Method of processing a substrate

Abstract

The present application relates to the technical field of semiconductor chemical mechanical polishing (CMP) equipment, in particular to a processing method of a substrate. The present application provides a processing method of a substrate. In view of the problems of difficult planarization processing and low yield of large-size substrates, according to the surface type of the incoming substrate, a non-equal-thickness air film is selected to realize the structure of a ring-shaped multi-zone polishing head with different film thicknesses, and the partition pressure adjustment capability of the single-substrate CMP equipment is matched to independently adjust the air pressure. In the pressure response stage, the deviation is small, the surface type of the large-size substrate can be controlled, the problems of "not polishing" or "over-polishing" at the edge of the large-size substrate are solved, and the surface ultra-precision planarization processing of the large-size substrate wafer is realized. The TTV of the substrate can be finally controlled within 1.0 μm, and the present application is especially suitable for the third-generation semiconductor silicon carbide substrate mass production level CMP processing.

Description

Technical Field

[0001] This invention relates to the field of semiconductor chemical mechanical polishing (CMP) equipment technology, specifically a substrate processing method. Background Technology

[0002] Silicon carbide (SiC) chips, as a core material for third-generation semiconductors, offer significant advantages over traditional silicon chips in terms of high voltage resistance, high temperature resistance, high frequency, and low loss, greatly improving system efficiency and power density. These characteristics have led to their widespread application in high-end fields such as new energy vehicles, photovoltaic energy storage, smart grids, 5G communications, and AI data centers. As semiconductor manufacturing technology iterates towards larger sizes, higher precision, and higher integration, silicon carbide wafers are rapidly moving towards large-size production. Technological breakthroughs focus on improving crystal growth yield, dicing loss, and epitaxial uniformity, which will significantly reduce device costs and enhance performance.

[0003] Silicon carbide substrates, as the basic carriers for epitaxial growth and chip fabrication, have extremely strict requirements for surface planarity. TTV and LTV, as important data for measuring planarity, are important indicators for measuring processing quality in the silicon carbide industry. Due to the inherent hardness of silicon carbide and the large difference in properties between its two sides, although single-wafer CMP processing is in high demand, its obvious drawback is that the surface quality cannot be guaranteed, which cannot meet market demand and achieve mass production.

[0004] Single-wafer CMP primarily relies on the polishing head to pick up the wafer and apply controlled pressure to optimize flatness through zoned pressurization. However, zoned pressurization is limited by the gas film material and design issues, resulting in a significant difference between the actual pressure and the ideal pressure during gas bladder inflation. Conventional homogeneous polishing gas film materials are uniform in material and thickness. However, with increasing service life, uneven gas film thickness distribution easily occurs on the same bearing surface. Coupled with stronger edge wear and corrosion erosion, the thickness difference gradually increases in the center, middle, and edge regions of the ring. This makes it difficult to maintain stable surface flatness control during single-wafer CMP processing, especially for large-size silicon carbide wafers. The initial surface flatness is not uniform, and the surface flatness varies greatly depending on the process steps. Current technology cannot make targeted adjustments to localized areas, making surface flattening of large-size wafers particularly difficult.

[0005] Single-wafer CMP primarily achieves efficient removal through high pressure, high rotation speed, and a strong acidic oxidation system. During the removal process, the linear velocity at the substrate edge is higher than that at the center, resulting in more severe oxidation erosion and abrasive friction at the edge. This leads to more severe wear on the gas film edge, easily resulting in a distribution difference where the film thickness at the edge is less than that at the center. This phenomenon causes a significant discrepancy between the predicted and actual results from the initial CMP formulation design, which is difficult to repair and affects the overall flatness and local flatness uniformity of the substrate wafer.

[0006] Meanwhile, significant local film thickness variations can affect the back-side bonding of the wafer, creating micro-gaps and localized stress imbalances, disrupting contact conditions and polishing stability, and exacerbating overall removal dispersion. Traditional zoned air pressure regulation can only achieve weak pressure compensation, failing to offset the stiffness and deformation differences caused by uneven film thickness, and cannot fundamentally suppress TTV degradation. Under long-term continuous processing, film thickness deviations continue to widen, batch stability decreases, and severely restricts the yield of ultra-precision planarization processing of large-size silicon carbide substrates. Summary of the Invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a substrate processing method. For the processing of large-size substrates, the method achieves significant optimization of TTV and LTV by using a partitioned, unequal-thickness design of the gas film in the polishing head. This overcomes the problems of traditional gas films being of a single material and uniform thickness, where the thickness change after wear during long-term high-pressure polishing directly affects the pressure distribution, resulting in differences in removal rates in different areas of the large-size substrate, poor surface flatness uniformity, and the inability to perform localized targeted processing on uniform-thickness gas films for different types of incoming materials, thus failing to achieve flattening of the substrate surface.

[0008] This invention provides a method for processing a substrate, comprising the following steps: Chemical mechanical polishing is performed on the substrate to be processed using a polishing head with a partitioned gas film of unequal thickness. The partitioned unequal thickness air film includes, from the center to the edge, a circular region A, an annular region B, and an annular region C in that order. The circular region A, annular region B, and annular region C have a gradient thickness difference at their contact surfaces with the polishing head. The substrate to be processed has a concave or convex surface. The concave surface is one that gradually rises from the center region to the edge region along the radial direction of the substrate, and the convex surface is one that gradually decreases from the center region to the edge region along the radial direction of the substrate. When the substrate to be processed is concave and the TTV value is ≤3 μm, in μm as the thickness unit, the thickness of the circular region A is (2.9~3.1) times larger than the thickness of the annular region B by a TTV value, preferably 3 times larger; the thickness of the circular region B is (1.9~2.1) times larger than the thickness of the annular region C by a TTV value, preferably 2 times larger; the thickness of the circular region C is 990 µm ~1010 µm; When the substrate to be processed is concave and the TTV value is >3 μm, in μm as the thickness unit, the thickness of the circular region A is (4.9~5.1) times larger than the thickness of the annular region B by a TTV value, preferably 5 times larger; the thickness of the circular region B is (4.9~5.1) times larger than the thickness of the annular region C by a TTV value, preferably 5 times larger; the thickness of the circular region C is 990 µm ~1010 µm; When the substrate to be processed is convex and the TTV value is ≤3 μm, in μm as the thickness unit, the thickness of the circular region A is (2.9~3.1) times smaller than the thickness of the annular region B by a TTV value, preferably 3 times larger; the thickness of the circular region B is (1.9~2.1) times smaller than the thickness of the annular region C by a TTV value, preferably 2 times larger; the thickness of the circular region C is 990 µm ~1010 µm; When the substrate to be processed is convex and the TTV value is >3 μm, in μm as the thickness unit, the thickness of the circular region A is (4.9~5.1) times smaller than the thickness of the annular region B by a TTV value, preferably 5 times larger; the thickness of the circular region B is (4.9~5.1) times smaller than the thickness of the annular region C by a TTV value, preferably 5 times larger; the thickness of the circular region C is 990 µm ~1010 µm; In some embodiments of the present invention, when the substrate to be processed is concave and the TTV value is ≤3 μm, the thicknesses of the circular region A, the annular region B, and the annular region C are (5 times the TTV value + 1000) µm, (2 times the TTV value + 1000) µm, and 1000 µm, respectively; when the substrate to be processed is concave and the TTV value is >3 µm, the thicknesses of the circular region A, the annular region B, and the annular region C are (10 times the TTV value + 1000) µm, (5 times the TTV value + 1000) µm, and 1000 µm, respectively; when the substrate to be processed is convex and the TTV value is ≤3 µm, the thicknesses of the circular region A, the annular region B, and the annular region C are (1000 - 5 times the TTV value) µm, (1000 - 2 times the TTV value) µm, and 1000 µm, respectively; when the substrate to be processed is convex and the TTV value is >3 µm, the thicknesses of the circular region A, the annular region B, and the annular region C are (1000 - 5 times the TTV value) µm, (1000 - 2 times the TTV value) µm, and 1000 µm, respectively; when the substrate to be processed is convex and the TTV value is >3 µm, the thicknesses of the circular region A, the annular region B, and the annular region C are (1000 - 5 times the TTV value) µm, (1000 - 2 times the TTV value) µm, and 1000 µm, respectively. When the thickness is µm, the thicknesses of the circular region A, the annular region B, and the annular region C are (1000-10 times the TTV value) µm, (1000-5 times the TTV value) µm, and 1000 µm, respectively.

[0009] The partitioned unequal thickness gas film of this invention is an integrated annular structure, made entirely of a polymer material, preferably reinforced rubber or polyurethane. Its function is to uniformly transmit the downward pressure of the polishing head to the wafer through back pressure. The partitioned unequal thickness gas film of this invention, radially from center to edge, includes: a circular region A, an annular region B, and an annular region C, corresponding to the gas film's central region, an annular intermediate region, and an annular edge region, respectively. Specifically, the center point of the circular region A coincides with the center point of the partitioned unequal thickness gas film; the annular region C is the outermost annular region of the entire partitioned unequal thickness gas film; the remaining annular intermediate region is the annular region B, serving as a transition region, located between the circular region A and the annular region C.

[0010] In the partitioned unequal thickness gas film of the present invention, the radius of region A is 45%~55% of the radius of the partitioned unequal thickness gas film; the width of region C is 5%~15% of the radius of the partitioned unequal thickness gas film; and the width of region B is 35%~45% of the radius of the partitioned unequal thickness gas film. Preferably, the radius of region A is 49%~51% of the radius of the partitioned unequal thickness gas film; the width of region C is 9%~11% of the radius of the partitioned unequal thickness gas film; and the width of region B is 39%~41% of the radius of the partitioned unequal thickness gas film. The annular region C of the present invention, as the outermost annular region of the entire gas film, has its width set to a small proportion of the gas film radius, mainly considering that the high or low points of the surface of the substrate to be processed are mainly concentrated in the edge region, and a narrower edge partition is more conducive to localized targeted adjustment.

[0011] The circular region A, annular region B, and annular region C of the partitioned unequal thickness gas film of this invention exhibit a gradient thickness difference, forming a modulus heterogeneous composite structure used to control the uniformity of the substrate surface. Furthermore, the overall thickness of the partitioned unequal thickness gas film gradually changes radially from the center to the edge. The gradient thickness difference between the circular region A, annular region B, and annular region C of the partitioned unequal thickness gas film is located on the contact surface between the partitioned unequal thickness gas film and the polishing head, rather than on the side of the partitioned unequal thickness gas film used to contact the substrate to be processed (also known as the gas mold substrate surface). In addition, the gas film substrate surface of the partitioned unequal thickness gas film of this invention undergoes a planarization treatment to ensure a greater buffering effect when the gas film contacts the substrate, ensuring the safety of single-piece CMP processing. The planarization process ensures that the overall thickness of the side of the gas film with unequal thickness that contacts the substrate to be processed changes gently from the center to the edge radially. After the back pressure is applied, the gas film substrate surface presents an arc-shaped curve. This not only enables the achievement of specific film thicknesses in different regions to ensure the planarization of large-size substrates, but also ensures a smooth transition of the substrate surface through the gentle change of the gas film substrate surface, increasing the buffering capacity, reducing LTV, and avoiding the risk of pressure imbalance and fragmentation caused by the decrease in thickness gradient.

[0012] This invention obtains the TTV (Total Thickness Deviation) and LTV (Local Thickness Deviation) values ​​of the substrate to be processed through surface profile testing, and determines the surface profile of the substrate based on the TTV and LTV values. Preferably, the surface profile test is a full-surface test with 200-30,000 test points. This invention outputs a thickness variation image of the substrate to be processed through surface profile testing, obtaining the TTV and LTV values, which facilitates the customization of the gas film. After chemical mechanical polishing, the TTV and LTV values ​​of the processed substrate can be tested again to confirm the effect. Due to the significant difference in roughness and cleanliness between the two tests, different equipment can be used for measurement, ensuring that the same equipment is used in the same process.

[0013] This invention utilizes a polishing head with a gas film of unequal thickness in the aforementioned partitioned areas to perform chemical mechanical polishing on a substrate to be processed. The substrate to be processed includes, but is not limited to, silicon carbide substrates, diamond substrates, gallium nitride substrates, or gallium arsenide substrates. The size of the substrate to be processed in this invention is at least 6 inches, specifically including 6-inch, 8-inch, 12-inch, and larger sizes. The wafer handling process for the substrate to be processed in this invention is not particularly limited and may include thinning, double-sided DMP, double-sided CMP, single-sided CMP (return polishing), etc.

[0014] This invention utilizes a polishing head with the aforementioned partitioned, unevenly thick gas film to perform chemical mechanical polishing on a substrate. The polishing head includes, from the outside to the inside, a holding ring pressure region, a first annular pressure region, a second annular pressure region, a third annular pressure region, and a fourth circular pressure region arranged radially from the outside in. The center point of the fourth circular pressure region coincides with the center point of the polishing head. Specifically, the radius of the polishing head excluding the holding ring pressure region is defined as 100% (the radius of the polishing head excluding the holding ring pressure region is also the radius of the first annular pressure region, the second annular pressure region, the third annular pressure region, and the fourth circular pressure region). The total width of the first annular pressure zone and the third annular pressure zone, and the radius of the fourth circular pressure zone, are combined. The width of the first annular pressure zone is 12% to 18% of the radius of the polishing head excluding the holding ring pressure zone; the width of the second annular pressure zone is 32% to 38% of the radius of the polishing head excluding the holding ring pressure zone; the width of the third annular pressure zone is 27% to 33% of the radius of the polishing head excluding the holding ring pressure zone; and the radius of the fourth circular pressure zone is 17% to 23% of the radius of the polishing head excluding the holding ring pressure zone. During chemical mechanical polishing, the pressures of the first annular pressure zone, the second annular pressure zone, the third annular pressure zone, and the fourth circular pressure zone of the polishing head are (10.5~11.5) psi, (6.5~7.0) psi, (7.0~7.5) psi, and (7.0~7.5) psi, respectively; the pressure of the holding ring pressure zone is (11.5~12.5) psi.

[0015] This invention uses a polishing head with the aforementioned partitioned, unequal-thickness gas film, and selects suitable consumables (polishing pads, polishing fluids, etc.) and formulations for single-piece CMP (chemical mechanical polishing) of the substrate to be processed, ensuring that the removal rate and other indicators such as roughness are within the required range. Preferably, this invention uses a polishing head with the aforementioned partitioned, unequal-thickness gas film to perform CMP on both sides of the substrate to be processed, with a removal depth of 1.5 μm to 2 μm on both sides. Preferably, the coarse polishing pad used for CMP is a polyurethane polishing pad with a grooved pattern of ring or square. Preferably, the polishing fluid used for CMP is one or more of alumina, cerium oxide, and abrasive-free polishing fluid; the pH of the polishing fluid is 3 to 5; the flow rate of the polishing fluid is 70 mL to 150 mL; and the temperature of the polishing fluid is controlled below 60°C. Preferably, the rotation speed of the polishing head during CMP is 900 rpm to 120 rpm, and the rotation speed of the polishing disc is 100 rpm to 140 rpm. Preferably, the chemical mechanical polishing time is 5 min to 30 min.

[0016] This invention involves chemically and mechanically polishing the substrate before cleaning it, allowing for the testing of TTV and LTV data to verify the results. In some embodiments of this invention, the cleaning solutions used are SPM, SC1, and SC2 solutions, etc. The cleaning process is determined according to actual needs to ensure that the wafer surface is free of cleaning solutions, watermarks, and large particles, thus avoiding any impact on the surface shape test results.

[0017] This invention provides a substrate processing method. Addressing the challenges and low yield of planarization processing for large-size substrates, this method utilizes a suitable non-uniform thickness gas film to achieve a ring-shaped, multi-region polishing head structure with varying film thicknesses, based on the surface profile of the incoming substrate. Combined with the independent gas pressure regulation capability of a single-wafer CMP device, the method exhibits minimal deviation during the pressure response phase, enabling targeted control of the surface profile of large-size substrates. This solves the problems of "underpolishing" or "overpolishing" the edges of large-size substrates, thereby achieving ultra-precision surface planarization of large-size substrate wafers. The substrate TTV can ultimately be stably controlled within 1.0 μm, making it particularly suitable for mass production-level CMP processing of third-generation semiconductor silicon carbide substrates. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the setting of different thicknesses in different regions of the polishing head described in this invention; Figure 2 A longitudinal section diagram showing the main regions of a polishing head having the air film described in this invention; Figure 3 This is a diagram showing the surface distribution of a concave-shaped substrate. Figure 4 This is a diagram showing the surface distribution of a convex-shaped substrate. Figure 5 This is a data diagram of the substrate surface after polishing using the three-zone unequal thickness air film of the present invention in Embodiment 1 of the present invention; Figure 6 This is a data diagram of the substrate surface after polishing using the three-zone unequal thickness air film of the present invention in Embodiment 2 of the present invention; Figure 7 This is a data diagram of the substrate surface after conventional air film polishing in Comparative Example 1 of the present invention; Figure 8 This is a data diagram of the substrate surface after polishing with a non-inventory three-zone unequal thickness air film, which is a comparative example of the present invention in Example 2. Figure 9 This is a data diagram of the substrate surface after polishing using two regions of unequal thickness air film in Comparative Example 3 of the present invention; Figure 10 This is a data diagram of the substrate surface after polishing with a four-zone unequal thickness air film, which is a comparative example of the present invention (4). Detailed Implementation

[0019] This invention discloses a method for processing silicon carbide substrates. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to implement and apply the technology of this invention.

[0020] In a specific embodiment of the present invention, the center point of the circular region A of the partitioned unequal thickness air film coincides with the center point of the entire air film, and its radius is 50% of the radius of the entire air film; the width of the annular region C of the partitioned unequal thickness air film is only 10% of the air film radius; the width of the annular region B of the partitioned unequal thickness air film is 40% of the air film radius. Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram illustrating the different thickness settings in different regions of the polishing head described in this invention. Figure 2 This is a longitudinal section diagram showing the main regions of a polishing head having the air film described in this invention. Figure 1 and Figure 2 As can be seen, the air film of the present invention is divided into annular sections with different thicknesses, where 1 represents region A, 2 represents region B, 3 represents region C, 4 represents the retaining ring, and 5 represents the support structure.

[0021] The substrate to be processed according to the present invention includes two types: concave surface type (concave in the center, convex at the edge) and convex surface type (convex in the center, concave at the edge), such as... Figure 3 and Figure 4 As shown, Figure 3 This is a diagram showing the surface distribution of a concave-shaped substrate. Figure 4 This is a surface profile diagram of a convex surface substrate. The substrate to be processed in this invention is cleaned using ultrasonic cleaning with alcohol to avoid surface contaminants or large particles affecting the surface profile test results. After processing, the flatness of the wafer is tested, the total thickness deviation and local thickness deviation of the substrate are calculated, and a surface profile diagram is output.

[0022] The thickness setting range for different regions of the air-supported membrane is mainly based on the changing trend of the sheet surface and the total thickness deviation (TTV). If the TTV data of the previous sheet is denoted as X (keeping only one decimal place), taking the concave surface of the sheet as an example, the thickness of the air-supported membrane from the edge to the center should gradually decrease. When the X value is ≤3 µm, the thickness setting values ​​of the three adjacent regions A, B, and C should be 5X+1000 µm, 2X+1000 µm, and 1000 µm, respectively. When the X value is >3 µm, the thickness setting values ​​of the three adjacent regions A, B, and C should be 10X+1000 µm, 5X+1000 µm, and 1000 µm, respectively. Similarly, taking a convex surface as an example, the thickness of the air film from the edge to the center should gradually increase. When X value ≤ 3 µm, the thickness settings for the three adjacent regions A, B, and C should be 1000-5X µm, 1000-2X µm, and 1000 µm, respectively; while when X value > 3 µm, the thickness settings for the three adjacent regions A, B, and C should be 1000-10X µm, 1000-5X µm, and 1000 µm, respectively. The substrate surface of the air film is planarized to ensure a large buffering effect when the air film contacts the substrate, ensuring the safety of single-piece CMP processing.

[0023] In a specific embodiment of the present invention, the polishing head includes a retaining ring pressure area, a first annular pressure area, a second annular pressure area, a third annular pressure area, and a fourth circular pressure area arranged sequentially from the outside to the inside along its radial direction. The radius of the polishing head excluding the retaining ring pressure area is 100%. The width of the first annular pressure area is 15% of the radius of the polishing head excluding the retaining ring pressure area, the width of the second annular pressure area is 35% of the radius of the polishing head excluding the retaining ring pressure area, the width of the third annular pressure area is 30% of the radius of the polishing head excluding the retaining ring pressure area, and the radius of the fourth circular pressure area is 20% of the radius of the polishing head excluding the retaining ring pressure area.

[0024] The present invention will be further described below with reference to the embodiments: Example 1 (Results of polishing a concave substrate using the three-zone unequal thickness air film of the present invention) 1. Select a concave substrate (TTV value of 1.811 µm). Utilize the ultra-precision planarization capability of the customized air film of this invention to customize a three-region unequal thickness customized air film based on the TTV data and surface change trend of the substrate wafer. The thickness value of each region of the air film is obtained according to the thickness setting basis of each region of this invention.

[0025] 2. Perform single-piece CMP polishing on the above substrate using a polishing head equipped with the air mold described in this invention. The pressure values ​​of the first annular pressure zone, the second annular pressure zone, the third annular pressure zone, and the fourth circular pressure zone are set from the outside to the inside as 11 psi-6.8 psi-7.2 psi-7.2 psi, respectively. Maintain the pressure of the annular pressure zone at 12 psi. Use a polyurethane grid polishing pad with abrasive-free acidic polishing slurry. The polishing head speed is 100 rpm, the large disk speed is 120 rpm, the flow rate is 100 mL, the Si surface is processed for 15 min, and the C surface is processed for 5 min.

[0026] 3. Clean the polished substrate thoroughly, test the final surface profile data, and verify the processing results. For example... Figure 5 As shown, Figure 5 The image shows the substrate surface data after polishing using the three-zone unequal thickness air film of the present invention in Embodiment 1 of the present invention. The final TTV value is 0.901 and the LTV value is 0.320. The overall surface flatness is high after polishing, indicating that the planarization process of large-size substrates can be achieved by using the unequal thickness air film.

[0027] Example 2 (Results of polishing a convex substrate using the three-zone unequal thickness air film of the present invention)

[0028] 1. Select a convex substrate (TTV value of 2.459 µm). Utilize the ultra-precision planarization capability of the customized air film of this invention to customize a three-region unequal thickness customized air film based on the TTV data and surface change trend of the substrate wafer. The thickness value of each region of the air film is obtained according to the thickness setting basis of each region of this invention.

[0029] 2. Perform single-piece CMP polishing on the above substrate using a polishing head equipped with the air mold described in this invention. The pressure values ​​of the first annular pressure zone, the second annular pressure zone, the third annular pressure zone, and the fourth circular pressure zone are set from the outside to the inside as 9.0 psi-6.8 psi-7.2 psi-7.2 psi, respectively. Maintain the pressure of the annular pressure zone at 12 psi. Use a polyurethane grid polishing pad with abrasive-free acidic polishing slurry. The polishing head speed is 100 rpm, the large disk speed is 120 rpm, the flow rate is 100 mL, the Si surface is processed for 15 min, and the C surface is processed for 5 min.

[0030] 3. Clean the polished substrate thoroughly, test the final surface profile data, and verify the processing results. For example... Figure 6 As shown, Figure 6The image shows the substrate surface data after polishing using the three-zone unequal thickness gas film of the present invention in Embodiment 2 of the present invention. The final TTV value is 0.866 and the LTV value is 0.356. The overall surface flatness after polishing is high, which further illustrates that using the unequal thickness gas film can achieve planarization processing of large-size substrates for substrates of different types.

[0031] Comparative Example 1 (Results after conventional air-supported membrane processing)

[0032] 1. Select a concave substrate (TTV value of 2.422 µm), choose an appropriate formulation and adjust the pressure in different zones to achieve the ideal surface shape as much as possible.

[0033] 2. The above substrate was subjected to single-piece CMP polishing using a polishing head with a traditional gas film (traditional gas film has no zone design, and the overall thickness is consistent, about 1 mm). The zone pressure values ​​of the first annular pressure zone, the second annular pressure zone, the third annular pressure zone, and the fourth circular pressure zone were set from the outside to the inside as 11psi-6.8psi-7.2psi-7.2psi (4-zone head). The pressure of the annular pressure zone was kept at 12psi. The material was a polyurethane grid polishing pad with abrasive-free acidic polishing slurry. The polishing head speed was 100 rpm, the large disk speed was 120 rpm, the flow rate was 100 ml, the Si surface was processed for 15 min, and the C surface was processed for 5 min.

[0034] 3. Clean the processed substrate thoroughly, test the final surface area data, and verify the processing results. For example... Figure 7 As shown, Figure 7 The image shown is a data diagram of the substrate surface after conventional air film polishing in Comparative Example 1 of this invention. The final TTV value is 2.800 and the LTV value is 0.894, which is not ideal.

[0035] Comparative Example 2 (Results after polishing with a non-inventory three-zone unequal thickness air film)

[0036] 1. A concave substrate was selected for the wafer (TTV value of 1.943 µm). A three-region unequal-thickness gas film was also used, but the thickness values ​​of the three regions did not meet the gas film thickness settings described in this invention. Specifically, it was modified as follows: The thickness of the air film should gradually decrease from the edge to the center. The thickness settings for the three adjacent regions, A, B and C, should be 1004µm, 1002µm and 1000µm, respectively. 2. The process parameters and material combinations of the single-piece CMP equipment remain unchanged, ensuring that the air film is the only variable in this experiment, and the same processing time is maintained to complete this polishing.

[0037] 3. Clean the polished substrate thoroughly, test the final surface profile data, and verify the processing results. For example... Figure 8As shown, Figure 8 The image shown is a substrate surface data diagram after polishing with a non-inventory three-zone unequal thickness air film, which is Comparative Example 2 of this invention. The final TTV value is 1.451 and the LTV value is 0.402, which is an improvement compared to the traditional air film, but is still not ideal compared to the air film processing results described in this invention.

[0038] Comparative Example 3 (Results after polishing with two zones of unequal thickness air film)

[0039] 1. Select a concave substrate (TTV value of 1.838 µm) and use two regions with unequal thickness gas films. The region distribution is as follows: refer to the A+B region in this invention, which is defined as region A', and region C remains unchanged. The thickness values ​​of the gas film region A' and region C are 5X+1000 µm and 1000 µm, respectively.

[0040] 2. The process parameters and material combinations of the single-piece CMP equipment remain unchanged, ensuring that the air film is the only variable in this experiment, and the same processing time is maintained to complete this polishing.

[0041] 3. Clean the polished substrate thoroughly, test the final surface profile data, and verify the processing results. For example... Figure 9 As shown, Figure 9 The image shown is a substrate surface data diagram after polishing with two regions of unequal thickness gas film in Comparative Example 3 of this invention. The final TTV value is 2.078 and the LTV value is 1.027. After reducing the number of zones, the wafer edge shows over-polishing, and the surface improvement effect is reduced.

[0042] Comparative Example 4 (Results after polishing with a four-zone unequal thickness air film)

[0043] 1. Select a concave substrate (TTV value of 2.022 µm) and use a four-region unequal thickness air film. The region distribution is as follows: referring to regions B and C in this invention, keep them unchanged, and draw a circular region with the center of the polishing head as the origin and half the radius of region A as the radius. The new region is defined as region A1, and the other part of region A is defined as region A2. The thickness values ​​of air film regions A1, A2, B and C are 5X+1000 µm, 3X+1000 µm, 2X+1000 µm and 1000 µm, respectively.

[0044] 2. The process parameters and material combinations of the single-piece CMP equipment remain unchanged, ensuring that the air film is the only variable in this experiment, and the same processing time is maintained to complete this polishing.

[0045] 3. Clean the polished substrate thoroughly, test the final surface profile data, and verify the processing results. For example... Figure 10 As shown, Figure 10The image shown is a data diagram of the substrate surface after polishing with a four-zone unequal thickness air film in Comparative Example 4 of this invention. The final TTV value is 1.553 and the LTV value is 0.846. The overall thickness deviation is low, but it still cannot meet the requirements for high surface flatness.

[0046] Note: To verify the planarization effect and local surface shape adjustment capability of the unequal thickness gas film, the above conditions were compared under the same equipment, process parameters, and material conditions. The comparison results show that the traditional gas film has very limited ability to improve the surface shape. Moreover, when the unequal thickness region of the gas film is divided into two or four zones, and the thickness difference design does not conform to the description of this invention, the thickness difference of different positions of the substrate after polishing is large, which does not meet the expected effect. However, the unequal thickness gas film in this invention can optimize TTV and LTV by about 50%, and finally meet the requirement of TTV < 1, realizing the ultra-precision planarization of large-size silicon carbide substrates.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for processing a substrate, characterized in that, Includes the following steps: Chemical mechanical polishing is performed on the substrate to be processed using a polishing head with a partitioned gas film of unequal thickness. The partitioned unequal thickness air film includes, from the center to the edge, the following in sequence: a circular region A, an annular region B, and an annular region C. The circular region A, the annular region B, and the annular region C have a gradient thickness difference at their contact surfaces with the polishing head. The substrate to be processed has a concave or convex surface. The concave surface is one that gradually rises from the center region to the edge region along the radial direction of the substrate, and the convex surface is one that gradually decreases from the center region to the edge region along the radial direction of the substrate. When the substrate to be processed is concave and the TTV value is ≤3 μm, in μm as the thickness unit, the thickness of the circular region A is (2.9~3.1) times larger than the thickness of the annular region B by a TTV value, the thickness of the circular region B is (1.9~2.1) times larger than the thickness of the annular region C by a TTV value, and the thickness of the circular region C is 990 µm~1010 µm; When the substrate to be processed is concave and the TTV value is >3 μm, in μm as the thickness unit, the thickness of the circular region A is (4.9~5.1) times larger than the thickness of the annular region B by a TTV value, the thickness of the circular region B is (4.9~5.1) times larger than the thickness of the annular region C by a TTV value, and the thickness of the circular region C is 990 µm~1010 µm; When the substrate to be processed is convex and the TTV value is ≤3 μm, in μm as the thickness unit, the thickness of the circular region A is (2.9~3.1) times smaller than the thickness of the annular region B, the thickness of the circular region B is (1.9~2.1) times smaller than the thickness of the annular region C, and the thickness of the circular region C is 990 µm~1010 µm; When the substrate to be processed is convex and the TTV value is >3 μm, in μm as the thickness unit, the thickness of the circular region A is (4.9~5.1) times smaller than the thickness of the annular region B, the thickness of the circular region B is (4.9~5.1) times smaller than the thickness of the annular region C, and the thickness of the circular region C is 990 µm~1010 µm.

2. The processing method according to claim 1, characterized in that, The polishing head includes a retaining ring pressure area, a first annular pressure area, a second annular pressure area, a third annular pressure area, and a fourth circular pressure area arranged sequentially from the outside to the inside along its radial direction. The radius of the polishing head excluding the retaining ring pressure area is 100%. The width of the first annular pressure area is 12% to 18% of the radius of the polishing head excluding the retaining ring pressure area; the width of the second annular pressure area is 32% to 38% of the radius of the polishing head excluding the retaining ring pressure area; the width of the third annular pressure area is 27% to 33% of the radius of the polishing head excluding the retaining ring pressure area; and the radius of the fourth circular pressure area is 17% to 23% of the radius of the polishing head excluding the retaining ring pressure area. During chemical mechanical polishing, the pressures of the first annular pressure zone, the second annular pressure zone, the third annular pressure zone, and the fourth circular pressure zone are (10.5~11.5) psi, (6.5~7.0) psi, (7.0~7.5) psi, and (7.0~7.5) psi, respectively.

3. The method according to claim 2, characterized in that, During chemical mechanical polishing, the pressure in the holding ring pressurization zone is (11.5~12.5) psi.

4. The method according to claim 1, characterized in that, When the substrate to be processed is concave and the TTV value is ≤3μm, the thicknesses of the circular region A, the annular region B and the annular region C are (5 times the TTV value + 1000) µm, (2 times the TTV value + 1000) µm, and 1000 µm, respectively. When the substrate to be processed is concave and the TTV value is >3 µm, the thicknesses of the circular region A, the annular region B and the annular region C are (10 times the TTV value + 1000) µm, (5 times the TTV value + 1000) µm and 1000 µm, respectively. When the substrate to be processed is convex and the TTV value is ≤3 µm, the thicknesses of the circular region A, the annular region B and the annular region C are (1000-5 times the TTV value) µm, (1000-2 times the TTV value) µm and 1000 µm, respectively. When the substrate to be processed is convex and the TTV value is >3 µm, the thicknesses of the circular region A, the annular region B and the annular region C are (1000-10 times the TTV value) µm, (1000-5 times the TTV value) µm and 1000 µm, respectively.

5. The processing method according to any one of claims 1 to 4, characterized in that, The radius of the circular region A is 45% to 55% of the radius of the unequal thickness air film in the partition; The width of the annular region C is 5% to 15% of the radius of the unequal thickness air film in the partition; The width of the annular region B is 35% to 45% of the radius of the unequal thickness air film of the partition.

6. The processing method according to claim 5, characterized in that, The radius of the circular region A is 49% to 51% of the radius of the unequal thickness air film in the partition; The width of the annular region C is 9% to 11% of the radius of the unequal thickness air film in the partition; The width of the annular region B is 39% to 41% of the radius of the unequal thickness air film of the partition.

7. The processing method according to any one of claims 1 to 3, characterized in that, The unequal thickness gas film in the partitioned section has an overall thickness that gradually changes radially from the center to the edge on the side that contacts the substrate to be processed.

8. The processing method according to any one of claims 1 to 4, characterized in that, Chemical mechanical polishing is performed on both sides of the substrate to be processed, and the removal amount on both sides of the substrate to be processed is 1.5 μm to 2 μm.

9. The processing method according to any one of claims 1 to 4, characterized in that, The substrate to be processed is a silicon carbide substrate, a diamond substrate, a gallium nitride substrate, or a gallium arsenide substrate.

10. The processing method according to any one of claims 1 to 4, characterized in that, The substrate to be processed is at least 6 inches in size.

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