JP2017078021A - ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon carbide ingot by a sublimation recrystallization method of suppressing a crack generation.SOLUTION: In a growth process of a silicon carbide ingot 1 having a seed substrate 11 comprising of a 4H-type silicon carbide and a silicon carbide layer 13 grown on the seed substrate 11, the silicon carbide layer 13 is grown in a state where a temperature fluctuation on the growth surface 13a is suppressed by adjusting a current value of a heating coil such that a difference between a maximum temperature and minimum temperature of a growth surface 13a facing the seed substrate 11 side in the silicon carbide layer 13 is 30°C or less, and has a thickness of 15 mm or more in a growth direction. The silicon carbide ingot 1 shows a difference of 0.004 nm or less between a maximum lattice index and a minimum lattice index when a lattice index is measured at multiple points S1, S2, and S3 which are adjacent to each other at a distance of 5 mm along the growth direction of the silicon carbide layer 13, and has a width of 125 mm or more and 175 mm or less seen from the growth direction of the silicon carbide layer 13.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an ingot, a silicon carbide substrate, and an ingot manufacturing method, and more particularly to an ingot made of silicon carbide, a silicon carbide substrate obtained from the ingot, and an ingot manufacturing method made of silicon carbide.

  In recent years, in order to enable a semiconductor device to have a high breakdown voltage and a low loss, silicon carbide is being adopted as a material constituting the semiconductor device. Silicon carbide is a wide band gap semiconductor having a larger band gap than silicon that has been widely used as a material constituting a semiconductor device. Therefore, by adopting silicon carbide as a material constituting the semiconductor device, it is possible to achieve a high breakdown voltage and a low on-resistance of the semiconductor device.

  A silicon carbide ingot is manufactured, for example, by growing a silicon carbide single crystal on a seed substrate using a sublimation recrystallization method. In this silicon carbide ingot, strain or the like is generated in the grown crystal, which may cause cracks in the ingot or the silicon carbide substrate cut out from the ingot. On the other hand, for example, by reducing the processing conditions of the substrate or increasing the amount of removal of the substrate, it is also possible to obtain a flat substrate free from cracks from a strained ingot. However, in this case, there is a possibility that the substrate may be broken by a slight impact, resulting in a problem that the yield is lowered. In response to such a problem, for example, in Japanese Patent Laid-Open No. 2012-250864 (hereinafter referred to as Patent Document 1), by reducing the concentration gradient of metal atoms in the growth direction of the ingot, strain and stress in the crystal are alleviated. Is disclosed.

JP 2012-250864 A

  In Patent Document 1, although the strain in the crystal is alleviated to some extent, sufficient knowledge about the cause of the strain and stress in the crystal is not obtained, and cracks are generated in the silicon carbide ingot or the silicon carbide substrate. It was difficult to sufficiently suppress this.

  This invention is made | formed in view of the said subject, The objective can suppress the generation | occurrence | production of a crack, the silicon carbide substrate obtained by cut | disconnecting the said ingot, and the generation | occurrence | production of a crack. It is to provide a manufacturing method of a simple ingot.

  The ingot according to the present invention includes a seed substrate made of silicon carbide and a silicon carbide layer grown on the seed substrate. The silicon carbide layer has a thickness of 15 mm or more in the growth direction. In the silicon carbide layer, when the lattice constant is measured at a plurality of measurement points that exist along the growth direction and the distance between two adjacent points is 5 mm, the maximum value of the lattice constant and the minimum value of the lattice constant The difference is 0.004 nm or less.

  The present inventor has made a detailed study on the cause of distortion in a crystal when a silicon carbide layer is grown on a seed substrate by using a sublimation recrystallization method, and as a result, the following results are obtained. The knowledge was obtained and the present invention was conceived.

  In general, the sublimation recrystallization method is performed by placing a seed substrate and a raw material made of silicon carbide in a crucible, and sublimating the raw material to grow a silicon carbide layer on the seed substrate. In the initial stage of crystal growth, the heat inside the silicon carbide layer is consumed by heat transfer from the crucible, so that the temperature of the silicon carbide layer is kept low. On the other hand, since the thickness of the silicon carbide layer increases in the latter stage of crystal growth, the heat on the growth surface (surface opposite to the seed substrate side) of the silicon carbide layer is consumed by heat transfer from the crucible. As a result, the region on the growth surface side is likely to have a higher temperature than the region on the seed substrate side. As shown in the temperature dependence of the thermal conductivity of silicon carbide in FIG. 10, this is because the thermal conductivity of silicon carbide is remarkably lowered at a temperature of 2000 ° C. or higher, which is the crystal growth temperature of silicon carbide. (In FIG. 10, the horizontal axis indicates temperature (K), and the vertical axis indicates thermal conductivity (W / cm · K) of silicon carbide). As described above, the temperature difference between the growth surface side region and the seed substrate side region in the silicon carbide layer causes a variation in lattice constant in the growth direction, resulting in strain in the crystal. Etc. occur. This is particularly remarkable when the thickness of the silicon carbide layer is large.

  In contrast, in the ingot according to the present invention, when the thickness in the growth direction of the silicon carbide layer is as large as 15 mm or more and the lattice constant is measured at the measurement point of the silicon carbide layer, the maximum value of the lattice constant is The difference from the minimum value of the lattice constant is 0.004 nm or less. That is, in this ingot, variation in lattice constant in the growth direction of the silicon carbide layer is reduced. Therefore, according to the ingot according to the present invention, it is possible to provide an ingot in which generation of cracks due to strain in the crystal is suppressed. In this ingot, the measurement point may include a point on the growth surface opposite to the seed substrate side in the silicon carbide layer.

  The ingot may have a width of 100 mm or more when viewed from the growth direction. Thereby, a larger-diameter ingot is obtained, and a larger-diameter silicon carbide substrate can be obtained by cutting the ingot.

  In the ingot, the polytype may be 4H type. Thus, the polytype in the ingot may be a 4H type which is a typical silicon carbide polytype.

  The silicon carbide substrate according to the present invention is obtained by cutting the ingot according to the present invention in which the occurrence of cracks is suppressed. Therefore, according to the silicon carbide substrate according to the present invention, it is possible to provide a high-quality silicon carbide substrate in which generation of cracks is suppressed.

  The method for producing an ingot according to the present invention includes a step of preparing a seed substrate and a raw material made of silicon carbide, and a step of growing a silicon carbide layer on the seed substrate by sublimating the raw material. In the step of growing the silicon carbide layer, the maximum value of the temperature of the growth surface opposite to the seed substrate side in the silicon carbide layer and the growth surface of the silicon carbide layer from the start of the growth of the silicon carbide layer to the completion of the growth of the silicon carbide layer. The difference from the minimum value of the temperature is maintained at 30 ° C. or less.

  As described above, in the manufacture of an ingot using a conventional sublimation recrystallization method, the growth surface temperature increases as the growth of the silicon carbide layer proceeds. As a result, the silicon carbide layer has a large variation in lattice constant in the growth direction, and the manufactured ingot is prone to cracks in the crystal.

  On the other hand, in the ingot manufacturing method according to the present invention, silicon carbide in a state where the temperature fluctuation of the growth surface is suppressed as described above (the state where the difference between the maximum value and the minimum value is maintained at 30 ° C. or less). Grow layers. Therefore, the variation in lattice constant in the growth direction of the silicon carbide layer is reduced, and the generation of strain due to this can be suppressed. Therefore, according to the ingot manufacturing method according to the present invention, it is possible to manufacture an ingot in which the occurrence of cracks is suppressed.

  As is clear from the above description, according to the ingot according to the present invention, it is possible to provide an ingot in which the occurrence of cracks is suppressed. Moreover, according to the silicon carbide substrate according to the present invention, it is possible to provide a high-quality silicon carbide substrate in which generation of cracks is suppressed. Moreover, according to the manufacturing method of the ingot according to this invention, the ingot in which generation | occurrence | production of the crack was suppressed can be manufactured.

It is a schematic side view which shows the ingot which concerns on this Embodiment. 1 is a schematic perspective view showing a silicon carbide substrate according to the present embodiment. It is the schematic which shows the hexagonal lattice structure of silicon carbide. It is a schematic side view for demonstrating the measurement of the lattice constant in the ingot which concerns on this Embodiment. It is a schematic side view for demonstrating the measurement of the lattice constant in the ingot which concerns on this Embodiment. It is a flowchart which shows schematically the manufacturing method of the ingot which concerns on this Embodiment. It is a schematic sectional drawing for demonstrating the manufacturing method of the ingot which concerns on this Embodiment. It is a schematic sectional drawing for demonstrating the manufacturing method of the ingot which concerns on this Embodiment. It is a schematic sectional drawing for demonstrating the method to measure the temperature fluctuation of the growth surface in the manufacturing method of the ingot which concerns on this Embodiment. It is a graph which shows the temperature change of the thermal conductivity of silicon carbide.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated. In the present specification, the individual orientation is indicated by [], the collective orientation is indicated by <>, the individual plane is indicated by (), and the aggregate plane is indicated by {}. As for the negative index, “−” (bar) is attached on the number in crystallography, but in this specification, a negative sign is attached before the number.

  First, an ingot and a silicon carbide substrate according to an embodiment of the present invention will be described. Referring to FIG. 1, ingot 1 according to the present embodiment is made of silicon carbide having a polytype of 4H, and includes seed substrate 11 and silicon carbide layer 13 grown on surface 11a of seed substrate 11. I have. Silicon carbide layer 13 is grown on seed substrate 11 in the <0001> direction (arrow direction in FIG. 1) by sublimation recrystallization. Therefore, the growth direction of silicon carbide layer 13 is the <0001> direction. Referring to FIG. 2, silicon carbide substrate 10 according to the present embodiment is obtained by cutting ingot 1 (see FIG. 1) in an arbitrary direction.

  Referring to FIG. 1, silicon carbide layer 13 has a thickness in the <0001> direction of 15 mm or more, may be 15 mm, may be 20 mm, or may be 50 mm. Further, the width (caliber) of the ingot 1 when viewed from the <0001> direction is 100 mm or more, which may be 125 mm, 150 mm, or 175 mm.

  In the silicon carbide layer 13, when the lattice constant is measured at a plurality of measurement points existing along the <0001> direction, the difference between the maximum value of the lattice constant and the minimum value of the lattice constant is 0.004 nm or less. Preferably it is 0.003 nm or less, More preferably, it is 0.002 nm or less. The measurement point has a distance of 2 mm between two adjacent points. Therefore, in silicon carbide layer 13, variation in lattice constant in the <0001> direction is reduced. Moreover, in the silicon carbide layer 13, the lattice constant may change so as to increase linearly in the direction from the seed substrate 11 side toward the growth surface 13a side, or may change so as to have a plurality of inclinations. Also good.

  Referring to FIG. 3, “lattice constant” is a lattice constant C (nm) in the <0001> direction in a hexagonal lattice structure of silicon carbide. The lattice constant C can be measured, for example, by X-ray diffraction (XRD: X-Ray Diffraction) using Cu-Kα1 (wavelength: 0.15405 nm) as an X-ray source. In the silicon carbide layer 13, when the XRD measurement is performed at the measurement point, the difference between the maximum value and the minimum value of 2θ at the peak due to diffraction on the (0004) plane is 0.05 ° or less.

  Referring to FIGS. 4 and 5, the measurement points at which the lattice constant C is measured include a measurement point S1 on the growth surface 13a opposite to the seed substrate 11 side. Therefore, when the thickness of the silicon carbide layer 13 is 15 mm, for example, the distance between the measurement point S1 and the measurement point S1 is 5 mm, and the distance from the measurement point S2 is 5 mm. The measurement point S3 is included in the measurement points (see FIG. 4). When silicon carbide layer 13 has a thickness of, for example, 50 mm, measurement points S1 to S10 are similarly included in the measurement points. Further, as shown in FIGS. 4 and 5, the measurement point includes the central portion in the radial direction of the ingot 1 and is not included in the region from the surface 11 a of the seed substrate 11 to 0.5 mm. Further, the lattice constant at each of the measurement points S1 to S10 can be measured by cutting the substrate including the measurement points S1 to S10 from the ingot 1 and performing XRD measurement on the substrate.

  As described above, in the ingot 1 according to the present embodiment, when the thickness in the <0001> direction of the silicon carbide layer 13 is as large as 15 mm or more and the lattice constant is measured at the measurement point of the silicon carbide layer 13, The difference between the maximum value of the lattice constant and the minimum value of the lattice constant is reduced to 0.004 nm or less. For this reason, in the ingot 1, the occurrence of strain in the crystal due to the variation in lattice constant is suppressed. Therefore, the ingot 1 according to the present embodiment is one in which the occurrence of cracks is suppressed.

  Silicon carbide substrate 10 according to the present embodiment is obtained by cutting ingot 1 according to the present embodiment in which the occurrence of cracks is suppressed. Therefore, this silicon carbide substrate 10 has a high quality in which generation of cracks is suppressed.

  Next, an ingot manufacturing method according to the present embodiment will be described. In the ingot manufacturing method according to the present embodiment, the ingot 1 according to the present embodiment in which the generation of cracks is suppressed can be manufactured.

  With reference to FIG. 6, in the ingot manufacturing method according to the present embodiment, first, a seed substrate and a raw material preparation step are performed as step S <b> 10). In this step (S10), referring to FIG. 7, seed substrate 11 made of silicon carbide single crystal and raw material 12 made of polycrystalline silicon carbide powder or silicon carbide sintered body are prepared. And the seed substrate 11 and the raw material 12 are arrange | positioned in the state which mutually opposed in the crucible 2 made from carbon, as shown in FIG.

Next, a temperature raising step is performed as a step (S20). In this step (S20), referring to FIG. 7, while supplying argon (Ar) gas and nitrogen (N ₂ ) gas into the crucible 2, a heating coil (not shown) arranged outside the crucible 2 is used. The temperature in the crucible 2 is raised to the crystal growth temperature of silicon carbide. At this time, the inside of the crucible 2 is heated so that the temperature gradually decreases in the direction from the raw material 12 side to the seed substrate 11 side (a temperature gradient is formed). Moreover, the temperature of the upper part 2a which arrange | positions the seed substrate 11 in the crucible 2 can be measured with the radiation thermometer 21 arrange | positioned on the exterior (upper side) of the crucible 2. FIG.

  Next, as a step (S30), a crystal growth step is performed. In this step (S30), after the inside of the crucible 2 is heated to a predetermined temperature, the inside of the crucible 2 is decompressed to a predetermined pressure. Thereby, the raw material 12 is sublimated to generate a raw material gas of silicon carbide, and the raw material gas reaches the surface 11 a of the seed substrate 11. As a result, silicon carbide layer 13 grows on surface 11a of seed substrate 11 as shown in FIG. Then, the inside of the crucible 2 is pressurized after a predetermined time, and the growth of the silicon carbide layer 13 is stopped. Thereafter, the crucible 2 is cooled, and the ingot 1 is taken out from the crucible 2 after the cooling process is completed.

  In this step (S30), during the period from the start of growth of silicon carbide layer 13 to the completion of growth, the maximum value of the temperature of growth surface 13a opposite to the seed substrate 11 side in silicon carbide layer 13 and the growth surface 13a The current value of the heating coil (not shown) is adjusted so that the difference from the minimum temperature value is 30 ° C. or less. More specifically, the temperature of the growth surface 13a gradually increases as the silicon carbide layer 13 grows, whereas the current value of the heating coil is adjusted to be small. In this step (S30), the difference between the maximum value and the minimum value is preferably 20 ° C. or less, more preferably 15 ° C. or less, and further preferably 10 ° C. or less. Thus, in this step (S30), silicon carbide layer 13 is grown in a state where temperature fluctuation on growth surface 13a is suppressed.

  In this step (S30), the temperature fluctuation of the growth surface 13a can be suppressed as follows. Referring to FIG. 9, first, a crucible 3 in which a hole 3 a is formed in a lower part is prepared, and a raw material 12 and a seed substrate 11 are arranged in the crucible 3. Then, silicon carbide layer 13 is grown on seed substrate 11 by sublimating raw material 12. Then, at an arbitrary time during the growth of the silicon carbide layer 13, the carbon plate 30 is disposed on the growth surface 13 a as shown in FIG. 9, and the temperature of the growth surface 13 a is measured by the radiation thermometer 22 through the carbon plate 30. Measure. In this way, while confirming the temperature of the growth surface 13a during the growth of the silicon carbide layer 13, the current value of the heating coil (not shown) is adjusted so that the temperature fluctuation of the growth surface 13a is 30 ° C. or less. In this manner, heating conditions for suppressing temperature fluctuations on the growth surface 13a of the silicon carbide layer 13 can be set in advance before the step (S30) is performed.

  As described above, the steps (S10) to (S30) are performed to manufacture the ingot 1 according to the present embodiment (see FIG. 1), and the ingot manufacturing method according to the present embodiment is performed. Complete. And silicon carbide substrate 10 concerning this embodiment can be obtained by cutting manufactured ingot 1.

  As described above, in the ingot manufacturing method according to the present embodiment, since silicon carbide layer 13 is grown in a state in which temperature fluctuation on growth surface 13a is suppressed, the occurrence of strain in the crystal can be suppressed. Therefore, according to the ingot manufacturing method according to the present embodiment, the ingot 1 in which the occurrence of cracks is suppressed can be manufactured.

  An experiment for confirming the effect of the present invention was performed for suppressing the occurrence of cracks in an ingot or a silicon carbide substrate. Referring to FIG. 8, first, seed substrate 11 and raw material 12 made of silicon carbide were prepared, and these were placed in crucible 2. Next, the inside of the crucible 2 was heated while supplying argon gas and nitrogen gas into the crucible 2. The flow rate of argon gas was 100 ml / min, the flow rate of nitrogen gas was 10 ml / min, and the pressure of argon gas in the crucible 2 was 70 kPa. The temperature increase rate of the crucible 2 was set to 500 ° C./h, and the upper portion 2a of the crucible 2 was heated from room temperature to 2200 ° C.

  Next, after the temperature of the upper part 2a of the crucible 2 reached 2200 ° C., the pressure in the crucible 2 was reduced to 2 kPa, and the raw material 12 was sublimated. Then, the silicon carbide layer 13 was grown for 100 hours. At this time, the current value of the heating coil (not shown) is adjusted so that the difference between the maximum value and the minimum value on the growth surface 13a is 30 ° C. or less during the period from the start to the completion of the growth of the silicon carbide layer 13. did. Next, after the growth of the silicon carbide layer 13 was completed, the pressure in the crucible 2 was increased to 70 kPa to stop the growth. Thereafter, the crucible 2 was cooled at a rate of 100 ° C./h, and the ingot 1 was taken out after the cooling process was completed. The thickness of the ingot 1 was 15 mm or 50 mm, and the diameter of the ingot 1 was 100 mm, 125 mm or 150 mm.

  Next, when the thickness of silicon carbide layer 13 was 15 mm, lattice constants were measured at measurement points S1, S2, and S3 shown in FIG. Further, when the thickness of silicon carbide layer 13 was 50 mm, the lattice constants were measured at measurement points S1 to S10 shown in FIG. Further, for each ingot, the difference value between the maximum value of the lattice constant and the minimum value of the lattice constant was calculated. And the presence or absence of a crack was investigated about each ingot. These results are shown in Table 1. In addition, the investigation on the presence or absence of the occurrence of cracks was performed by dropping an iron ball having a weight of 500 g from a high position of 50 cm onto the facet portion of the ingot. The case where there was no occurrence of cracks is set to “None”.

  The results of the experiment will be described. As shown in Table 1, when the difference between the maximum value and the minimum value of the temperature on the growth surface is 30 ° C. or less, the difference between the maximum value and the minimum value of the lattice constant in the silicon carbide layer 13 is 0. In this case, no crack was observed. On the other hand, when the difference between the maximum value and the minimum value of the growth surface exceeds 30 ° C., the difference between the maximum value and the minimum value of the lattice constant exceeds 0.004 nm. The occurrence of was seen. From this experimental result, it was found that by performing crystal growth while suppressing temperature fluctuations on the growth surface, the variation in lattice constant in the silicon carbide layer was reduced, and as a result, the occurrence of cracks in the ingot was suppressed.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The ingot, silicon carbide substrate, and ingot manufacturing method according to the present invention can be applied particularly advantageously in the ingot, silicon carbide substrate, and ingot manufacturing method that are required to suppress the occurrence of cracks.

  1 ingot, 2, 3 crucible, 2a upper part, 3a hole, 10 silicon carbide substrate, 11 seed substrate, 11a surface, 12 raw material, 13 silicon carbide layer, 13a growth surface, 21, 22 radiation thermometer, 30 carbon plate, C Lattice constant, S1, S2, S3, S4, S5, S6, S7, S8, S9, S10 Measurement points.

Claims (2)

A seed substrate made of silicon carbide having a polytype of 4H,
A silicon carbide layer grown on the seed substrate,
The silicon carbide layer has a thickness of 15 mm or more in the growth direction,
In the silicon carbide layer, the lattice constant in the <0001> direction in the hexagonal lattice structure is measured at a plurality of measurement points that exist along the growth direction and the distance between two adjacent points is 5 mm. The difference between the maximum value of the constant and the minimum value of the lattice constant is 0.004 nm or less,
An ingot having a width of 125 mm or more and 175 mm or less when viewed from the growth direction.   The ingot according to claim 1, wherein the measurement point includes a point on the growth surface opposite to the seed substrate side in the silicon carbide layer.

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