A method for reducing the bending and warping degrees in multi-wire cutting of silicon carbide-like crystals

Abstract

The present invention discloses a method for reducing the bending and warping degrees in multi-wire cutting of silicon carbide-like crystals, comprising the following steps: (1) Select an even number of standard crystals that have been shaped, and use A and B to represent the two faces of each crystal respectively; (2) Select the even number of crystals in step (1), and bond the even number of crystals into a whole on the adhesive table in the order and direction of A-B-B-A-A-B-B-A; apply pressure for 12 hours; (3) Bond the crystals processed in step (2) to the cutting workpiece plate, and multi-wire cutting can be carried out after the adhesive has completely cooled. The present invention proposes a method for reducing the bending and warping degrees in multi-wire cutting of silicon carbide-like crystals. By using the method of bonding crystals back to back with an even number of crystals, while increasing the cutting length, the bending and warping of the cut wafers are controlled, a cutting sheet with a low bending and warping degree is obtained, which brings convenience to subsequent processing, reduces the difficulty of grinding and polishing, and improves the wafer processing quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystal cutting, and relates to a crystal processing method, in particular to a multi-wire cutting method for crystals. Background Art

[0002] Cutting is an important front-end process in crystal processing. The crystal is cut into sheets by mechanical means and then polished through subsequent grinding to obtain standard wafers. Traditional cutting methods include outer circle cutting and inner circle cutting. However, these two cutting methods are inefficient, only one piece can be cut at a time, and the cutting marks are wide, resulting in large losses and high costs. Moreover, for cutting high-hardness crystal materials, it is easy to cause damage such as cracks and chipping, and the geometric parameters of the cut wafers are poor. Although laser cutting has high precision, it has high cost and low efficiency. In recent years, the emerging laser cold cutting is more similar to the cold peeling technology of ion implantation, and it is also very difficult to process hard and brittle crystal materials with low efficiency. Therefore, multi-wire cutting has become the mainstream method in current crystal processing, especially for hard and brittle crystal cutting.

[0003] The multi-wire cutting method is to simultaneously cut the crystal into multiple thin slices, called cutting slices, by the high-speed reciprocating motion of a multi-wire metal cutting wire mesh arranged at equal intervals, while bringing in the mixed cutting abrasive. Nowadays, the commonly used numerical control multi-wire cutting can cut out hundreds of slices at a time. Compared with the traditional outer and inner circle cutting, multi-wire cutting has high efficiency, high precision, and low loss, and the geometric parameters of the cut wafers are far superior to those of outer and inner circle cutting. The wire mesh of multi-wire cutting can be arranged wider, so larger-sized crystals can be cut. At the same time, the diameter of the cutting wire is small, usually less than 0.2 mm, so the cutting loss is small and the cutting damage is low. Multi-wire cutting has become the preferred method for current crystal cutting, especially for hard and brittle crystals.

[0004] When using the multi-wire cutting method to cut silicon carbide-like crystal materials, the cutting slices often tend to bend to the same side, which is related to the polarity of the crystal material itself. At the same time, there are many parameters in the multi-wire cutting process that affect the geometric parameters of the cutting slices. These parameters include the concentration and solid content of the cutting fluid, the temperature and viscosity of the cutting fluid, the flow rate of the cutting fluid, the tension of the cutting wire, the wire speed, the swing angle, etc. Any inappropriate parameter may be fatal. Moreover, from the perspective of cost, the thickness requirement of the cutting slices is getting smaller and cannot be much larger than the thickness of the product wafer. In this way, the amount of material removed by subsequent grinding and polishing of the cutting slices is also correspondingly reduced. Therefore, the change in the bending and warping degree of the cutting slices has a more sensitive impact on the subsequent processing. So the process of cutting non-polar crystals is not suitable for cutting silicon carbide-like crystal materials.

[0005] Taking silicon carbide crystal material as an example, most of the silicon carbide wafers on the market require processing at a certain angle. The chemical bonds broken on the two faces of the crystal are different, and the cutting effects on the two faces are also significantly different, which brings greater difficulties to multi-wire cutting. If the bending and warping degree of the cutting sheet is relatively large, it is easy to break into pieces during the subsequent grinding and polishing process, and it is very difficult to reduce the bending and warping degree to a lower value, which brings difficulties to the epitaxy and use of the wafer, and reduces the yield of the processed wafer. Most of the existing process improvements focus on the adjustment of cutting parameters, the change of the cutting-in angle, etc. Although these improvements have some effects, how to minimize the bending and warping degree value of the cutting sheet during multi-wire cutting is still the key issue of concern. Summary of the Invention

[0006] Object of the Invention: Aiming at the above problems, the present invention proposes a method for reducing the bending and warping degree in multi-wire cutting of silicon carbide-like crystals. By using the method of bonding the crystals back to back in pairs, while increasing the cutting length, the bending and warping of the cut wafers are controlled, and a cutting sheet with a low bending and warping degree is obtained, which brings convenience to the subsequent processing and reduces the difficulty of grinding and polishing.

[0007] Technical Solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for reducing the bending and warping degree in multi-wire cutting of silicon carbide-like crystals, comprising the following steps:

[0009] Step (1): Select an even number of standard crystals that have been shaped. Represent the two faces of each crystal as A and B respectively.

[0010] Step (2): Select the even number of crystals in Step (1), and bond the even number of crystals into a whole on the bonding table in the order and direction of A-B-B-A-A-B-B-A; apply pressure for 12 hours.

[0011] Step (3): Bond the crystals processed in Step (2) to the cutting workpiece plate, and multi-wire cutting can be carried out after the adhesive is completely cooled.

[0012] Further, in Step (1), the shaped standard crystal means that the outer circle grinding is completed and qualified, without chipping and cracks; the plane grinding is completed and qualified, the parallelism is less than 0.04 mm, the crystal orientation is consistent, the crystal orientation error is less than 0.2°, and the surface roughness is less than 0.5 microns.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention provides a method for reducing the bending and warping degrees in the multi-wire cutting of silicon carbide-like crystals. By using the method of bonding crystals back to back in an even number, while increasing the cutting length, the bending and warping of the cut wafers are controlled, resulting in cut wafers with low bending and warping degrees, which brings convenience to subsequent processing, reduces the difficulty of grinding and polishing, and improves the wafer processing quality. Compared with the process of bonding crystals in the same direction, this method does not increase the process steps, and the process is simple and easy to operate. The bending and warping degrees of the cut wafers are reduced, the product yield is increased, and the comprehensive product cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flowchart of the crystal bonding structure of the present invention; A and B represent different crystal planes;

[0016] Figure 2 It is a schematic diagram of bonding to the workpiece plate: 1. 4 bonded crystals, 2. Workpiece plate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention.

[0018] In view of the above difficulties existing in the prior art, the present invention provides a method for reducing the bending and warping degrees in the multi-wire cutting of silicon carbide-like crystals. By using the method of bonding crystals back to back in an even number, while increasing the cutting length, the bending and warping of the cut wafers are controlled, resulting in cut wafers with low bending and warping degrees, which brings convenience to subsequent processing, reduces the difficulty of subsequent grinding and polishing processing, and improves the product processing quality.

[0019] Embodiment

[0020] (1) Select 4 pieces of 6-inch ultra-hard silicon carbide ingots, and after shaping processing, they become standard crystals to be cut. The A surface is the silicon surface, and the B surface is the carbon surface. The parallelism of the 4 crystals is 0.02 mm, 0.03 mm, 0.02 mm, and 0.02 mm respectively. The crystal orientation is 4° off the

[0001] direction towards the [11-20] direction, with an error of less than 10 arc minutes, and the surface roughness is less than 0.5 micrometers. The crystals have no chipping or cracks.

[0021] (2) Select the 4 crystals in step (1), and bond the 4 crystals into a whole with commercially available X glue on the bonding table in the order and direction of A-B-B-A-A-B-B-A; and apply a pressure of 60 Kg and maintain it for 12 hours;

[0022] (3) Bond the crystals processed in step (2) to the cutting workpiece plate with commercially available Y glue, and multi-wire cutting can be carried out after the glue is completely cooled.

[0023] (4) Cut using an SJ multi-wire cutting device with a cutting time of 120 hours, a tension of 40 N, a wire speed of 28 m / s, and a flow rate of 4500 kg / m. 3 .

[0024] (5) A total of 81 cutting slices are obtained. After removing 8 head and tail slices, 73 qualified cutting slices are obtained. The TTV range is between 4.651 μm - 7.542 μm, the bow range is between 0.212 μm - 12.340 μm, and the warp range is between 5.768 μm - 18.324 μm.

[0025] Thus, the present invention provides a method for reducing the bow and warp in the multi-wire cutting of silicon carbide-like crystals. By using the method of bonding the crystals back to back in an even number, while increasing the cutting length, the bow and warp of the cut wafers are controlled, and cutting slices with low bow and warp are obtained.

[0026] In the description of this specification, the descriptions referring to terms such as "embodiment", "specific embodiment", "some embodiments", etc. mean that the specific features, materials, structures, or characteristics described in connection with the embodiment or example are included in at least one embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment. Moreover, the specific features, materials, structures, or characteristics described can be combined in a suitable manner in any one or more embodiments.

[0027] Although the embodiments of the present invention have been given and described, those skilled in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for reducing the bending and warping degrees in multi-wire cutting of silicon carbide-like crystals, characterized in that: It includes the following steps: Step (1): Select standard crystals that have been shaped in an even number of pieces, and use A and B to represent the two faces of each crystal respectively; Step (2): Select the crystals in an even number of pieces in Step (1), and bond the even number of crystals into a whole on the adhesive table in the order and direction of A - B - B - A - A - B - B - A; Apply pressure for 12 hours; Step (3): Bond the crystals processed in Step (2) to the cutting workpiece plate, and multi-wire cutting can be carried out after the adhesive has completely cooled; In the said Step (1), the shaped standard crystals refer to those that have passed the outer circle grinding, passed the plane grinding, have consistent crystal orientations, qualified parallelism, no chipping and no cracks; The consistent crystal orientation means that the error is less than 0.2°, the parallelism is less than 0.04 mm, and the surface roughness is less than 0.5 µm.

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