Polishing method of silicon carbide substrate with high surface shape precision for bonding

Abstract

The invention discloses a polishing method of a silicon carbide substrate with high surface shape precision for bonding, which comprises the following steps of: 1, performing diamond mechanical polishing (DMP) on the silicon carbide substrate by adopting diamond polishing solutions with different particle sizes by taking a resin copper disc as a polishing disc to obtain an intermediate substrate with high surface shape precision; and 2, an asphalt disc is used as a polishing disc, polishing liquid containing an oxidizing agent is adopted to carry out chemical mechanical polishing (CMP) on the middle substrate, and the silicon carbide substrate with the ultra-smooth surface is obtained on the basis of keeping the high surface shape precision in the step 1. The problem that the surface shape and the roughness are difficult to obtain at the same time in the polishing process of the silicon carbide substrate is solved through a specific combination sequence and process that a resin copper disc is combined with a DMP machining method to achieve high surface shape precision and a shape modification asphalt disc is combined with a CMP machining method to maintain the high surface shape precision and reduce the roughness at the same time. Therefore, a processing scheme with high surface shape precision and low surface roughness is provided for the silicon carbide substrate for bonding.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide substrate polishing technology, specifically referring to a polishing method for silicon carbide substrates with high surface accuracy for bonding. Background Technology

[0002] With the booming development of industries such as semiconductors and optoelectronics, silicon carbide (SiC), a third-generation semiconductor material with advantages such as high thermal conductivity, high electron mobility, and good thermal and chemical stability, is increasingly being used in high-end manufacturing. Silicon carbide's thermal conductivity is four times that of silicon (Si), a first-generation semiconductor material. This high thermal conductivity enables optical, optoelectronic, and semiconductor devices based on silicon carbide to achieve high integration and excellent performance. Therefore, silicon carbide shows great application potential in integrated circuits, rail transportation, new energy, and aerospace. In the semiconductor and optoelectronic fields, silicon carbide, with its excellent thermal conductivity, high rigidity, high damage threshold, low coefficient of thermal expansion, and large bandgap, has become an excellent substrate material for semiconductor devices, optoelectronic devices, and optical devices. With the development of high-quality silicon carbide crystal growth processes and heterogeneous bonding processes, using large-size silicon carbide crystals as substrates and employing heterogeneous bonding processes to fabricate high-performance optoelectronic devices is becoming more feasible and is receiving increasing attention.

[0003] In bonding applications in optics and optoelectronics, such as high-power laser mirrors and high-power laser gain medium heat sink substrates, high-quality surface activation bonding between different materials is required for the optical processing of silicon carbide substrates. This places very high demands on the optical processing technology of silicon carbide substrates. The silicon carbide substrates are required to have an ultra-smooth surface (Ra<0.5nm) and a very high overall surface accuracy (PV<λ / 10@632.8nm). Currently, extensive research has been conducted both domestically and internationally on silicon carbide processing methods. The main processing scheme is chemical mechanical polishing (CMP) based on polyurethane polishing pads. This method can achieve ultra-smooth silicon carbide substrates with extremely low surface roughness, but it is difficult to simultaneously achieve high overall surface accuracy (PV < λ / 10 @ 632.8 nm). For example, patent (CN109321980B) (2019) discloses a method for preparing low-damage, high-flatness silicon carbide substrates using chemical mechanical polishing, which can achieve very low surface roughness Ra ≤ 0.2 nm, but the substrate warpage value reaches Warp < 70 μm, which cannot meet the high surface accuracy requirements of PV < λ / 10 @ 632.8 nm in high-quality bonding applications. The Indian Space Research Organisation's Tayaramma D. PV Jalluri et al. (2023) published in the *Journal of...* The article in Volume 3, Issue 52 of "of Optics" (pages 969-983) reports a silicon carbide processing scheme that mainly uses mechanical polishing combined with manual fine-tuning of the surface shape. It ultimately achieves silicon carbide processing with surface shape accuracy (PV = 0.186λ) and surface roughness (Ra = 0.75nm). However, the surface shape accuracy and surface roughness of silicon carbide prepared by this processing scheme are still difficult to meet the requirements of applications such as high-quality surface activation bonding. Summary of the Invention

[0004] The purpose of this invention is to provide a polishing method for silicon carbide substrates with high surface accuracy for bonding, which can effectively solve the problem of difficulty in achieving both surface accuracy and surface roughness in silicon carbide substrate processing.

[0005] To achieve the above objectives, this invention proposes a polishing method for a silicon carbide substrate with high surface accuracy for bonding, comprising the following steps: Step 1: Using a resin copper disk as a polishing disk, diamond mechanical polishing (DMP) is performed on the silicon carbide substrate using diamond polishing slurries with different particle sizes. At the same time, surface shape detection and processing parameter feedback control are performed during the polishing process to obtain an intermediate substrate with high surface accuracy.

[0006] Step 2: Using an asphalt disc as a polishing disc, the intermediate substrate is chemically and mechanically polished (CMP) with a polishing slurry containing an oxidant. At the same time, surface shape and surface roughness are detected and processing parameters are controlled during the polishing process. While maintaining the high surface shape accuracy described in Step 1, a high-quality silicon carbide substrate for bonding with low surface roughness is obtained.

[0007] Before step one, the resin copper disk is pre-trimmed; before step two, the surface shape of the asphalt disk is trimmed using the high surface shape precision intermediate substrate processed in step one, so that the surface shape of the asphalt disk matches the surface shape of the intermediate substrate.

[0008] As a further aspect of the present invention: after the resin copper disk is pre-trimmed before step one, the overall surface undulation PV value is no greater than 3μm.

[0009] As a further aspect of the present invention: in step one, diamond polishing fluids with different particle sizes are used for polishing, with the particle size range gradually decreasing from the micrometer level to the submicrometer level.

[0010] As a further aspect of the present invention, the different particle sizes include at least five of the following: 10 μm, 6 μm, 3 μm, 1 μm, 500 nm and 100 nm.

[0011] As a further aspect of the present invention: in step two, the polishing slurry containing the oxidant includes a first polishing slurry and a second polishing slurry; the first polishing slurry uses CeO2 as the main abrasive, the second polishing slurry uses SiO2 as the main abrasive, and the abrasive particle size of the second polishing slurry is smaller than that of the first polishing slurry.

[0012] As a further aspect of the present invention: the mass concentration of CeO2 in the first polishing solution is 2%-6%, and the oxidant is potassium permanganate with a concentration of 0.02-0.1 mol / L.

[0013] As a further aspect of the present invention: the mass concentration of SiO2 in the second polishing solution is 1%-3%, and the oxidant is potassium permanganate with a concentration of 0.01-0.05 mol / L.

[0014] As a further aspect of the present invention: the surface shape detection is performed using a laser interferometer at intervals of no more than 15 minutes, and the surface roughness detection is performed using a white light interferometer at intervals of no more than 15 minutes.

[0015] As a further aspect of the present invention: the surface accuracy PV value of the intermediate substrate processed in step one is less than λ / 12@632.8nm, and the surface roughness Ra value is less than 2nm; the surface accuracy PV value of the final substrate processed in step two is less than λ / 10@632.8nm, and the surface roughness Ra value is less than 0.3nm.

[0016] As a further aspect of the present invention: the processing parameters include polishing pressure, polishing speed, and polishing removal path, wherein the polishing pressure refers to the pressure of the polishing disc on the grinding and polishing machine, and the polishing speed and polishing path are determined by setting the rotation speed of the polishing disc, the speed of the swing shaft, and the distance between the center of the polishing disc and the center of the silicon carbide substrate on the grinding and polishing machine.

[0017] Compared with existing technologies, the resin copper disk used in the diamond mechanical polishing (DMP) process of this invention has the characteristics of moderate elastic modulus, good rigidity, strong self-healing ability, and strong wear resistance, which can quickly achieve high surface accuracy processing of silicon carbide substrates. On the other hand, the pitch polishing disk used in the chemical mechanical polishing (CMP) process has the characteristics of excellent surface plasticity, which can achieve very low surface roughness of silicon carbide substrates while maintaining the high surface accuracy of DMP processing. By combining the above two processes, the problem of difficulty in achieving both surface accuracy and surface roughness in silicon carbide substrate processing is effectively solved, thus providing a processing solution with high surface accuracy PV<λ / 10@632.8nm and low surface roughness Ra<0.3nm for high-quality heterobonding of silicon carbide substrates. Attached Figure Description

[0018] Figure 1 This is a flowchart of the polishing method for a high-precision silicon carbide substrate used for bonding according to the present invention.

[0019] Figure 2 The image shown is a surface interference fringe pattern of a silicon carbide sample obtained by a laser interferometer after DMP processing in this embodiment.

[0020] Figure 3 The surface roughness parameters of the silicon carbide sample obtained by white light interferometer after DMP processing in the embodiment are shown.

[0021] Figure 4 The image shown is a surface interference fringe pattern of a silicon carbide sample obtained by a laser interferometer after CMP processing in this embodiment.

[0022] Figure 5 The parameters are the final surface roughness parameters of the silicon carbide sample after CMP processing, measured by a white light interferometer in the example. Detailed Implementation

[0023] The invention will now be further described with reference to the accompanying drawings.

[0024] The working principle of this invention: This invention achieves high-quality bonding silicon carbide substrate processing with a surface profile accuracy of PV < λ / 10 @ 632.8 nm and a surface roughness Ra < 0.3 nm through a two-step combined polishing process that combines diamond mechanical polishing (DMP) using a resin-copper disk as the polishing pad with chemical mechanical polishing (CMP) using an asphalt disk as the polishing pad. Its core principle is to solve the problem of achieving both surface profile accuracy and surface roughness in silicon carbide substrate polishing by combining a specific sequence and process of "achieving high surface profile accuracy with a resin-copper disk combined with DMP processing" and "maintaining high surface profile accuracy while reducing surface roughness with a modified asphalt disk combined with CMP processing." The processing first utilizes the moderate elastic modulus, high rigidity, strong self-healing ability, and high wear resistance of the resin copper disc. During polishing, it does not undergo significant elastic or plastic deformation due to the polishing pressure on the silicon carbide substrate. Combined with diamond polishing slurries of different particle sizes, it achieves a high material removal rate and rapid convergence of the silicon carbide surface shape using the diamond mechanical polishing (DMP) method, ultimately achieving extremely high surface shape accuracy of the silicon carbide substrate. Building upon this high surface shape accuracy, an asphalt disc is further used as the polishing disc. Leveraging the excellent surface shape plasticity of the asphalt disc, under specific temperature, pressure, and lubricating fluid conditions, the DMP-processed, high-precision silicon carbide substrate is first trimmed with the asphalt. The blue disc allows the pitch disc to perfectly conform to the high surface accuracy of the silicon carbide substrate. Therefore, during the subsequent chemical mechanical polishing (CMP) process, the pressure of the pitch polishing disc can be evenly distributed across the entire surface of the silicon carbide substrate being polished. By optimizing the polishing path, every part of the silicon carbide surface can be polished uniformly. Thus, a uniform amount of material removal can be achieved on the entire surface of the silicon carbide without damaging the high-precision surface of the silicon carbide substrate processed by DMP. This eliminates surface / subsurface damage, scratches and other defects during DMP processing. Ultimately, excellent surface roughness is obtained while maintaining high surface accuracy, thereby achieving high-quality bonding silicon carbide substrate processing with high surface accuracy and low surface roughness.

[0025] like Figure 1 As shown, a polishing method for a silicon carbide substrate with high surface accuracy for bonding includes the following steps:

[0026] Step 1: Using a resin copper disk as a polishing disk, diamond mechanical polishing of silicon carbide substrate is performed using diamond polishing slurries with different particle sizes. At the same time, surface shape detection and processing parameter feedback control are performed during the polishing process to obtain an intermediate substrate with high surface shape accuracy.

[0027] Step 2: Using an asphalt disc as a polishing disc, the intermediate substrate is chemically and mechanically polished with a polishing slurry containing an oxidant. At the same time, the surface shape and surface roughness are detected and the processing parameters are controlled by feedback during the polishing process. While maintaining the high surface shape accuracy described in Step 1, a high-quality silicon carbide substrate for bonding with low surface roughness is obtained.

[0028] Before step one, the resin copper disk is pre-trimmed; before step two, the surface shape of the asphalt disk is trimmed using the high surface shape precision intermediate substrate processed in step one, so that the surface shape of the asphalt disk matches the surface shape of the intermediate substrate.

[0029] Example:

[0030] This embodiment describes a polishing method for a high-precision silicon carbide substrate used for bonding, with a diameter of 50 mm and a thickness of 6 mm.

[0031] Step 1: First, apply a protective film to the back of the silicon carbide sample to be processed. Heat the silicon carbide sample and the aluminum disk to 100°C. Apply low-temperature wax evenly to the protective film and the surface of the aluminum disk. Place the back of the silicon carbide sample on the aluminum disk and apply a certain pressure to ensure close contact between the aluminum disk and the silicon carbide sample. After the entire sample cools to room temperature, fix the silicon carbide sample on the disk and wait for polishing. Use a 150mm diameter cast iron disk as a grinding disk. Grind the 100mm diameter resin copper disk on a four-axis grinding and polishing machine using 40μm boron carbide abrasive until the surface flatness PV < 2μm.

[0032] Step Two: Using the resin copper disk prepared in Step One as the polishing disk, the silicon carbide substrate is processed on a four-axis grinding and polishing machine using the DMP method. During the process, the silicon carbide substrate is first mechanically polished using 10μm diamond polishing slurry. The polishing disk pressure is 30N, the polishing disk speed is 67rpm, and the swing shaft speed is 81rpm. The swing shaft position is set to ensure a minimum distance of 15mm between the center of the silicon carbide sample and the center of the resin copper disk. The polishing time is 1.5 hours. After cleaning the sample and the resin copper disk, 6μm diamond polishing slurry is used to mechanically polish the silicon carbide substrate. During the polishing process, the polishing disk pressure remains at 30N, and the polishing disk speed, swing shaft speed, and swing shaft position are maintained. The polishing time remained unchanged for 1 hour. After cleaning the sample and the resin copper disk, a 3μm diamond polishing slurry was used to mechanically polish the silicon carbide substrate. During the polishing process, the polishing disk pressure was reduced to 20N, the polishing disk speed was reduced to 59rpm, the pendulum speed was reduced to 71rpm, and the pendulum position remained unchanged. Simultaneously, the surface shape of the processed silicon carbide substrate was inspected every 15 minutes using a laser interferometer. Based on the inspection results, the polishing disk speed, pendulum speed, and pendulum position were fine-tuned. The polishing time was 1 hour. After cleaning the sample and the resin copper disk, a 1μm diamond polishing slurry was used to mechanically polish the silicon carbide substrate. The polishing disk pressure was maintained at 20N during the polishing process, and again, the surface shape of the processed silicon carbide substrate was inspected every 15 minutes using a laser interferometer. The surface shape of the processed silicon carbide substrate was inspected. Based on the inspection results, the polishing disk speed was adjusted to 50-70 rpm, the swing shaft speed to 50-80 rpm, and the swing shaft position was adjusted to ensure that the minimum distance between the center of the silicon carbide sample and the center of the resin copper disk was 0-30 mm. The polishing time was 1 hour. After cleaning the sample and the resin copper disk, a diamond polishing slurry with a particle size of 500 nm was used to mechanically polish the silicon carbide substrate. During the polishing process, the pressure of the polishing disk was reduced to 10 N. Similarly, the surface shape of the processed silicon carbide substrate was inspected every 15 minutes using a laser interferometer. Based on the inspection results, the polishing disk speed was adjusted to 40-60 rpm, the swing shaft speed to 40-70 rpm, and the swing shaft position was adjusted to ensure that the minimum distance between the center of the silicon carbide sample and the center of the resin copper disk was 0-30 mm. The minimum distance between the center of the silicon carbide sample and the center of the resin copper disk is 0-30 mm, and the polishing time is 1 hour. After cleaning the sample and the resin copper disk, the silicon carbide substrate is mechanically polished with diamond polishing fluid with a particle size of 100 nm. During the polishing process, the pressure of the polishing disk is reduced to 5 N. Similarly, the surface shape of the processed silicon carbide substrate is detected every 15 minutes using a laser interferometer. Based on the detection results, the polishing disk speed is kept within the range of 20-40 rpm, the swing shaft speed is kept within the range of 20-50 rpm, and the swing shaft position is adjusted to keep the minimum distance between the center of the silicon carbide sample and the center of the resin copper disk within the range of 0-30 mm. The polishing time is not less than 1 hour until the overall surface shape accuracy of the silicon carbide substrate PV<λ / 12@632 is achieved.The silicon carbide sample was machined with a high surface shape precision of 8nm and a surface roughness Ra<2nm. After polishing with DMP process, the surface shape interference fringe morphology of the silicon carbide sample was measured by laser interferometer. Figure 2 As shown, the surface roughness parameters of the silicon carbide sample measured by a white light interferometer are as follows: Figure 3 As shown;

[0033] Step 3: Prepare a lubricant solution consisting of 2% sodium dodecylbenzenesulfonate, 1% fatty alcohol polyoxyethylene ether, 0.5% sodium citrate, 0.2% hydroxyethyl cellulose, and deionized water. Use a 100mm diameter asphalt disc as the polishing disc. On a four-axis grinding and polishing machine, use the silicon carbide substrate with high surface accuracy processed by the DMP process in Step 2 to adjust the surface shape of the asphalt polishing disc. Set the polishing disc pressure to 20N, the polishing disc speed to 30rpm, and the swing shaft speed to 37rpm. At the same time, set the swing shaft position so that the minimum distance between the center of the silicon carbide sample and the center of the resin copper disc is 15mm, so that the surface shape of the asphalt polishing disc basically matches the surface shape of the silicon carbide substrate processed by DMP.

[0034] Step Four: Using the asphalt disk with its surface shaped in Step Three as the polishing disk, further utilize the chemical mechanical polishing (CMP) process. Use a 6% CeO2 (500nm particle size) polishing slurry (with 0.05mol potassium permanganate added as an oxidant) to process the silicon carbide substrate. During processing, maintain the polishing disk pressure at 20N. Every 15 minutes, use a laser interferometer to inspect the surface shape of the processed silicon carbide substrate. Based on the inspection results, maintain the polishing disk speed at 40-70rpm, the pendulum speed at 40-90rpm, and adjust the pendulum position to ensure the minimum distance between the center of the silicon carbide sample and the center of the resin copper disk is within 0-30mm. This ensures uniform material removal across the entire surface while maintaining the high-precision surface shape of the silicon carbide substrate processed by DMP. The polishing time should be no less than 1 hour. Use a white light interferometer to inspect the roughness of the silicon carbide substrate to ensure the elimination of surface damage, scratches, and other defects introduced during DMP processing. After cleaning the sample and the asphalt disk, replace the slurry with a 6% CeO2 (500nm particle size) polishing slurry. The silicon carbide substrate was further polished using a 2% silica sol (100nm particle size) polishing slurry (with 0.03mol potassium permanganate added as an oxidant). The polishing disk pressure was reduced to 5N. The surface shape of the processed silicon carbide substrate was checked every 15 minutes using a laser interferometer. Based on the results, the polishing disk speed was adjusted to 20-40rpm, the swing shaft speed to 20-50rpm, and the swing shaft position was adjusted to ensure the minimum distance between the center of the silicon carbide sample and the center of the resin copper disk was 0-30mm. This ensured uniform material removal across the entire surface without significantly altering the high-precision surface shape of the DMP-processed silicon carbide substrate. The polishing time was no less than 1 hour. The roughness of the silicon carbide substrate was checked every 15 minutes using a white light interferometer until a high-quality bonding silicon carbide substrate with a surface shape accuracy PV < λ / 10 @ 632.8nm and a surface roughness Ra < 0.3nm was achieved. After CMP polishing, the final surface interference fringe morphology of the silicon carbide sample was measured using a laser interferometer. Figure 4 As shown, the final surface roughness parameters of the silicon carbide sample measured by a white light interferometer are as follows: Figure 5 As shown.

[0035] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polishing method for a silicon carbide substrate with high surface accuracy for bonding, characterized in that, Includes the following steps: Step 1: Using a resin copper disk as a polishing disk, diamond mechanical polishing of silicon carbide substrate is performed using diamond polishing slurries with different particle sizes. At the same time, surface shape detection and processing parameter feedback control are performed during the polishing process to obtain an intermediate substrate with high surface shape accuracy. Step 2: Using an asphalt disc as a polishing disc, the intermediate substrate is chemically and mechanically polished with a polishing slurry containing an oxidant. At the same time, the surface shape and surface roughness are detected and the processing parameters are controlled by feedback during the polishing process. While maintaining the high surface shape accuracy described in Step 1, a high-quality silicon carbide substrate for bonding with low surface roughness is obtained. Before step one, the resin copper disk is pre-trimmed; before step two, the surface shape of the asphalt disk is trimmed using the high surface shape precision intermediate substrate processed in step one, so that the surface shape of the asphalt disk matches the surface shape of the intermediate substrate.

2. The method according to claim 1, characterized in that, Before step one, the resin copper disk is pre-trimmed, and its overall surface undulation PV value is no greater than 3μm.

3. The method according to claim 1, characterized in that, In step one, polishing is performed using diamond polishing slurries with different particle sizes, with the particle size range gradually decreasing from the micrometer level to the submicrometer level.

4. The method according to claim 3, characterized in that, The different particle sizes include at least five of the following: 10 μm, 6 μm, 3 μm, 1 μm, 500 nm, and 100 nm.

5. The method according to claim 1, characterized in that, In step two, the polishing slurry containing the oxidant includes a first polishing slurry and a second polishing slurry; the first polishing slurry uses CeO2 as the main abrasive, the second polishing slurry uses SiO2 as the main abrasive, and the abrasive particle size of the second polishing slurry is smaller than that of the first polishing slurry.

6. The method according to claim 5, characterized in that, The CeO2 mass concentration in the first polishing solution is 2%-6%, and the oxidant is potassium permanganate with a concentration of 0.02-0.1 mol / L.

7. The method according to claim 5, characterized in that, The mass concentration of SiO2 in the second polishing solution is 1%-3%, and the oxidant is potassium permanganate with a concentration of 0.01-0.05 mol / L.

8. The method according to claim 1, characterized in that, The surface shape detection is performed using a laser interferometer at intervals of no more than 15 minutes, and the surface roughness detection is performed using a white light interferometer at intervals of no more than 15 minutes.

9. The method according to claim 1, characterized in that, The surface accuracy PV value of the intermediate substrate processed in step one is less than λ / 12@632.8nm, and the surface roughness Ra value is less than 2nm; the surface accuracy PV value of the final substrate processed in step two is less than λ / 10@632.8nm, and the surface roughness Ra value is less than 0.3nm.

10. The method according to claim 1, characterized in that, The processing parameters include polishing pressure, polishing speed, and polishing removal path. Polishing pressure refers to the pressure of the polishing disc on the grinding and polishing machine. Polishing speed and polishing path are determined by setting the rotation speed of the polishing disc, the speed of the swing shaft, and the distance between the center of the polishing disc and the center of the silicon carbide substrate on the grinding and polishing machine.

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