Method for improving laser slicing effect of semiconductor single crystal substrate

Abstract

The invention discloses a method for improving the laser slicing effect of a semiconductor single crystal substrate, which comprises the following steps of: spraying low-temperature liquid or solid to the surface of the semiconductor single crystal substrate along the direction of a laser scanning line during laser scanning cutting. Low-temperature liquid or solid such as liquid nitrogen or dry ice particles are cold-sprayed to the surface of semiconductor single crystal such as a silicon carbide crystal ingot or a gallium nitride wafer, a large temperature difference is formed through low-temperature cooling of the semiconductor single crystal and high temperature of a laser scanning focusing position, and modified cracks are promoted to be transversely expanded, fused and connected into a whole. The method has the advantages of being in situ, rapid, free of pollution and the like, after cracks are connected into a whole, the separation difficulty is reduced, and the separation effect and efficiency are improved. And a smoother surface can be obtained through uniform crack fusion, and the material loss and the subsequent grinding difficulty are reduced.

Description

Technical Field

[0001] The invention relates to a method for improving the laser slicing effect of a semiconductor single crystal substrate, and belongs to the technical field of semiconductor material processing. Background Art

[0002] In the production process of silicon carbide, the preparation of silicon carbide substrate is the most core link, with high technical barriers and the main difficulty lies in crystal growth and cutting. Since the Mohs hardness of silicon carbide is 9.2, second only to diamond, it is a high-hardness and brittle material. It is very difficult to cut the grown silicon carbide crystal into sheets, so the cutting process is time-consuming and easy to crack. Achieving low cutting loss and cutting out high-quality SiC wafers with uniform thickness and small warping is an important technical difficulty currently faced. The cutting technologies of silicon carbide crystals include: diamond wire cutting (consolidated abrasive wire saw cutting), mortar wire cutting (free abrasive wire saw cutting), and laser cutting. Wire saw cutting technology is mature and is the mainstream cutting technology. Laser stripping technology focuses the laser below the surface of the wafer, scans at a certain depth inside the silicon carbide ingot to generate a modified layer, and then under the action of external tension, the cracks in the modified layer expand in a direction perpendicular to the wafer surface, thereby stripping the wafer from the silicon carbide ingot. Laser lift-off technology has the advantages of low material loss, high processing efficiency, and large number of slices produced, and is expected to become an ideal alternative to diamond wire cutting technology.

[0003] The silicon carbide laser stripping technology is to focus a nanosecond, picosecond or femtosecond laser inside the crystal to modify it. Due to the thermal effect of the laser and the volume expansion of the modified layer, cracks are generated in the silicon carbide, and the ingot is sliced ​​by mechanical tension or cold cracking. During the laser stripping process, if the cracks expand laterally and merge into one, it is beneficial to improve the effect of silicon carbide laser cutting. The German Silvertech GmbH proposed the "cold cutting (Cold Split)" technology, the technical point of which is to use laser to form a modified layer inside the ingot, and then adhere a polymer (such as PDMS) to the surface of the end to be separated, and quickly cool the polymer and the entire ingot (such as liquid nitrogen). When the temperature is lower than the glass transition temperature of the polymer, the polymer phase changes and shrinks sharply to generate stress on the ingot, so that the wafer is automatically separated. Although this method does not require external force to stretch when cutting a single wafer, it adds polymer coating and cooling links, in which cooling is carried out in two steps. The cooling temperature is low and liquid nitrogen is required, which greatly increases the cost and process flow and the total time for single-chip separation. Our previously submitted patent CN202311467203.7 proposed a method for treating the surface of laser invisible slices using high-speed moving dry ice particles. High-speed dry ice is cold-sprayed onto the surface of silicon carbide or gallium nitride laser slices, and the low temperature and volatile characteristics of dry ice are used to quickly, non-pollutingly, and non-damagingly remove surface particles and protrusions. When the laser is focused and irradiated inside the crystal, the high thermal effect causes the material to be modified. If the material is cooled and cooled synchronously, the crack extension and fusion can be promoted, thereby improving the splitting effect and slicing efficiency. The above-mentioned patented method and equipment are used to spray onto the sample surface during the laser scanning modification process, and the sample is cooled to promote the extension and fusion of the cracks produced by the modification, which can effectively improve the slicing effect and efficiency. This method is also applicable to semiconductor single crystal substrates with high thermal conductivity, such as gallium nitride, diamond, etc. Summary of the invention

[0004] The object of the present invention is to provide a method for improving the laser slicing effect of a semiconductor single crystal substrate.

[0005] The technical solution adopted by the present invention is:

[0006] A method for improving the laser slicing effect of a semiconductor single crystal substrate, during the laser scanning and cutting process, a cryogenic liquid or solid is sprayed onto the surface of the semiconductor single crystal substrate in an in-situ online manner along the direction of the laser scanning line. The in-situ online method means that the nozzle spraying the cryogenic liquid or solid moves along the direction of the laser scanning line, so that the laser scanning and the spraying of the cryogenic liquid are performed synchronously. In actual operation, the nozzle and the laser scanning lens can be integrated on the same device to achieve synchronization.

[0007] Preferably, the cryogenic liquid or solid refers to liquid nitrogen or dry ice particles.

[0008] Preferably, the semiconductor single crystal substrate is a silicon carbide single crystal substrate, a gallium nitride single crystal substrate or a diamond single crystal substrate.

[0009] Preferably, the particle size of the dry ice particles is 20-500 μm.

[0010] Preferably, before the laser scanning and cutting process is performed, a low-temperature liquid or solid is sprayed onto the surface of the semiconductor single crystal substrate to cool the semiconductor single crystal substrate as a whole.

[0011] Preferably, the spraying time for overall cooling is 5-20 minutes.

[0012] The principle of the present invention is as follows: When laser cutting a semiconductor single crystal substrate, the laser is focused inside the crystal, and the high heat causes the crystal to be modified. The thermal effect of the laser and the volume expansion of the modified layer cause cracks. If the cracks generated by the laser line scanning expand and fuse together, it is easy to peel off, but the high heat generated by the laser focusing will quickly diffuse away. In the present invention, the cooling nozzle moves in the direction of the laser scanning line, and a large temperature difference is formed by the low temperature characteristics of the cryogenic liquid and the high temperature of the laser scanning focus position, thereby utilizing the temperature difference effect to generate stress so that the cracks expand and fuse with each other, causing the cracks to connect into one, thereby reducing the difficulty of peeling. After the laser scanning is completed, the wafer can be separated using conventional mechanical separation methods.

[0013] Beneficial effects of the present invention:

[0014] The present invention cold sprays low-temperature liquid or solid such as liquid nitrogen or dry ice particles onto the surface of semiconductor single crystals such as silicon carbide ingots or gallium nitride wafers, and utilizes its low-temperature characteristics and the high temperature of the laser scanning focus position to form a large temperature difference, thereby promoting the lateral expansion, fusion and integration of the modified cracks. This method has the advantages of being in situ, fast, and pollution-free. After the cracks are connected together, the separation difficulty is reduced and the separation effect and efficiency are improved. Liquid nitrogen can cause a larger temperature difference, but the cost is higher; compared to liquid nitrogen, dry ice particles are cheaper and will vaporize quickly without residue, and will not affect the laser incidence. Uniform crack fusion can obtain a smoother surface, reduce material loss and subsequent grinding difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The schematic diagram of the cryogenic cooling device and process is shown in FIG. The scanning direction in the figure is the direction of movement of the laser focus, and the dry ice nozzle moves along the scanning direction along with the scanning platform.

[0016] Figure 2 Comparative Example 1 (left) / Example 2 (right), crack color stripes formed by laser invisible slice modification. After using dry ice cold spray technology, the color stripes are more uniform, indicating that the cracks are fused into one. DETAILED DESCRIPTION

[0017] The present invention is further described below by specific examples, which should not be construed in any way as limiting the scope of application of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, equipment, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources.

[0018] Comparative Example 1

[0019] 1. Clean the surface of the silicon carbide ingot and fix it on the scanning platform of the laser slicing equipment through a ceramic tray.

[0020] 2. Control the focus of the laser beam to the predetermined depth of the silicon carbide ingot and start the movement of the laser and the scanning platform.

[0021] 3. Remove the ingot and perform wafer separation. (Before separation, use an optical microscope to photograph the scanned wafer or ingot and observe the crack morphology produced by the scan. The results are as follows: Figure 2 ).

[0022] Example 1

[0023] A method for improving the laser invisible slicing effect of a semiconductor single crystal substrate by in-situ low temperature cooling, the steps comprising:

[0024] 1. Clean the surface of the silicon carbide ingot and fix it on the scanning platform of the laser slicing equipment through a ceramic tray.

[0025] 2. Adjust the dry ice nozzle to near the silicon carbide surface, set the nozzle angle to 30°, and the air compressor pressure to 0.5 MPa. In this embodiment, the particle size of the dry ice particles is about 0.1 mm.

[0026] 3. Start the movement of the laser and scanning platform, and turn on the air compressor at the same time. The compressed air will press the dry ice particles stored in the insulation box to the nozzle. The dry ice particles and the laser will be sprayed onto the sample surface synchronously. Figure 1 After the entire scan is completed, turn off the compressed air and nozzle.

[0027] 4. Remove the ingot and perform wafer separation operation.

[0028] Example 2

[0029] A method for improving the laser invisible slicing effect of a semiconductor single crystal substrate by in-situ low temperature cooling, the steps comprising:

[0030] 1. Clean the surface of the silicon carbide ingot and fix it on the scanning platform of the laser slicing equipment through a ceramic tray.

[0031] 2. Adjust the dry ice nozzle to near the silicon carbide surface, set the nozzle angle to 30°, and the air compressor pressure to 0.5 MPa. In this embodiment, the particle size of the dry ice particles is about 0.1 mm.

[0032] 3. Turn on the air compressor, and the compressed air will press the dry ice particles stored in the insulation box to the nozzle, and the dry ice particles will be sprayed onto the surface of the sample to cool the sample as a whole. The cooling time is 5-20 minutes.

[0033] 4. Start the movement of the laser and scanning platform, and at the same time, the dry ice nozzle moves to spray dry ice particles onto the sample surface along the laser scanning path. After the overall scan is completed, turn off the compressed air and nozzle.

[0034] 5. Remove the ingot and perform wafer separation. (Before separation, use an optical microscope to photograph the scanned wafer or ingot and observe the crack morphology produced by the scan. The results are as follows: Figure 2 .)

[0035] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for improving the laser slicing effect of a semiconductor single crystal substrate, characterized in that: During the laser scanning and cutting process, a cryogenic liquid or solid is sprayed onto the surface of a semiconductor single crystal substrate in an in-situ online manner along the direction of the laser scanning line.

2. The method for improving the laser slicing effect of a semiconductor single crystal substrate according to claim 1, characterized in that: The cryogenic liquid or solid refers to liquid nitrogen or dry ice particles.

3. The method for improving the laser slicing effect of semiconductor single crystal substrate according to claim 2, characterized in that: The semiconductor single crystal substrate refers to a silicon carbide single crystal substrate, a gallium nitride single crystal substrate or a diamond single crystal substrate.

4. The method for improving the laser slicing effect of semiconductor single crystal substrate according to claim 3, characterized in that: The particle size of the dry ice particles is 20-500 μm.

5. The method for improving the laser slicing effect of a semiconductor single crystal substrate according to any one of claims 1 to 4, characterized in that: Before the laser scanning and cutting process is performed, a low-temperature liquid or solid is sprayed onto the surface of the semiconductor single crystal substrate to cool the semiconductor single crystal substrate as a whole.

6. The method for improving the laser slicing effect of semiconductor single crystal substrate according to claim 5, characterized in that: The spraying time for overall cooling is 5-20 minutes.

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