Double-sided polishing method for mask substrate glass

Abstract

The invention relates to a double-sided polishing method for mask substrate glass, which comprises the following steps: polishing glass by using a double-sided polishing machine which comprises an upper polishing disk, a lower polishing disk, an upper polishing pad, a lower polishing pad, a sun wheel, a gear ring and a plurality of wandering star wheels; during polishing, the rotating speed of the lower polishing disc is higher than that of the upper polishing disc, and the rotating directions of the lower polishing disc, the upper polishing disc, the gear ring and the sun gear are opposite. In the polishing process, the back face type of the glass is kept to be a concave face type with the low center and the high periphery, the front face type of the glass is prevented from deteriorating, and the flatness effect of the front face of the polished glass is effectively improved.

Description

Technical Field

[0001] The invention relates to the field of processing components related to photolithography technology, and in particular to a polishing method for correcting glass flatness. Background Art

[0002] At present, almost all modern chips need to be manufactured using photolithography. The principle of photolithography is to transmit light through a mask with a circuit diagram, scale down the circuit diagram on the mask and map it onto the photoresist on the surface of the silicon wafer, and then go through a series of subsequent processing such as development, hardening, etching, etc. to finally get the chip.

[0003] The mask is the master of the pattern on the chip, so the performance of the mask directly affects the quality of the photolithography process. The mask is mainly composed of two parts: the mask substrate and the light-shielding film. The mask substrate is divided into a resin substrate and a glass substrate, which are suitable for different process requirements. Among them, quartz glass has stable chemical properties, high optical transmittance, and low thermal expansion coefficient. Quartz glass mask substrates are currently widely used in the production of ultra-large-scale integrated circuit masks.

[0004] In order for the performance of the mask to meet the requirements of the subsequent photolithography process, the flatness of the glass used as the substrate must first meet certain standards. As chips develop towards ultra-high speed, integration, and intelligence, the technical nodes of integrated circuits continue to shrink, and the requirements for the flatness of mask substrates, especially the flatness of the front side of the substrate, continue to increase. At present, the flatness is often graded according to different flatness levels such as 2μm, 1μm, and 0.5μm. The product technology nodes and product added value corresponding to different levels of flatness vary greatly. Masks with unqualified flatness have fluctuations in the focus position when imaging on the wafer surface, resulting in a reduction in the photolithography process window, affecting the quality and accuracy of the photolithography. Strictly controlling the flatness of the quartz glass substrate helps to ensure that the fluctuation of the focus position is much smaller than the focus depth, thereby ensuring the quality of the photolithography process. Flatness is also called flatness, and is usually expressed by the total indicator reading (TIR). This value can usually be expressed using Corning The flatness measuring machine can directly measure it. TIR refers to the sum of the absolute values ​​of the maximum positive and negative deviations between the substrate surface and the reference plane, with the surface with the smallest sum of intercepts between the substrate surface and all points in the local area as the reference plane when the substrate is in close contact. The larger the TIR value, the worse the flatness effect.

[0005] The current mainstream flatness correction method is usually chemical mechanical polishing (CMP). Double-sided polishing machine is a commonly used CMP tool, such as Figure 1 and Figure 2As shown, it includes an upper polishing disc 11, an electric push rod, a lower polishing disc 12, a base 20, an upper polishing pad 13, a lower polishing pad 14, a sun gear 15, a gear ring 16, a plurality of planetary gears 17, four motors and a polishing liquid supply pipeline (the electric push rod, the motor and the polishing liquid supply pipeline are not shown in the figure). The upper polishing disc 11 is rotatably mounted on the electric push rod and can be moved up and down in the vertical direction by the electric push rod. The rotating shaft of the upper polishing disc 11 is connected to an independent motor and is driven to rotate independently by the motor. The lower polishing disc 12 is rotatably mounted on the base 20, and its rotating shaft is connected to an independent motor and is driven to rotate independently by the motor. The lower polishing disc 12 and the upper polishing disc 11 are arranged with their axes facing each other in parallel. The upper polishing pad 13 and the lower polishing pad 14 are respectively covered on the opposite surfaces of the upper polishing disc 11 and the lower polishing disc 12, and the thickness of the upper polishing pad 13 and the lower polishing pad 14 is 0.5-5mm. The diameter of the sun gear 15 is smaller than that of the lower polishing plate 12. The outer ring is provided with teeth. The sun gear 15 is rotatably mounted on the base 20 and is located between the upper polishing plate 11 and the lower polishing plate 12. The rotation center line of the sun gear 15 coincides with the rotation center line of the lower polishing plate. The sun gear 15 is connected to an independent motor and is driven to rotate independently by the motor. A through hole is provided inside the planetary gear for placing the glass 19 workpiece. The outer ring of the planetary gear 17 has teeth. Several planetary gears 17 mesh with the outer ring teeth of the sun gear 15, and the planetary gears do not contact each other. The diameter of the gear ring 16 is larger than that of the sun gear 15. The sun gear 16 is rotatably mounted on the base 20 and is located in the same plane as the sun gear 15. The rotation center line of the sun gear 15 coincides with the rotation center line of the sun gear 15. The sun gear 15 is connected to an independent motor and is driven to rotate independently by the motor. The inner ring is provided with teeth and meshes with the planetary gear. The upper polishing disc 11 is also provided with a liquid guide hole 18. The polishing liquid supply pipeline sprays the polishing liquid onto the upper polishing disc 11. The polishing liquid can flow along the liquid guide hole 18 to the upper polishing pad, and then further infiltrate between the upper and lower polishing pads and the glass 19. The polishing liquid is a liquid composed of multiple chemical components, mainly including abrasive particles, solvents, surfactants, and pH regulators. Among them, abrasive particles are the main component of the polishing liquid, which is responsible for removing the uneven parts of the surface of the object. The polishing liquid for glass generally uses cerium oxide abrasive particles; the solvent plays the role of diluting and dispersing the abrasive; the surfactant helps the polishing liquid to be evenly distributed on the surface of the object.

[0006] When polishing the glass, the upper polishing disc 11 is lifted up, and the glass is placed in the through hole of the planetary wheel 17. The upper polishing disc 11 is pressed down with a certain processing pressure, so that the upper polishing disc 11 and the lower polishing disc 12 apply pressure to the front side (i.e., the lower surface) and the back side (i.e., the upper surface) of the glass through the upper polishing pad 13 and the lower polishing pad 14 respectively. The upper polishing disc 11 and the lower polishing disc 12 rotate respectively, driving the upper polishing pad 13 and the lower polishing pad 14 to rub the glass. The polishing liquid infiltrates through the polishing liquid supply pipe and the liquid guide hole 18. Under the action of the polishing pressure, the Ce atoms of cerium dioxide in the polishing liquid can react with the Si-O bonds in the quartz glass to form Ce-O-Si bonds. The quartz glass will form a scrap and be peeled off by the cerium dioxide abrasive particles, and be polished away when the polishing pad rubs against the glass. At the same time, the sun gear 15 and the ring gear 16 rotate at different speeds, driving the planetary gear 17 and the glass 19 therein to rotate and revolve, so that all parts of the glass surface are evenly polished and the flatness of the glass 19 is corrected. CMP combines chemical reaction and mechanical grinding, which can effectively avoid surface damage caused by simple mechanical polishing and defects such as slow polishing speed, poor surface flatness and polishing consistency caused by simple chemical polishing. The double-sided polishing machine polishes the front and back of the glass at the same time, which can effectively improve the uniformity, stability and optical quality of the glass 19.

[0007] In the prior art, technicians usually use a double-sided polishing machine to perform rough polishing and fine polishing steps on the glass 19. In the rough polishing, technicians usually adjust the rotation speed, processing pressure, processing time and other parameters of each polishing disc and gear ring of the double-sided polishing machine, and use cerium oxide polishing liquid purchased on the market to quickly remove the excessively high part of the glass surface and reduce the thickness difference of the same batch of glass; then further polish the glass surface through fine polishing to further improve the flatness. However, technicians found that it is still difficult to achieve a good flatness using this method, especially it is difficult to achieve a flatness below 0.5μm. Summary of the invention

[0008] Based on this, the object of the present invention is to provide a double-sided polishing method for mask substrate glass, comprising: polishing the glass using a double-sided polishing machine, the double-sided polishing machine comprising an upper polishing disc, a lower polishing disc, an upper polishing pad, a lower polishing pad, a sun gear, a gear ring, and a plurality of planetary gears; the upper polishing disc can rotate independently; the lower polishing disc can rotate independently; the lower polishing disc and the upper polishing disc have opposite axes and are arranged in parallel; the upper polishing disc and the lower polishing disc can move away from or close to each other; the upper polishing pad and the lower polishing disc can rotate independently; the upper polishing disc and the lower polishing disc can rotate independently; the upper polishing pad and the lower polishing disc can rotate independently; the upper polishing disc and the lower polishing disc can rotate independently; the upper polishing pad and the lower polishing pad can rotate independently; the upper polishing disc and the lower polishing disc can rotate independently; the upper polishing disc and the lower polishing pad ... The lower polishing pads cover the surfaces opposite to the upper polishing disc and the lower polishing disc respectively; the sun gear is located between the upper polishing disc and the lower polishing disc, and its rotation center line coincides with the rotation center line of the lower polishing disc, and can rotate independently, its diameter is smaller than the lower polishing disc, and its outer ring is provided with teeth; the outer ring of the planetary gear has teeth, and a through hole is provided inside; a plurality of planetary gears mesh with the outer ring teeth of the sun gear, and the planetary gears do not contact each other; the gear ring can rotate independently, and its rotation center line coincides with the rotation center line of the sun gear, and its inner ring is provided with teeth, and meshes with the planetary gear;

[0009] During polishing, the rotation speed of the lower polishing plate is greater than that of the upper polishing plate, and the rotation direction of the lower polishing plate is opposite to the rotation direction of the upper polishing plate, the gear ring and the sun gear.

[0010] Compared with the prior art, the present invention is conceived to keep the back surface of the glass as a concave shape with a low center and high surroundings during the polishing process to prevent the front surface of the glass from deteriorating, thereby effectively improving the flatness of the front surface of the glass after polishing.

[0011] Furthermore, the speed of the upper polishing disc is 2-20 rpm, and the speed of the lower polishing disc is 8-24 rpm.

[0012] Furthermore, the speed of the upper polishing disc is 2-9 rpm, and the speed of the lower polishing disc is 9-18 rpm.

[0013] Furthermore, the glass is polished using a polishing liquid in cooperation with the double-sided polishing machine; the polishing liquid comprises 4-20wt% cerium oxide, 0.2-1.5wt% surfactant, 2-6wt% dispersant, pure water, and a pH of 8-12.

[0014] Furthermore, the concentration of the cerium oxide is 5-16wt%.

[0015] Furthermore, the polishing includes sequentially performing rough polishing and fine polishing steps on the glass; wherein the cerium oxide particle size distribution used in the polishing liquid used in the rough polishing step is 0.1-20 μm; the cerium oxide particle size distribution used in the polishing liquid used in the fine polishing step is 0.1-10 μm.

[0016] Furthermore, the particle size distribution of cerium oxide in the coarse polishing liquid is 0.1-9 μm, and the particle size distribution of the fine polishing liquid is 0.1-5 μm.

[0017] Furthermore, the surfactant is polyacrylate, and the dispersant is sodium hexametaphosphate and / or sodium citrate.

[0018] Furthermore, in the rough polishing step, the speed difference between the ring gear and the sun gear is 1-5 rpm, wherein the speed of the ring gear is 2-8 rpm, and in the fine polishing step, the speed difference between the ring gear and the sun gear is 0-4 rpm, wherein the speed of the ring gear is 2-8 rpm.

[0019] Furthermore, the pressure in the rough polishing step is 25-54 g / cm 2 The polishing time is 30-90 minutes, and the pressure in the fine polishing step is 25-45g / cm 2 , polishing time is 30-90 minutes.

[0020] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the side structure of a double-sided polishing machine;

[0022] Figure 2 It is a schematic diagram of the top view of the double-sided polishing machine;

[0023] The reference numerals in the accompanying drawings are: 11 upper polishing plate, 12 lower polishing plate, 13 upper polishing pad, 14 lower polishing pad, 15 sun gear, 16 ring gear, 17 planetary gear, 18 liquid guide hole, 19 glass, and 20 base. DETAILED DESCRIPTION

[0024] In order to solve the problem that the prior art cannot achieve a high level of flatness, the present invention analyzes the causes and explores the effects of the various steps and effects of the existing polishing method. The present invention finds that due to the effect of gravity, when the double-sided polishing machine with the structure described in the background technology is used for polishing, the pressure conditions of the various parts of the front and back sides of the glass 19 are different, and the effect of the polishing liquid staying on the front and back sides of the glass 19 is also different, so the flatness and surface shape of the front and back sides of the glass 19 after polishing will be different. After a large number of experimental explorations, the present invention finds that under the same other conditions, when the back side of the glass 19 presents a convex shape with a high center and low surroundings, the polishing effect of the front side of the glass 19 will be poor, and the flatness effect will deteriorate. In the prior art, the technicians only considered reducing the thickness difference between the glasses 19 and removing the excessively high parts of the glass 19 surface during the parameter adjustment process, but did not consider the influence of the back side of the glass 19 on the flatness effect of the front side. Therefore, the present invention is based on the idea of ​​keeping the back side of the glass 19 as a concave shape with a low center and high surroundings during the polishing process to improve the flatness effect of the front side of the glass 19 after polishing. Through further experiments, the present invention concludes that when the rotation speed of the lower polishing disk 12 is faster than that of the upper polishing disk 11, the back surface of the glass 19 can be made into a concave surface with a low center and high surroundings. Preferably, when the rotation speed of the lower polishing disk 12 is 8-24rpm and the rotation speed of the upper polishing disk 11 is 2-20rpm, the flatness effect of the front side of the glass 19 is significantly improved after polishing.

[0025] Subsequently, the present inventors found that although the flatness effect of glass 19 was improved after the improvement, there was still room for improvement, and it took a long time, the loss of polishing liquid and polishing pad was large, and the cost was high. Therefore, the present inventors further optimized the scheme to further improve the flatness effect and polishing efficiency. Therefore, the present inventors think from the principle of CMP. CMP is a combination of chemical and mechanical effects, in which the mechanical effect mainly grinds and removes the higher part of the surface of glass 19, which determines the removal rate of the surface of glass 19, that is, the polishing efficiency; the chemical effect mainly affects the uniformity of the polishing effect of glass 19, so that the surface of glass 19 is evenly polished, and the overall flatness is improved, but the removal speed is slow. Therefore, the key to improving the flatness effect and improving the polishing efficiency is to achieve a balance between mechanical and chemical effects, with both a fast removal rate and strong uniformity.

[0026] After analysis, it is found that since the cerium oxide abrasive particles in the glass 19 polishing liquid can directly mechanically rub against the surface of the glass 19 and can also react with the glass 19 to form removed substances, the presence of cerium oxide is the key to the combination of mechanical and chemical effects. Among them, the concentration of abrasive particles is crucial to the balance of mechanical and chemical effects. When the concentration of cerium oxide abrasive particles is extremely low, the polishing of the glass 19 mainly depends on the friction of the polishing pad, and the polishing liquid has little mechanical or chemical effect on the glass 19. According to experiments, when the concentration of abrasive particles increases, the number of polishing particles increases, and the contact area between the abrasive particles and the surface of the glass 19 increases, so the mechanical and chemical effects are enhanced, the polishing removal rate increases, and the flatness value of the glass 19 substrate also decreases (that is, the flatness effect becomes better). When the concentration reaches 14wt% and continues to increase, the increase in mechanical friction is greater than the increase in chemical action, so although the removal rate is further increased, the flatness value also begins to increase (that is, the flatness effect shows a deteriorating trend). Even so, the present invention concludes through experiments that when the cerium oxide concentration is within 4-20wt%, the mechanical action and chemical action are in a relatively balanced range, which can achieve a faster removal speed and a smaller flatness value of the glass 19, that is, a better flatness effect.

[0027] Furthermore, the present invention also found that the particle size and particle size distribution of cerium oxide abrasives will also affect the removal rate and flatness effect. When the particle size and particle size distribution are small, the corresponding mechanical grinding effect is small, and only relying on chemical action, the polishing removal rate is low but the polishing effect is more uniform; when it is large, the mechanical action is dominant, the polishing removal rate is fast but the effect is not uniform enough, and it is easy to produce scratches and other defects on the surface of the glass 19 substrate. Therefore, the present invention designs abrasives with larger particle size and particle size distribution in the rough polishing step to quickly improve the overall flatness effect and reduce the thickness difference between the same batch of glass 19, and then uses abrasives with smaller particle size and particle size distribution in fine polishing to polish the surface of glass 19 finely and evenly, and further correct the flatness. Finally, the present invention selects cerium oxide with a particle size distribution of 0.1-20μm, preferably 0.1-9μm, as the polishing liquid of the rough polishing step, that is, the abrasive of the rough polishing liquid through experimental comparison; cerium oxide abrasives with a particle size distribution of preferably 0.1-5μm are selected as the abrasive of the fine polishing liquid.

[0028] Furthermore, when the rotation speeds of the ring gear 16 and the sun gear 15 are different, the planetary gear 17 will drive the glass 19 to perform orbital and rotational motions in the double-sided polishing machine, forming a complex motion trajectory, and then rub against the polishing pad to be polished evenly. When the speed difference between the ring gear 16 and the sun gear 15 is small, the motion trajectory of the glass 19 is relatively sparse, the relative friction speed between the glass 19 and the polishing pad is slow, and the friction uniformity is low, but the polishing liquid can contact and react with the surface of the glass 19 more fully; when the speed difference is large, the motion trajectory is relatively dense, the relative friction speed between the glass 19 and the polishing pad is faster, the mechanical action gradually increases, the removal rate gradually increases, and the friction uniformity is high, while the chemical action is weakened due to the shortened contact time between the polishing liquid and the surface of the glass 19. The present invention has concluded through experiments that when the speed difference between the ring gear 16 and the sun gear 15 is 0-5rpm, the mechanical action and the chemical action are relatively balanced, that is, the removal rate and the polishing uniformity are relatively balanced. Furthermore, in order to reduce the polishing time, the present invention preferably makes the speed difference between the ring gear 16 and the sun gear 15 1-5rpm in the rough polishing step, so that the removal speed is faster, the higher part of the surface of the glass 19 can be quickly removed, and the flatness is initially optimized; and then in the fine polishing step, the speed difference between the ring gear 16 and the sun gear 15 is 0-4rpm. At this time, the rotation and revolution motion trajectory of the glass 19 is still dense enough, and the friction is uniform enough, but the removal speed is slightly slower, which can allow the polishing liquid more reaction time, make the polishing effect more uniform, and further improve the flatness effect.

[0029] Furthermore, the processing pressure is relatively small, the load borne by a single cerium oxide abrasive is small, and the mechanical action is relatively weak. As the polishing pressure increases, the load borne by a single cerium dioxide abrasive increases, resulting in an increase in the depth of the abrasive embedded in the surface of the glass 19 substrate, an increase in the grinding ability, an increase in the mechanical action, and an increase in the removal rate of the glass 19 substrate. However, when the polishing pressure is too high, the depth of the abrasive embedded in the glass 19 substrate is too deep, causing scratches and pits on the surface of the glass 19. At the same time, after the polishing pad is squeezed, the deformation of the polishing pad increases and the porosity decreases, the content of the stored polishing liquid decreases, and the effect of the polishing liquid is weakened, resulting in an increase in mechanical friction, affecting the polishing effect, and even the risk of glass 19 breaking. Similar to the concept described above, the present invention has experimentally confirmed that the processing pressure is set to 25-54g / cm during rough polishing. 2 The processing pressure during fine polishing is 25-43g / cm 2 , which can achieve good flatness while achieving high polishing efficiency.

[0030] After optimizing the above parameters, the present invention concludes that: in the rough polishing step, cerium oxide powder with a particle size distribution of 0.1-20 μm and a concentration of 4-20 wt% is used as abrasive, 2-6 wt% of sodium hexametaphosphate and / or sodium citrate is used as a dispersant, 0.2-1.5 wt% of polyacrylate is used as a surfactant, the pH is adjusted to 10 using NaOH, and the polishing liquid uniformly dispersed in pure water is used as the rough polishing liquid; the speed of the upper polishing disc 11 is 2-20 rpm, the speed of the lower polishing disc 12 is 8-24 rpm, the upper and lower polishing discs 12 are reversed and the lower polishing disc 12 is faster than the upper polishing disc 11; the speed difference between the ring gear 16 and the sun gear 15 is 1-5 rpm, and the pressure is 25-54 g / cm 2 When the polishing time is 30-60 minutes, the average flatness of the front surface of the glass 19 can reach about 1 μm. In the fine polishing step, cerium oxide powder with a particle size distribution of 0.1-10 μm and a concentration of 4-20wt% is used as abrasive, 2-6wt% sodium hexametaphosphate and / or sodium citrate is used as a dispersant, 0.2-1.5wt% polyacrylate is used as a surfactant, the pH is adjusted to 10 using NaOH, and the polishing liquid uniformly dispersed in pure water is used as the fine polishing liquid, the speed of the upper polishing disc 11 is 2-20rpm, the speed of the lower polishing disc 12 is 8-24rpm, the upper and lower polishing discs 12 are reversed and the lower polishing disc 12 is faster than the upper polishing disc 11; the speed difference between the ring gear 16 and the sun gear 15 is 0-4rpm, and the pressure is 25-45g / cm 2 When the polishing time is 30-60 minutes, the average flatness of the front surface of the glass 19 can reach an effect of less than 0.5 μm.

[0031] The solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] The glass 19 is polished using a conventional double-sided polisher as described in the background technology. In this embodiment, a 22BF-4M5P double-sided polisher is used. In the rough polishing step, the polishing pad used by the double-sided polisher is a polyurethane polishing pad, and in the fine polishing step, the polishing pad used by the double-sided polisher is a non-woven fabric polishing pad. 12 glass 19 substrates with an initial flatness of about 5um are selected and placed in the through hole of the planetary wheel 17 of the double-sided polisher for polishing.

[0034] The polishing liquid used in the rough polishing step is the rough polishing liquid, and the polishing liquid used in the fine polishing step is the fine polishing liquid. The configuration method is as follows:

[0035] Prepare rough polishing liquid: use cerium oxide powder with a concentration of 14wt%, a powder particle size distribution of 0.120-7.586μm, a D50 of 1.231μm, and a D90 of 3.708μm as abrasive, 4wt% of an equal proportion mixture of sodium hexametaphosphate and sodium citrate as a dispersant, and 0.8wt% of polyacrylate as a surfactant. Evenly disperse them in pure water, and adjust the pH to 10 using NaOH.

[0036] Prepare fine polishing liquid: use cerium oxide powder with a concentration of 11wt%, a powder particle size distribution of 0.119-3.044μm, D50 of 0.823μm, and D90 of 1.832μm as abrasive, 4wt% of an equal proportion of sodium hexametaphosphate and sodium citrate as a dispersant, and 0.8wt% of a polyacrylate surfactant, uniformly dispersed in pure water, and adjusted to pH 10 using NaOH.

[0037] The specific polishing steps are:

[0038] Rough polishing of glass: Adjust the parameters of the double-sided polishing machine to: the upper polishing disc 11 rotates at 4 rpm, the lower polishing disc 12 rotates at 12 rpm. The ring gear 16 rotates at 7.5 rpm, and the sun gear 15 rotates at 5.13 rpm, that is, the speed difference between the ring gear 16 and the sun gear 15 is 2.37 rpm. The lower polishing disc 12 rotates in the opposite direction to the upper polishing disc 11, the ring gear 16, and the sun gear 15. Set the pressure to 40 g / cm 2 , the polishing time is 70 minutes.

[0039] Steps for fine polishing of glass: Adjust the parameters of the double-sided polishing machine to: the speed of the upper polishing disc 11 is 4rpm, the speed of the lower polishing disc 12 is 12rpm, the speed of the ring gear 16 is 6.54rpm, and the speed of the sun gear 15 is 3.08rpm, that is, the speed difference between the ring gear 16 and the sun gear 15 is 3.46rpm. The lower polishing disc 12 rotates in the opposite direction to the upper polishing disc 11, the ring gear 16 and the sun gear 15. The set pressure is 43g / cm 2 , the polishing time is 60 minutes.

[0040] Using Corning The flatness measuring machine detects the flatness of the front surface of the polished glass 19. After rough polishing, the average flatness of the front surface of the glass 19 is 0.86 μm, and after fine polishing, the average flatness of the front surface of the glass 19 is 0.38 μm, which meets the requirements of the subsequent coating process.

[0041] As comparative example 1, the difference from example 1 is that the speed of the upper polishing disc 11 and the lower polishing disc 12 is 20 rpm during rough polishing, and the speed of the upper polishing disc 11 and the lower polishing disc 12 is 15 rpm during fine polishing. After measurement, the average flatness of the front surface of the glass 19 after rough polishing is 1.09 μm, and the average flatness of the front surface after fine polishing is 0.65 μm.

[0042] This shows that compared with the same rotation speed, the lower polishing disk 12 has a faster rotation speed than the upper polishing disk 11, which can effectively optimize the flatness of the front side of the glass 19; when all parameters fall within the range described in the present invention, the flatness of the front side of the glass 19 can reach about 1μm after rough polishing, and the average flatness of the front side can reach less than 0.5μm after fine polishing.

[0043] Example 2

[0044] The difference between this embodiment and embodiment 1 is that:

[0045] The cerium oxide concentration of the rough polishing liquid is 10wt%, and the dispersant is 2wt% sodium hexametaphosphate;

[0046] The cerium oxide concentration of the fine polishing liquid is 6wt%, and the dispersant is 6wt% sodium citrate;

[0047] In the rough polishing step, the upper polishing disc 11 rotates at 13 rpm, the lower polishing disc 12 rotates at 18 rpm, the ring gear 16 rotates at 6.48 rpm, and the sun gear 15 rotates at 3.00 rpm, i.e., the speed difference between the ring gear 16 and the sun gear 15 is 3.48 rpm. The lower polishing disc 12 rotates in the opposite direction to the other three. The set pressure is 47 g / cm 2 , the polishing time is 60 minutes.

[0048] In the fine polishing step, the upper polishing disc 11 rotates at 6 rpm, the lower polishing disc 12 rotates at 15 rpm, the ring gear 16 rotates at 4.4 rpm, and the sun gear 15 rotates at 2.2 rpm, that is, the speed difference between the ring gear 16 and the sun gear 15 is 2.2 rpm. The lower polishing disc 12 rotates in the opposite direction to the other three. The set pressure is 32.5 g / cm 2 , the polishing time is 60 minutes.

[0049] According to measurement, the average flatness of the front surface of the glass 19 after rough polishing is 0.83 μm, and the average flatness after fine polishing is 0.34 μm, which meets the requirements of the subsequent coating process.

[0050] As comparative example 2, the difference from example 2 is that the speed of the upper polishing disc 11 and the lower polishing disc 12 is 20 rpm during rough polishing, and the speed of the upper polishing disc 11 and the lower polishing disc 12 is 15 rpm during fine polishing. According to measurement, the average flatness of the front surface of the glass 19 after rough polishing in comparative example 1 is 1.34 μm, and the average flatness of the front surface of the glass 19 after fine polishing is 0.65 μm.

[0051] This shows that compared with the same rotation speed, the lower polishing disk 12 has a faster rotation speed than the upper polishing disk 11, which can effectively optimize the flatness of the front side of the glass 19; when all parameters fall within the range described in the present invention, the flatness of the front side of the glass 19 can reach about 1μm after rough polishing, and the average flatness of the front side can reach less than 0.5μm after fine polishing.

[0052] Embodiment 3, 4, 5

[0053] The difference between Examples 3, 4 and 5 and Example 1 is that the concentration of cerium oxide powder in the fine polishing solution is 6wt%, 14wt% and 18wt% respectively. After measurement, the average flatness of the front surface of the glass 19 after polishing is 0.45μm, 0.35μm and 0.48μm respectively.

[0054] It shows that when other parameters fall within the range of the present invention and the concentration of cerium oxide powder is within the range of 4-20wt%, the average flatness of the front surface of the polished glass 19 can reach below 0.5μm, meeting the requirements of the subsequent coating process, and the best result is achieved when the concentration is 14wt%.

[0055] Embodiment 6, 7, 8, 9

[0056] The difference between Examples 6, 7, 8, and 9 and Example 4 is that the speed differences between the ring gear 16 and the sun gear 15 during fine polishing are 0.75 rpm (ring gear 3.08 rpm, sun gear 2.33 rpm), 2.57 rpm (ring gear 6.80 rpm, sun gear 4.23 rpm), 1.29 rpm (ring gear 5.52 rpm, sun gear 4.23 rpm), and 3.9 rpm (ring gear 7.16 rpm, sun gear 3.26 rpm), respectively.

[0057] After measurement, the average flatness of the front surface of the glass 19 after polishing is 0.49 μm, 0.41 μm, 0.37 μm, and 0.48 μm, respectively.

[0058] It shows that when other parameters fall within the range described in the present invention and the speed difference between the ring gear 16 and the sun gear 15 is within the range of 0-4rpm, the average flatness of the front side of the glass 19 after rough polishing and fine polishing can reach below 0.5μm, meeting the requirements of the subsequent coating process, and the speed difference is optimal when it reaches 1.29rpm.

[0059] Embodiment 10, 11, 12

[0060] The difference between Examples 10, 11, and 12 and Example 7 is that the processing pressure during fine polishing is 26 g / cm 2 , 34.6g / cm2, 60g / cm 2 .

[0061] According to measurement, the average flatness of the front surface of the glass 19 after polishing in Examples 10, 11, and 12 is 0.34 μm, 0.40 μm, and 0.82 μm, respectively.

[0062] It is shown that when other parameters fall within the range of the present invention and the processing pressure is within the range of the present invention, the average flatness of the front surface of the glass 19 after rough polishing and fine polishing can reach less than 0.5 μm, which meets the requirements of the subsequent coating process. However, when the polishing pressure exceeds 54 g / cm 2 After that, that is, Example 12, the front surface flatness of the glass 19 deteriorates after polishing.

[0063] Compared with the prior art, the present invention has the following advantages:

[0064] 1. The present invention can make the front flatness of the glass 19 reach about 1 μm after rough polishing and reach below 0.5 μm after fine polishing, which significantly improves the effect and meets the requirements of the subsequent coating process.

[0065] 2. By optimizing parameters to make the lower polishing disc 12 rotate faster than the upper polishing disc 11, the surface shape of the back side of the glass 19 can be controlled to prevent the flatness of the front side from deteriorating, which effectively optimizes the flatness of the glass 19 compared to the prior art.

[0066] 3. In the process of rough polishing and fine polishing, the present invention makes the removal rate as large as possible under the premise of ensuring the polishing uniformity, which can avoid excessive consumption of polishing liquid and wear of polishing pad due to long-term polishing, and save processing costs.

[0067] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A double-sided polishing method for a mask substrate glass, characterized in that: The glass is polished using a double-sided polishing machine. During polishing, the rotation speed of the lower polishing plate is greater than that of the upper polishing plate, and the rotation direction of the lower polishing plate is opposite to that of the upper polishing plate, the gear ring and the sun gear.

2. The double-sided polishing method of mask substrate glass according to claim 1, characterized in that: The upper polishing disc speed is 2-20rpm, and the lower polishing disc speed is 8-24rpm.

3. The double-sided polishing method of mask substrate glass according to claim 2, characterized in that: The upper polishing disc speed is 2-9rpm, and the lower polishing disc speed is 9-18rpm.

4. The double-sided polishing method of mask substrate glass according to claim 3, characterized in that: The glass is polished by using a polishing liquid in cooperation with the double-sided polishing machine; the polishing liquid comprises cerium oxide with a concentration of 4-20wt%, a surfactant of 0.2-1.5wt%, a dispersant of 2-6wt%, pure water, and a pH of 8-12.

5. The double-sided polishing method of mask substrate glass according to claim 4, characterized in that: The concentration of the cerium oxide is 5-16 wt %.

6. The double-sided polishing method of mask substrate glass according to claim 5, characterized in that: The polishing comprises the steps of rough polishing and fine polishing of the glass in sequence; wherein the cerium oxide particle size distribution of the polishing liquid used in the rough polishing step is 0.1-20 μm; the cerium oxide particle size distribution of the polishing liquid used in the fine polishing step is 0.1-10 μm.

7. The double-sided polishing method of mask substrate glass according to claim 6, characterized in that: The cerium oxide particle size distribution of the polishing liquid in the rough polishing step is 0.1-9 μm, and the particle size distribution of the polishing liquid in the fine polishing step is 0.1-5 μm.

8. The double-sided polishing method of mask substrate glass according to claim 7, characterized in that: The surfactant of the polishing liquid is polyacrylate, and the dispersant is sodium hexametaphosphate and / or sodium citrate.

9. The double-sided polishing method of mask substrate glass according to claim 8, characterized in that: In the rough polishing step, the speed difference between the ring gear and the sun gear is 1-5 rpm, wherein the speed of the ring gear is 2-8 rpm. In the fine polishing step, the speed difference between the ring gear and the sun gear is 0-4 rpm, wherein the speed of the ring gear is 2-8 rpm.

10. The double-sided polishing method of mask substrate glass according to claim 9, characterized in that: The pressure in the rough polishing step is 25-54 g / cm 2 The polishing time is 30-90 minutes, and the pressure in the fine polishing step is 25-45g / cm 2 , polishing time is 30-90 minutes.

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