Silicon carbide ingot

Abstract

To provide a silicon carbide ingot capable of blocking a micro pipe in a seed crystal and reducing the aggregation of screw dislocations; a method for manufacturing the same; and a method for manufacturing a silicon carbide wafer.SOLUTION: A silicon carbide ingot includes: a seed crystal 2 consisting of a silicon carbide single crystal and having a micro pipe 5 being a hollow defect; a buffer layer 3 provided on the seed crystal 2 and consisting of silicon carbide; and a bulk crystal growth layer 4 provided on the buffer layer 3 and consisting of silicon carbide. The buffer layer 3 and the bulk crystal growth layer 4 have a plurality of screw dislocations 6 continued to the micro pipe 5 blocked by the buffer layer 3, and an interval between the plurality of screw dislocations 6 common to the micro pipe 5 in the bulk crystal growth layer 4 is 150 μm or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a silicon carbide ingot, a method for manufacturing a silicon carbide ingot, and a method for manufacturing a silicon carbide wafer.

Background Art

[0002] Silicon carbide (hereinafter also referred to as SiC) has excellent physical property values such as a band gap that is about three times that of Si, a saturation drift velocity that is about twice that of Si, and a dielectric breakdown field strength that is about ten times that of Si, and has a large thermal conductivity. Therefore, it is expected as a material for realizing next-generation high-voltage and low-loss semiconductor devices that greatly surpass the performance of currently used Si single-crystal semiconductors.

[0003] As one of the methods for manufacturing SiC wafers used in such semiconductor devices, the sublimation method is known. When a seed crystal contains a hollow defect called a micropipe, when a single-crystal layer made of SiC (hereinafter referred to as a bulk crystal growth layer) is formed on the seed crystal by the sublimation method, the micropipe will continue into the bulk crystal growth layer.

[0004] In order to solve the problem of such micropipes, Patent Document 1 discloses a method for manufacturing a SiC single-crystal film in which a source gas containing C and Si is made Si-rich and epitaxial growth is performed by the CVD method. According to this manufacturing method, when an epitaxial film of about 100 - 150 μm is grown at a film formation rate of several tens of μm / h, the micropipe is decomposed into a plurality of 1c screw dislocations, so a SiC single-crystal film with reduced continuation of the micropipe from the seed crystal can be obtained. However, even after the micropipe is blocked and decomposed, when the plurality of 1c screw dislocations are dispersed and not sufficiently spatially spread (about 10 μm), the screw dislocations locally aggregate and the crystallinity is low.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In view of the above circumstances, an object of the present invention is to provide a silicon carbide ingot that closes micropipes in a seed crystal and reduces the aggregation of screw dislocations, a method for manufacturing the same, and a method for manufacturing a silicon carbide wafer. MEANS FOR SOLVING THE PROBLEMS

[0007] An aspect of the present invention for achieving the above object includes a seed crystal made of a silicon carbide single crystal and having a micropipe which is a hollow defect, a buffer layer made of silicon carbide provided on the seed crystal, and a bulk crystal growth layer made of silicon carbide provided on the buffer layer. The buffer layer and the bulk crystal growth layer have a plurality of screw dislocations continuing to the micropipe blocked by the buffer layer, and the distance between the plurality of screw dislocations sharing the micropipe in the bulk crystal growth layer is 150 μm or more. This is a feature of the silicon carbide ingot.

[0008] Another aspect of the present invention for achieving the above object includes a first step of forming a buffer layer made of silicon carbide on a seed crystal made of a silicon carbide single crystal and having a micropipe which is a hollow defect, and a second step of forming a bulk crystal growth layer made of silicon carbide on the buffer layer. In the first step, the buffer layer having a thickness of 100 μm or more is formed at a temperature of 2400 ° C. or higher by a gas method using a source gas having an atomic number ratio (C / Si ratio) of carbon atoms to silicon atoms of 0.5 or more and 0.9 or less. In the second step, the bulk crystal growth layer is formed by a gas method or a sublimation method. This is a feature of the method for manufacturing a silicon carbide ingot. Another aspect of the present invention for achieving the above object is the method for manufacturing the silicon carbide ingot wherein, in the second step, the bulk crystal growth layer is formed by a gas method using a source gas having a higher C / Si ratio than that in the first step, the method for manufacturing a silicon carbide ingot being characterized by this.

[0009] Another aspect of the present invention for achieving the above object is a method for manufacturing a silicon carbide wafer, which comprises forming a silicon carbide ingot by the above method for manufacturing a silicon carbide ingot and slicing the bulk crystal growth layer.

Advantages of the Invention

[0010] According to the present invention, there are provided a silicon carbide ingot in which micropipes in a seed crystal are blocked and aggregation of screw dislocations is reduced, a method for manufacturing the same, and a method for manufacturing a silicon carbide wafer.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] Fig. 1(a) is a front view of a SiC ingot according to the present embodiment. The SiC ingot 1 includes a seed crystal 2, a buffer layer 3 provided on one surface side of the seed crystal 2, and a bulk crystal growth layer 4 provided on one surface side of the buffer layer 3 (opposite to the seed crystal 2).

[0013] The seed crystal 2 is made of a SiC single crystal having micropipes 5. The seed crystal 2 is not particularly limited in the manufacturing method, and is formed by, for example, a sublimation method.

[0014] The micropipe 5 is a hollow defect having a diameter of several hundred nm to several μm. The micropipe 5 has a Burgers vector of nc and is considered to be a large screw dislocation. On the other hand, a non-hollow through screw dislocation has a Burgers vector of 1c and propagates in the c-axis direction of the SiC crystal. (Here, as the through screw dislocation, in addition to a pure screw dislocation having a Burgers vector b = 1c, a through mixed dislocation having a Burgers vector of the a component, b = c + a / 3 <11-20>, is also included in the consideration.)

[0015] The buffer layer 3 is a layer made of SiC. The buffer layer 3 has a thickness of 100 μm or more and is formed under Si-rich conditions where the atomic number ratio of carbon atoms to silicon atoms (hereinafter, C / Si ratio) is 0.5 or more and 0.9 or less.

[0016] In the buffer layer 3, the micropipes 5 in the seed crystal 2 are blocked, and the blocked micropipes 5 are decomposed into a plurality of screw dislocations 6. Specifically, one micropipe 5 with a Burgers vector of nc is decomposed into n screw dislocations 6. Hereinafter, a plurality of screw dislocations 6 that share the same micropipe 5 and have the same sense (a structure of screw dislocation with left-handed or right-handed) are referred to as "screw dislocations 6 of the same sense". In FIG. 1(a), two "screw dislocations 6 of the same sense that share the same micropipe 5" are shown. All the micropipes 5 are blocked in the buffer layer 3.

[0017] Also, in the buffer layer 3, since the screw dislocations 6 of the same sense repel each other, the distance between them spreads and disperses. Such dispersion of the screw dislocations 6 is realized by forming a buffer layer 3 with a predetermined thickness, for example, 100 μm or more, by the gas method described later.

[0018] The bulk crystal growth layer 4 is a layer made of a SiC single crystal on the buffer layer 3 and is formed by bulk growth. Also, the screw dislocations 6 continue from the buffer layer 3 to the bulk crystal growth layer 4. In the bulk crystal growth layer 4, the distance between at least the screw dislocations 6 of the same sense is 150 μm or more. Also, the C / Si ratio during the formation of the bulk crystal growth layer 4 is at least larger than the C / Si ratio of the buffer layer 3.

[0019] FIG. 1(b) is a plan view of a SiC 10 wafer obtained by slicing the bulk crystal growth layer 4 of the SiC ingot 1. FIG. 1(c) is a plan view of a SiC wafer 100 which is a comparative example. It shows that the inside of the circle mark indicating the screw dislocation 6 is "+" for left-handed and "-" for right-handed.

[0020] The SiC wafer 10 shown in Fig. 1(b) is obtained by slicing the bulk crystal growth layer 4 of the SiC ingot 1. The "+" surrounded by a dotted circle represents a screw dislocation 6 with the same sense "+", and the distance between screw dislocations 6 with the same sense in plan view is 150 μm or more. That is, when focusing on one of the multiple screw dislocations 6 with the same sense, the distance from all other screw dislocations 6 is 150 μm or more.

[0021] The SiC wafer 100 shown in Fig. 1(c) is a wafer in which micropipes are blocked by an epitaxial film formed by CVD. The CVD method has a film formation rate of several tens of μm / h. Even when growing an epitaxial film of about 100 - 150 μm, screw dislocations are only dispersed by about 10 μm. The screw dislocations 6 with the same sense "+" surrounded by a dotted circle are aggregated without an increase in the distance in plan view. Thus, in a conventional SiC epitaxial wafer by CVD, although the micropipes 5 of the seed crystal 2 are blocked, screw dislocations locally aggregate in the bulk crystal growth layer 4, resulting in low crystallinity.

[0022] On the other hand, in the SiC ingot 1 and its SiC wafer 10 of the present invention shown in Fig. 1(b), screw dislocations 6 with the same sense are dispersed while maintaining a sufficient distance due to the action of mutual repulsive forces, resulting in a good crystal with high uniformity.

[0023] The manufacturing method of the above-described SiC ingot 1 and SiC wafer 10 will be described with reference to Fig. 2. The manufacturing method of the SiC ingot 1 includes a first step and a second step.

[0024] In the first step, a buffer layer 3 shown in Fig. 2(b) is formed on one surface side of the seed crystal 2 having a micropipe 5 shown in Fig. 2(a) by a gas method (high-temperature CVD method). The thickness of the buffer layer 3 is preferably at least 100 μm or more, preferably 1 mm or more. Since the gas method has a growth rate of several mm / h, it is possible to form thick crystals (buffer layer and bulk crystal) in a short time compared to the CVD method.

[0025] The source gas used in the gas method of the first step has a composition for growing SiC. As an example, a mixture of various gases such as SiH4 as a Si-based reaction species, C3H8 as a carbon-based reaction species, and H2 or Ar as a carrier gas can be used. The C / Si ratio contained in the source gas is set to 0.9 or less, and more preferably 0.5 or more and 0.9 or less. Also, during the formation of the buffer layer 3, the C / Si ratio may be fixed or changed.

[0026] The pressure of the source gas in the gas method of the first step is 1.013×10 2 Pa or more and 1.013×10 5 Pa or less. Also, the temperature of the source gas is 2400°C or more, and more preferably 2400°C or more and 2600°C or less.

[0027] According to such a first step, the micropipes of the seed crystal 2 are blocked by the buffer layer 3 formed of a Si-rich source gas and decomposed into a plurality of aggregated screw dislocations 6. And in the buffer layer 3 formed by the gas method of growing at a high temperature and a high crystal growth rate, screw dislocations 6 of the same sense disperse earlier and more easily compared to the CVD method for forming a thin film. For this reason, when the thickness of the buffer layer 3 is grown to several mm or more, in the bulk crystal growth layer 4 formed next, the screw dislocations 6 are dispersed with a sufficient interval maintained, resulting in a good crystal with high uniformity.

[0028] As shown in FIG. 2(c), in the second step, a bulk crystal growth layer 4 is formed on the buffer layer 3. The thickness of the bulk crystal growth layer 4 is not particularly limited. In this embodiment, the gas method is used as in the first step, but the manufacturing conditions use a source gas with a C / Si ratio (at least larger than the C / Si ratio in the first step) suitable for growing a SiC single crystal in bulk. The pressure and temperature may be the same as or different from those in the first step. Thereby, in the bulk crystal growth layer 4, the interval between screw dislocations 6 of the same sense is sufficiently maintained, and a good crystal with high uniformity can be obtained.

[0029] Generally, the gas method enables the change of the C / Si ratio even during the crystal growth. Therefore, in the second step, since the same gas method as in the first step is used, it is only necessary to change the C / Si ratio of the source gas, and the bulk crystal growth layer 4 can be efficiently formed. Note that the second step is not limited to the gas method and may be the sublimation method. By slicing the bulk crystal growth layer 4 of the SiC ingot 1 formed in this way, an SiC wafer 10 is obtained. The SiC wafer 10 has a promoted dispersion of screw dislocations 6 and has a good crystal with high uniformity.

[0030] As described above, the SiC ingot 1 of the present invention includes a seed crystal 2 having a micropipe 5, a buffer layer 3, and a bulk crystal growth layer 4. The buffer layer 3 and the bulk crystal growth layer 4 have a plurality of screw dislocations 6 that continue to the micropipe 5 blocked by the buffer layer 3. In the bulk crystal growth layer 4, the distance between a plurality of screw dislocations 6 of the same sense is 150 μm or more. Such an SiC ingot 1 has a high quality with the micropipe 5 blocked and the screw dislocations 6 dispersed. Further, the SiC wafer 10 formed from such an SiC ingot 1 has no micropipe 5, promotes the dispersion of screw dislocations 6, and has a good crystal with high uniformity.

[0031] Also, it is preferable that the SiC ingot 1 has a buffer layer 3 with a thickness of 100 μm or more. According to this, the distance between screw dislocations 6 of the same sense is dispersed, and the SiC ingot 1 becomes a good crystal with high uniformity.

[0032] Further, it is preferable that the SiC ingot 1 is formed under Si-rich conditions where the atomic number ratio (C / Si ratio) of carbon atoms to silicon atoms in the buffer layer 3 is 0.5 or more and 0.9 or less. According to this, a high-quality SiC ingot with the micropipe 5 more reliably blocked is obtained.

[0033] The manufacturing method of the SiC ingot 1 of the present invention comprises a first step of forming a buffer layer 3 on a seed crystal 2 and a second step of forming a bulk crystal growth layer 4 on the buffer layer 3. In the first step, a buffer layer with a thickness of 100 μm or more is formed at a temperature of 2400 °C or higher by a gas method using a raw material gas with a C / Si ratio rich in Si. In the second step, the bulk crystal growth layer 4 is formed by a gas method or a sublimation method. Thereby, a high-quality SiC ingot 1 with the micropipes 5 blocked and the screw dislocations 6 dispersed can be manufactured. Also, a SiC wafer 10 can be formed from such a SiC ingot 1. Thereby, a SiC wafer 10 having good crystals with high uniformity can be manufactured, without micropipes 5 and with the dispersion of the screw dislocations 6 promoted.

[0034] Further, in the manufacturing method of the SiC ingot 1, the bulk crystal growth layer 4 is formed by a gas method using a raw material gas with a C / Si ratio higher than that in the first step in the second step. The second step is the same gas method as the first step. Therefore, since the bulk crystal growth layer 4 can be continuously formed simply by changing the C / Si ratio, the SiC ingot 1 can be efficiently manufactured.

Description of reference numerals

[0035] 1... SiC ingot, 2... seed crystal, 3... buffer layer, 4... bulk crystal growth layer, 5... micropipe, 6... screw dislocation, 10... SiC wafer

Claims

1. A seed crystal made of a single crystal of silicon carbide and having micropipes which are hollow defects, A buffer layer made of silicon carbide provided on the seed crystal and being Si-rich, A bulk crystal growth layer made of silicon carbide provided on the buffer layer, and comprising: The buffer layer and the bulk crystal growth layer have a plurality of screw dislocations continuing to the micropipes blocked by the buffer layer, In the bulk crystal growth layer, the distance between the plurality of screw dislocations sharing the micropipes is 150 μm or more. A silicon carbide ingot, characterized by the above.

2. The silicon carbide ingot according to Claim 1, wherein the buffer layer has a thickness of 100 μm or more. A silicon carbide ingot, characterized by the above.

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