embodiment, known steps can be employed in addition to the steps associated with using a predetermined 4H — SiC single crystal substrate and using the above-described SiC wafer (SiC substrate). In addition, a method for manufacturing a SiC epitaxial wafer according to another embodiment of the present invention is preferably a method including the steps of:

selecting the thickness of the epitaxial film from the range of 20 μm or more;

obtaining a width satisfying the inclination of the formula (1) from the thickness of the selected epitaxial film,

Y＝20X-400···(1)

(wherein Y represents a width (μm) of the tilt, and X represents a thickness (μm) of the epitaxial film);

preparing a 4H-SiC single crystal substrate having an inclination width equal to or greater than the inclination width obtained by the formula (1) and having an inclined portion at a peripheral portion; and

and growing an epitaxial film having a predetermined thickness by using the prepared 4H-SiC single crystal substrate.

The method for producing a SiC epitaxial wafer of the present invention can suitably produce the SiC epitaxial wafer of the present invention.

Industrial applicability

The invention provides a SiC epitaxial wafer having a SiC epitaxial film with a film thickness of 20 [ mu ] m or more and a low density of outer end interface dislocations.

Description of the reference numerals

1 SiC single crystal substrate

1a major surface (Flat portion)

1A bevel

1Aa inclined plane part

1Ab peripheral end portion

2 SiC epitaxial layer

2a outer peripheral end

3 width of the inclined plane part

4 plane of orientation

5 epitaxial film

9 TED pair

10 SiC epitaxial wafer

11 pairs of sequences

12 interface (I)

13 substrate

14 interfacial transfer

15 basal plane dislocations

16 (0001) basal plane

The boundary line Y of the A outer end interface with the dislocation density becoming zero is 20X-400