A method for roughening the back surface of a sapphire wafer

Abstract

This invention relates to a method for roughening the back side of sapphire wafers. Based on a planetary double-sided polishing machine platform, the method first attaches the front side of a low-TTV sapphire wafer, after double-sided fine grinding and polishing, to the surface of a ceramic disk. Next, the ceramic disk is fixed to a planetary wheel, which is then placed on a lower polishing disk, with the back side of the wafer facing down. The upper polishing disk is disabled. Using a sun gear and internal gear transmission mechanism, the planetary wheel rotates on the lower polishing disk, forming a precision polishing interface. Roughening of the back side of the sapphire wafer is achieved by adjusting the rotational speeds of the sun gear, internal gear, and planetary wheel. This method, on the one hand, relies on the double-sided polishing process to achieve wafer thickness uniformity and parallelism control; on the other hand, through a combination of equipment design and process innovation, it achieves low TTV control for the resulting single-polished wafer during the roughening process. It is suitable for 8-12 inch sapphire wafers and can be applied to fields requiring high-precision thickness control, such as LED or semiconductor manufacturing.

Description

Technical Field

[0001] This invention relates to the field of crystal material processing technology, and specifically to a method for roughening the back surface of a sapphire wafer. Background Technology

[0002] Sapphire substrates are crucial materials in semiconductor lighting, optoelectronic devices, and other fields. The back surface roughness processing technology directly affects the transmittance, luminous efficiency, and reliability of these devices. As LEDs, lasers, and other devices evolve towards larger sizes and higher performance, the requirements for total thickness variation (TTV) of the substrate have significantly increased. In the future, with the mass production of 12-inch substrates and the expansion of new application scenarios such as Mini / Micro LEDs, TTV standards may become even more stringent. Traditional single-sided polishing processes use waxing or adsorption pads to fix the wafer, but due to their asymmetric processing, the thickness of the removed layers on both sides is inconsistent, leading to a significant increase in wafer TTV.

[0003] Against this backdrop, the "double-polishing to single-polishing" process technology has emerged. This technology, through selective surface treatment, transforms the double-sided ultra-smooth structure of traditional double-polished wafers into an asymmetric morphology of "single-sided polishing + single-sided roughening." For example, sandblasting or etching roughening of the back side of the substrate (non-epitaxial side) can improve light extraction efficiency, optimize interface adhesion, and improve thermal conductivity without damaging the polished layer on the front side. While sandblasting roughening is low-cost, it may result in poor control of roughness uniformity, with higher Ra values ​​leading to poorer uniformity. Traditional methods such as wet etching have poor reactivity with sapphire, and the concentrated acids and alkalis used pose environmental risks. Dry etching equipment requires high investment, and currently there is no equipment available for 8-inch or larger wafers.

[0004] Chinese patent CN217750973U discloses a single-sided grinding structure for sapphire wafers. The inner diameter of its planetary gear (approximately 100mm) is only suitable for processing small wafers of 4 inches and below. Moreover, its sun gear can only drive a single planetary gear, making it a single-station experimental device that cannot meet the high-efficiency industrial production requirements of large-size wafers.

[0005] Chinese patent CN106863025A discloses a method for repairing defects on the back side of 2-inch and 4-inch sapphire substrates. It discloses the use of a double-sided grinding machine platform for single-sided grinding, but its core purpose is to repair existing defects, rather than to achieve a "morphological transformation" from double-polished to single-polished while maintaining a low TTV. Moreover, the processing object is a small-sized 2-4 inch sapphire wafer, and it does not involve the processing challenges of large-sized 8-12 inch wafers. It also does not disclose how to achieve back-side roughening without TTV degradation under no additional pressure conditions through the synergy of multiple planetary gears, optimization of rotation speed ratio, and the combined effect of high-rigidity ceramic disks and planetary gears.

[0006] This invention is based on a planetary double-sided grinding machine platform and aims to achieve back-side roughening of large-size 8-12 inch sapphire wafers. To achieve this goal and ensure mass production efficiency, a system is employed where a sun gear synchronously drives multiple planetary gears that carry the wafers. By precisely setting the rotational speed ratio between the sun gear, internal gear, and planetary gears, combined with a specific high-rigidity ceramic disk mounting process, high throughput is achieved while ensuring high uniformity and low TTV control in the back-side roughening of large-size wafers. Summary of the Invention

[0007] The purpose of this invention is to provide a method for roughening the back surface of sapphire wafers, which effectively solves the problems of poor roughness uniformity and large TTV after roughening the back surface of large-size sapphire wafers in the prior art, and reduces costs.

[0008] The technical solution of this invention to solve the technical problem is as follows: A method for roughening the back side of a sapphire wafer, based on a planetary double-sided grinding machine platform, firstly fixes the front side of a sapphire wafer that has been pre-finished and polished on both sides onto a ceramic disk, then fixes the ceramic disk onto a planetary wheel, and then places the planetary wheel on a lower grinding disk, while disabling the upper grinding disk, wherein the back side of the sapphire wafer faces the lower grinding disk. Using a sun gear and an internal gear transmission mechanism, the planetary wheel is made to rotate on the lower grinding disk to form a precision grinding interface, thereby reconstructing the surface of the back side of the sapphire wafer and achieving roughening of the back side of the sapphire. At the same time, the low-stress substrate after double-sided polishing is used to suppress deformation.

[0009] The fundamental difference between this invention and the prior art is that this invention is for 8-12 inch large-size sapphire wafers. On a double-polished wafer with good thickness uniformity (TTV≤3μm) and high surface quality (Ra≤0.5nm), the morphology transformation from a double-polished wafer to a single-polished wafer is achieved through a back roughening process, while keeping the TTV at a low value (usually ≤4μm). Its core technology is reflected in the following synergistic effects: (1) A high-rigidity, high-flatness ceramic disk with a diameter of 400~560mm is used as the attachment carrier. Its elastic modulus matches that of sapphire, which can achieve uniform back-side grinding and effectively resist system vibration under no external pressure conditions; (2) By using a specific speed ratio (1:(3~5)) between the sun gear and the internal gear, and controlling the rotation and revolution speed of the planetary gear, the large-size wafers on multiple planetary gears are subjected to uniform force during the grinding process, avoiding over-grinding of the edges, which is a problem that does not need to be considered in small-size processes; (3) The upper grinding disk is not used in the entire roughening process. Only the lower grinding disk and the planetary gear system are used to complete single-sided grinding. Combined with boron carbide grinding fluid with a specific particle size (D50 is 60~80μm), micron-level surface reconstruction is achieved instead of deep removal, thereby maximizing the preservation of the original TTV.

[0010] Through the design of this roughening equipment and innovative process flow, on the one hand, the TTV uniformity and parallelism of sapphire wafers, both inside and between different batches, are controlled by relying on double-sided polishing technology; on the other hand, by disabling the upper polishing disc and only activating the rotation of the lower polishing disc, a planetary wheel combined with a high-rigidity ceramic disc composite polishing system is used to perform micron-level surface reconstruction on the back of the sapphire wafer without applying additional pressure, which can minimize the impact of roughening processing on TTV and achieve low TTV control for large-size single-polished wafers. Therefore, this method can be applied to fields such as LED or semiconductor manufacturing that require high-precision thickness control.

[0011] A method for roughening the back surface of a sapphire wafer includes the following steps:

[0012] Step 1, Surface Mount Protection: Using a high-precision automatic surface mounter and liquid wax, the front side of the sapphire wafer, which has undergone double-sided fine grinding and polishing, is fixed onto a ceramic disk;

[0013] Step 2, Backside Roughening: Fix the ceramic disk with the sapphire wafer fixed in Step 1 onto the planetary wheel of the double-sided grinding machine, and then place the planetary wheel on the lower grinding disk so that the backside of the sapphire wafer faces the lower grinding disk. Turn off the upper grinding disk and use the sun gear and internal gear transmission mechanism to drive the planetary wheel to rotate on the lower grinding disk. With the help of roughening polishing fluid, the backside of the sapphire wafer is roughened.

[0014] Step 3, Cleaning and Annealing: The sapphire wafer obtained in Step 2 after back roughening is cleaned with alkaline and acidic solutions in sequence, and then annealed after drying.

[0015] In step one, a high-precision automatic chip mounter is used to fix the front side of the double-sided finely ground and polished sapphire wafer onto a ceramic disk with a diameter of 400~560mm using liquid wax, with a wax-spinning speed of 1000~3000rpm.

[0016] After the liquid wax solidifies, it forms a buffer layer that can absorb vibrations generated during subsequent roughening processes, protecting the polished surface (front side of the sapphire wafer) from damage.

[0017] In step one, the sapphire wafer that has undergone double-sided fine grinding and polishing has a surface roughness Ra≤0.5nm, a total thickness deviation TTV≤3μm, and no defects such as scratches, gaps, or orange peel on the surface.

[0018] In step two, the size of the planetary wheel is larger than the size of the ceramic disk, and the diameter of the ceramic disk is 400~560mm.

[0019] In step two, the upper grinding disc is disabled during the entire back roughening process, and only the lower grinding disc is used. The lower grinding disc rotates at 10~30 rpm, the planetary wheel rotates at 10~20 rpm, and the planetary wheel revolves at 0~0.2 rpm. The planetary wheel with ceramic disc is driven to rotate by the sun gear and internal gear, without the need to apply additional pressure.

[0020] In step two, the ratio of the rotational speeds of the internal gear and the sun gear is 1:(3~5), where the internal gear rotates at 2~15 rpm and the sun gear rotates at 6~45 rpm, to avoid excessive edge wear caused by centrifugal force.

[0021] In step two, the roughening temperature is 20~40℃ and the roughening time is 5~20min;

[0022] In step two, the flow rate of the roughening polishing fluid is 100~500mL / min. The roughening polishing fluid includes boron carbide powder, suspending dispersant and water, and the ratio of the three is boron carbide powder: suspending dispersant: water = (5~15kg): 1L: 50L. The particle size D50 of the boron carbide powder is 60~80μm, which improves the roughening processing efficiency and reduces scratches.

[0023] In step three, the alkaline solution cleaning can saponify grease, decompose liquid wax residue and organic matter, and help remove positively charged particles or ions. The concentration of the alkaline solution is 1~5wt%, including one or more mixed solutions of sodium hydroxide and potassium hydroxide. The cleaning method is soaking combined with mechanical brushing.

[0024] In step three, the acidic solution can dissolve metal impurities through chemical reaction and reduce physically adsorbed particles. The concentration of the acidic solution is 1~10wt%, including one or more mixed solutions of hydrochloric acid and sulfuric acid. The cleaning temperature is 40±5℃, the cleaning time is 5~10 minutes, and it is supplemented by shaking or ultrasonic cleaning. Alkali washing tank, rinsing tank, acid washing tank and multiple rinsing tanks are set up in sequence to ensure that the chemical residue is completely removed. High-purity deionized water is used for rinsing. Finally, after spin drying, it enters the annealing process.

[0025] In step three, the sapphire wafer spacer after back roughening is placed in a graphite boat for annealing. The annealing atmosphere is a vacuum. Annealing can eliminate lattice distortion and residual stress during processing, and optimize lattice integrity.

[0026] In step three, the annealing process is divided into a heating stage, a holding stage, and a cooling stage. The heating stage involves heating from room temperature to a maximum temperature of 1400~1600℃ with a heating gradient of 1.0~5.0℃ / min. The holding stage involves holding at the maximum temperature for 6~12 hours. The cooling stage involves slowly cooling to room temperature with a cooling gradient of 0.5~3℃ / min.

[0027] After annealing, the sapphire wafer is cleaned, and the surface roughness Ra of the front and back sides is measured. The surface roughness is measured using an atomic force microscope, and the surface roughness is measured using a roughness meter. The total thickness deviation (TTV) is measured using a fully automated surface profile inspection device.

[0028] Compared with the prior art, the beneficial effects of the present invention lie in the design of the single-sided roughening process and the control of low TTV after roughening of large-size wafers, as follows:

[0029] (1) The back roughening process of the present invention involves a unique equipment configuration. The entire roughening process does not require equipment modification. It only forms a single-sided processing system by disabling the upper grinding disc and retaining the lower grinding disc, and combines it with planetary gear transmission to achieve single-sided grinding, thereby realizing micron-level surface reconstruction of the non-adhesive surface (back side).

[0030] (2) The planetary wheel, in conjunction with the high-rigidity ceramic disk, can resist deformation under grinding pressure, ensure the flatness of the grinding, and ensure that the total thickness deviation (TTV) of the sapphire wafer reaches the minimum. After double-sided polishing, the sapphire wafer mainly changes the surface morphology before and after the single-sided roughening process, and the overall thickness distribution does not change. Therefore, the TTV value is kept at a small value. Thus, compared with the traditional process, the sapphire wafer processed by the roughening process of this invention has a smaller TTV and better concentration.

[0031] (3) This invention targets large-size sapphire wafers of 8 to 12 inches. It drives multiple planetary gears to work synchronously through a sun gear and optimizes the speed ratio of the sun gear, internal gear and planetary gear. This solves the problem of edge over-grinding and TTV deterioration caused by centrifugal force in planetary grinding of large-size sapphire wafers. This is a technical problem that has not been addressed in the processing technology of small-size sapphire wafers.

[0032] (4) The present invention uses boron carbide polishing slurry with a specific particle size (D50=60~80μm) to achieve efficient and uniform back roughening without external pressure, avoiding the environmental unfriendly and poor uniformity problems of traditional sandblasting or etching processes, and is especially suitable for mass production of large-size sapphire wafers. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the sapphire wafer back surface roughening method of the present invention;

[0034] Figure 2 This is a schematic diagram of the sapphire wafer back surface roughening device of the present invention, wherein: 1-upper grinding disc, 2-lower grinding disc, 3-internal gear, 4-sun gear, 5-planet gear;

[0035] Figure 3This is a schematic diagram of the sapphire wafer fixing process in the sapphire wafer back roughening method of the present invention, wherein: 5-planetary wheel, 6-ceramic disk, 7-sapphire wafer. Detailed Implementation

[0036] The features and advantages of the present invention will be described in detail through specific embodiments and in conjunction with the accompanying pictures.

[0037] Example 1:

[0038] Part 1: Pre-processing of 12-inch sapphire wafers:

[0039] Step 1, Pre-processing: The sapphire crystal ingot is wire-cut into sapphire wafers with a diameter of 12 inches and a thickness of 1150±20μm. The wire-cut sapphire wafers are then double-sided polished using boron carbide polishing slurry on a cast iron polishing disc. After polishing, the thickness of the sapphire wafers is 900±5μm. After cleaning, the sapphire wafers are T-shaped chamfered with a face width of 250±100μm on both sides and a diameter of 300.0±0.2mm.

[0040] Step 2, Double-sided fine grinding and polishing: The annealed sapphire wafer is finely ground on both sides using molten diamond solution. The grinding disc is a resin disc, the grinding speed is 28 rpm, and the pressure is 350 g / cm. 2 The grinding time was 60 minutes, the removal rate was 90 μm, and the thickness of the sapphire wafer after double-sided fine grinding was 810±5 μm. The finely ground sapphire wafer was then subjected to double-sided chemical mechanical polishing using a highly wear-resistant and chemically resistant elastic polyurethane pad and an alumina polishing slurry with a particle size of 2 μm. The polishing speed was 25 rpm and the pressure was 450 g / cm². 2 Polishing time ≥120 minutes, the finished sapphire wafer Ra≤0.5nm, thickness 775±50μm, TTV is 2.5μm.

[0041] Part Two: Backside Roughening of Sapphire Wafers

[0042] Step 1, Patch Protection: Using a high-precision patch machine, the front side of the sapphire wafer 7, which has undergone double-sided fine grinding and polishing in the first part, is pasted onto the ceramic disk 6. Liquid wax is used, and the wax spinning speed is 2000 rpm. When illuminated with a flashlight, there are no bubbles larger than 3mm.

[0043] Step 2, Backside Roughening: Place the ceramic disk 6 with the sapphire wafer 7 attached onto the planetary wheel 5 of the double-sided polishing machine platform. Place the planetary wheel 5 on the lower polishing disk 2 so that the backside of the sapphire wafer 7 faces the lower polishing disk 2. Disable the upper polishing disk 1 and start the lower polishing disk 2 to begin operation: the planetary wheel 5 rotates at 10 rpm, the planetary wheel 5 revolves at 0 rpm, the roughening polishing fluid flow rate is 200 mL / min, and the roughening time is 5 min. The roughening polishing fluid composition is boron carbide: suspending agent: water = 10 kg: 1.5 L: 50 L, and the boron carbide particle size D50 is 80 μm.

[0044] Step 3, Cleaning and Annealing: The roughened sapphire wafer 7 is ultrasonically cleaned sequentially using an alkaline solution containing sodium hydroxide and an acidic solution containing hydrochloric acid; the cleaned and dried sapphire wafer 7 is placed in a graphite boat for vacuum annealing, heated to 1450°C at a rate of 3°C / min, kept at 1450°C for 6 hours, and then slowly cooled to room temperature at a cooling gradient of 1.5°C / min.

[0045] Part Three, Testing:

[0046] The annealed sapphire wafer with roughened back side is inspected using an automatic surface morphology and thickness measuring device, and a roughness meter and atomic force microscope.

[0047] Test data results:

[0048] The roughening process of this invention transforms double-sided polished sapphire wafers into single-sided polished wafers. The Ra of the roughened back surface is 1.0±0.2μm, and the total thickness deviation (TTV) is 4μm. Compared with the traditional single-sided polishing process, the TTV obtained by this roughening method is smaller. Microscopic observation shows that there are no scratches or other defects on the front side of the wafer, which meets the product quality requirements.

[0049] Example 2:

[0050] Part 1: Pre-processing of 12-inch sapphire wafers:

[0051] Step 1, Pre-processing: The sapphire crystal ingot is wire-cut into sapphire wafers with a diameter of 12 inches and a thickness of 1380±20μm. The wire-cut sapphire wafers are then double-sided polished using boron carbide polishing slurry on a cast iron polishing disc. After polishing, the thickness of the sapphire wafers is 1100±5μm. After cleaning, the sapphire wafers are T-shaped chamfered with a face width of 250±100μm on both sides and a diameter of 300.0±0.2mm.

[0052] Step 2, Double-sided fine grinding and polishing: The annealed sapphire wafer is finely ground on both sides using molten diamond. The grinding pad is a honeycomb pad, the grinding speed is 30 rpm, and the pressure is 300 g / cm.2 The grinding time was 50 minutes, the removal rate was 80μm, and the thickness of the sapphire wafer after double-sided fine grinding was 1020±5μm. The finely ground sapphire wafer was then subjected to double-sided chemical mechanical polishing using a highly wear-resistant and chemically resistant elastic polyurethane pad and an alumina polishing slurry with a particle size of 2μm. The polishing speed was 30rpm and the pressure was 300g / cm. 2 Polishing time ≥ 120 minutes, the finished sapphire wafer Ra ≤ 0.5nm, thickness 1005±20μm, TTV is 2.0μm.

[0053] Part Two: Backside Roughening of Sapphire Wafers

[0054] Step 1, Patch Protection: Using a high-precision patch machine, the front side of the sapphire wafer 7, which has undergone double-sided fine grinding and polishing in the first part, is pasted onto the ceramic disk 6. Liquid wax is used, and the wax spinning speed is 3000 rpm. When illuminated with a flashlight, there are no bubbles larger than 3mm.

[0055] Step 2, Backside Roughening: Place the ceramic disk 6 with the sapphire wafer 7 attached onto the planetary wheel 5 of the double-sided polishing machine platform. Place the planetary wheel 5 on the lower polishing disk 2, so that the backside of the sapphire wafer 7 faces the lower polishing disk 2. Disable the upper polishing disk 1 and start the lower polishing disk 2 to begin working: the planetary wheel 5 rotates at 15 rpm, the planetary wheel 5 revolves at 0.1 rpm, the roughening polishing fluid flow rate is 250 mL / min, and the roughening time is 8 min. The roughening polishing fluid composition is boron carbide: suspending agent: water = 11 kg: 1.5 L: 50 L, and the boron carbide particle size D50 is 82 μm.

[0056] Step 3, Cleaning and Annealing: The roughened sapphire wafer 7 is ultrasonically cleaned sequentially using an alkaline solution containing sodium hydroxide and an acidic solution containing hydrochloric acid; the cleaned and dried sapphire wafer 7 is placed in a graphite boat for vacuum annealing, heated to 1450℃ at a rate of 2.5℃ / min, kept at 1450℃ for 6 hours and then slowly cooled to room temperature at a cooling gradient of 1.2℃ / min.

[0057] Part Three, Testing:

[0058] The annealed sapphire wafer with roughened back side is inspected using an automatic surface morphology and thickness measuring device, and a roughness meter and atomic force microscope.

[0059] Test data results:

[0060] The roughening process of this invention transforms double-sided polished sapphire wafers into single-sided polished wafers. The Ra of the roughened back surface is 1.0±0.2μm, and the total thickness deviation (TTV) is 3μm. Compared with the traditional single-sided polishing process, the TTV obtained by this roughening method is smaller. Microscopic observation shows that there are no scratches or other defects on the front side of the wafer, which meets the product quality requirements.

[0061] Example 3:

[0062] Part 1: Pre-processing of 8-inch sapphire wafers:

[0063] Step 1, Pre-processing: The sapphire crystal ingot is wire-cut into sapphire wafers with a diameter of 8 inches and a thickness of 1380±20μm. The wire-cut sapphire wafers are then double-sided polished using boron carbide polishing slurry on a cast iron polishing disc. After polishing, the thickness of the sapphire wafers is 1100±5μm. After cleaning, the sapphire wafers are T-shaped chamfered with a face width of 250±100μm on both sides and a diameter of 200.0±0.2mm.

[0064] Step 2, Double-sided fine grinding and polishing: The annealed sapphire wafer is finely ground on both sides using molten diamond, with a honeycomb pad pattern, at a grinding speed of 30 rpm and a pressure of 220 g / cm. 2 The grinding time was 80 minutes, the removal rate was 80 μm, and the thickness of the sapphire wafer after double-sided fine grinding was 1020±5 μm. The finely ground sapphire wafer was then subjected to double-sided chemical mechanical polishing using a highly wear-resistant and chemically resistant elastic polyurethane pad and an alumina polishing slurry with a particle size of 2 μm. The polishing speed was 30 rpm and the pressure was 250 g / cm². 2 Polishing time ≥ 120 minutes, the finished sapphire wafer Ra ≤ 0.5nm, thickness 1005±50μm, TTV is 2μm.

[0065] Part Two: Backside Roughening of Sapphire Wafers

[0066] Step 1, Patch Protection: Using a high-precision patch machine, the front side of the sapphire wafer 7, which has undergone double-sided fine grinding and polishing in the first part, is pasted onto the ceramic disk 6. Liquid wax is used, and the wax spinning speed is 1500 rpm. When illuminated with a flashlight, there are no bubbles larger than 3mm.

[0067] Step 2, Backside Roughening: Place the ceramic disk 6 with the sapphire wafer 7 attached onto the planetary wheel 5 of the double-sided polishing machine platform. Place the planetary wheel 5 on the lower polishing disk 2 so that the backside of the sapphire wafer 7 faces the lower polishing disk 2. Disable the upper polishing disk 1 and start the lower polishing disk 2 to begin operation: the planetary wheel 5 rotates at 20 rpm, the planetary wheel 5 revolves at 0.2 rpm, the roughening polishing fluid flow rate is 300 mL / min, and the roughening time is 10 min. The roughening polishing fluid composition is boron carbide: suspending agent: water = 13 kg: 1.5 L: 50 L, and the boron carbide particle size D50 is 80 μm.

[0068] Step 3, Cleaning and Annealing: The roughened sapphire wafer 7 is ultrasonically cleaned sequentially using an alkaline solution containing sodium hydroxide and an acidic solution containing hydrochloric acid; the cleaned and dried sapphire wafer 7 is placed in a graphite boat for vacuum annealing, heated to 1450℃ at a rate of 3.5℃ / min, kept at 1450℃ for 6 hours and then slowly cooled to room temperature, with a cooling gradient of 1.8℃ / min.

[0069] Part Three, Testing:

[0070] The annealed sapphire wafer with roughened back side is inspected using an automatic surface morphology and thickness measuring device, and a roughness meter and atomic force microscope.

[0071] Test data results:

[0072] The roughening process of this invention transforms double-sided polished sapphire wafers into single-sided polished wafers. The Ra of the roughened back surface is 0.75±0.15μm, and the total thickness deviation (TTV) is 3μm. Compared with the traditional single-sided polishing process, the TTV of this roughening method is relatively small. Microscopic observation shows that there are no scratches or other defects on the front side of the wafer, which meets the product quality requirements.

[0073] Comparison 1: 12-inch traditional single throw:

[0074] Step 1, Pre-processing: The sapphire crystal ingot is wire-cut into sapphire wafers with a diameter of 12 inches and a thickness of 1380±20μm. The wire-cut sapphire wafers are then double-sided polished using boron carbide polishing slurry on a cast iron polishing disc, resulting in a wafer thickness of 1055±5μm. The sapphire wafers are then ultrasonically cleaned sequentially using an alkaline solution containing sodium hydroxide and an acidic solution containing hydrochloric acid. After cleaning and drying, the sapphire wafers are placed in a graphite boat for vacuum annealing. The temperature is increased to 1450℃ at a rate of 3℃ / min, held at 1450℃ for 6 hours, and then slowly cooled to room temperature at a cooling gradient of 1.5℃ / min. After annealing, the sapphire wafers are T-shaped chamfered, with both sides having a face width of 250±100μm and a diameter of 300.0±0.2mm.

[0075] Step 2, Single-sided polishing: Single-sided polishing is performed using an alumina polishing slurry with a particle size of 2μm. The carrier is a wax-free pad made of highly wear-resistant and chemical-resistant elastic non-woven fabric. The polishing speed is 45 rpm, and the pressure is 400 g / cm. 2 The grinding time was 240 minutes, the removal amount was 45μm, and the thickness of the wafer after polishing was 1010±5μm; the processed wafer Ra≤0.3nm, the thickness was about 1005±20μm, and the TTV was 15μm;

[0076] Microscopic examination revealed no scratches or other defects on the front of the wafer, indicating it met product quality requirements, but the total volume (TTV) was significantly larger.

[0077] Comparison 2: 8-inch traditional single throw:

[0078] Step 1, Pre-processing: The sapphire crystal ingot is wire-cut into sapphire wafers with a diameter of 8 inches and a thickness of 1380±20μm. The wire-cut sapphire wafers are then double-sided polished using boron carbide polishing slurry on a cast iron polishing disc, resulting in a wafer thickness of 1055±5μm. The sapphire wafers are then ultrasonically cleaned sequentially using an alkaline solution containing sodium hydroxide and an acidic solution containing hydrochloric acid. After cleaning and drying, the wafers are vacuum annealed, heated to 1450℃ at a heating rate of 3℃ / min, held at 1450℃ for 6 hours, and then slowly cooled to room temperature at a cooling gradient of 1.5℃ / min. After annealing, the sapphire wafers are T-beveled, with both sides having a face width of 250±100μm and a diameter of 200.0±0.2mm.

[0079] Step 2, Single-sided grinding and polishing: Using a high-precision pick-and-place machine, attach the back of the grinding disc to the ceramic disc. Use liquid wax, spin-wax at 2000 rpm, and ensure no bubbles larger than 3mm are visible when illuminated with a flashlight. Then, perform single-sided grinding with diamond liquid, using a copper disc and a highly wear-resistant and chemical-resistant diamond liquid. Grinding speed is 45 rpm, pressure is 300 g / cm. 2 The grinding time was 35 minutes, the removal amount was 35μm, and the wafer thickness after grinding was 1020±5μm. The sapphire wafers after single-sided grinding were then polished on one side using an alumina polishing slurry with a particle size of 2μm. The carrier was a wax-free pad made of highly wear-resistant and chemical-resistant elastic non-woven fabric. The polishing speed was 45rpm and the pressure was 400g / cm. 2 The grinding time was 90 minutes, the removal amount was 15μm, the processed wafer Ra≤0.3nm, the thickness was 1005±20μm, and the TTV was 10μm;

[0080] Microscopic examination revealed no scratches or other defects on the front of the wafer, indicating it met product quality requirements, but the total volume (TTV) was significantly larger.

Claims

1. A method for roughening the back surface of a sapphire wafer, characterized in that, Includes the following steps: Step 1, Patch Protection: Fix the front side of the sapphire wafer (7) that has been finely ground and polished on both sides onto the ceramic disk (6). The surface roughness Ra of the sapphire wafer (7) is ≤0.5nm, the total thickness deviation TTV is ≤3μm, and the diameter is 8~12 inches. Step 2, back roughening: Fix the ceramic disk (6) with the sapphire wafer (7) fixed on it obtained in Step 1 onto the planetary wheel (5), and then place the planetary wheel (5) on the lower grinding disk (2) with the back of the sapphire wafer (7) facing the lower grinding disk (2). Drive the planetary wheel (5) to rotate on the lower grinding disk (2) using the transmission mechanism of the sun gear (4) and the internal gear (3). With the roughening polishing fluid, roughen the back of the sapphire wafer (7). The upper grinding disk (1) is not used throughout the process. The speed of the internal gear (3) is 2~15 rpm, the speed of the sun gear (4) is 6~45 rpm, the speed ratio of the internal gear (3) and the sun gear (4) is 1:(3~5), the rotation speed and revolution speed of the planetary wheel (5) are 10~20 rpm and 0~0.2 rpm respectively, and the speed of the lower grinding disk (2) is 10~30 rpm. Step 3, Cleaning and Annealing: The sapphire wafer (7) obtained in Step 2 after back roughening is cleaned, dried and then annealed. The TTV of the final sapphire wafer (7) is ≤4μm.

2. The sapphire wafer back surface roughening method as described in claim 1, characterized in that, In step one, a high-precision automatic chip mounter is used to bond and fix the sapphire wafer (7) that has been finely ground and polished on both sides onto a ceramic disk (6) using liquid wax. The wax spin speed is 1000~3000 rpm.

3. The method for roughening the back surface of a sapphire wafer as described in claim 1, characterized in that, In step two, the planetary wheel (5) is larger than the ceramic disk (6), and the diameter of the ceramic disk (6) is 400~560mm.

4. The sapphire wafer back surface roughening method as described in claim 1, characterized in that, In step two, the roughening time is 5~20 min and the roughening temperature is 20~40℃.

5. The method for roughening the back surface of a sapphire wafer as described in claim 1, characterized in that, In step two, the flow rate of the roughening grinding fluid is 100~500mL / min. The roughening grinding fluid includes boron carbide powder, suspending dispersant and water, wherein the ratio of boron carbide powder: suspending dispersant: water is (5~15kg): 1L: 50L, and the particle size D50 of boron carbide powder is 60~80μm.

6. The method for roughening the back surface of a sapphire wafer as described in claim 1, characterized in that, In step three, alkaline and acidic solutions are used for cleaning in sequence. The alkaline solution includes a mixture of one or more of sodium hydroxide and potassium hydroxide; the acidic solution includes a mixture of one or more of hydrochloric acid and sulfuric acid.

7. The sapphire wafer back surface roughening method as described in claim 6, characterized in that, In step three, the concentration of the alkaline solution is 1~5wt%, and the cleaning method is soaking combined with mechanical brushing. After cleaning, rinse with deionized water. The concentration of the acidic solution is 1~10wt%, the cleaning temperature is 40±5℃, the cleaning time is 5~10 minutes, and the cleaning is supplemented by shaking or ultrasonication. After cleaning, rinse with deionized water and spin dry.

8. The method for roughening the back surface of a sapphire wafer as described in claim 1, characterized in that, In step three, the sapphire wafer (7) after back roughening is placed in a graphite boat and annealed under vacuum. First, the temperature is raised to 1400~1600℃ at 1.0~5.0℃ / min, then kept at a constant temperature for 6~12h, and finally cooled to room temperature at 0.5~3℃ / min.

Images