Wafer polishing method

Abstract

The application discloses a wafer polishing method, comprising the following steps: preparing a rough polishing pad and a fine polishing pad; after a wafer to be polished is put into a phosphoric acid solution to soak an activation reaction interface, and temperature measurement meets polishing requirements, the wafer is placed on a heating carrier, and after ultrasonic pretreatment of a polishing solution, rough polishing is carried out first, then fine polishing is carried out, and a polished wafer is obtained after cleaning. The method can effectively improve TTv of the obtained wafer to be less than 2 microns, and meanwhile, flatness of the product is improved, warping of the wafer is less than 20 microns, and bowing of the wafer is less than 8 microns.

Description

Technical Field

[0001] This application relates to the field of crystal polishing technology, and in particular to a wafer polishing method. Background Technology

[0002] Sapphire is a high-purity, high-performance single-crystal alumina material with extremely high hardness (Mohs hardness 9, second only to diamond). It also possesses excellent optical transmittance (covering the ultraviolet to mid-infrared band), high temperature resistance (melting point approximately 2045℃), corrosion resistance, and low dielectric loss, making it widely used in optoelectronics, LEDs and semiconductors, and aerospace. Ruby, like sapphire, belongs to the corundum mineral family. Ruby also exhibits high hardness (Mohs hardness 9), wear resistance, chemical stability, and good optical properties, and is used in laser applications and precision instruments.

[0003] The main processing steps for crystals currently involve dicing, grinding, and polishing. Precision grinding and polishing of wafers can achieve ultra-smooth and damage-free surfaces. Polishing, in particular, as the final step in machining, effectively unifies and improves the flatness and integrity of the wafer surface. Commonly used polishing methods include copper polishing and chemical mechanical polishing.

[0004] The surface quality and material removal rate of the finished wafer are affected by the polishing process parameters. The wafer material removal rate is mainly controlled by the particle size and polishing pressure parameters.

[0005] In current polishing processes, polishing pads are often laid out, and the polishing disc polishes the wafer surface by grinding the polishing pads. However, the frequent replacement of polishing pads in current polishing processes increases production costs. On the other hand, reducing the replacement frequency can lead to inconsistent material removal rates between the inner and outer rings of the wafer, resulting in thickness variations. Furthermore, current wafer polishing is divided into rough grinding and fine grinding. Before rough grinding, the surface material of the wafer has poor activity, leading to longer polishing times and increased accumulation of non-uniform wear deformation on the surface of the polishing pads, affecting the quality of rough grinding and consequently, the quality of fine grinding.

[0006] The information disclosed in the background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] This application provides a wafer polishing method to address the above-mentioned technical problems. This method can effectively improve the TTv of the obtained wafer to <2μm, while improving the flatness of the product: the warp of the wafer to <20μm and the bow to <8μm.

[0008] This application provides a wafer polishing method, including the following steps: Preparation of coarse grinding polishing pads and fine grinding polishing pads; After the polishing wafer is immersed in phosphoric acid solution to activate the reaction interface, and the temperature is measured to meet the polishing requirements, it is placed on a heated carrier plate. After ultrasonic pretreatment of the polishing solution, coarse polishing is performed first, followed by fine polishing, and then cleaning is performed to obtain the polished wafer. The polishing pad used in coarse grinding and polishing is a coarse grinding polishing pad, and the particle size of the abrasive added to the coarse grinding polishing pad is 710~850nm; The polishing pad used in fine grinding and polishing is a fine grinding and polishing pad; the particle size of the abrasive added to the fine grinding and polishing pad is 24~31nm.

[0009] Preferably, the preparation methods for both coarse grinding polishing pads and fine grinding polishing pads are as follows: after mixing the raw materials evenly, scraping them flat to form a film, shaping them, and then heating and curing them.

[0010] Preferably, the raw materials include: polyamide with a linear density of 8-10D, short fibers of polyacrylonitrile, polyacrylate prepolymer, abrasive, and benzoyl peroxide initiator.

[0011] Preferably, the short fibers of polyamide and polyacrylonitrile are mixed in a volume ratio of 1:1; The polyamide short fibers used are polyamide fibers with a length of 29~38mm:51~65mm, mixed in a volume ratio of 3:1; The polyacrylonitrile short fibers used are polyacrylonitrile fibers with a length of 29~38mm:51~65mm, mixed in a volume ratio of 5:1.

[0012] Preferably, the amount of polyacrylate prepolymer used is 32-41 wt% of the mass of the short fiber mixture used; the amount of benzoyl peroxide added is 1% of the mass of the polyacrylate prepolymer.

[0013] Preferably, the abrasive is alumina powder material; the amount of abrasive added is 13~21wt% of the mass of the short fiber mixture used.

[0014] Preferably, the abrasive particle size in the polishing slurry used for coarse grinding is 1~1.2μm; and the abrasive particle size in the polishing slurry used for fine grinding is 320~431nm.

[0015] Preferably, the concentration of the phosphoric acid solution used is between 83% and 88%; the wafer is immersed in the phosphoric acid solution at 80 to 100°C for at least 30 minutes.

[0016] Preferably, the temperature measurement to meet the polishing requirements is to measure the temperature of the wafer to 50~60℃ using an infrared thermometer after removal; the temperature of the polishing slurry used during the polishing process is 50~55℃, and the temperature of the carrier plate is 78~80℃.

[0017] The beneficial effects that this application can produce include: 1) Improve product quality: This method can effectively improve the TTv of the obtained wafer to <2μm, while improving the flatness of the product: the warp of the wafer to <20μm and the bow to <8μm.

[0018] 2) Improve the reactivity of the polished wafer interface: This method improves the surface element reactivity of the wafer by preheating it to 50-60°C in a phosphoric acid solution, and then uses an ultrasonically pre-dispersed alumina polishing slurry at a temperature maintained at 50-55°C for rough and fine grinding. This effectively improves the reliability of the rough grinding results and provides a basis for achieving higher TTV and flatness results after fine grinding.

[0019] 3) Homemade polishing pads ensure polishing results while extending usage time: The polishing pad uses short fibers of polyamide and polyacrylonitrile mixed in a 1:1 volume ratio as the main material. The short fibers have a length of 29-38 mm and a volume ratio of 51-65 mm (3:1), with a linear density of 8-10 D. Polyacrylate prepolymer is added as a binder. The short fiber main material, after mixing long and short fibers, improves the polishing pad's adsorption capacity for polishing fluid, while the long fibers form a skeleton structure, creating a stable and reliable wetting interface during polishing, protecting the polishing pad, and reducing the replacement frequency to once every 5 pads. At the same time, using short fibers as the main material also helps control the glazing of the polishing interface and extends the service life.

[0020] 4) Homemade polishing pads improve removal rate: This polishing pad uses alumina with a particle size of 710~850nm as the abrasive for fine grinding to make a coarse polishing pad, and uses alumina with a particle size of 24~31nm as the abrasive for coarse grinding to make a fine polishing pad, thereby improving the specificity of the polishing pad used and providing a reliable foundation for fine grinding through coarse grinding. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to embodiments, but this does not limit the present invention in any way. Any modifications or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0022] Unless otherwise specified, all materials and instruments used in the following embodiments were obtained through commercial channels; and all detection methods used are existing methods unless otherwise specified.

[0023] Example 1 1. Select short fibers of polyamide and polyacrylonitrile with lengths of 29~38mm and 51~65mm respectively and linear densities of 8~10D. Mix the short fibers of polyamide and polyacrylonitrile at a volume ratio of 1:1. The volume ratio of 29~38mm to 51~65mm fiber lengths in the polyamide short fibers is 3:1; the volume ratio of 29~38mm to 51~65mm fiber lengths in the polyacrylonitrile short fibers is 5:1; and the linear density of the short fibers is between 8 and 10D.

[0024] 2. Mix the weighed short fiber mixture of polyamide and polyacrylonitrile with the polyacrylate prepolymer. The amount of polyacrylate prepolymer used is 40 wt% of the mass of the short fiber mixture. Alumina powder is used as the abrasive, and the amount of abrasive added is 16 wt% of the mass of the short fiber mixture. The abrasive used is selected according to the polishing process. The abrasive particle size of the polishing pad used for coarse grinding is 710~850 nm. The abrasive particle size of the polishing pad used for fine grinding is 24~31 nm. Add 1% benzoyl peroxide by mass of the polyacrylate prepolymer. After mixing all the raw materials, stir evenly, pour the material into a leveling plate, level it into a film, shape it, and then heat it to 85℃ to cure it to obtain the polishing pad.

[0025] 3. Immerse the wafer to be polished in a phosphoric acid solution with a concentration between 83% and 88% at 80-100°C for at least 30 minutes. After immersion, remove the wafer and measure its temperature with an infrared thermometer until it reaches 55°C. Then, install the coarse polishing pad on the polishing surface where the wafer contacts the grinding head. Preheat the polishing tray to 79°C before starting the polishing process to maintain the temperature of all parts of the wafer during polishing. The polishing slurry temperature is 54°C. Before polishing, pre-treat the polishing slurry for 10 minutes using the ultrasonic generator in the slurry tank. Pre-treatment improves the uniformity of abrasive dispersion in the slurry. The ultrasonic treatment frequency is 20-30kHz, and the ultrasonic treatment device is continuously turned on during polishing to prevent slurry deposition. The abrasive particle size in the polishing slurry used for coarse grinding is 1-1.2μm; the abrasive particle size in the polishing slurry used for fine grinding is 320-431nm.

[0026] 4. Polishing: Perform rough grinding for 35-45 minutes and fine grinding for 90-120 minutes respectively. After polishing, clean the finished wafer.

[0027] Comparative Example 1 The difference from Example 1 is that a commercially available polyurethane polishing pad was used. During the polishing process, the abrasive particles in the polishing slurry used for coarse grinding had a particle size of 3~5μm, and the abrasive particles in the polishing slurry used for fine grinding had a particle size of 90~100nm. No ultrasonic device was used to treat the polishing slurry.

[0028] One hundred sapphire wafers with a thickness of 0.1-0.2 mm and a diameter of 4-8 inches were produced using the methods described in Example 1 and Comparative Example 2, respectively. The TTV, Warp, and Bow of each wafer were then measured using existing methods. The number of replacements of the rough and fine grinding pads was also recorded. Wafers were classified as good products if they had no visible surface damage or cracks, and as defective products if they did not meet this standard. The proportion of good wafers in the total production was calculated, and the results are shown in the table below.

[0029] surface

[0030] As can be seen from the table above, the method provided in this application can effectively improve the TTv, Warp, and Bow of the obtained wafer, while reducing the number of times the polishing pad needs to be replaced, and also improving the yield of the obtained wafer.

[0031] Example 2 The difference from Example 1 is that: the amount of polyacrylate prepolymer used is 32 wt% of the mass of the short fiber mixture used. The amount of abrasive added is 13 wt% of the mass of the short fiber mixture used. The temperature is measured to meet the polishing requirements by removing the wafer and measuring the temperature to 50°C with an infrared thermometer; the temperature of the polishing slurry used during polishing is 50°C, and the temperature of the tray is 78°C.

[0032] Example 3 The difference from Example 1 is that: the amount of polyacrylate prepolymer used is 41 wt% of the mass of the short fiber mixture used. The amount of abrasive added is 21 wt% of the mass of the short fiber mixture used. The temperature required for polishing is measured to 60°C using an infrared thermometer after the wafer is removed; the temperature of the polishing slurry used during polishing is 55°C, and the temperature of the tray is 80°C.

[0033] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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 wafer polishing method, characterized in that, Includes the following steps: Preparation of coarse grinding polishing pads and fine grinding polishing pads; After the polishing wafer is immersed in phosphoric acid solution to activate the reaction interface, and the temperature is measured to meet the polishing requirements, it is placed on a heated carrier plate. After ultrasonic pretreatment of the polishing solution, it is first rough polished, then fine polished, and cleaned to obtain the polished wafer. The polishing pad used in coarse grinding and polishing is a coarse grinding polishing pad, and the particle size of the abrasive added to the coarse grinding polishing pad is 710~850nm; The polishing pad used in fine grinding and polishing is a fine grinding and polishing pad; the particle size of the abrasive added to the fine grinding and polishing pad is 24~31nm.

2. The wafer polishing method according to claim 1, characterized in that, The preparation methods for both coarse and fine polishing pads are as follows: mix all raw materials evenly, scrape them flat to form a film, shape them, and then heat and cure them.

3. The wafer polishing method according to claim 2, characterized in that, The raw materials include: polyamide with a linear density of 8-10D, short fibers of polyacrylonitrile, polyacrylate prepolymers, abrasives, and benzoyl peroxide initiator.

4. The wafer polishing method according to claim 3, characterized in that, The short fibers of polyamide and polyacrylonitrile will be mixed in a volume ratio of 1:1; The polyamide short fibers used are polyamide fibers with a length of 29~38mm:51~65mm, mixed in a volume ratio of 3:1; The polyacrylonitrile short fibers used are polyacrylonitrile fibers with a length of 29~38mm:51~65mm, mixed in a volume ratio of 5:

1.

5. The wafer polishing method according to claim 3, characterized in that, The amount of polyacrylate prepolymer used is 32-41 wt% of the mass of the short fiber mixture used; the amount of benzoyl peroxide added is 1% of the mass of the polyacrylate prepolymer.

6. The wafer polishing method according to claim 3, characterized in that, The abrasive is alumina powder material; the amount of abrasive added is 13~21 wt% of the mass of the short fiber mixture used.

7. The wafer polishing method according to claim 1, characterized in that, The abrasive particles in the polishing slurry used for coarse grinding have a particle size of 1~1.2μm; the abrasive particles in the polishing slurry used for fine grinding have a particle size of 320~431nm.

8. The wafer polishing method according to claim 1, characterized in that, The concentration of the phosphoric acid solution used is between 83% and 88%; the wafer is immersed in the phosphoric acid solution at 80-100°C for at least 30 minutes.

9. The wafer polishing method according to claim 1, characterized in that, Temperature measurement to meet polishing requirements is to remove the wafer and measure its temperature to 50~60℃ using an infrared thermometer; the temperature of the polishing slurry used during polishing is 50~55℃, and the temperature of the tray is 78~80℃.

Images