Composite silicon carbide substrate fragmentation method

Abstract

The invention discloses a fragmentation method for a composite silicon carbide substrate. The fragmentation method comprises the following steps: 1) combining a single crystal silicon carbide crystal ingot with a substrate layer; 2) performing internal modification processing on the single crystal silicon carbide crystal ingot by using laser, forming a modification processing layer in the single crystal silicon carbide crystal ingot, and enabling the incident surface of the laser to deviate from the substrate layer; 3) separating the single crystal silicon carbide crystal ingot along the modified processing layer to obtain a residual single crystal silicon carbide crystal ingot and a composite layer with a substrate layer and a single crystal silicon carbide layer; (4) repeating the steps (1)-(3) on the residual single crystal silicon carbide crystal ingot; wherein the sequence of the step 1) and the step 2) can be exchanged. The problems that in the prior art, saw bite loss is large, surface damage is obvious, and wire saw wire loss is large can be solved through the laser fragmentation technology; the utilization rate of the single crystal silicon carbide is improved by utilizing the substrate layer, structural support is provided for the single crystal silicon carbide layer, and subsequent processing of the single crystal silicon carbide layer is facilitated.

Description

Technical Field

[0001] This invention relates to a method for wafering composite silicon carbide substrates, belonging to the field of semiconductor material wafering technology. Background Technology

[0002] Since silicon carbide has a Mohs hardness of 9.5, which is close to the hardness of diamond (10), in the current technology, single-crystal silicon carbide is sliced ​​using a wire saw cutting process to divide the single-crystal silicon carbide ingot into several silicon carbide substrates. However, the existing processing method has problems such as large saw cut loss, obvious surface damage and large wire saw wire loss, which makes the substrate processing cost high. Summary of the Invention

[0003] To improve the utilization rate of high-quality, high-cost single-crystal silicon carbide substrates and reduce substrate usage costs, this invention provides a composite silicon carbide substrate slab preparation method. A general-quality, low-cost substrate is used as the base layer, and a high-quality, high-cost single-crystal silicon carbide substrate is used as the seed layer. The base layer and seed layer are composited to improve overall strength before slab preparation, resulting in thinner single-crystal silicon carbide substrates. This improves the utilization rate of high-quality, high-cost single-crystal silicon carbide substrates and reduces substrate usage costs. The specific technical solution is as follows.

[0004] A method for wafering composite silicon carbide substrates, characterized by comprising the following steps:

[0005] 1) Bonding single-crystal silicon carbide ingots to a substrate layer;

[0006] 2) Using laser to perform internal modification processing on single-crystal silicon carbide ingots, forming a modification processing layer inside the single-crystal silicon carbide ingots, with the incident surface of the laser facing away from the base layer;

[0007] 3) Separate the single-crystal silicon carbide ingot along the modified processing layer to obtain the remaining single-crystal silicon carbide ingot and a composite layer with a base layer and a single-crystal silicon carbide layer.

[0008] 4) Repeat steps 1)-3) above with the remaining single-crystal silicon carbide ingots, wherein the order of steps 1) and 2) can be interchanged.

[0009] Using the above technical solution, thinner single-crystal silicon carbide substrates can be fabricated. The substrate layer provides structural support for the single-crystal silicon carbide seed layer, facilitating subsequent processing of the seed layer. Simultaneously, using lasers to internally modify the single-crystal silicon carbide ingot helps reduce losses during the high-quality, high-cost single-crystal silicon carbide wafer slab fabrication process.

[0010] Furthermore, the substrate layer is made of polycrystalline silicon carbide. The polycrystalline silicon carbide substrate layer can provide reliable structural support for the monocrystalline silicon carbide seed layer, and its material is readily available, low in cost, and has no significant negative impact on the subsequent processing of the monocrystalline silicon carbide seed layer.

[0011] Further, in step 2), the modified processing layer is within a range of 5-50 μm from the substrate layer. Preferably, the laser wavelength is 1000-1100 nm, the laser pulse width is 10 ps-60 ns, the laser scanning speed is 5-1000 mm / s, the average laser power is 0.1-3 W, the pulse repetition frequency is 1.6-300 kHz, the single pulse energy is 0.3-188 μJ, and the number of sub-pulses is 1-10; the laser scanning path consists of several parallel straight lines, and the scanning interval between adjacent straight lines is 10-800 μm.

[0012] Preferably, the laser pulse width is 10ps-500ps; preferably, the laser pulse width is 100ps, the pulse repetition frequency is 100kHz, the single pulse energy is 10-20μJ, the laser scanning speed is 300-500mm / s, and the scanning interval is 15-25μm.

[0013] Preferably, the laser pulse width is 1.5ns-14ns; preferably, the laser pulse width is 1.5ns, the average laser power is 1W, the laser scanning speed is 100mm / s, the pulse repetition frequency is 25kHz, the single pulse energy is 20-30μJ, and the interval between adjacent lines is 50-200μm.

[0014] Furthermore, in step 1), the single-crystal silicon carbide ingot is bonded to the substrate layer. Good bonding ensures that the substrate layer and the single-crystal silicon carbide seed layer remain stable and fixed throughout subsequent processing and use.

[0015] Further, in step 3), the modified processing layer is first expanded using ultrasound, and then the single-crystal silicon carbide ingot is separated along the modified processing layer. Ultrasound helps the transverse cracks on the laser modified processing path to propagate horizontally, allowing crack propagation coupling between adjacent laser scanning paths, thus reducing the separation strength of the modified processing layer. Preferably, the ultrasound frequency is 50-200kHz, the ultrasound power is 400-800W, the ultrasound is a continuous wave or pulsed wave, and the ultrasound application time is 10-60s.

[0016] Compared with existing technologies, the silicon carbide substrate slicing method of this invention overcomes the problems of large saw cut loss, significant surface damage, and large wire saw material loss in existing technologies. The use of the substrate layer not only improves the utilization rate of single-crystal silicon carbide, but also provides structural support for the single-crystal silicon carbide seed layer, which is beneficial to the subsequent processing of the single-crystal silicon carbide layer. At the same time, it helps to reduce slicing loss and improve material utilization. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of the composite silicon carbide substrate slicing method of the present invention;

[0018] Figure 2 This is a schematic flowchart of another composite silicon carbide substrate slicing method of the present invention;

[0019] Figure 3 This is a schematic diagram of laser internal modification;

[0020] Figure 4 This is a schematic diagram of mechanical separation after ultrasonic processing;

[0021] Figure 5 It is a scanning electron microscope image of the peeled surface;

[0022] Figure 6 These are actual photos of the peeled surface;

[0023] Figure 7 This is a photograph of the area after peeling in Example 1;

[0024] Figure 8 This is a laser confocal microscope image of the area after peeling in Example 1;

[0025] Figure 9 This is the morphology of the peeled surface after peeling in Example 1;

[0026] Figure 10 This is a laser confocal microscope image of the area after peeling in Example 2;

[0027] Figure 11 These are the morphologies of the peeled surface obtained under different parameters in Example 3;

[0028] Figure 12 These are comparison diagrams of different crack layer peeling conditions in Example 3;

[0029] Figure 13 These are laser-modified morphology images obtained at different single-pulse energies in Example 3;

[0030] Figure 14 These are laser-modified morphology images obtained at different scanning speeds in Example 3;

[0031] Figure 15These are laser-modified morphology images obtained at different scanning intervals in Example 3;

[0032] Figure 16 This is a schematic diagram of laser refining loss;

[0033] Figure 17 These are the laser-modified optical morphology images obtained with different single-pulse energies in Example 4;

[0034] Figure 18 This is a statistical graph of laser refining loss obtained at different single-pulse energies in Example 4;

[0035] Figure 19 These are the laser-modified optical morphology images obtained at different scanning intervals in Example 4;

[0036] Figure 20 This is a statistical chart of laser quality improvement loss obtained at different scanning intervals in Example 4.

[0037] In the figure: 1. Single crystal silicon carbide ingot, 1.1. Single crystal silicon carbide layer, 2. Substrate layer, 3. Composite layer, 4. Modified processing layer. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings.

[0039] like Figure 1 As shown, the silicon carbide substrate slab preparation method mainly includes the following steps:

[0040] 1) Bonding the single-crystal silicon carbide ingot 1 to the substrate layer 2;

[0041] 2) The single-crystal silicon carbide ingot 1 is internally modified by laser to form a modified layer 4 inside the single-crystal silicon carbide ingot 1, and the incident surface of the laser is away from the base layer 2.

[0042] 3) Separate the single-crystal silicon carbide ingot 1 along the modified processing layer 4 to obtain the remaining single-crystal silicon carbide ingot 1 and the composite layer 3 having a base layer 2 and a single-crystal silicon carbide layer 1.1;

[0043] 4) Repeat steps 1)-3 above with the remaining single-crystal silicon carbide ingot 1.

[0044] Figure 2 The diagram illustrates a scheme where steps 1) and 2) are swapped, i.e., the laser modification process is performed first, followed by the bonding of the single-crystal silicon carbide ingot 1 to the substrate layer 2.

[0045] The substrate layer 2 is made of polycrystalline silicon carbide. Polycrystalline silicon carbide can provide reliable structural support for the monocrystalline silicon carbide layer. At the same time, the material is readily available, low in cost, and has no significant negative impact on the subsequent processing of the monocrystalline silicon carbide layer.

[0046] In step 2), the modified processing layer 4 is located within a range of 25-50 μm from the substrate layer. Preferably, the laser wavelength is 1000-1100 nm, the laser pulse width is 10 ps-60 ns, the laser scanning speed is 5-1000 mm / s, the average laser power is 0.1-3 W, the pulse repetition frequency is 1.6 kHz-300 kHz, the single pulse energy is 0.3-188 μJ, and the number of sub-pulses is 1-10; the laser scanning path consists of several parallel straight lines, the scanning interval between adjacent straight lines is 10-800 μm, and the focal depth is 10-30 μm. Figures 2-6 The diagram illustrates the laser-modified processing path and the peeling (separation) surface of single-crystal silicon carbide.

[0047] To improve bonding strength, in step 1), the single-crystal silicon carbide ingot is bonded to the substrate layer 2. Good bonding ensures that the substrate layer 2 and the single-crystal silicon carbide layer remain stable and fixed throughout subsequent processing and use.

[0048] Preferably, in step 3), the transverse cracks in the modified processing layer 4 are first propagated using ultrasound, and then the single-crystal silicon carbide ingot is separated along the modified processing layer 4. Ultrasound helps the transverse cracks on the laser modified processing path to propagate horizontally, allowing cracks in adjacent laser scanning paths to merge and reducing the separation strength of the modified processing layer 4. Preferably, the ultrasound frequency is 50-200kHz, the ultrasound power is 400-800W, the ultrasound is a continuous wave or pulse wave, and the ultrasound application time is 10-60s.

[0049] Compared with existing technologies, the composite silicon carbide substrate slicing method of this invention can overcome the problems of large saw cut loss, obvious surface damage and large wire saw material loss in existing technologies. The use of substrate layer 2 not only improves the utilization rate of high-quality and high-cost single-crystal silicon carbide, but also provides structural support for the single-crystal silicon carbide seed layer, which is beneficial to the subsequent processing of the single-crystal silicon carbide seed layer.

[0050] Example 1

[0051] See Figures 7-9 In Example 1, the parameters for laser modification of single-crystal silicon carbide ingot 1 were as follows: laser pulse width 14ns, pulse repetition frequency 3kHz, laser scanning speed 15mm / s, adjacent scanning interval 200μm, and average laser power 0.33W. Figure 7 This is a real-life image showing the light transmittance of a SiC wafer obtained by laser internal modification followed by stripping. Figure 8 It is a roughness image of the peeled surface obtained using a laser confocal microscope, where different colors represent different heights, and areas with the same color indicate areas with the same height. Figure 9 The left image shows the optical morphology of the peeled surface.Figure 9 The middle image shows the scanning electron microscope morphology of the peeled surface. Figure 9 The right image shows the scanning electron microscope morphology observed roughly parallel to the exfoliated surface. From Figures 7-8 As can be seen, the roughness of the peeled surface is low, and the SiC wafer obtained by peeling has very good light transmittance. Figure 9 The right-hand image also shows a 4° tilted cut on the peeling surface relative to the vertical direction. This is because there is a 4° tilted axis angle during the wafer growth process.

[0052] Example 2

[0053] See Figure 10 In Example 2, the parameters for laser modification of single-crystal silicon carbide ingot 1 were as follows: laser pulse width 14ns, pulse repetition frequency 2kHz, laser scanning speed 15mm / s, adjacent scanning interval 100-200μm, and average laser power 0.1-0.22W. Figure 10 The top image in the first column shows the optical morphology of the peeled surface with an adjacent scanning interval of 100 μm, and the bottom image shows the roughness imaging of the peeled surface using a laser confocal microscope. Figure 10 The top image in the second column shows the optical morphology of the peeled surface with an adjacent scanning interval of 150 μm, and the bottom image shows the roughness imaging of the peeled surface using a laser confocal microscope. Figure 10 The top image in the third column shows the optical morphology of the peeled surface with an adjacent scanning interval of 200 μm, and the bottom image shows the roughness imaging of the peeled surface using a laser confocal microscope. Specifically, the tensile strength of the peeled sections with a scanning interval of 100 μm is 2.3 MPa, and the roughness is 3.876 μm; the tensile strength of the peeled sections with a scanning interval of 150 μm is 2.6 MPa, and the roughness is 4.487 μm; and the tensile strength of the peeled sections with a scanning interval of 200 μm is 2.3 MPa, and the roughness is 4.848 μm.

[0054] Example 3

[0055] See Figures 11 to 15 , Figure 11 The optical in-situ morphology, the optical morphology of the peeled surface, and the roughness imaging of the peeled surface are shown for different crack layers produced by different processes within the laser pulse width range of 10ps to 500ps. Figure 12 The charts show the roughness, tensile strength, and failure rate of different types of cracked layers, indicating that a smooth cracked layer is the optimal result. Figure 13 The effect of single-pulse energy on crack layer morphology was shown. Other parameters were: laser pulse width of 100 ps, ​​pulse repetition frequency of 100 kHz, laser scanning speed of 500 mm / s, and scanning interval of 15 μm; among them, the single-pulse energy of 10 μJ was optimal. Figure 14The effect of laser scanning speed on crack layer morphology was shown. Other parameters were: laser pulse width of 100 ps, ​​pulse repetition frequency of 100 kHz, single pulse energy of 10 μJ, and scanning interval of 15 μm. It can be seen that the laser modification effect decreases significantly when the laser scanning speed exceeds 500 mm / s. Figure 15 The effect of scanning interval on crack layer morphology was shown. Other parameters were: laser pulse width of 100 ps, ​​pulse repetition frequency of 100 kHz, single pulse energy of 10 μJ, and laser scanning speed of 500 mm / s. It can be seen that a scanning interval within the range of 15-25 μm has no significant negative impact on the modification effect. Picosecond laser processing, due to its significantly higher peak power than nanosecond lasers, easily exceeds the critical self-focusing power of silicon carbide (SiC) materials, resulting in self-focusing phenomena, leading to unstable focal positions and unstable crack propagation. Furthermore, picosecond laser processing suffers from insufficient heat accumulation, requiring multi-pulse high overlap to achieve crack propagation. However, the incubation effect caused by the interaction between pulses further leads to greater modification losses and unstable crack layer formation. The overall goal of picosecond laser processing is to control the formation of a smooth crack layer to ensure effective separation.

[0056] Example 4

[0057] See Figures 16 to 20 , Figure 16 A schematic diagram of laser refining loss is shown. Figure 17 , Figure 18 The effect of different single-pulse energies on laser quality improvement loss was shown when the laser pulse width was 1.5 ns. Other parameters were: pulse repetition frequency of 25 kHz, laser scanning speed of 100 mm / s, scanning interval of 50 μm, and average laser power of 1 W. The results showed that the loss was small when the single-pulse energy did not exceed 30 μJ. Figure 19 , Figure 20 The effect of scanning interval on laser refining loss was shown when the laser pulse width was 1.5 ns. Other parameters were: pulse repetition frequency of 25 kHz, laser scanning speed of 100 mm / s, single pulse energy of 20 μJ, and average laser power of 1 W. This indicates that the loss is relatively small when the scanning interval is not less than 50 μm. In nanosecond laser processing, due to the low peak power, the critical self-focusing power is not reached. By controlling the energy, laser refining of the predetermined slice plane can be achieved without self-focusing, ensuring low laser refining loss. Furthermore, nanosecond lasers have sufficient heat accumulation, and within the preferred energy range, laser refining slice processing with low overlap can be achieved, crack propagation is stable, and the hatching effect is suppressed, further controlling the laser refining loss and contributing to the formation of straight crack layers. The overall goal of nanosecond laser processing is to control the refining loss and ensure low-loss slice formation. Experiments show that with a laser pulse width in the range of 1.5-14 ns, low laser refining loss can be basically guaranteed by adjusting other parameters.

[0058] The embodiments of the present invention have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention is not limited to the specific embodiments described above; these embodiments are merely illustrative and not limiting. Those skilled in the art, under the guidance of the present invention, can make many modifications without departing from the spirit and scope of the claims, and all such modifications fall within the scope of protection of the present invention.

Claims

1. A method for wafering composite silicon carbide substrates, characterized in that, Includes the following steps: 1) Bonding single-crystal silicon carbide ingots to a substrate layer; 2) Using laser to perform internal modification processing on single-crystal silicon carbide ingots, forming a modification processing layer inside the single-crystal silicon carbide ingots, with the incident surface of the laser facing away from the base layer; 3) Separate the single-crystal silicon carbide ingot along the modified processing layer to obtain the remaining single-crystal silicon carbide ingot and a composite layer with a base layer and a single-crystal silicon carbide layer. 4) Repeat steps 1)-3) above with the remaining single-crystal silicon carbide ingots, wherein the order of steps 1) and 2) can be interchanged.

2. The method for wafering a composite silicon carbide substrate according to claim 1, characterized in that, The substrate layer is made of polycrystalline silicon carbide.

3. The method for wafering a composite silicon carbide substrate according to claim 1, characterized in that, The laser wavelength is 1000-1100nm, the laser pulse width is 10ps-60ns, the laser scanning speed is 5-1000mm / s, the average laser power is 0.1-3W, the pulse repetition frequency is 1.6-300kHz, the single pulse energy is 0.3-188μJ, and the number of sub-pulses is 1-10; the laser scanning path consists of several parallel straight lines, with an interval of 10-800μm between adjacent lines.

4. The method for wafering a composite silicon carbide substrate according to claim 3, characterized in that, The laser pulse width is 10-500ps.

5. The method for wafering a composite silicon carbide substrate according to claim 4, characterized in that, The laser pulse width is 100 ps, ​​the pulse repetition frequency is 100 kHz, the single pulse energy is 10-20 μJ, the laser scanning speed is 300-500 mm / s, and the scanning interval is 15-25 μm.

6. The method for wafering a composite silicon carbide substrate according to claim 3, characterized in that, The laser pulse width is 1.5ns-14ns.

7. The method for wafering a composite silicon carbide substrate according to claim 6, characterized in that, The laser pulse width is 1.5 ns, the average laser power is 1 W, the laser scanning speed is 100 mm / s, the pulse repetition frequency is 25 kHz, the single pulse energy is 20-30 μJ, and the interval between adjacent lines is 50-200 μm.

8. The method for wafering a composite silicon carbide substrate according to claim 1, characterized in that, In step 1), the single-crystal silicon carbide ingot is bonded to the substrate layer for fixation.

9. The method for wafering a composite silicon carbide substrate according to claim 1, characterized in that, In step 3), the modified processing layer is first expanded using ultrasound, and then the single-crystal silicon carbide ingot is separated along the modified processing layer.

10. A method for wafering a composite silicon carbide substrate according to claim 7, characterized in that, The ultrasonic frequency is 50-200kHz, the ultrasonic power is 400-800W, the ultrasonic wave is a continuous wave or a pulse wave, and the ultrasonic wave is applied for 10-60s.

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