JP2015222766A - Wire processing method of silicon carbide single crystal ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire processing method capable of reducing generation of a crack when cutting out a silicon carbide single crystal substrate by cutting a silicon carbide single crystal ingot by using a wire processing apparatus.SOLUTION: The wire processing method for cutting a silicon carbide single crystal ingot 2 to obtain a silicon carbide single crystal substrate is characterized by specifying a crystal orientation of the silicon carbide single crystal ingot against a travel direction of a saw wire 1 and installing.

Description

  The present invention cuts (slices) a silicon carbide single crystal ingot to reduce cracks that occur when slicing (cutting out) a plate-like body such as a substrate (sometimes referred to as a wafer). The present invention relates to a wire processing method for a crystal ingot.

  In the manufacturing process of a silicon carbide single crystal substrate (wafer) used as a semiconductor material, a slicing step of cutting a substrate (wafer) from the ingot after manufacturing a silicon carbide single crystal ingot is essential. In this slicing step, wafer cutting processing using an inner peripheral slicer has been conventionally performed, but this method is inefficient because it slices and cuts wafers one by one, and in recent years, a large number of wafers are simultaneously cut. Multi-wire processing technology using a multi-wire saw that can be sliced and cut has been developed and put into practical use.

  About this multi-wire processing technology, it has a pair of multi-groove pulleys (work rollers) arranged in parallel opposite to each other, and a large number of saw wires are arranged in parallel to each other in a large number of grooves of these multi-groove pulleys. A large number of saw wires are run at a high speed, and a workpiece is pressed against the saw wire that runs at a high speed, and free abrasive grains and coolant are supplied to sliding portions of the workpiece and the saw wire so that the workpiece is processed. There are known a method of cutting and a method of using a fixed abrasive wire having abrasive grains fixed on its surface as a saw wire and using only a coolant without using free abrasive grains.

  For example, Patent Document 1 discloses that a silicon carbide single crystal substrate is obtained by slicing a silicon carbide single crystal at a predetermined angle with respect to a central axis to a predetermined thickness. Further, in Patent Document 2, cutting is performed in a direction in which the angle formed between the crystal orientation <11-20> direction or the crystal orientation <1-100> direction is 15 ± 5 ° in the orthogonal projection to the {0001} plane. It is disclosed that an ingot is sliced to progress to obtain a silicon carbide substrate.

JP 2009-102196 A JP2013-89937A

  By the way, in the case of a method of processing a silicon carbide (SiC) single crystal with a wire saw, as the ingot diameter increases to 6 inches, the residual stress remaining in the ingot also increases due to the crystal growth process. There is a tendency that the frequency of occurrence of cracks during processing tends to increase.

  Prior Patent Document 1 relates to a technique for preventing a SiC single crystal ingot from cracking at the time of slicing, but even if slicing is performed after removing irregularities on the outer periphery as in Patent Document 1, the diameter of the ingot is reduced. If this becomes larger, the frequency of occurrence of cracks will increase.

  Patent Document 2 relates to a technique for preventing warpage of the obtained SiC single crystal substrate by cutting at a predetermined angle with respect to the crystal orientation, and cracks during cutting cannot be suppressed.

  Accordingly, an object of the present invention is to provide a method for processing a silicon carbide single crystal ingot that can significantly reduce the rate of occurrence of cracks that occur when slicing a silicon carbide single crystal ingot.

  Silicon carbide single crystal has a (1-100) plane that is easy to cleave, and the crystal orientation <11-20>, which is perpendicular to the (1-100) plane, matches the traveling direction of the saw wire. In this case, the stress applied to the silicon carbide single crystal ingot by cutting is maximized. In particular, when the cutting position reaches the center of the silicon carbide single crystal ingot, the contact distance between the wire saw and the silicon carbide single crystal ingot is maximized, so that cracks frequently occur.

  Therefore, in order to solve the above-mentioned problems, the present inventors used a wire processing apparatus to cut a silicon carbide single crystal ingot to cut a silicon carbide single crystal substrate, so that the crystal orientation of the silicon carbide single crystal ingot <11 The relationship between the angle of the saw wire traveling direction relative to the -20> direction and the probability of crack occurrence was examined in detail. As a result, the crack generation rate is reliably reduced by shifting the angle from the crystal orientation <11-20> direction, and when the angle of deviation is 30 °, that is, the crystal orientation <1-100> direction, The inventors have found that the crack generation rate can be significantly reduced, and have reached the present invention.

That is, the gist of the present invention is as follows.
(1) In a method of cutting a silicon carbide single crystal ingot with a wire saw while processing a saw wire to process it into a silicon carbide single crystal substrate, the crystal orientation of the silicon carbide single crystal ingot is confirmed, and the silicon carbide single crystal ingot A silicon carbide single crystal in which the traveling direction of the saw wire is maintained within ± 5 ° with respect to the <1-100> orthographic projection obtained by projecting the crystal orientation <1-100> direction onto the ingot cut surface by the saw wire. A method for wire processing a silicon carbide single crystal ingot, characterized by cutting an ingot.
(2) The wire processing method for a silicon carbide single crystal ingot according to (1), wherein a traveling direction of the saw wire is maintained within ± 3 ° with respect to the <1-100> orthographic projection. .
(3) A wire sawing method for a silicon carbide single crystal ingot, wherein the wire saw according to (1) or (2) is a multi-wire saw and is simultaneously processed into a plurality of silicon carbide single crystal substrates.
(4) The wire processing method for a silicon carbide single crystal ingot according to any one of (1) to (3), wherein the diameter of the silicon carbide single crystal ingot is 6 inches or more.

  ADVANTAGE OF THE INVENTION According to this invention, the incidence rate of the crack which generate | occur | produces when slicing a silicon carbide single crystal ingot by wire processing can be reduced notably.

FIG. 1A is an explanatory view showing a crystal orientation in a silicon carbide single crystal, and FIG. 1B is an explanatory view showing an orientation position relationship in a silicon carbide single crystal ingot. FIG. 2 is an explanatory diagram showing the positional relationship between the wire saw and the ingot during cutting of the silicon carbide single crystal ingot, and the relationship between the traveling direction of the saw wire and the crystal orientation of the ingot. 3 (a) and 3 (b) are explanatory views showing the relationship between the saw wire and the ingot, and FIG. 3 (c) shows the relationship of the traveling direction of the saw wire to the <1-100> orthographic projection of the ingot cut surface. It is explanatory drawing shown.

The present invention will be described in detail below.
A silicon carbide single crystal has a crystal structure in which a combination of carbon atoms and silicon atoms is periodically stacked. In particular, a polytype having a hexagonal crystal structure of 4H having excellent characteristics as a material for power devices in particular. It is used. As shown in FIG. 1 (a), in the case of the hexagonal structure, the structure has one longitudinal axis (c-axis) and three lateral axes (a-axis), and the crystal orientation determined thereby is shown in the figure. Exist as if. The direction along the a-axis is the crystal orientation <11-20> direction, and the direction shifted by 30 ° is the crystal orientation <1-100> direction. In the case of a silicon carbide single crystal, the planes that are parallel to the a-axis direction, that is, parallel to the crystal orientation <11-20> direction (six planes as hexagonal column side faces in the figure) are “cleavage planes”. And has the property of being easily broken along this surface during processing.

FIG. 1 (b) is a schematic diagram of the actually obtained cylindrical ingot. The two crystal orientations shown in FIG. 1 (a) on the left (the crystals are symmetrical, so that they are shifted by 60 ° in the circumferential direction. Directions with the same properties appear at different positions).
When cutting a silicon carbide single crystal substrate from a silicon carbide single crystal ingot, a cylinder is generally cut in a plane direction for reasons such as electrical characteristics (direction in which a circular silicon carbide single crystal substrate can be cut). When cutting, confirm the crystal orientation of the silicon carbide single crystal ingot, and <11-20> direction, <1-100> direction as the crystal orientation with respect to the traveling direction of the saw wire, or between them (30 ° It can be set in any direction.

  FIG. 2 shows the positional relationship (plan view) between the saw wire and the silicon carbide single crystal ingot in the multi-wire processing apparatus. The saw wire 1 and the silicon carbide single crystal ingot 2 are in an arrangement relationship shown in the XY coordinate system in FIG. 2, the saw wire 1 runs in the X direction, and the silicon carbide single crystal ingot 2 is relatively Slowly pressed against the saw wire 1 in the Y direction and cut. That is, the silicon carbide single crystal ingot 2 can be set at an arbitrary angle with respect to the crystal orientation of the silicon carbide single crystal ingot with respect to the X direction in FIG. 2, and the effect of the present invention is manifested by setting the angle at that time. Will be.

  In terms of “crack suppression”, which is an effect of the present invention, the effect becomes more remarkable when the angle shifted from the direction parallel to the above “cleavage plane” (that is, the crystal orientation <11-20> direction) is large. Crack generation can be suppressed most at the maximum 30 °. Here, since the direction shifted by 30 ° from the crystal orientation <11-20> direction is the crystal orientation <1-100> direction, the direction in which crack generation can be suppressed is along the crystal orientation <1-100> direction. Is most effective. In practice, in order to suppress the occurrence of cracks, it is effective to maintain the traveling direction of the saw wire within a range of ± 5 ° with respect to the crystal orientation <1-100> direction (indicated by a broken line in FIG. 2). Range of saw wire 1). More preferably, it is set within a range of ± 3 ° with respect to the crystal direction <1-100>.

  In some cases, it is conceivable to cut the ingot by tilting the c-axis at an arbitrary angle, but this time also crosses the “cleavage plane” existing inside the crystal at the portion where the contact distance with the ingot is maximum during cutting. The distance becomes the largest when the wire saw traveling direction is parallel to the crystal orientation <11-20> direction, and the distance becomes the smallest when the wire saw traveling direction is parallel to the crystal orientation <1-100> direction. Since this is the case, this method can be applied as it is.

  Here, the case where the c-axis of the ingot is inclined at an arbitrary angle is, for example, a silicon carbide single crystal ingot grown by a sublimation recrystallization method (an improved Rayleigh method) using a seed crystal having an off angle. Even if the c-axis is inclined with respect to the growth direction of the ingot, or even if the growth direction of the ingot coincides with the c-axis, the growth direction of the ingot with respect to the cut surface of the ingot by the saw wire This includes the case of cutting without being vertical. That is, in the latter case, when the relationship between the saw wire 1 and the silicon carbide single crystal ingot 2 is viewed from the side as shown in FIG. In addition, the silicon carbide single crystal ingot 2 is not perpendicular to the growth direction L of the silicon carbide ingot 2, but is cut at an angle less than α = 90 ° with respect to the growth direction L of the ingot as shown by the broken line arrow in (ii) As shown in FIG. 3B, when the relationship between the saw wire 1 and the silicon carbide single crystal ingot 2 is viewed in a plane, the wire saw 1 (the traveling direction of the wire saw 1) is the silicon carbide single crystal ingot. Examples of the wire processing include cutting at an angle of less than β = 90 ° with respect to the growth direction L of the ingot, not perpendicular to the growth direction L of 2. In addition, although it changes also with the state of a silicon carbide single crystal ingot and the kind (application) of the board | substrate to cut out, (alpha) in FIG. May be cut in the range of 0 ° to 90 °. Also, the broken line arrow (i) in FIG. 3A corresponds to the Y direction shown in FIG.

  Further, in the case of the wire processing of FIG. 3B, with respect to the <1-100> orthographic projection in which the crystal orientation <1-100> direction of the silicon carbide single crystal ingot 2 is projected onto the ingot cut surface by the saw wire. Set the traveling direction of the saw wire 1. That is, as shown in FIG. 3C, the traveling direction of the saw wire 1 is ± 5 with respect to the <1-100> orthographic projection in which the <1-100> direction is projected onto the ingot cutting surface 2a by the saw wire. The silicon carbide single crystal ingot 2 is cut so as to be maintained within an angle of ± °, preferably within ± 3 °.

In the present invention, the wire saw is preferably a multi-wire saw in terms of mass productivity. In addition, the saw wire of the multi-wire saw only needs to have a tensile strength that can withstand machining, specifically a steel wire such as a piano wire, a metal wire such as a brass wire, a tungsten wire, a molybdenum wire, A carbon fiber etc. can be illustrated. The abrasive grain, must have a high hardness than the ingot, can be specifically exemplified example diamond, CBN, abrasive grains B ₄ C and the like.

  Also, when using a fixed abrasive wire with abrasive grains fixed on the surface of the wire body as the saw wire, the fixing means for fixing the abrasive grains to the wire body only needs to have strength sufficient to withstand machining. Specifically, for example, methods such as electroplating using a fixing agent such as Ni and Ti, metal solder, and resin can be exemplified. Here, a diamond fixed abrasive wire in which diamond abrasive grains are fixed to the surface of a piano wire by metal solder or electroplating is particularly preferable as a fixed abrasive wire used for cutting a hard silicon carbide single crystal ingot. .

  In the wire processing method of the present invention, the diameter of the target silicon carbide single crystal ingot is not particularly limited. However, if the diameter of the silicon carbide single crystal ingot is 6 inches or more, generation of cracks at the time of cutting cannot be ignored. It is particularly preferable to apply the present invention when the diameter of the silicon single crystal ingot is 6 inches or more.

  Hereinafter, based on an Example and a comparative example, this invention is demonstrated in detail. The present invention is not limited to the following examples and comparative examples.

[Example 1]
A total of ten silicon carbide single crystal ingots (SiC ingots) were produced by the sublimation recrystallization method (modified Rayleigh method) under the same growth conditions using the same apparatus. Each of these SiC ingots had a diameter of 150 mmφ (6 inchφ). In addition, these SiC ingots have the ingot growth direction and the c-axis aligned.

  First, for one of the SiC ingots obtained above, using a brass wire with a diameter of 0.2 mmφ, a new line was drawn out at 5 m / min, and the ingot was moved in the Y direction in FIG. 2 at 1 mm / hour, A total of 10 cuts were made by cutting 10 pieces of 6-inch φ SiC wafers having a thickness of 0.8 mm by multi-wire cutting.

  At that time, when the cutting direction was maintained while keeping the traveling direction of the saw wire in the crystal orientation <1-100> direction of the silicon carbide single crystal ingot, it was possible to cut without any cracks except for one occurrence of cracks. It was.

[Example 2]
In the same manner as in Example 1 above, except that the ingot crystal orientation, which is the traveling direction of the saw wire during the cutting process, was set by shifting by 3 ° from the <1-100> direction in the circumferential direction. All but one crack was able to be cut without cracks.

Example 3
When performing in the same manner as in Example 1 except that the ingot crystal orientation, which is the traveling direction of the saw wire during the cutting process, was set 5 ° shifted from the <1-100> direction in the circumferential direction. Except for the occurrence of cracks only three times, all could be cut without cracks.

[Comparative Example 1]
Example 1 except that the ingot crystal orientation which is the traveling direction of the saw wire at the time of cutting is set so as to be the <11-20> direction (an orientation even 30 ° from the <1-100> direction). When it carried out similarly, a crack generate | occur | produced in 9 times out of 10, and it was able to cut | disconnect without a crack only once.

[Comparative Example 2]
When performing in the same manner as in Example 1 except that the ingot crystal orientation, which is the traveling direction of the saw wire during the cutting process, was set to be shifted by 15 ° from the <1-100> direction in the circumferential direction, Cracks occurred at 8 times and could be cut without cracks only 2 times.

[Comparative Example 3]
When performing in the same manner as in Example 1 except that the ingot crystal orientation, which is the traveling direction of the saw wire during the cutting process, was set to be shifted by 10 ° from the <1-100> direction in the circumferential direction, Cracks occurred at 7 times and could be cut without cracks only 3 times.

1: saw wire, 2: silicon carbide single crystal ingot, 2a: ingot cut surface.

Claims (4)

  In a method of processing a silicon carbide single crystal ingot by cutting a silicon carbide single crystal ingot with a wire saw while running a saw wire, the crystal orientation of the silicon carbide single crystal ingot is confirmed, and the crystal orientation of the silicon carbide single crystal ingot < Cutting the silicon carbide single crystal ingot so that the traveling direction of the saw wire is maintained within ± 5 ° with respect to the <1-100> orthographic projection, where the 1-100> direction is projected onto the ingot cutting surface with the saw wire. A wire processing method for a silicon carbide single crystal ingot, wherein:   The wire processing method for a silicon carbide single crystal ingot according to claim 1, wherein a traveling direction of the saw wire is maintained within ± 3 ° with respect to the <1-100> orthographic projection.   The wire saw according to claim 1 or 2, wherein the wire saw is a multi-wire saw and simultaneously processed into a plurality of silicon carbide single crystal substrates.   The diameter of a silicon carbide single crystal ingot is 6 inches or more, The wire processing method of the silicon carbide single crystal ingot in any one of Claims 1-3 characterized by the above-mentioned.

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