Method for reducing cutting stress in processing of AlN crystal

Abstract

The present application relates to the field of aluminum nitride crystal growth processing, and particularly relates to a method for reducing cutting stress of AlN crystal processing. The method is as follows: a hollow cylinder as a buffer layer and an AlN crystal are both adhered to a metal plate through paraffin; then glue is poured into the hollow cylinder, so that the glue completely wraps the crystal; after the glue solidifies, the bottom of the metal plate is heated, the paraffin is melted, and then the metal plate is detached to obtain a sample to be cut; the sample is cut and the edge is trimmed to obtain a regular AlN wafer. The present application sets a buffer layer outside the AlN crystal to avoid damage of stress to the crystal; when the cutting line contacts the crystal, high stress is generated, the buffer layer can gradually release the stress and gradually transfer the stress to the crystal, so that the crystal can be simply and effectively protected, the crystal is prevented from cracking, and the complete AlN wafer can be cut; the buffer layer avoids the direct contact of the cutting line and the crystal, reduces the probability of cutting line breakage, and enables efficient cutting.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride crystal growth and processing, and specifically to a method for reducing cutting stress during AlN crystal processing. Background Technology

[0002] AlN crystals possess an ultra-wide bandgap (6.2 eV) and high thermal conductivity (3.2 W·cm⁻¹). -1 K -1 With its excellent physical properties such as high resistivity and high surface acoustic velocity (5600-6000 m / s), AlN crystals are increasingly being used in lasers, HEMTs, optoelectronic devices, and surface acoustic wave devices. However, AlN crystals prepared using current techniques are prone to internal defects. When external stress sources are applied to the AlN crystal, internal cracks may propagate, leading to wafer cracking and making it difficult to obtain large-sized AlN crystals. Common external stress sources include the lateral friction force generated by the high-speed rotation of diamond wires during wafer cutting. The stress on the crystal is greatest when the diamond wires are in contact with the AlN crystal. If the crystal's crystallization quality is poor, such as a high defect density or the presence of microcracks, the wafer may tear under high external stress.

[0003] To address the wafer breakage problem caused by the aforementioned cutting stress, existing technologies often employ methods such as applying a large amount of cutting fluid for lubrication or increasing the slurry flow rate to alleviate the issue. Although the lubrication of cutting fluid and slurry can reduce the friction between the diamond wire and the AlN crystal to some extent, it is still insufficient to overcome most of the stress during cutting. Therefore, wafer damage remains a problem that urgently needs to be solved in the crystal cutting process. Summary of the Invention

[0004] To address the challenge of crystal cracking caused by high stress upon contact between the crystal and diamond wire during AlN crystal cutting, this invention provides a method for reducing cutting stress during AlN crystal processing. This invention utilizes a buffer layer on the outer side of the crystal. This allows stress to gradually transfer from the diamond wire to the crystal sample upon contact, maximizing stress release and preventing direct stress damage. The buffer layer is constructed from materials of varying hardness from the outside in. Furthermore, the buffer layer prevents direct contact between the cutting wire and the crystal, reducing the probability of wire breakage and playing a crucial role in cutting complete AlN wafers.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for reducing cutting stress during AlN crystal processing includes the following steps:

[0007] S1: Select a vertically placed hollow cylinder, place the AlN crystal at the center of the hollow cylinder, and the height of the AlN crystal is less than the height of the hollow cylinder; then, the bottom of the hollow cylinder and the AlN crystal are both bonded to the metal plate with paraffin wax.

[0008] S2: Pour glue into the hollow cylinder of step S1 so that the glue completely encapsulates the crystal; after the glue solidifies, heat the bottom of the metal plate, and after the paraffin melts, the metal plate falls off to obtain the sample to be cut. The Mohs hardness of the hollow cylinder is 2-3 less than the Mohs hardness of the glue after solidification.

[0009] S3: Place the sample to be cut in step S2 horizontally on the cutting machine and cut it along the longitudinal section to obtain an AlN wafer with a buffer layer on the edge.

[0010] The specific operating steps are as follows:

[0011] The longitudinal section is divided into an entry zone, an intermediate zone, and an exit zone from top to bottom, with the same maximum height for all three. The AlN crystal is located in at least the entry zone and the intermediate zone. The feed rates for the entry zone, intermediate zone, and exit zone are 5-6 mm / h, 7-8 mm / h, and 10 mm / h, respectively.

[0012] S4: Trim the edges of the AlN wafer with the buffer layer from step S3 to obtain a regular AlN wafer.

[0013] Preferably, the hollow cylinder in step S1 is made of polyvinyl chloride, polytetrafluoroethylene, or polypropylene; the metal plate is an iron plate or a copper plate.

[0014] Preferably, in step S1, the ratio between the inner diameter of the hollow cylinder and the maximum outer diameter of the AlN crystal is 12 / 11-6 / 5.

[0015] Preferably, the adhesive used in step S2 is a special adhesive for bonding crystal rods; the Mohs hardness of the adhesive after solidification is 5-6.5.

[0016] In a further preferred embodiment, the specific operation of the glue pouring in step S2 is as follows: the A glue and B glue of the special glue for bonding silicon rods are mixed evenly at a ratio of 1:1 and then poured into the hollow cylinder in step S1 until the AlN crystal is completely covered, and the glue surface of the hollow cylinder after the glue is poured is kept horizontal, and then cooled for 40 minutes.

[0017] Preferably, the heating temperature in step S2 is 100-120°C, and the heating time is 10 minutes.

[0018] Preferably, after the metal plate falls off in step S2, the hollow cylinder above the glue surface in the sample to be cut is removed to prevent the material from falling off during later cutting and causing the wire to get stuck.

[0019] Preferably, the cutting machine in step S3 is a diamond wire cutter.

[0020] In this invention, the AlN crystal is cut from top to bottom, with the cutting line being a straight line. Cutting is achieved using the friction between the cutting line and the crystal. Without a buffer layer, the contact between the wafer and the cutting line begins from a single point, and the corresponding stress originates from that point as well. Therefore, stress easily diffuses into the crystal's interior. With the buffer layer, when cutting onto the AlN crystal, the contact between the wafer and the cutting line begins from the surface between the crystal and the buffer layer. Thus, most of the stress is released at the interface between the adhesive layer and the wafer, preventing stress from being transmitted into the crystal and causing cracking.

[0021] The present invention has the following beneficial technical effects:

[0022] (1) The present invention avoids damage to the crystal by setting a buffer layer on the outside of the AlN crystal; when the cutting line comes into contact with the crystal sample, high stress is generated. The buffer layer on the outside of the crystal can gradually release the stress and gradually transfer the stress to the crystal, which can simply and effectively protect the crystal, prevent the crystal from cracking, and facilitate the cutting of a complete AlN wafer.

[0023] (2) The presence of a buffer layer in the method of the present invention avoids direct contact between the cutting line and the crystal, reduces the probability of the cutting line breaking, and makes the cutting efficient. Attached Figure Description

[0024] Figure 1 This is a picture of the polyvinyl chloride tube and AlN crystals bonded to the iron plate with paraffin wax in Example 1.

[0025] Figure 2 The images show the polyvinyl chloride tube and the crystal after potting in Example 1.

[0026] Figure 3 This is a photograph of a crystal with a buffer layer being fixed onto a cutting machine in Example 1.

[0027] Figure 4 This refers to the division of the longitudinal section region during the cutting process in Example 1.

[0028] Figure 5 This is an image of the AlN wafer after it has been cut in Example 1.

[0029] Figure 6 The image shows the AlN ingot before cutting in Comparative Example 1.

[0030] Figure 7 This is an image showing the crystal cracking that occurred after cutting in Comparative Example 1.

[0031] Figure 8The image shows the AlN wafer cut before the cutting process was adjusted in Comparative Example 2. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer with the description. However, the embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0033] Example 1

[0034] A method for reducing cutting stress during AlN crystal processing includes the following steps:

[0035] S1: Select a cylindrical AlN crystal ingot with a maximum outer diameter of 52mm and a height of 10mm for cutting; and select a hollow cylindrical polyvinyl chloride tube with an inner diameter of 60mm, a height of 15mm, and a thickness of 3mm as a cutting auxiliary component.

[0036] like Figure 1 As shown, the bottoms of both the PVC tube and the AlN crystal are bonded to an iron plate with dimensions of 100mm × 100mm using paraffin wax, with the AlN crystal located at the center of the PVC tube.

[0037] S2: Mix adhesive A and adhesive B of the silicone rod bonding adhesive in a 1:1 ratio until homogeneous, then pour the mixture into the gap between the PVC tube and the AlN crystal until it completely covers the top of the crystal, ensuring the adhesive surface is level (e.g., ...). Figure 2 (As shown), cool and cure for 40 minutes; then heat the bottom of the iron plate at 120°C for 10 minutes. After the paraffin melts, the iron plate will automatically detach, yielding the sample to be cut. Remove the PVC tube extending beyond the surface of the cured adhesive and the adhesive layer above the crystal portion from the sample to be cut, in preparation for subsequent cutting.

[0038] S3: As Figure 3 As shown, the sample to be cut, after removing excess material, is placed horizontally on the diamond wire cutting machine and cut along the longitudinal section. Figure 4 As shown, the longitudinal section is divided into an entry zone, a middle zone, and an exit zone from top to bottom. All three zones have the same maximum height. The feed rate for the entry zone needs to be adjusted to 5-6 mm / h, for the middle zone to 8 mm / h, and for the exit zone to 10 mm / h. Cutting is performed along the PVC tube's cutting surface to obtain an AlN wafer consisting of a PVC tube, adhesive, and AlN crystals, arranged from the outside in. The PVC tube and adhesive form a buffer layer.

[0039] S4: Trim the edges of the AlN wafer obtained above to obtain a regular AlN wafer, such as... Figure 5 As shown in the image.

[0040] This embodiment avoids damage to the crystal caused by direct stress by first releasing the high stress generated when the wire contacts the sample into the buffer layer on the outside of the crystal, and then gradually transferring it to the crystal. The main objectives of this invention are achieved through the following points: 1) As... Figure 1 As shown, firstly, a PVC tube 5-7 mm higher than the crystal is bonded to an AlN crystal onto an iron plate using paraffin wax, with the crystal located at the center of the PVC tube. 2) As Figure 2 As shown, after the paraffin wax solidifies, it is then filled with adhesive. The adhesive is a special AB adhesive for bonding crystal rods, but other curing adhesives with a hardness between 5 and 6 can also be used. Lower hardness adhesives, once cured, can gradually transfer the cutting tension to the crystal, acting as a buffer. 3) After the adhesive solidifies, heat the iron sheet to 120℃; once the paraffin wax melts, the iron sheet can be removed. Figure 3 As shown, the crystal with the buffer layer removed from the iron plate is fixed onto the cutting machine for cutting. 4) As Figure 4 As shown, the longitudinal section of the crystal after adding the buffer layer is divided into three parts at the same height: the entry zone, the intermediate zone, and the exit zone. In the entry zone, since the cutting line contacts the buffer layer and the crystal first, the feed rate should not be too fast, and 5-6 mm / h is optimal. In the intermediate zone, since the entry zone acts as a transition zone, the intermediate zone can be appropriately accelerated for cutting, but since the proportion of the harder crystal is relatively large, the feed rate should not be too fast, and the feed rate can be controlled within the range of 7-8 mm / h. In the exit zone, the proportion of crystal is smaller, the proportion of buffer layer is larger, and the object being cut is softer, so the cutting can be accelerated again, with the rate controlled at 10 mm / h.

[0041] The above process can significantly improve cutting efficiency, reduce the direct damage of cutting stress to the crystal, and produce wafers that are as follows: Figure 5 As shown, by Figure 5 It can be seen that there are almost no cracks inside the wafer, and the shape is extremely regular, with no signs of chip cracking or breakage.

[0042] The method of this invention can improve the cutting quality and efficiency of AlN crystals. By using this method, the cutting stress can be released first in the buffer layer on the outside of the crystal, thereby avoiding damage to the crystal caused by direct stress. It can simply and effectively protect the crystal and prevent crystal cracking. At the same time, the presence of the buffer layer avoids direct contact between the cutting line and the crystal, reducing the probability of line breakage, and can efficiently cut complete AlN wafers.

[0043] Comparative Example 1

[0044] A method for cutting and processing AlN crystals includes the following steps:

[0045] S1: Select a cylindrical AlN ingot with a maximum outer diameter of 52mm and a height of 10mm for cutting, such as... Figure 6 As shown.

[0046] S2: The crystal ingot is bonded to the graphite block using high-strength AB glue, and then the graphite block is bonded to the material plate.

[0047] S3: Wrap a layer of AB glue around the outer layer of the crystal, wait 30 minutes for the glue to cool naturally, and then load the material plate onto the cutting machine.

[0048] S4: Following the method described in Example 1, the longitudinal section is divided into an entry zone, an intermediate zone, and an exit zone. The feed rate for the entry zone needs to be adjusted to 5-6 mm / h, for the intermediate zone to 8 mm / h, and for the exit zone to 10 mm / h. The AlN wafer is obtained by cutting along the longitudinal section.

[0049] Ingots cut using this method often have a thin outer protective layer, which cannot form effective protection. During the cutting process, significant stress is often generated inside the crystal, leading to a surge in crack numbers. This increase in cracks can eventually cause the crystal to crack. Figure 7 As shown, it is not even possible to form a complete and regular wafer. If the cut wafer is broken, it is equivalent to the failure of this cutting process.

[0050] Comparative Example 2

[0051] A method for cutting AlN crystals includes the following steps:

[0052] S1: Select a cylindrical AlN crystal ingot with a diameter of 52mm and a height of 10mm for cutting; and select a hollow cylindrical polyvinyl chloride tube with a diameter of 60mm, a height of 15mm, and a thickness of 3mm as a cutting auxiliary part.

[0053] The bottom ends of both the PVC tube and the AlN crystal were glued to a 100mm×100mm iron plate with paraffin wax, and the AlN crystal was located in the center of the PVC tube.

[0054] S2: Mix the A and B components of the silicone rod adhesive in a 1:1 ratio and pour the mixture into the gap between the PVC tube and the AlN crystal until it completely covers the top of the crystal. Keep the adhesive surface horizontal and allow it to cool and cure for 40 minutes. Then, heat the bottom of the iron plate at 120°C for 10 minutes. After the paraffin melts, the iron plate will automatically detach, yielding the sample to be cut. Remove the PVC tube that extends beyond the surface of the cured adhesive and the irregular adhesive layer that is higher than the crystal from the sample to be cut.

[0055] S3: Then, the sample to be cut is placed horizontally on the cutting machine and longitudinally cut at a uniform feed speed of 10 mm / h, resulting in an AlN wafer as shown. Figure 8 As shown in the image.

[0056] The ingots cut using this method are cylindrical in shape after being coated with adhesive. The stress is greatest when the cutting line comes into contact with the crystal in the early stages. Using a cutting speed of 10mm / h, which is too fast, will cause internal cracks to propagate and accelerate internal cracking. When cutting to the middle of the ingot, the cutting diameter increases and the cutting surface area in contact with the line also increases. Using the same fast feed speed will easily cause wire bowing. Excessive wire bowing will cause the cutting machine to break the wire. At the same time, a large number of wavy stripes will also be generated on the wafer surface, affecting subsequent processing.

[0057] The above description is only for illustrating the present invention and should be understood as not being limited to the above embodiments. Various modifications that conform to the spirit of the present invention are within the protection scope of the present invention.

Claims

1. A method of reducing cleaving stress in processing of AlN crystals, characterized by, The method comprises the following steps: S1: selecting a vertically placed hollow cylinder, placing an AlN crystal in the center of the hollow cylinder, the height of the AlN crystal being less than the height of the hollow cylinder; then bonding the bottom of the hollow cylinder and the AlN crystal to a metal plate through paraffin; S2: pouring glue into the hollow cylinder of step S1, so that the glue completely wraps the crystal; after the glue solidifies, heating the bottom of the metal plate, and after the paraffin melts, the metal plate falls off, obtaining a sample to be cut, the Mohs hardness of the hollow cylinder being 2-3 less than the Mohs hardness of the solidified glue; S3: placing the sample to be cut of step S2 horizontally on a cutting machine, and cutting along the longitudinal section to obtain an AlN wafer with a buffer layer on the edge; the specific operation steps are as follows: from top to bottom, the longitudinal section is divided into an entry area, a middle area and an exit area, the maximum heights of the three areas being the same, and the AlN crystal being located at least in the entry area and the middle area; the feed speeds of the entry area, the middle area and the exit area are 5-6 mm / h, 7-8 mm / h and 10 mm / h respectively; S4: trimming the edge of the AlN wafer with a buffer layer of step S3 to obtain a regular AlN wafer; In step S1, the ratio between the inner diameter of the hollow cylinder and the maximum outer diameter of the AlN crystal is 12 / 11-6 / 5.

2. The method of claim 1, wherein the AlN crystal is grown by a method comprising: The material of the hollow cylinder in step S1 is selected from polyvinyl chloride, polytetrafluoroethylene or polypropylene; and the metal plate is an iron plate or a copper plate.

3. The method for reducing cutting stress during AlN crystal processing as described in claim 1, characterized in that, The glue in step S2 is a special glue for crystal stick bonding; and the Mohs hardness of the solidified glue is 5-6.

5.

4. The method of claim 3, wherein the AlN crystal is grown by a method comprising: In step S2, the specific operation of pouring glue is as follows: mixing the A glue and the B glue of the special glue for crystal stick bonding in a mass ratio of 1:1, pouring the mixture into the hollow cylinder of step S1 until the AlN crystal is completely covered, and keeping the glue surface of the hollow cylinder after pouring glue horizontal, and then cooling for 40 minutes.

5. The method for reducing cutting stress during AlN crystal processing as described in claim 1, characterized in that, In step S2, the heating temperature is 100-120℃, and the heating time is 10 minutes.

6. The method for reducing cutting stress during AlN crystal processing as described in claim 1, characterized in that, After the metal plate falls off in step S2, the hollow cylinder above the glue surface in the sample to be cut is removed.

7. The method for reducing cutting stress during AlN crystal processing as described in claim 1, characterized in that, In step S3, the cutting machine is a diamond wire cutting machine.

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