Manufacturing methods for SiC ingots and SiC wafers

Abstract

To provide a SiC ingot that enables a replaced wafer before marking to be identified after that.SOLUTION: A SiC ingot according to an embodiment has a seed crystal and a single crystal grown on the seed crystal. The single crystal has a micro pipe penetrating in a growth direction thereinside. When a photoluminescence is observed for multiple wafers cut out in a direction crossing the growth direction from the single crystal, a S / N ratio of the micro pipe of a first wafer that has been cut out at a position closest to the seed crystal among the wafers is higher than the S / N ratio of a second wafer that has been cut out at a position farther away from the seed crystal than the first wafer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to SiC ingots and SiC wafers. Manufacturing method Regarding. [Background technology]

[0002] Silicon carbide (SiC) has a dielectric breakdown field that is an order of magnitude larger and a band gap that is three times larger than that of silicon (Si). Furthermore, SiC has properties such as a thermal conductivity that is approximately three times higher than that of silicon (Si). Therefore, SiC is expected to have applications in power devices, high-frequency devices, and high-temperature operating devices. For this reason, SiC epitaxial wafers have recently come into use in semiconductor devices such as those mentioned above.

[0003] SiC epitaxial wafers are manufactured by growing a SiC epitaxial film, which serves as the active region for SiC devices, on a SiC wafer using chemical vapor deposition (CVD).

[0004] SiC wafers are manufactured by cutting out pieces from SiC ingots. The cut SiC wafers undergo grinding, polishing, and other processes. Furthermore, as a manufacturing control measure, markers are attached to the wafers to confirm which ingot and which specific location each wafer was cut from.

[0005] Furthermore, photoluminescence-based defect measurement is used for quality control of SiC wafers (for example, Patent Documents 1 and 2). One type of defect identified by photoluminescence is micropipes. For example, Patent Document 2 shows that micropipes are observed as dark spots in photoluminescence measurements. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent No. 5633099 Publication Patent Document 2 Japanese Patent No. 3917154 Publication Summary of the Invention Problems to be Solved by the Invention

[0007] Before marking SiC wafers, swapping or the like of SiC wafers may occur. In this case, a predetermined marker is applied to an incorrect SiC wafer, which is unfavorable for manufacturing management.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a SiC ingot capable of subsequently identifying wafer swapping before marking. Means for Solving the Problems

[0009] The present invention provides the following means for solving the above problems.

[0010] (1) The SiC ingot according to the first aspect includes a seed crystal and a single crystal grown on the seed crystal, the single crystal has internally a micropipe penetrating in the growth direction, and when photoluminescence observation is performed on a plurality of wafers cut out from the single crystal in a direction intersecting the growth direction, an S / N ratio of the micropipe in a first wafer cut out from a position closest to the seed crystal among the plurality of wafers is higher than an S / N ratio of the micropipe in a second wafer cut out from a position farther from the seed crystal than the first wafer.

[0011] (2) In the SiC ingot according to the above aspect, the S / N ratio of the micropipe may be higher in the wafer cut out closer to the seed crystal.

[0012] (3) The SiC ingot according to the above embodiment may further contain impurities. The impurities are one or more of nitrogen, boron, aluminum, titanium, and vanadium, and the total impurity concentration of the first wafer is higher than that of the second wafer.

[0013] (4) In the SiC ingot according to the above embodiment, the total impurity concentration may be higher as the wafer is cut from closer to the seed crystal.

[0014] (5) In the SiC ingot according to the above embodiment, the total impurity concentration of the first wafer is 1 × 10 14 cm -3 The above is the total impurity concentration of the second wafer, which is 2 × 10⁻⁶. 19 cm -3 The following is also acceptable.

[0015] (6) In the SiC ingot according to the above embodiment, the diameter of the single crystal may be 150 mm or more.

[0016] (7) In the SiC ingot according to the above embodiment, the diameter of the single crystal may be 200 mm or more.

[0017] (8) The SiC wafer according to the second embodiment is cut from the SiC ingot according to the above embodiment.

[0018] (9) In the SiC wafer according to the above embodiment, the density of the micropipes is 0.003 cm³ -2 More than 10cm -2 The following is also acceptable. [Effects of the Invention]

[0019] In the above embodiment, the SiC ingot and SiC wafer can be identified after the fact if a wafer has been replaced before marking. [Brief explanation of the drawing]

[0020] [Figure 1]This is a schematic diagram of the SiC ingot according to this embodiment. [Figure 2] This is a schematic diagram of the characteristic features of a single crystal. [Figure 3] An example of a coordinate system used to extract the location of defects from a SiC substrate is shown. [Figure 4] This is a magnified image of a defect in a photoluminescent image. [Figure 5] This is a photoluminescence image of the same micropipe as the one in Figure 4, but located further from the seed crystal than the micropipe in Figure 4. [Modes for carrying out the invention]

[0021] The present embodiment will be described in detail below with reference to the drawings as appropriate. In the drawings used in the following description, characteristic parts may be enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc. exemplified in the following description are examples only, and the present invention is not limited to them, and can be implemented with appropriate modifications without changing the essence of the invention.

[0022] Figure 1 is a schematic diagram of a SiC ingot 10 according to the first embodiment. The SiC ingot 10 comprises a seed crystal 1 and a single crystal 2. Hereinafter, the height direction of the single crystal 2 will be referred to as the z direction. The z direction is an example of the growth direction of the single crystal 2. Two directions perpendicular to the z direction and mutually perpendicular will be referred to as the x direction and the y direction. The plane extending in the x and y directions will be referred to as the xy plane.

[0023] Seed crystal 1 is SiC. Seed crystal 1 may have a growth surface facing the raw material that has an offset angle with respect to the crystal plane, or it may not have an offset angle. If it has an offset angle, the offset angle is, for example, 2° to 8°. Single crystal 2 is grown on seed crystal 1. Single crystal 2 is SiC. The diameter of single crystal 2 when viewed from the z direction is, for example, 150 mm (6 inches) or more, preferably 200 mm (8 inches) or more.

[0024] Figure 2 is a schematic diagram of the characteristic features of single crystal 2 in SiC ingot 10. Single crystal 2 has micropipes 3 inside. Although Figure 2 shows the case where there is only one micropipe 3, there is not limited to just one micropipe 3. Micropipes 3 extend in the growth direction of single crystal 2. Micropipes 3 penetrate a part of single crystal 2 in the z direction. Micropipes 3 have defects that originate from the interface between seed crystal 1 and single crystal 2, and through defects originating from bulk growth that originate from points inside single crystal 2 (points other than the interface with the seed crystal), but the proportion of through defects originating from the seed crystal is high.

[0025] Micropipes 3 are often formed along the growth direction of the single crystal 2. For example, when a seed crystal 1 with an offset angle is used, the micropipes 3 are often inclined with respect to the z-direction of the single crystal 2. The inclination angle θ of the micropipes 3 with respect to the z-direction coincides with, for example, the offset angle. If the seed crystal 1 does not have an offset angle, the inclination angle θ is, for example, 0°.

[0026] Since the micropipes 3 penetrate in the growth direction, they can be observed in each wafer W cut from the single crystal 2. The wafer W is cut, for example, parallel to the xy plane. Alternatively, the wafer W may be cut at an angle to the xy plane.

[0027] Multiple wafers W can be obtained from a single crystal 2. The diameter of the wafer W is, for example, 150 mm (6 inches) or more, preferably 200 mm (8 inches) or more. Each wafer W is processed into a SiC device after a SiC epitaxial film is grown on the wafer W. The density of micropipes 3 in the wafer W is, for example, 0.003 cm³. -2 More than 10cm -2 The following applies. Hereinafter, among the multiple wafers W cut from the single crystal 2, the wafer cut closest to the seed crystal 1 will be referred to as the first wafer W1, and the wafer cut further from the seed crystal 1 than the first wafer W1 will be referred to as the second wafer W2.

[0028] The photoluminescence image of micropipe 3 differs between the first wafer W1 and the second wafer W2. The signal-to-noise ratio (S / N ratio) of micropipe 3 on the first wafer W1 is higher than that of micropipe 3 on the second wafer W2. The S / N ratio is the ratio of the photoluminescence light emission intensity at the center of a defect to that around the defect. The emission intensity at the center of a defect may be higher or lower than that around it. For example, micropipe 3 is observed as a white bright spot on the first wafer W1, while micropipe 3 is observed as a black spot on the second wafer W2.

[0029] Figures 4 and 5 show examples of photoluminescence images of micropipe 3. Figure 4 is a photoluminescence image of micropipe 3 on the first wafer W1, and Figure 5 is a photoluminescence image of micropipe 3 on the second wafer W2.

[0030] Photoluminescence images are measured using the photoluminescence method. The photoluminescence method involves irradiating a material with excitation light and measuring the light emitted when excited electrons return to their ground state. In this method, a wafer W is irradiated with excitation light having an energy greater than the band gap of SiC, and the intensity of the photoluminescence emitted from the wafer W is measured. Applying the photoluminescence method to the wafer W allows for the identification of defects, impurity aggregation sites, and other issues on the wafer W. Photoluminescence inspection can be performed, for example, using a SICA88 manufactured by Lasertec Corporation.

[0031] In photoluminescence inspection, the excitation light irradiated onto the wafer W has a wavelength of, for example, 200 nm to 380 nm, preferably 313 nm. Furthermore, when obtaining a photoluminescence image, it is preferable to detect the light emitted from the wafer W through a long-pass filter that allows wavelengths of 600 nm or higher to pass through.

[0032] In the first wafer W1 and the second wafer W2, the micropipe 3 to be measured is the same micropipe 3 extending in the z direction. Whether the micropipe 3 in the first wafer W1 and the micropipe 3 in the second wafer W2 are the same can be determined from their relative positions.

[0033] Figure 3 shows an example of a coordinate system used to extract the position of the micropipe 3 from the wafer W. The wafer W shown in Figure 3 has an orientation flat OF. For example, the position of the micropipe 3 is extracted with the direction parallel to the orientation flat OF as the x-direction and the direction perpendicular to the x-direction as the y-direction. The x-direction is, for example, [11-20] and the y-direction is, for example, [1-100]. If [11-20] and [1-100] differ from the main plane direction of the wafer W, the x-component may be the orthogonal projection direction component of [11-20] and the y-component may be the orthogonal projection direction component of [1-100].

[0034] When the position of the micropipe 3 in the first wafer W1 and the position of the micropipe 3 in the second wafer W2 are substantially the same, it can be identified that the micropipe 3 in each wafer W is derived from the same micropipe 3.

[0035] For example, when the seed crystal 1 does not have an offset angle and the inclination angle θ of the micropipe 3 with respect to the z-direction of the single crystal 2 is 0°, the position of the micropipe 3 in the first wafer W1 coincides with the position of the micropipe 3 in the second wafer W2. Further, for example, when the seed crystal 1 has an offset angle and the micropipe 3 has an inclination angle θ with respect to the z-direction, the position of the micropipe 3 in the first wafer W1 and the position of the micropipe 3 in the second wafer W2 are shifted from each other by a value (h tanθ) obtained by multiplying the distance h in the z-direction between the first wafer W1 and the second wafer W2 by tanθ.

[0036] The S / N ratio of the micropipe 3 tends to be larger in the earlier stage of crystal growth (closer to the seed crystal 1) and smaller in the later stage of crystal growth (farther from the seed crystal 1). Therefore, the S / N ratio of the micropipe 3 is higher for a wafer W cut out from a position closer to the seed crystal 1.

[0037] When there are a plurality of micropipes 3 in the single crystal 2, it is preferable that the relationship of the S / N ratio is satisfied for each of the plurality of micropipes 3.

[0038] The single crystal 2 may be doped with impurities in some cases. The impurities are, for example, nitrogen, boron, aluminum, titanium and vanadium. The concentration of these impurities varies depending on the location within the single crystal 2.

[0039] For example, the total impurity concentration in the first wafer W1 is higher than the total impurity concentration in the second wafer W2. The total impurity concentration of the first wafer W1 is, for example, 1×10 14 cm -3 or higher, and the total impurity concentration of the second wafer W2 is, for example, 2×10 19 cm -3The following applies. For example, the total impurity concentration is higher for wafers W cut closer to seed crystal 1. Here, the total impurity concentration is the sum of the individual impurity concentrations of nitrogen, boron, aluminum, titanium, and vanadium.

[0040] Impurity concentration is one of the parameters that affects the signal-to-noise ratio of micropipe 3. Impurities can act as light-emitting centers in photoluminescence testing. Impurities may also combine with micropipe 3. These combined areas are prone to becoming light-emitting centers in photoluminescence testing.

[0041] If the total impurity concentration in the first wafer W1 is higher than the total impurity concentration in the second wafer W2, the probability of composite regions being formed in the first wafer W1 increases, and the signal-to-noise ratio (S / N ratio) of the first wafer W1 tends to be higher. On the other hand, composite regions are less likely to be formed in the second wafer W2, and the S / N ratio tends to be lower. In the second wafer W2, surrounding impurities emit more light than micropipes, increasing background emission. As a result, the S / N ratio of the second wafer W2 tends to be lower.

[0042] Next, a method for manufacturing the SiC ingot 10 according to the first embodiment will be described. The SiC ingot 10 is manufactured, for example, by sublimation. The sublimation method is a method of growing a single crystal 2 by sublimating SiC raw material powder placed opposite the seed crystal 1 and recrystallizing it on the seed crystal 1.

[0043] The growth of single crystal 2 is carried out such that the concentration of each impurity simultaneously satisfies the following first and second conditions.

[0044] The first condition is that the concentration difference between the concentration of each impurity in the first region on the seed crystal 1 side and the concentration of each impurity in the second region located 10 mm or more away from the first region in the z direction satisfies the following relationship for each impurity. Difference in nitrogen impurity concentration: 1 × 10⁻⁶ 18 cm -3 That's all. Boron impurity concentration difference: 3 × 10 16 cm -3 That's all. Difference in aluminum impurity concentration: 3 × 10 16 cm -3 That's all. Titanium impurity concentration difference: 1 × 10 16 cm -3 That's all. Vanadium impurity concentration difference: 1 × 10 14 cm -3 That's all.

[0045] The second condition is that in single crystal 2, the concentration of each impurity at the outermost surface at the end of growth in the z direction satisfies the following relationship for each impurity. Nitrogen impurity concentration: 1 × 10 18 cm -3 That's all. Boron impurity concentration: 1 × 10 15 cm -3 That's all. Aluminum impurity concentration: 1 × 10 15 cm -3 That's all. Titanium impurity concentration: 1 × 10 15 cm -3 That's all. Vanadium impurity concentration: 1 × 10⁻⁶ 14 cm -3 That's all.

[0046] The first and second conditions can be satisfied by adjusting the temperature of the growth surface during crystal growth and the amount of impurities supplied during crystal growth.

[0047] One example is a sublimation method using raw materials containing these impurities, in which the temperature of the crystal growth surface is gradually increased. Gradually increasing the temperature of the crystal growth surface gradually decreases the amount of impurities incorporated into the single crystal 2.

[0048] As another example, in a sublimation method using raw materials containing these impurities, the heating temperature of the raw materials may be gradually lowered to gradually reduce the amount of impurities released.

[0049] It is preferable that the temperatures of these crystal growth surfaces and raw materials can be controlled independently. For example, the heater for heating the raw material and the heater for heating the single crystal 2 may be separate and controlled independently.

[0050] As another example, the amount of nitrogen gas introduced into the film deposition atmosphere may be gradually reduced as the film deposition progresses. Similarly, if the concentration of any of the boron, aluminum, titanium, or vanadium contained in the raw materials is 1 × 10⁻⁶ 14 cm -3 In the following cases, these elements may be supplied separately as gases, and the supply amount may be controlled according to the progress of film deposition.

[0051] A SiC ingot 10 is obtained by growing a single crystal 2 on a seed crystal 1 using the method described above. Multiple wafers W are obtained by slicing the SiC ingot 10.

[0052] Photoluminescence inspection of the wafer W is performed, for example, before or after marking. The photoluminescence inspection includes a first determination step of comparing the positional relationship of the micropipes 3 and a second determination step of comparing the signal-to-noise ratio of the micropipes 3 of the two wafers W.

[0053] The first determination step is performed to confirm that the defects being evaluated are based on the same micropipe 3. For example, if the positions of the micropipes 3 on the two wafers W being compared are less than or equal to htanθ, it is determined that the defects are based on the same micropipe 3. Also, regardless of the relative positions of the two wafers W being compared in the z direction, if the displacement of the two micropipes 3 is 0.2 mm or less, it is statistically highly likely that these defects are connected micropipes 3.

[0054] The second determination step is performed to identify which wafer W is closer to the seed crystal 1 by comparing the signal-to-noise ratio of the micropipes 3 of the two wafers W. If photoluminescence inspection is performed after marking, the marking history and the results of the second determination step are compared to determine if any mix-ups have occurred.

[0055] In the first embodiment, the signal-to-noise ratio (S / N ratio) of the micropipe 3 differs depending on the position of the cut wafer in the SiC ingot 10, and there is a predetermined relationship regarding the strength of the S / N ratio. Therefore, by using the SiC ingot 10 in the first embodiment, the positional relationship of the wafer W with respect to the seed crystal 1 can be determined by comparing the S / N ratio of the micropipe 3 between different wafers W. Markers may be applied to the wafer W for manufacturing control purposes, but even if a marking is made on a wafer other than the one that should have been marked due to a mistake, the marking error can be detected later by comparing the S / N ratio.

[0056] Although an example of this embodiment has been illustrated above, the present invention is not limited to these embodiments. For example, combinations of the characteristic configurations of each embodiment, or additions of other configurations may be made. [Examples]

[0057] (Example 1) A single crystal 2 was grown on a seed crystal 1 to produce a SiC ingot 10. Multiple wafers W were cut from the SiC ingot. The first wafer W1, located on the side opposite to the seed crystal 1, and the second wafer W2, cut from a position 15 mm away from the seed crystal 1 than the first wafer W1, were evaluated. The concentration differences of each impurity in the first wafer W1 and the second wafer W2 were as follows.

[0058] Nitrogen concentration difference: 2 × 10 18 cm -3 Boron concentration difference: 5 × 10 16 cm -3 Aluminum concentration difference: 4 × 10 16 cm -3 Titanium concentration difference: 2 × 10 16 cm -3 Vanadium concentration difference: 5 × 10 14 cm -3

[0059] Then, micropipe 3 located in approximately the same position was identified, and photoluminescence testing was performed on the micropipe 3 on both the first wafer W1 and the second wafer W2. Figure 4 shows the inspection results for the first wafer W1, and Figure 5 shows the inspection results for the second wafer W2.

[0060] The signal-to-noise ratio (S / N ratio) of micropipe 3 on the first wafer W1 was 1.5 or higher, while the S / N ratio of micropipe 3 on the second wafer W2 was 0.75 or lower. [Explanation of Symbols]

[0061] 1...Seed crystal, 2...Single crystal, 3...Micropipe, 10...SiC ingot, W...Wafer, W1...First wafer, W2...Second wafer

Claims

1. It has a seed crystal and a single crystal grown on the seed crystal, The aforementioned single crystal has micropipes inside that penetrate in the direction of growth, The aforementioned single crystal contains nitrogen, boron, aluminum, titanium, and vanadium as impurities. When photoluminescence observation is performed on a plurality of wafers cut from the single crystal in a direction intersecting the growth direction, the signal-to-noise ratio of the micropipe in the first wafer, which is cut closest to the seed crystal, is higher than the signal-to-noise ratio of the micropipe in the second wafer, which is cut from a position further away from the seed crystal than the first wafer. The signal-to-noise ratio of the first wafer is 1.5 or higher. The signal-to-noise ratio of the second wafer is 0.75 or less. In the aforementioned growth direction, the concentrations of each impurity on the outermost surface opposite to the seed crystal are: Nitrogen impurity concentration: 1 × 10¹⁸ cm⁻³ or higher. Boron impurity concentration: 1 × 10¹⁵ cm⁻³ or higher. Aluminum impurity concentration: 1 × 10¹⁵ cm⁻³ or higher. Titanium impurity concentration: 1 × 10¹⁵ cm⁻³ or higher. Vanadium impurity concentration: 1 × 10¹⁴ cm⁻³ or higher. This is a SiC ingot.

2. It has a seed crystal and a single crystal grown on the seed crystal, The aforementioned single crystal has micropipes inside that penetrate in the direction of growth, The aforementioned single crystal contains nitrogen, boron, aluminum, titanium, and vanadium as impurities. When photoluminescence observation is performed on a plurality of wafers cut from the single crystal in a direction intersecting the growth direction, the signal-to-noise ratio of the micropipe in the first wafer, which is cut closest to the seed crystal, is higher than the signal-to-noise ratio of the micropipe in the second wafer, which is cut from a position further away from the seed crystal than the first wafer. The single crystal is formed between the impurity concentration in the first region on the seed crystal side and the impurity concentration in the second region located 10 mm or more away from the first region in the growth direction. Difference in nitrogen impurity concentration: 1 × 10⁻⁶ １８ cm －３ That's all. Boron impurity concentration difference: 3 × 10 １６ cm －３ That's all. Difference in aluminum impurity concentration: 3 × 10 １６ cm －３ That's all. Titanium impurity concentration difference: 1 × 10 １６ cm －３ That's all. Vanadium impurity concentration difference: 1×10 １４ cm －３ or more This fulfills the first condition, In the aforementioned single crystal, the concentration of each impurity on the outermost surface opposite to the seed crystal in the growth direction is as follows: Nitrogen impurity concentration: 1 × 10¹⁸ cm⁻³ or higher. Boron impurity concentration: 1 × 10¹⁵ cm⁻³ or higher. Aluminum impurity concentration: 1 × 10¹⁵ cm⁻³ or higher. Titanium impurity concentration: 1 × 10¹⁵ cm⁻³ or higher. Vanadium impurity concentration: 1 × 10¹⁴ cm⁻³ or higher. And then there's the SiC ingot, which further satisfies the second condition.

3. The SiC ingot according to claim 1 or 2, wherein the signal-to-noise ratio of the micropipe is higher the closer the wafer is cut from the seed crystal.

4. The SiC ingot according to claim 1, wherein the total impurity concentration of the impurities is higher in the first wafer than in the second wafer.

5. The SiC ingot according to claim 4, wherein the total impurity concentration is higher the closer the wafer is cut from the seed crystal.

6. The SiC ingot according to any one of claims 1 to 5, wherein the diameter of the single crystal is 150 mm or more.

7. The SiC ingot according to any one of claims 1 to 5, wherein the diameter of the single crystal is 200 mm or more.

8. A method for manufacturing a SiC wafer, comprising slicing a SiC ingot according to any one of claims 1 to 7.

9. The density of the aforementioned micropipe is 0.003 cm³. －２ 10cm or more －２ The method for manufacturing a SiC wafer according to claim 8, which is as follows:

Images