JP5304712B2 - Silicon carbide single crystal wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a SiC single crystal wafer that has a small wafer warp and uniform crystal orientations in a wafer surface and can achieve high device performance and device yield when it is applied as a wafer for manufacturing a device. <P>SOLUTION: A caliber of a silicon carbide single crystal wafer 12 is 100 mm or more. An amount of warp represented by a difference in height is 60 &mu;m/100 mm or less in the wafer scaling ratio (amount of warp/caliber of wafer) of a caliber of 100 mm. Each deviation of &lt;0001&gt; crystal orientation at four measurement points a<SB POS="POST">1</SB>, a<SB POS="POST">2</SB>, a<SB POS="POST">1'</SB>, and a<SB POS="POST">2'</SB>on the diameter of a wafer against &lt;0001&gt; crystal orientation at the center of the wafer is within +/-1,000 seconds. All the four measurement points exist on a diameter L<SB POS="POST">1</SB>on the wafer 12. Among them, two points a<SB POS="POST">1</SB>and a<SB POS="POST">1'</SB>are located at positions that are inside by 2 mm from outer circumference of the wafer toward the center thereof. The remaining two points a<SB POS="POST">2</SB>and a<SB POS="POST">2'</SB>are located at the center of a segment connecting the two points a<SB POS="POST">1</SB>and a<SB POS="POST">1'</SB>on the outer circumference and the center a<SB POS="POST">0</SB>. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a silicon carbide single crystal wafer with low warpage and high crystal quality.

  Silicon carbide (SiC) is a wide band gap semiconductor with a wide forbidden band of 2.2 to 3.3 eV, and has been researched and developed as an environmentally resistant semiconductor material because of its excellent physical and chemical characteristics. ing. Particularly in recent years, SiC has been attracting attention as a material for short-wavelength optical devices from blue to ultraviolet, high-frequency electronic devices, and high-voltage / high-power electronic devices, and research and development has become active. However, SiC is considered difficult to produce high-quality large-diameter single crystals, and has heretofore hindered the practical application of SiC devices.

Conventionally, on a laboratory scale scale, for example, a SiC single crystal having a size capable of producing a semiconductor element by a sublimation recrystallization method (Rayleigh method) has been obtained. However, in this method, the area of the obtained single crystal is small, and it is not easy to control the size, shape, crystal polymorph (polytype), and impurity carrier concentration. On the other hand, a cubic SiC single crystal is also grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using chemical vapor deposition (CVD). With this method, large area single crystals can be obtained, but only SiC single crystals containing many defects (up to 10 ⁷ / cm ² ) can be grown due to the lattice mismatch between SiC and Si of about 20%. High-quality SiC single crystals have not been obtained. Accordingly, in order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal wafer as a seed crystal (Non-patent Document 1). By using this improved Rayleigh method, it is possible to grow a SiC single crystal while controlling the crystal polymorphism (6H type, 4H type, 15R type, etc.), shape, carrier type, and concentration of the SiC single crystal.

  Currently, SiC single crystal wafers having a diameter of 51 mm (2 inches) to 100 mm are cut out from SiC single crystals manufactured by the modified Rayleigh method, and are used for device manufacture in the field of power electronics and the like. Furthermore, it is reported that 150 mm wafers are under development, and realization of full-scale commercial production of devices using 100 mm or 150 mm wafers is expected. Under such circumstances, the accuracy of the warpage and the plane orientation of the wafer has become very important in recent years.

  A wafer having a large warp causes problems such as defocusing in the lithographic process and sneaking of the source gas to the back surface during the epitaxial growth process. In addition, it may be a hindrance to handling such as wafer transfer in the first place, and the risk of breakage due to the chuck must be considered.

  On the other hand, if the basal plane inside the wafer is bent and the crystal orientation in the wafer plane is deviated, problems such as abnormal step flow in the epitaxial growth process are caused and the device characteristics are greatly affected. This deviation in crystal orientation in the wafer plane is also called mosaicism, and is caused by the fact that a SiC single crystal wafer is formed from a large number of domains having slightly different orientations. In addition, the boundaries of these domains are crystallographically inconsistent interfaces and generally have a high density of dislocation defects (this region is called a low-angle grain boundary). This can also cause the quality of the thin film to deteriorate.

  Therefore, as means for reducing the amount of warpage of the wafer, for example, the following methods have been studied. In Patent Document 1, a wafer cut from a SiC single crystal ingot is annealed at a temperature of 1300 ° C. or more and 2000 ° C. or less to remove processing residual stress due to grinding or cutting of the ingot, thereby warping the wafer. Techniques for reducing the amount have been reported. Patent Document 2 discloses that SiC single crystal ingots or wafers are used in a non-corrosive gas atmosphere containing carbon and hydrogen, or in an atmosphere in which argon or helium is mixed with these non-corrosive gases. A technique for relieving internal stress of an ingot or a wafer by annealing at a temperature of 2800 ° C. or lower to prevent cracks and cracks in the processing of the ingot or the device process of the wafer has been reported. Further, in Patent Document 3, a wafer cut from a SiC single crystal ingot is heated at 800 ° C. or higher and 2400 ° C. while being pressurized at 10 MPa or higher and 0.5 MPa or lower, so that the curvature radius of the wafer is set to 35 m or higher. Technology has been reported.

  On the other hand, in Patent Document 4, in a sublimation recrystallization method using a seed crystal, a SiC single crystal is grown, the seed crystal is cut out from this, crystal growth is performed again, and this is repeated several times. A technique for obtaining a SiC single crystal wafer with a small mosaic property by making the shape convex with respect to the growth direction has been reported. This technology utilizes the property that a low-angle grain boundary propagates perpendicularly to the growth surface.By making the growth crystal convex with respect to the growth direction, the low-angle grain boundary is The region is moved to the peripheral part to form a region having a low low-angle grain boundary density in the central part.

In general, in the modified Rayleigh method, a crystal is grown by forming a temperature gradient in the crystal growth direction so that the seed crystal side has a lower temperature than the SiC crystal powder side that is the raw material of the grown crystal. The shape of the crystal growth surface can be determined by controlling the temperature distribution near the growth surface. That is, since the growth surface is formed along the isothermal surface, in order to make the shape of the growth crystal convex with respect to the growth direction as in, for example, Patent Document 4, in the growth crystal outer peripheral portion. Growth is performed in the growth space so that the difference (Δt = t _P −t _C ) between the temperature t _{P of the} growth surface and the temperature t _{C at the} center of the ingot having the same distance from this point and the seed crystal becomes positive. It is necessary to form an isotherm having an appropriate convex shape in the direction. The purpose of crystal growth while forming such an isotherm is to control the generation of polycrystals and at the same time stably produce the desired polytype to produce a high-quality single polytype SiC single crystal ingot. Is also important.

  However, the temperature difference Δt in the plane perpendicular to the growth direction forms stress on the single crystal grown by this. The internal stress of such a grown crystal does not reach the shape of a bulk crystal with high rigidity, but as soon as it is processed into a wafer, the internal stress is released as the rigidity decreases, Appears as a warp. Therefore, as described in Patent Documents 1 and 3, even if the residual stress inside the crystal is reduced by performing an annealing process after processing into a wafer, it is effective to reduce the warpage amount of a wafer having a diameter of 100 mm or more. It is insufficient. In addition, as in Patent Document 3, if the wafer is heat-treated while being subjected to external stress due to pressurization, new crystal defects such as dislocations may occur during the heat treatment. On the other hand, as described in Patent Document 2, annealing in a SiC single crystal ingot state is effective in reducing the internal stress of the grown crystal.

  However, in the method of Patent Document 2, as is clear from the contents of the examples, the internal stress is reduced to such an extent that cracks generated in the ingot and cracks when processed into a wafer are prevented. It cannot be confirmed that has been reduced to a predetermined value. In addition, applying a thermal load exceeding 2000 ° C. from the outside to the ingot to rearrange the atoms inside the ingot forms a new temperature distribution including the temperature rising and cooling processes, Temperature imbalance can also create a strong stress field inside the crystal.

JP 2004-131328 A JP 2006-290705 A JP 2005-93519 A JP 2001-294499 A

Yu. M. Tairov and V. F. Tsvetkov, Journal of Crystal Growth, vols. 52 (1981) pp.146-150

As described above, the internal stress of the grown crystal leads to the warpage of the wafer. In addition, the release of internal stress when the wafer is processed from the bulk state increases the warpage of the wafer. In this way, with a wafer with a large warp,
The lithographic process in the device fabrication process cannot be focused correctly, resulting in a problem that the yield of good devices obtained from one wafer is lowered.

  Therefore, as described above, the method of reducing the internal stress by performing the annealing process in the state of the ingot is carried out to reduce the warpage of the wafer, but only to reduce the warpage of the wafer. It has been found that a wafer obtained by annealing under the above conditions does not improve the device yield, or that a good epitaxial thin film cannot be formed on the wafer. When the diameter of the wafer is less than 100 mm, it is only necessary to reduce the warp. However, when the diameter of the wafer becomes 100 mm or more, the above problem has become apparent.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a SiC single crystal wafer in which the amount of warpage of the wafer is small and the crystal orientation in the wafer plane is uniform. .

  In order to solve the above-mentioned problems, the present inventors studied to remove internal stress and optimize the new temperature distribution generated at that time while relocating atoms in the SiC single crystal ingot. As a result, surprisingly, the above problem can be solved by reducing the amount of warpage of the cut wafer to a predetermined value and simultaneously making the SiC single crystal wafer with the crystal orientation in the wafer plane aligned to the target level. As a result, the present invention has been completed. That is, even if the warpage of the wafer is reduced, if the crystal orientation in the wafer plane is shifted, the device yield may be low, or a good epitaxial thin film cannot be formed on the wafer. As a result, the present invention has been completed.

That is, this invention consists of the following structures.
(1) A silicon carbide single crystal wafer having a diameter of 100 mm or more,
The amount of warpage represented by the height difference in the wafer surface is 60 μm / 100 mm or less in terms of a wafer conversion ratio (warpage amount / wafer diameter) of a diameter of 100 mm, and
A silicon carbide single crystal wafer, wherein a deviation of <0001> crystal orientation at the following four measurement points is within ± 1000 seconds with respect to <0001> crystal orientation at the wafer center.
Measurement point a ₁ : Position 2 mm inside from the wafer outer circumference toward the wafer center Measurement point a ₂ : Position corresponding to the midpoint of the line segment connecting the measurement point a ₁ and the wafer center Measurement point a ₁ ′: On the wafer diameter The position that is symmetrical with the measurement point a ₁ across the wafer center Measurement point a ₂ ′: The position that is on the wafer diameter and is symmetrical with the measurement point a ₂ across the wafer center (2 ) The deviation of the <0001> crystal orientation at the four measurement points relative to the <0001> crystal orientation at the wafer center is plotted based on the distance from the wafer center to each measurement point, and the linearity of the obtained graph The silicon carbide single crystal wafer according to (1), wherein an average peak shift value obtained from the slope of the approximate expression is 20 seconds / mm or less.
(3) The silicon carbide single crystal wafer according to (1) or (2), wherein a conversion ratio (warpage / wafer diameter) relating to the warpage is 40 μm / 100 mm or less.
(4) The silicon carbide single crystal wafer according to any one of (1) to (3), which is cut from a silicon carbide single crystal ingot obtained by a sublimation recrystallization method using a seed crystal.
(5) The silicon carbide single crystal wafer according to any one of (1) to (4), wherein the density of etch pits corresponding to dislocations of a 4 ° off-wafer is 5.0 × 10 ⁴ cm ⁻² or less.
(6) The silicon carbide single crystal wafer according to any one of (1) to (5), wherein the wafer surface excluding the edge exclusion region is configured by a single polytype.

  Since the SiC single crystal wafer of the present invention has a small amount of warpage and a uniform crystal orientation in the wafer surface, it is possible to realize a good device characteristic with a high yield in device fabrication in the field of power electronics. . For example, it is possible to correctly focus on the lithographic process, to prevent a problem such as a raw material gas sneaking around the back surface of the wafer during the epitaxial growth process, and to obtain an epitaxial thin film grown by step flow. In particular, in the present invention, since the SiC single crystal wafer having such a quality is realized by a large-diameter wafer having a diameter of 100 mm or more, its practicality is extremely high.

FIG. 1 is an explanatory plan view showing an example of measurement points a ₀ , a ₁ , a ₂ , a ₁ ′, and a ₂ ′ at which the deviation of the <0001> crystal orientation is measured on a wafer with a diameter of 100 mm. FIG. 2 is a schematic diagram showing a procedure for measuring the deviation of the <0001> crystal orientation of the measurement points a ₀ , a ₁ , a ₂ , a ₁ ′, a ₂ ′ using an X-ray diffractometer. FIG. 3 is an explanatory plan view showing a location where the dislocation density of a wafer having a diameter of 100 mm is measured. FIG. 4 is an explanatory plan view showing a location where the dislocation density of a wafer having a diameter of 125 mm is measured. FIG. 5 is an explanatory plan view showing an example of measurement points a ₀ , a ₁ , a ₂ , a ₁ ′, a ₂ ′ where the deviation of the <0001> crystal orientation is measured on a wafer having a diameter of 125 mm. FIG. 6 is a configuration diagram showing an example of a single crystal manufacturing apparatus used for manufacturing a SiC single crystal ingot.

  First, the SiC single crystal wafer in the present invention has a diameter of 100 mm or more, and the amount of warpage is 60 μm / 100 mm or less, preferably 40 μm / 100 mm or less, in terms of a wafer conversion ratio (warp amount / wafer diameter) of 100 mm. Preferably, it is 20 μm / 100 mm or less. The amount of warpage of the wafer is expressed by the height difference in the wafer surface, and there are several methods for the measurement. In the present invention, the value measured using an optical interferometer is used. In general, an optical interferometer irradiates and reflects a coherent light on a wafer surface and observes a difference in height within the wafer surface as a phase shift of reflected light. Using this optical interferometer, the height in the direction perpendicular to the reference plane is measured on the surface of the SiC single crystal wafer, which is placed on the reference plane without restraining force and excluding the 2 mm area from the periphery. The difference between the highest and lowest points is the amount of warpage. In the present invention, a wafer conversion ratio with a diameter of 100 mm is used to represent the amount of warpage, and the SiC single crystal wafer of the present invention needs to have a warpage amount of 60 μm / 100 mm or less. In the case of a wafer having a diameter of 125 mm, the warp amount is 75 μm / 125 mm or less.

Further, in the SiC single crystal wafer of the present invention, the deviation of the <0001> crystal orientation at the following four measurement points with respect to the <0001> crystal orientation at the wafer center is within ± 1000 seconds, preferably ± It must be within 500 seconds, more preferably within ± 250 seconds.
Measurement point a ₁ : Position 2 mm inside from the wafer outer circumference toward the wafer center Measurement point a ₂ : Position corresponding to the midpoint of the line segment connecting the measurement point a ₁ and the wafer center Measurement point a ₁ ′: On the wafer diameter Position that is symmetrical with measurement point a ₁ across the wafer center Measurement point a ₂ ': Position that is on the wafer diameter and symmetrical with measurement point a ₂ across the wafer center

The four measurement points all exist on the diameter of the wafer. For a wafer having a diameter of 100 mm, for example, as shown in FIG. 1, if the wafer center is represented by a ₀ , the measurement points a ₁ , a ₂ , a ₁ ′ and a ₂ ′ is arranged on the wafer diameter L _{1 at} intervals of 24 mm. For the alignment of crystal orientations in the plane of the SiC single crystal wafer of the present invention, the measurement points a ₁ , a ₂ , a ₁ ′ and a are based on the <0001> crystal orientation at the wafer center a _0. Whether the <0001> crystal orientation at ₂ ′ is aligned, that is, whether the deviation of the <0001> crystal orientation between the two points of the wafer center a ₀ and the measurement point a ₁ is within ± 1000 seconds. Judgment is made based on the standard, and this is similarly judged for the measurement points a ₂ , a ₁ ′ and a ₂ ′, and all of them match the crystal orientation in the wafer plane when the standard is satisfied. By confirming the deviation of the crystal orientation in the diameter direction of the wafer, it is possible to correctly evaluate the alignment of the plane orientation of the wafer cut from the SiC single crystal ingot produced by the improved Rayleigh method, including the wafer center and the outer periphery of the wafer. (Edge) to center Measurement point position of _{2mm (a 1, a 1 '} ), and the midpoint between these and the wafer center (a _2, a _2' by measuring the), overall within the wafer in consideration of practicality Evaluation is possible. Preferably, apart from the wafer diameter L ₁ , the same four measurement points as described above may be evaluated at the other wafer diameter L _{2. In} this case, the diameter L ₁ and the diameter L ₂ are orthogonal to each other. By doing so, the above evaluation becomes even more reliable. However, even if measurement is performed with one diameter, sufficiently reliable evaluation can be performed.

In evaluating the alignment of such crystal orientations, the specific measurement method is not particularly limited, but preferably includes the following measurement methods. First, the 2θ axis of the X-ray irradiation / detection system is fixed to the measurement point (a ₀ , a ₁ or a ₂ ) under the condition of 0004 reflection, perpendicular to the diameter direction in which the measurement points of the wafer are arranged, and the wafer A rocking curve obtained by rotating the wafer about the Ω axis parallel to the (0001) plane is obtained at each measurement point. At this time, the rotation angle of the Ω axis at which the intensity of the diffracted X-ray is maximum at the center a ₀ of the wafer is 0, and the angle at which the intensity of the diffracted X-ray is maximum at the measurement point a ₂ or a ₃ is Ω, respectively. _2, and Ω _3. The rotation angle Ω thus obtained represents how much the <0001> crystal orientation at the measurement point deviates from the <0001> crystal orientation at the wafer center a ₀ . In a wafer having an ideal (0001) c-plane, the rotation angle of the Ω axis is theoretically zero over the entire wafer surface.

The above measurement method will be described with reference to the drawings. As shown in FIG. 2 (b1), in the plane including the normal p of the wafer surface passing through the wafer center a ₀ (this plane is referred to as plane P). P is the intersection vertically and the wafer surface, Iarawaseru also plane passing through the wafer center a _0), the center a ₀ of the SiC single crystal wafer 12 is irradiated with X-rays <0001> to be a positional relationship corresponding surface reflection Then, the X-ray irradiation device 13 and the X-ray detection device 14 are set (the incident angle is θ ₁ and the reflection angle θ ₂ is set). Next, X-ray diffraction data is measured while rotating the wafer about an axis h that is in the plane P, is parallel to the wafer surface, and passes through the center in the thickness direction of the wafer. Find the slope that maximizes. For a wafer having an off angle of 0 ° and an ideal (0001) c-plane, theoretically θ ₁ = θ ₂ and the inclination of the axis h is zero. When the SiC single crystal wafer has an off-angle, the X-ray irradiation device 13 and the X-ray detection device 14 are symmetric with respect to the (0001) axis and (0001) is the plane P in consideration of the off-angle. To be in parallel with each other. An axis X ₀ is determined as an axis that is parallel to the surface of the wafer at the position where the intensity of the diffracted X-ray is maximized, passes through the center in the thickness direction of the wafer, and is orthogonal to the rotation axis h. Figure 2 (b2) are those viewing the state decided axis X ₀ from the side in FIG. 2 (b1) (arrow direction in the drawing), in the following with reference to the this axis X _0, this axis X ₀ is the rotation angle Ω ₀ = 0. In addition, this FIG.2 (b1) is seen from the II cross section direction of the top view described to Fig.2 (a).

Next, with the incident and reflection angles θ ₁ and θ ₂ fixed, and while maintaining the distance (height) between the X-ray irradiation device 2 and the X-ray detection device 3 and the wafer 12, the axis h and in the direction orthogonal by relatively translating the wafer 12, the measuring point a ₂ is inputted and reflected X-rays, at the measurement point a _2, so that the intensity of the diffracted X-rays is maximized, axial h was translated The wafer 12 is rotated about the rotation axis. And, at the position where the intensity is maximum, the axis parallel to the surface of the wafer, passing through the center in the thickness direction of the wafer and orthogonal to the rotation axis h is defined as the axis X _{2 at the} measurement point a ₂ , As shown in FIG. 2C, an angle formed by the axis X ₂ and the previously determined axis X ₀ is defined as a rotation angle Ω ₂ at the measurement point a ₂ . The rotation angle Ω ₂ thus determined represents how much the <0001> crystal orientation at the measurement point a ₂ is deviated from the <0001> crystal orientation at the wafer center a ₀ . Similarly, for the measurement points a ₁ , a ₂ ′, a ₁ ′, the respective axes X ₁ , X ₂ ′, X ₁ ′ are determined, and the respective rotation angles Ω are determined from the angles formed with the axis X _{0. 1} , Ω ₂ ′, Ω ₁ ′ are obtained. These rotation angles Ω ₁ , Ω ₂ , Ω ₂ ′, and Ω ₁ ′ are shift amounts (positive or negative) based on the rotation angle Ω ₀ at the wafer center a ₀ .

By measuring the wafer diameter direction in this way, it is possible to evaluate how much the <0001> crystal orientation at each measurement point is deviated from the <0001> crystal orientation at the wafer center a ₀ . That is, using the X-ray diffractometer as described above, the diffraction peak position of the <0001> equivalent plane is set to the wafer rotation angle while sliding in the wafer diameter direction with reference to the diffraction peak position of the <0001> equivalent plane at the wafer center. If detected by Ω, the shift of the rotation angle in the wafer diameter direction directly reflects the bending of the basal plane of the SiC single crystal wafer as seen in the wafer diameter direction. Compared to the method of evaluating the mosaic property of the crystal from the full width at half maximum (FWHM) of the rocking curve, the degree of bending of the basal plane can be more correctly evaluated. The SiC single crystal wafer of the present invention has a plane orientation specified based on such evaluation, and the rotation angles Ω ₁ , Ω ₂ , Ω ₂ ′, and Ω ₁ ′ obtained as described above are all ± 1000. Within seconds, preferably within ± 500 seconds, more preferably within ± 250 seconds. If the shift amount is ± 1000 seconds or less, it is possible to manufacture a high-quality device. If the shift amount is ± 500 seconds or less, an improvement in device manufacturing yield can be expected, and if the shift amount is ± 250 seconds or less. In other words, it can be said that the basal plane bending is at a level that can be substantially ignored. In the examples described below, the alignment of the plane orientation of the SiC single crystal wafer was evaluated by this method.

Further, relative to the <0001> crystallographic orientation on the wafer center a _0, the measurement points _{a 1, a 2, a 1} ', a 2' a deviation of <0001> crystallographic orientation on the each from the wafer center a ₀ Plotting can be performed based on the distance to the measurement point, and the average peak shift value can be obtained from the slope of the linear approximation formula of the obtained graph to evaluate the bending of the basal plane in the wafer diameter direction. In other words, Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ' and the measurement position (distance from the center) at each measurement point including the wafer center are plotted on a graph, and the slope when linear approximation is performed From this, an average peak shift value (second / mm) is obtained, and if this average peak shift value is 20 seconds / mm or less, it can be said that it is a SiC single crystal wafer having a uniform crystal orientation within the wafer plane, preferably Is 10 seconds / mm or less, more preferably 5 seconds / mm or less. In the present invention, a wafer means a disk-shaped plate produced by slicing a silicon carbide single crystal ingot, and the silicon carbide single crystal ingot is sliced to a thickness of 1 mm or less. Usually, the thickness is 0.3 mm to 1.0 mm, and examples include a thickness of 0.255 mm, a thickness of 0.475 mm, and a thickness of 0.775 mm.

  As in the present invention, a SiC single crystal wafer with a small amount of wafer warpage and a uniform crystal orientation within the wafer surface is obtained from an SiC single crystal ingot manufactured by a known crystal growth method, including an improved Rayleigh method. In this case, the internal stress is removed while rearranging the atoms in the ingot, and the temperature distribution in the newly generated ingot is optimized to create a stress field. Must be prevented. The method for removing internal stress employed in the present invention will be described in detail below, but the means for obtaining the SiC single crystal wafer of the present invention is not limited to this.

  First, according to the modified Rayleigh method, a silicon carbide single crystal ingot obtained by a sublimation recrystallization method using a seed crystal is subjected to annealing heat treatment (annealing treatment). In this case, the annealing temperature is preferably 2300 ° C. or higher and 2800 ° C. or lower, More preferably, it is good to carry out at 2450 degreeC or more and 2800 degrees C or less. At a temperature of 2300 ° C. or lower, since the rearrangement of atoms constituting the single crystal is not active, the stress may not be sufficiently removed. On the other hand, at temperatures exceeding 2800 ° C., the sublimation decomposition of SiC single crystals and the dissolution of Si components become significant, and there is a risk that ingots will become smaller or new defects will occur before problems arise in productivity. .

  The holding time of the ingot at the annealing temperature is different depending on the diameter and size of the ingot. For example, if the ingot has a diameter of about 100 mm and a height of about 30 mm, the ingot is held at the annealing temperature for 5 hours or more. Preferably 8 hours or longer. If the holding time is less than 5 hours, the effect of removing internal stress may be insufficient. Even if the holding time exceeds 24 hours, the effect is saturated, which is not economical. In addition, about the apparatus used for an annealing process, general heating equipment, such as a resistance heating furnace and an induction heating furnace, can be used, for example.

  By the way, in the annealing process, it is considered that atomic rearrangement in the ingot occurs at a temperature of 1850 ° C. or higher. Therefore, a new stress field may be formed in the ingot in the temperature increasing process from 1850 ° C. to the annealing temperature and the temperature decreasing process from the annealing temperature to 1850 ° C. Therefore, when the annealing process is performed at an annealing temperature of 2300 ° C. or higher and 2800 ° C. or lower, it is preferable that the average heating rate from 1850 ° C. to the annealing temperature and the average cooling rate from the annealing temperature to 1850 ° C. are both 150 ° C./hour. In the following, it is more preferable that both be performed at 100 ° C./hour or less. At present, this reason is not fully elucidated. However, if the average speed exceeds 150 ° C / hour during the heating process and the cooling process, respectively, rapid temperature changes and uneven temperature in the ingot. Distribution may occur, and the stress formed by this may be a factor that causes warpage of the wafer and uneven surface orientation in the wafer surface.

  In addition, since the SiC single crystal has a relatively small atomic diffusion distance even at high temperatures, it is extremely unlikely that dislocations move to the surface of the ingot and disappear. Therefore, the dislocations once generated basically remain in the ingot unless dislocations close to each other are united and disappeared. Therefore, paying attention to the thermal uniformity of the single crystal ingot during annealing, and performing annealing without generating new internal stress while avoiding temperature imbalance in the temperature rising and cooling processes as much as possible, It is also important for obtaining small wafers. There is no particular lower limit to the average rate of temperature increase from 1850 ° C. to the annealing temperature and the average cooling rate from the annealing temperature to 1850 ° C., but both the temperature increasing process and the temperature decreasing process take 24 hours or more. Is not economical. Further, since the atomic transfer of SiC is almost negligible at temperatures lower than 1850 ° C., there is no particular limitation on the temperature change (average speed) between room temperature and 1850 ° C. In order to prevent destruction, it is desirable to change the temperature at a rate smaller than 600 ° C./hour in both the temperature rise and temperature drop processes.

  The pressure atmosphere during the annealing treatment should be 0.05 MPa or more, and preferably 0.09 MPa or more, so that annealing treatment at a high temperature can be performed while suppressing sublimation decomposition of the SiC single crystal. It becomes like this. For the gas atmosphere of the annealing treatment, a general Ar gas or the like can be used. By mixing a carbon atom-containing gas such as propane or a nitrogen atom-containing gas such as nitrogen gas in the atmosphere gas, SiC can be obtained. Since the sublimation can be suppressed by changing the equilibrium state of the sublimation decomposition reaction, it is suitable for performing the annealing treatment without decomposing the SiC single crystal. Specifically, the atmosphere of the annealing treatment may be a carbon atom-containing gas atmosphere containing 10 atomic% or more of carbon atoms, or a nitrogen atom-containing gas atmosphere containing 10 atomic% or more of nitrogen atoms.

  During annealing, the atoms constituting the crystal are rearranged in a direction that relaxes internal stress, so it is practically difficult to eliminate the occurrence of dislocations, but dislocations generated by annealing treatment are difficult during ingot growth. The Burgers vector is considered to be in the opposite direction to the generated dislocation. Therefore, the dislocations that originally existed in the crystal of the ingot and some of the dislocations that are generated by the annealing process are merged and disappear, so that the annealing process under the above-described conditions does not significantly increase the dislocations. It is possible to maintain a dislocation density equivalent to that of an as-grown crystal even after annealing.

  The annealing treatment needs to be performed not in a wafer size but in an ingot or bulk crystal (a crystal mass obtained by dividing the ingot, a crystal mass obtained by removing a part of the surface or end face of the ingot, etc.). This is because, even if the internal stress is relaxed to some extent by processing into a thin wafer and the crystal in the already warped state is annealed, it is not sufficient in terms of removing the internal stress. In addition, when the wafer is annealed, a decomposition layer may be formed on the surface to the extent that it cannot be removed even if the wafer is ground or polished thereafter. By annealing the bulk crystal, some of the decomposed layer generated on the surface can be removed as a processing margin, and the annealing process in the bulk state has higher productivity in the annealing process. When annealing a SiC single crystal ingot, it is not always necessary to anneal it in an as-grown ingot state, and it may be after some machining, but in the case of a φ100 mm standard wafer to be the final product In addition, at least the thickness of the ingot to be annealed is 600 μm or more, preferably 1 mm or more, and the annealing is performed with a bulk crystal having a size of 102 mm or more, preferably 103 mm or more.

  Also, when growing a SiC single crystal ingot by the sublimation recrystallization method using a seed crystal, from the viewpoint of preventing contamination on the growth surface, the seed crystal is arranged so that the growth surface faces vertically downward. Generally, when annealing the SiC single crystal ingot obtained in this way, preferably, the cut surface cut out from the seed crystal or the cut surface cut out from the crucible lid is set vertically downward. It is good to carry out annealing treatment. By annealing the ingot in this way, it is considered that there is an effect of releasing the internal stress due to its own weight formed during crystal growth during the annealing.

  When obtaining a SiC single crystal wafer from the annealed SiC single crystal ingot or bulk SiC single crystal, a known wafer processing technique, polishing method, or the like can be employed. As described above, in addition to the annealing temperature, the internal stress in the grown crystal can be appropriately removed by annealing with the temperature rising / falling rate between 1850 ° C. and annealing temperature set to a predetermined condition. As a result, the amount of warpage when processing into a wafer is reduced, and the plane orientation in the wafer surface can be aligned, so no special processing conditions are required, but new defects, etc., can be obtained by processing or polishing the wafer. It is desirable to take care not to form.

  The diameter of the SiC single crystal wafer in the present invention is not particularly limited, but the warpage of the wafer and the deviation of the plane orientation become more prominent as the wafer diameter increases, so that the diameter is larger than 100 mm. Suitable for wafers. Specifically, as described in the following examples, a wafer having a diameter of 100 mm and a diameter of 125 mm, a SiC single crystal wafer having a small amount of warpage and having a uniform crystal orientation in the wafer surface is realized, If estimated from the wafer diameter conversion ratio regarding the warpage amount and the average peak shift value regarding the alignment of crystal orientations, it is possible to realize the SiC single crystal wafer in the present invention at least up to the diameter of 150 mm and further up to the diameter of 200 mm. Conceivable. Further, the thickness of the SiC single crystal wafer can be appropriately designed in consideration of device fabrication within a range of 1 mm or less.

In addition, in the present invention, a predetermined annealing treatment after growing a SiC single crystal ingot realizes a reduction in the amount of warpage of the wafer and alignment of the plane orientation, thereby forming a single polytype and an ingot having a low dislocation density. For example, the density of etch pits corresponding to 4 ° off-wafer dislocation required for high-quality device fabrication is 5.0 × 10 ⁴ cm ⁻² or less, more preferably 2.0 ×. It is also possible to obtain a SiC single crystal wafer of 10 ⁴ cm ⁻² or less.

Hereinafter, based on an Example and a comparative example, this invention is demonstrated concretely.
FIG. 6 shows an apparatus for growing a single crystal by an improved Rayleigh method used for producing a SiC single crystal ingot for producing a SiC single crystal wafer according to an example of the present invention and a comparative example. Crystal growth is performed by sublimating the sublimation raw material 2 by induction heating and recrystallizing on the seed crystal 1. The seed crystal 1 is attached to the inner surface of the graphite lid 4, and the sublimation raw material 2 is filled inside the graphite crucible 3. The graphite crucible 3 and the graphite lid 4 are coated with a heat insulating material 7 for heat shielding, and are installed on a graphite support rod 6 inside the double quartz tube 5. After evacuating the inside of the quartz tube 5 to less than 1.0 × 10 ⁻⁴ Pa using the vacuum exhaust device 11, a high-purity Ar gas having a purity of 99.9999% or more is supplied through the pipe 9 to the mass flow controller 10. Then, a high-frequency current is passed through the work coil 8 while maintaining the pressure in the quartz tube at 80 kPa, and the lower part of the graphite crucible is raised to the target temperature of 2400 ° C. Similarly, nitrogen gas (N ₂ ) is allowed to flow through the pipe 9 while being controlled by the mass flow controller 10, and the nitrogen partial pressure in the atmospheric gas is controlled to adjust the concentration of the nitrogen element incorporated into the SiC crystal. . The crucible temperature is measured with a two-color thermometer provided with an optical path having a diameter of 2 to 15 mm in the upper and lower graphite felts 7. The crucible upper temperature was the seed crystal temperature, and the crucible lower temperature was the raw material temperature. Thereafter, the pressure inside the quartz tube was reduced from 0.8 kPa to 3.9 kPa as a growth pressure over about 15 minutes, and this state was maintained for 60 to 80 hours to carry out crystal growth.

[Preparation of SiC single crystal ingot (type A) for 100 mm diameter wafer fabrication]
A SiC single crystal ingot (type A) for producing a wafer having a diameter of 100 mm was grown under the following conditions. First, as the seed crystal 1, an SiC single crystal wafer composed of a single polytype of 4H having a (0001) plane having a diameter of 101 mm was used. The growth pressure is 1.33 kPa, and the partial pressure of nitrogen gas is 180 Pa to 65 Pa. The nitrogen partial pressure was changed depending on the growth time. The growth time is 60 hours. As an example, the SiC single crystal ingot thus obtained had a diameter of 104.8 mm and a height of 32.8 mm. In this way, a total of 14 SiC single crystal ingots for producing wafers with a diameter of 100 mm were produced.

[Preparation of SiC single crystal ingot (type B) for 100 mm diameter wafer fabrication]
Subsequently, a SiC single crystal ingot (type B) for producing a wafer having a diameter of 100 mm was grown. The growth conditions are the temperature of the outer periphery of the ingot so that the in-plane temperature gradient of the ingot is increased by 2 ° C./cm by calculation by changing the crucible structure, the relative position of the coil and the crucible from the type A manufacturing conditions. It is the same as A type except having carried out on the conditions to raise. As an example, the SiC single crystal ingot thus obtained had a diameter of 106.1 mm and a height of 29.6 mm. In this manner, a total of four SiC single crystal ingots for wafer diameter 100 mm fabrication were manufactured.

  In order to confirm the quality of the grown single crystal, the dislocation density of the ingot that was not annealed was measured in advance on a 4 ° off-wafer. One 4 ° off-wafer was processed from 10 A-type ingots and 2 B-type ingots, and the Si surface was polished. The wafer was etched in a potassium hydroxide bath at 520 ° C. for 5 minutes. Etch pits generated by etching are located at the positions shown in FIG. 3 (on the wafer diameter, at two points each spaced 30 mm across the wafer center, and on another wafer diameter perpendicular to the wafer diameter including these two points). Thus, the density was averaged by counting at a total of 4 points including 2 points each at a distance of 30 mm across the wafer center to obtain the dislocation density of each single crystal ingot. The measurement was performed in a square area of 250 μm × 250 μm with each measurement point as the center. Hereinafter, this is referred to as a standard dislocation counting method for a 100 mm wafer.

Then, the dislocation density was calculated for the 10 wafers cut out from 10 A-type ingots by the method described above. Among the 10 type A ingots, the minimum value of the dislocation density is 0.4 × 10 ⁴ cm ⁻⁴ and the maximum value is 2.4 × 10 ⁴ cm ^−4. The dislocation density of these 10 ingots The average value was 1.0 × 10 ⁴ cm ⁻⁴ . Similarly, among the dislocation densities measured for two wafers cut out from two B-type ingots, the minimum value is 2.6 × 10 ⁴ cm ⁻⁴ and the maximum value is 8.6 × 10 ⁴ cm ^−4. The average dislocation density of these two ingots was 5.5 × 10 ⁴ cm ⁻⁴ . The SiC single crystal ingot type A and type B used in the following examples and the like obtained by the same manufacturing method are also considered to have the same dislocation density as above at the stage before the annealing treatment.

[Preparation of SiC single crystal ingot for 125mm diameter wafer fabrication]
A single crystal ingot for producing a wafer having a diameter of 125 mm was grown under the following conditions. First, as the seed crystal 1, an SiC single crystal wafer composed of a single polytype of 4H having a (0001) plane having a diameter of 127 mm was used. The growth pressure is 1.33 kPa, and the partial pressure of nitrogen gas is 160 Pa to 70 Pa. The nitrogen partial pressure was changed depending on the growth time. The growth time is 80 hours. As an example, the SiC single crystal ingot thus obtained had a diameter of 129 mm and a height of 37 mm. A total of four SiC single crystal ingots for wafer diameter 125 mm fabrication were manufactured.

In order to confirm the quality of the grown single crystal, the dislocation density of the ingot that was not annealed was measured in advance on a 4 ° off-wafer in the same manner as the SiC single crystal ingot for producing a wafer having a diameter of 100 mm. A single 4 ° off-wafer is processed from two ingots, the wafer is etched in a potassium hydroxide bath at 520 ° C. for 5 minutes, and the etch pits are located at the positions shown in FIG. 4 (measurement points in the case of FIG. 3). The intervals were changed to 40 mm, and the density was averaged. The measurement was performed in a square area of 250 μm × 250 μm with each measurement point as the center. Hereinafter, this is referred to as a standard dislocation counting method for a 125 mm wafer. And among the measured dislocation densities of two ingots, the minimum value is 0.7 × 10 ⁴ cm ⁻⁴ , the maximum value is 2.9 × 10 ⁴ cm ⁻⁴ , and the average value is 1.4. × 10 ⁴ cm ^-4 . It is considered that the SiC single crystal ingot for producing a wafer having a diameter of 125 mm used in the following examples and the like obtained by the same method has a dislocation density of the same level before the annealing treatment.

Example 1
First, an annealing treatment was performed on one of the above-described 100 mm wafer ingots (type A) as follows. At that time, using an induction heating furnace equivalent to the single crystal growth apparatus shown in FIG. 1 as the heating apparatus for the annealing process, the ingot was placed inside the graphite crucible and the annealing process was performed. In addition, the thermal insulation installed around the graphite crucible and the graphite crucible is designed using a numerical calculation method so that the entire ingot becomes nearly isothermal in the annealing treatment. Thus, the temperature gradient of the space where the ingot is placed is designed to be as small as possible. In calculation, the temperature gradient inside the ingot placed inside the crucible and heated to the annealing temperature is 2 ° C./cm or less.

First, prior to the annealing treatment, the inside of the quartz tube 5 is evacuated to less than 1.0 × 10 ⁻⁴ Pa using the evacuation apparatus 11, and then high purity Ar gas having a purity of 99.9999% or more is obtained. A high-frequency current was passed through the work coil 8 while maintaining the pressure in the quartz tube at 0.6 MPa through the pipe 9 while being controlled by the mass flow controller 10. When the temperature in the graphite crucible is heated from room temperature to 1850 ° C., the average temperature increase rate is 500 ° C./hour, and from 1850 ° C. to 2350 ° C., the temperature is increased at an average temperature increase rate of 120 ° C./hour. Was annealed at this temperature for 5 hours. Thereafter, the temperature was cooled from 2350 ° C. to 1850 ° C. at an average cooling rate of 120 ° C./hour, and from 1850 ° C. to 500 ° C. was cooled at an average rate of 300 ° C./hour. Thereafter, the furnace was cooled to room temperature, and the ingot was taken out from the induction heating furnace.

  When the annealed SiC single crystal ingot was taken out of the crucible, a carbonized layer was generated on the surface due to decomposition. From this SiC single crystal ingot, a 4 ° off wafer having a thickness of 500 μm was cut out by a known processing method such as mechanical grinding or multi-wire saw cutting, and both surfaces were mirror finished by a known polishing process such as diamond lapping and polishing. The finished SiC single crystal wafer had a diameter of 100.0 mm and a thickness of 390 μm. Further, the warpage of the polished SiC single crystal wafer was examined by optical interference measurement. For measurement, a flatness tester FT-17 manufactured by NIDEK was used, and the SORI of the region excluding the edge exclusion region of 2 mm was used as the warp of the substrate. The warpage was 51.1 μm, and the wafer conversion ratio (warpage / wafer diameter) of a diameter of 100 mm was 51.1 μm / 100 mm.

With respect to the SiC single crystal wafer obtained above, as described with reference to FIG. 2, the measurement points a ₁ and a ₂ with reference to the <0001> crystal orientation at the wafer center a ₀ using an X-ray diffractometer. , A ₁ ′, a ₂ ′, the deviation of <0001> crystal orientation was evaluated using the rotation angles Ω ₁ , Ω ₂ , Ω ₂ ′, and Ω ₁ ′ as indices. In actual measurement, a CuKα ₁ line was used using an X′Pert MPD manufactured by Philips as an X-ray diffractometer, and as shown in FIG. 1, at a distance of 24 mm from the center (a ₀ ) of the wafer. Two points (a ₂ , a ₂ ′) and 2 points (a ₁ , a ₁ ′) located 48 mm from the center, a total of 5 points, 0004 reflection under the condition of X-ray irradiation spot size 1 mm × 1 mm The position (rotation angle) at which the intensity of the diffracted X-ray was maximized was determined. The measurement results are shown in Table 1.

In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted in a linear approximation was 15 seconds / mm. Furthermore, in order to confirm the dislocation density of the obtained SiC single crystal wafer, when the standard dislocation counting method for the 100 mm wafer described above was applied to the SiC single crystal wafer obtained in Example 1, an etch corresponding to dislocation was obtained. The density of pits was 2.7 × 10 ⁴ cm ⁻² on an average of 4 points.

(Example 2)
One of the 125 mm wafer manufacturing ingots described above was annealed. The heating apparatus and the crucible for annealing are the same as in the first embodiment, and the vacuum and gas replacement prior to the annealing are the same as in the first embodiment. A SiC single crystal wafer was obtained in the same manner as in Example 1 except for the following.

  When the quartz tube is placed in an Ar gas atmosphere with a pressure of 0.09 MPa, a high-frequency current is passed through the work coil 8 and the temperature in the graphite crucible is heated from room temperature to 1850 ° C., the average temperature rise rate is 300 ° C./hour. The temperature was increased up to 2500 ° C. at an average rate of temperature increase of 100 ° C./hour, and the annealing treatment was performed with 2500 ° C. being the annealing temperature and holding at this temperature for 8 hours. Thereafter, cooling from 2500 ° C. to 1850 ° C. was performed at an average cooling rate of 9.03 ° C./hour, and cooling from 1850 ° C. to 500 ° C. was performed at an average rate of 200 ° C./hour. Thereafter, the furnace was cooled to room temperature, and the ingot was taken out from the induction heating furnace.

  When the annealed SiC single crystal ingot was taken out of the crucible, a carbonized layer was generated on the surface due to decomposition. From this SiC single crystal ingot, a wafer having a thickness of 500 μm was cut out in the same manner as in Example 1 and polished to finish both surfaces as mirror surfaces. The finished SiC single crystal wafer had a diameter of 124.9 mm and a thickness of about 410 μm. The warpage of the polished SiC single crystal wafer was examined in the same manner as in Example 1. As a result, the warpage was 18 μm, and the wafer conversion ratio (warpage amount / wafer diameter) of the diameter of 100 mm was 14.4 μm / 100 mm.

With respect to the SiC single crystal wafer obtained above, as described with reference to FIG. 2, the measurement points a ₁ and a ₂ with reference to the <0001> crystal orientation at the wafer center a ₀ using an X-ray diffractometer. , A ₁ ′, a ₂ ′, the deviation of <0001> crystal orientation was evaluated using the rotation angles Ω ₁ , Ω ₂ , Ω ₂ ′, and Ω ₁ ′ as indices. As shown in FIG. 5, the center (a ₀ ) of the wafer, two points (a ₂ , a ₂ ′) at a distance of 30.25 mm from the center, and two points (a ₂ ) at a position 60.5 mm from the center ₁ and a ₁ ′), the positions (rotation angles) at which the intensity of the diffracted X-rays of <0004> equivalent surface reflection is maximized were determined in the same manner as in Example 1. The measurement results are shown in Table 1. In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted in a linear approximation was 7.0 seconds / mm.

In addition, in order to confirm the dislocation density of the obtained SiC single crystal wafer, when the standard dislocation counting method for the 125 mm wafer described above was applied to the SiC single crystal wafer obtained in Example 2, an etch pit corresponding to the dislocation was obtained. The density was 2.4 × 10 ⁴ cm ⁻² on an average of four points.

(Example 3)
One of the aforementioned ingots for producing a 100 mm wafer (type A) was annealed. The heating apparatus and the crucible for annealing are the same as in the first embodiment, and the vacuum and gas replacement prior to the annealing are the same as in the first embodiment. A SiC single crystal wafer was obtained in the same manner as in Example 1 except for the following.

The atmosphere in the quartz tube in Example 3 was Ar and N ₂ , the flow rate was controlled so that N atoms were 45 atomic% in the atmosphere, and the pressure was 0.10 MPa. When heating the temperature in the graphite crucible from room temperature to 1850 ° C., the average temperature increase rate is 300 ° C./hour, and from 1850 ° C. to 2650 ° C., the temperature is increased at an average temperature increase rate of 67 ° C./hour. As the temperature, the annealing treatment was performed by holding at this temperature for 12 hours. Thereafter, the temperature was cooled from 2650 ° C. to 1850 ° C. at an average temperature drop rate of 50 ° C./hour, and from 1850 ° C. to 500 ° C. was cooled at an average rate of 125 ° C./hour. Thereafter, the furnace was cooled to room temperature, and the ingot was taken out from the induction heating furnace.

  When the annealed SiC single crystal ingot was taken out of the crucible, a carbonized layer was generated by decomposition on the most part of the ingot surface, but a surface that was not substantially carbonized remained. A wafer having a thickness of 500 μm was cut out from this single crystal ingot in the same manner as in Example 1 and polished to finish both surfaces to a mirror surface. Then, the Si surface was subjected to chemical mechanical polishing (CMP) to further flatten the Si surface. Finished. The finished SiC single crystal wafer had a diameter of 100.0 mm and a thickness of 404 μm. The warp of the polished SiC single crystal wafer was examined in the same manner as in Example 1. As a result, the warp was 9.5 μm, and the wafer conversion ratio (warp amount / wafer diameter) of caliber 100 mm was 9.5 μm / 100 mm. It was.

With respect to the SiC single crystal wafer obtained above, as described with reference to FIG. 2, the measurement points a ₁ and a ₂ with reference to the <0001> crystal orientation at the wafer center a ₀ using an X-ray diffractometer. , A ₁ ′, a ₂ ′, the deviation of <0001> crystal orientation was evaluated using rotation angles Ω ₁ , Ω ₂ , Ω ₂ ′, Ω ₁ ′ as indices. As shown in FIG. 1, the center (a ₀ ) of the wafer, two points (a ₂ , a ₂ ′) at a distance of 24 mm from the center, and two points (a ₁ , a ₁ ) at a position 48 mm from the center. As in Example 1, the positions (rotation angles) at which the intensity of diffracted X-rays of <0004> equivalent surface reflection was maximized were obtained for a total of 5 points'). The measurement results are shown in Table 1. In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted and linearly approximated was 2.4 seconds / mm.

Further, in order to confirm the dislocation density of the obtained SiC single crystal wafer, when the standard dislocation counting method for the 100 mm wafer described above was applied to the SiC single crystal wafer obtained in Example 3, an etch pit corresponding to the dislocation was obtained. The density was 9.6 × 10 ³ cm ⁻² on average at four points.

(Comparative Example 1)
A wafer was fabricated from one of the above-described 100 mm wafer fabrication ingots (type A) without being annealed. The cut-out thickness of the wafer was 500 μm as in Example 1, and was polished to finish both surfaces to be mirror surfaces. The finished SiC single crystal wafer had a diameter of 99.9 mm and a thickness of 390 μm. The warpage of the polished SiC single crystal wafer was examined in the same manner as in Example 1. As a result, the warpage was 189 μm, and the wafer conversion ratio (warpage amount / wafer diameter) with a diameter of 100 mm was 189.2 μm / 100 mm.

With respect to the SiC single crystal wafer obtained above, as described with reference to FIG. 2, the measurement points a ₁ and a ₂ with reference to the <0001> crystal orientation at the wafer center a ₀ using an X-ray diffractometer. , A ₁ ′, a ₂ ′, the deviation of <0001> crystal orientation was evaluated using rotation angles Ω ₁ , Ω ₂ , Ω ₂ ′, Ω ₁ ′ as indices. As shown in FIG. 1, the center (a ₀ ) of the wafer, two points (a ₂ , a ₂ ′) at a distance of 24 mm from the center, and two points (a ₁ , a ₁ ) at a position 48 mm from the center. As in Example 1, the positions (rotation angles) at which the intensity of diffracted X-rays of <0004> equivalent surface reflection was maximized were obtained for a total of 5 points'). The measurement results are shown in Table 1. In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted in a linear approximation was 21 seconds / mm.

Further, in order to confirm the dislocation density of the obtained SiC single crystal wafer, when the standard dislocation counting method for the 100 mm wafer described above was applied to the SiC single crystal wafer obtained in Comparative Example 1, an etch pit corresponding to the dislocation was obtained. The density was about 2.1 × 10 ⁴ cm ⁻² on an average of four points.

(Comparative Example 2)
A thick wafer was fabricated from the aforementioned 125 mm wafer fabrication ingot without being annealed. The cut-out thickness of the wafer is 2000 μm. When polished and finished to a mirror finish, the finished SiC single crystal wafer had a diameter of 125.0 mm and a thickness of about 1870 μm. The warpage of the polished SiC single crystal wafer was examined in the same manner as in Example 1. As a result, the warpage was 29 μm, and the wafer conversion ratio (warpage amount / wafer diameter) with a diameter of 100 mm was 23.2 μm / 100 mm.

About the SiC single crystal wafer obtained above, the center (a ₀ ) of the wafer, two points (a ₂ , a ₂ ′) at a distance of 30.25 mm from the center, and 2 at a position of 60.5 mm from the center With respect to a total of five points (a ₁ , a ₁ ′) (see FIG. 5), as described in FIG. 2, using the X-ray diffractometer, <0004> The position (rotation angle) at which the intensity of the diffracted X-ray was maximized was determined. The measurement results are shown in Table 1. In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted in a linear approximation was 94 seconds / mm. Furthermore, in order to confirm the dislocation density of the obtained SiC single crystal wafer, when the wafer of Comparative Example 2 was evaluated by the standard dislocation counting method for a 125 mm wafer, the density of etch pits corresponding to dislocations was a four-point average. It was 9.8 * 10 ^{< 3} > cm ^<-2 >.

(Comparative Example 3)
One of the aforementioned ingots for producing a 100 mm wafer (type A) was annealed. The heating apparatus and the crucible for annealing are the same as in the first embodiment, and the vacuum and gas replacement prior to the annealing are the same as in the first embodiment. A SiC single crystal wafer was obtained in the same manner as in Example 1 except for the following.

  The atmosphere in the quartz tube in Comparative Example 3 was Ar mixed with 1% ethylene gas, and the pressure was 0.10 MPa. The temperature in the graphite crucible was increased from room temperature to 2500 ° C. at an average temperature increase rate of 300 ° C./hour, and the annealing treatment was performed by keeping the temperature at 2150 ° C. for 12 hours. Then, it cooled from 2150 degreeC to 1400 degreeC with the average temperature-fall rate of 150 degreeC / hour. The ingot was taken out of the induction heating furnace after cooling to room temperature by furnace cooling.

  When the SiC single crystal ingot after the annealing treatment was taken out of the crucible, there was almost no carbonization layer due to decomposition on the ingot surface. A wafer having a thickness of 500 μm was cut out from this single crystal ingot in the same manner as in Example 1 and polished to finish both surfaces as mirror surfaces. The finished SiC single crystal wafer had a diameter of 100.0 mm and a thickness of 392 μm. The warpage of the polished SiC single crystal wafer was examined in the same manner as in Example 1. As a result, the warpage was 88.0 μm, and the wafer conversion ratio (warpage amount / wafer diameter) of 100 mm in diameter was 88.0 μm / 100 mm. It was.

About the SiC single crystal wafer obtained above, the center (a ₀ ) of the wafer, two points (a ₂ , a ₂ ′) at a distance of 24 mm from the center, and two points (a ₁ ) at a position 48 mm from the center , A ₁ ') (see FIG. 1), as described in FIG. 2, using an X-ray diffractometer, as in Example 1, <0004> The position (rotation angle) at which the strength was maximized was determined. The measurement results are shown in Table 1. In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted in a linear approximation was 23 seconds / mm. Further, when the wafer of Comparative Example 3 was evaluated by the standard dislocation counting method for a 100 mm wafer, the density of etch pits corresponding to dislocations was about 1.7 × 10 ⁵ cm ⁻² on an average of four points.

(Comparative Example 4)
A wafer was fabricated from one of the aforementioned 100 mm wafer fabrication ingots (type B) in the same manner as in Comparative Example 1 without being annealed. The cut-out thickness of the wafer was 500 μm as in Example 1, and was polished to finish both surfaces to be mirror surfaces. The finished SiC single crystal wafer had a diameter of 100.0 mm and a thickness of 385 μm. The warpage of the polished SiC single crystal wafer was examined in the same manner as in Example 1. As a result, the warpage was 234 μm, and the wafer conversion ratio (warpage / wafer diameter) of 100 mm in diameter was 234.0 μm / 100 mm.

With respect to the SiC single crystal wafer obtained above, as described with reference to FIG. 2, the measurement points a ₁ and a ₂ with reference to the <0001> crystal orientation at the wafer center a ₀ using an X-ray diffractometer. , A ₁ ′, a ₂ ′, the deviation of <0001> crystal orientation was evaluated using the rotation angles Ω ₁ , Ω ₂ , Ω ₂ ′, and Ω ₁ ′ as indices. As shown in FIG. 1, the center (a ₀ ) of the wafer, two points (a ₂ , a ₂ ′) at a distance of 24 mm from the center, and two points (a ₁ , a ₁ ) at a position 48 mm from the center. As in Example 1, the positions (rotation angles) at which the intensity of diffracted X-rays of <0004> equivalent surface reflection was maximized were obtained for a total of 5 points'). The measurement results are shown in Table 1. In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted in a linear approximation was 51 seconds / mm.

Further, in order to confirm the dislocation density of the obtained SiC single crystal wafer, when the standard dislocation counting method for the 100 mm wafer described above was applied to the SiC single crystal wafer obtained in Comparative Example 4, an etch pit corresponding to the dislocation was obtained. The density of the sample was about 5.7 × 10 ⁴ cm ⁻² on an average of four points.

(Comparative Example 5)
One of the aforementioned ingots for producing a 100 mm wafer (type B) was annealed. The annealing heating device and the crucible, the annealing atmosphere, and the annealing temperature conditions are the same as in the first embodiment, and the vacuum and gas replacement prior to the annealing are the same as in the first embodiment.

  When the SiC single crystal ingot after annealing was taken out of the crucible, a carbonized layer was formed by decomposition on the ingot surface. A wafer having a thickness of 500 μm was cut out from this single crystal ingot in the same manner as in Example 1 and polished to finish both surfaces as mirror surfaces. The finished SiC single crystal wafer had a diameter of 99.9 mm and a thickness of 388 μm. The warpage of the polished SiC single crystal wafer was examined in the same manner as in Example 1. As a result, the warpage was 57.0 μm, and the wafer conversion ratio (warpage amount / wafer diameter) of the diameter of 100 mm was 57.1 μm / 100 mm. It was.

About the SiC single crystal wafer obtained above, the center (a ₀ ) of the wafer, two points (a ₂ , a ₂ ′) at a distance of 24 mm from the center, and two points (a ₁ ) at a position 48 mm from the center , A ₁ ') (see FIG. 1), as described in FIG. 2, using an X-ray diffractometer, as in Example 1, <0004> The position (rotation angle) at which the strength was maximized was determined. The measurement results are shown in Table 1. In addition, the graph shows the rotation angle (Ω ₀ , Ω ₁ , Ω ₂ , Ω ₂ ', Ω ₁ ') at each measurement point determined above as the vertical axis and the measurement position (distance from the center) as the horizontal axis. The slope (average peak shift value) when plotted in a linear approximation was 18 seconds / mm. Further, when the wafer of Comparative Example 5 was evaluated by a standard dislocation counting method for a 100 mm wafer, the density of etch pits corresponding to dislocations was an average of about 3.6 × 10 ⁵ cm ^{−2 over} four points.

1: Seed crystal (SiC single crystal)
2: Sublimation raw material 3: Graphite crucible 4: Graphite lid 5: Double quartz tube 6: Support rod 7: Felt made of graphite 8: Work coil 9: High purity Ar gas piping 10: Mass flow controller for high purity Ar gas 11: Vacuum Exhaust device 12: SiC single crystal wafer 13: X-ray irradiation device 14: X-ray detection device

Claims (6)

A silicon carbide single crystal wafer having a diameter of 100 mm or more,
The amount of warpage represented by the height difference in the wafer surface is 60 μm / 100 mm or less in terms of a wafer conversion ratio (warpage amount / wafer diameter) of a diameter of 100 mm, and
A silicon carbide single crystal wafer, wherein a deviation of <0001> crystal orientation at the following four measurement points is within ± 1000 seconds with respect to <0001> crystal orientation at the wafer center.
Measurement point a ₁ : Position 2 mm inside from the wafer outer circumference toward the wafer center Measurement point a ₂ : Position corresponding to the midpoint of the line segment connecting the measurement point a ₁ and the wafer center Measurement point a ₁ ′: On the wafer diameter Position that is symmetrical with measurement point a ₁ across the wafer center Measurement point a ₂ ': Position that is on the wafer diameter and symmetrical with measurement point a ₂ across the wafer center   The deviation of the <0001> crystal orientation at the four measurement points based on the <0001> crystal orientation at the wafer center is plotted based on the distance from the wafer center to each measurement point, and a linear approximation of the obtained graph 2. The silicon carbide single crystal wafer according to claim 1, wherein an average peak shift value obtained from an inclination of the equation is 20 seconds / mm or less.   The silicon carbide single crystal wafer according to claim 1 or 2, wherein a conversion ratio (amount of warpage / wafer diameter) relating to the amount of warpage is 40 μm / 100 mm or less.   The silicon carbide single crystal wafer according to any one of claims 1 to 3, wherein the silicon carbide single crystal wafer is cut from a silicon carbide single crystal ingot obtained by a sublimation recrystallization method using a seed crystal. The silicon carbide single crystal wafer according to any one of claims 1 to 4, wherein the density of etch pits corresponding to dislocations of a 4 ° off-wafer is 5.0 x 10 ⁴ cm ^-2 or less.   The silicon carbide single crystal wafer according to any one of claims 1 to 5, wherein the wafer surface excluding the edge exclusion region is composed of a single polytype.

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