A method for correcting the flatness of a glass

Abstract

The application relates to a glass flatness correction method. The glass flatness correction method comprises a first group of polishing of the glass, and the polishing comprises alternately performing polishing step A and polishing step B; the polishing step A is a polishing correction step for producing a center-low and four-side-high surface type effect after single polishing of one side of the glass; and the polishing step B is a polishing correction step for producing a center-high and four-side-low surface type effect after single polishing of one side of the glass. The glass flatness correction method can avoid accumulation of surface type defects of the glass in the polishing correction process through complementary surface types, and finally can correct the glass flatness to below 0.5 microns.

Description

Technical Field

[0001] This invention relates to the field of photolithography-related component processing, and in particular to a method for correcting glass flatness. Background Technology

[0002] Almost all modern chips are manufactured using photolithography. The principle of photolithography is to transmit a light source through a mask on which a circuit pattern is drawn, and to project the circuit pattern on the mask onto the photoresist on the surface of a silicon wafer in a proportionally reduced manner. After a series of subsequent processing steps such as development, hardening, and etching, the chip is finally obtained.

[0003] A photomask is the master template for the pattern on a wafer, therefore its performance directly affects the quality of the photolithography process. A photomask mainly consists of two parts: a mask substrate and a light-shielding film. The mask substrate is divided into resin substrates and glass substrates, used for different process requirements. Quartz glass, with its stable chemical properties, high optical transmittance, and low coefficient of thermal expansion, is currently widely used in the fabrication of photomasks for very large-scale integrated circuits.

[0004] To ensure the performance of a photomask meets the requirements of subsequent photolithography processes, the flatness of the glass substrate must first meet certain standards. As chips evolve towards ultra-high speed, integration, and intelligence, the technology nodes of integrated circuits are constantly shrinking, leading to increasingly stringent requirements for the flatness of the photomask substrate, especially the front side. Currently, flatness is often graded according to different levels such as 2μm, 1μm, and 0.5μm, with significant differences in the product technology nodes and added value corresponding to different flatness levels. A photomask with substandard flatness will have fluctuations in the focused position during wafer imaging, resulting in a smaller photolithography window and affecting photolithography quality and accuracy. Strictly controlling the flatness of the quartz glass substrate helps ensure that the fluctuations in the focused position are much smaller than the depth of focus, ensuring the quality of the photolithography process. Flatness, also known as smoothness, is usually expressed using the Total Indicator Reading (TIR), a value that can typically be obtained using... Flatness can be directly measured using a flatness measuring machine. 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 plane having the smallest sum of intercepts between the substrate surface and all points in a local area under close contact. Therefore, the larger the TIR value, the worse the flatness performance.

[0005] Currently, the mainstream method for flatness correction is chemical mechanical polishing (CMP). A double-sided polishing machine is a commonly used CMP tool, such as... Figure 1 and Figure 2As shown, the system 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, an internal gear ring 15, an external gear ring 16, several planetary gears 17, four motors, and a polishing fluid supply pipe (the electric push rod, motors, and polishing fluid supply pipe are not shown in the figure). The upper polishing disc 11 is rotatably mounted on the electric push rod and can move up and down vertically via 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 axially opposite and arranged parallel to each other. The upper polishing pad 13 and the lower polishing pad 14 respectively cover 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 inner gear ring 15 has a smaller diameter than the lower polishing disc 12, and its outer ring has teeth. It is rotatably mounted on the base 20, located between the upper polishing disc 11 and the lower polishing disc 12. Its rotation centerline coincides with the rotation centerline of the lower polishing disc, and its shaft is connected to an independent motor, driving it to rotate independently. The planetary wheel has a through hole for placing the glass 19 workpiece. The outer ring of the planetary wheel 17 has teeth, and several planetary wheels 17 mesh with the outer teeth of the inner gear ring 15, without contacting each other. The outer gear ring 16 has a larger diameter than the inner gear ring 15, and is rotatably mounted on the base 20, located on the same plane as the inner gear ring 15. Its rotation centerline coincides with the rotation centerline of the inner gear ring 15, and its shaft is connected to an independent motor, driving it to rotate independently. Its inner ring has teeth and meshes with the planetary wheels. The upper polishing disc 11 is also provided with a liquid guiding hole 18. The polishing liquid supply pipe sprays the polishing liquid onto the upper polishing disc 11. The polishing liquid can flow along the liquid guiding hole 18 to the upper polishing pad, and then further wet the upper and lower polishing pads and the glass 19.

[0006] During glass polishing, the upper polishing disc 11 is raised, 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 upper surface (reverse side) and the lower surface (front side) of the glass respectively through the upper polishing pad 13 and the lower polishing pad 14. 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 slurry seeps in through the polishing slurry supply pipe and the liquid guide hole 18. Since the polishing slurry contains cerium dioxide, under the action of polishing pressure, the Ce atoms of cerium dioxide in the polishing slurry can react with the Si-O bonds in the quartz glass to form Ce-O-Si bonds. The quartz glass will form clumps and be peeled off by the cerium dioxide abrasive grains, which are then polished away by the friction between the polishing pad and the glass. Meanwhile, the inner gear ring 15 and the outer gear ring 16 rotate at different speeds, driving the planetary wheel 17 and the glass 19 inside it to rotate and revolve, so that all parts of the glass surface are uniformly polished, thus correcting the flatness of the glass 19. 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 that are easily caused by simple chemical polishing. The double-sided polishing machine polishes the front and back of the glass at the same time, which can efficiently improve the uniformity, stability and optical quality of the glass 19.

[0007] In existing technologies, technicians typically use a double-sided polishing machine to perform a first set of rough polishing and a second set of fine polishing on glass 19. The first set of rough polishing primarily determines the flatness of glass 19, while the second set of fine polishing aims to remove scratches on the glass surface, reduce surface roughness, and facilitate downstream coating processes. During rough polishing, technicians usually adjust and optimize parameters such as the double-sided polishing machine's rotation speed, processing pressure, and processing time to remove excessively high areas from the glass surface, initially optimizing flatness and reducing thickness differences within the same batch of glass. Then, the glass surface is further polished to optimize flatness. However, technicians have found that existing methods still struggle to achieve high flatness, especially below 0.5 μm. Summary of the Invention

[0008] Based on this, the purpose of the present invention is to provide a glass flatness correction method, which includes performing a first set of polishing on the glass, including alternately performing polishing step A and polishing step B on the front side of the glass;

[0009] Polishing step A is a polishing correction step that produces a surface shape effect with a low center and high edges after polishing one side of the glass in one go.

[0010] Polishing step B is a polishing correction step that produces a surface shape effect with a high center and low periphery after polishing one side of the glass in one pass.

[0011] The glass flatness correction method described in this invention can avoid the accumulation of glass surface defects during the polishing correction process by using complementary surface shapes, and can ultimately correct the glass flatness to below 0.5μm.

[0012] Furthermore, polishing step A is performed first, followed by polishing step B.

[0013] Furthermore, while polishing and correcting the front side of the glass, the back side of the glass is also polished.

[0014] Furthermore, both polishing steps A and B use a double-sided polishing machine, which includes an upper polishing disc, a lower polishing disc, an upper polishing pad, a lower polishing pad, an internal gear ring, an external gear ring, and several planetary wheels.

[0015] The upper polishing disc can rotate independently;

[0016] The lower polishing disc can rotate independently; the lower polishing disc and the upper polishing disc are axially opposite and parallel; the upper polishing disc and the lower polishing disc can be moved away from or closer to each other.

[0017] The upper polishing pad and the lower polishing pad respectively cover the opposite surfaces of the upper polishing disk and the lower polishing disk;

[0018] The internal gear ring is located between the upper polishing disc and the lower polishing disc, with its rotation center line coinciding with the rotation center line of the lower polishing disc. It can rotate independently, and its diameter is smaller than that of the lower polishing disc. The outer ring is equipped with teeth.

[0019] The outer ring of the planetary wheel has teeth, and the inside has through holes; several planetary wheels mesh with the outer ring teeth of the inner gear ring, but the planetary wheels do not contact each other;

[0020] The outer gear ring can rotate independently, and its rotation center line coincides with the rotation center line of the inner gear ring. The inner ring is equipped with teeth that mesh with the planetary gear.

[0021] In polishing step A, the load speed ratio of the upper polishing disc to the lower polishing disc is 50-80%, the load speed ratio of the internal gear ring to the lower polishing disc is 80-100%, and the load speed ratio of the external gear ring to the lower polishing disc is 5-30%. The rotation directions of the lower polishing disc, the upper polishing disc, the internal gear ring, and the external gear ring are opposite.

[0022] This step can make preliminary corrections to the flatness of the glass, which has a surface that is lower in the center and higher around the edges. If it is a flatness correction for a batch of glass, it can also reduce the thickness difference of the same batch of glass to within 20μm.

[0023] Furthermore, in polishing step B, the load speed ratio of the upper polishing disc relative to the lower polishing disc is 50-80%, the load speed ratio of the inner gear ring relative to the lower polishing disc is 80-100%, and the load speed ratio of the outer gear ring relative to the lower polishing disc is 20-50%. The lower polishing disc rotates in the opposite direction to the upper polishing disc, the inner gear ring, and the outer gear ring. This step can further correct the flatness of the glass, achieving a flatness below 0.5μm. Simultaneously, this load speed ratio causes the glass's front surface shape to change towards a higher center and lower periphery during a single polishing cycle. Therefore, the final effect is superimposed on the surface shape effect of polishing step A, optimizing the flatness.

[0024] Furthermore, in polishing step A, the rotation speed of the lower polishing disc is 10-50 rpm.

[0025] Furthermore, in polishing step B, the rotation speed of the lower polishing disc is 5-30 rpm.

[0026] Furthermore, in polishing step A, the pressure applied to the glass by the upper and lower polishing discs is 20-50 g / cm². 2 Polishing time is 2-4 hours.

[0027] Furthermore, in polishing step B, the pressure applied to the glass by the upper and lower polishing discs is 10-30 g / cm². 2 Polishing time is 0.5-2 hours.

[0028] Furthermore, the process includes a second polishing of the glass using a double-sided polishing machine. The lower polishing disc rotates at 10-50 rpm, the load speed ratio of the upper polishing disc to the lower polishing disc is 50-80%, the load speed ratio of the internal gear ring to the lower polishing disc is 80-100%, and the load speed ratio of the external gear ring to the lower polishing disc is 5-30%. The lower polishing disc rotates in the opposite direction to the upper polishing disc, the internal gear ring, and the external gear ring. The processing pressure is 10-30 g / cm². 2 The polishing time is 0.1-1 hour. The second group can reduce the surface roughness of the glass to below 1nm, and the superimposed surface features a slightly lower center and higher edges.

[0029] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0030] Figure 1 This is a side view of the double-sided polishing machine.

[0031] Figure 2 This is a top view of the double-sided polishing machine.

[0032] Figure 3 The image shows the front surface of the glass after polishing step A, as a comparative example.

[0033] Figure 4 The image shows the front surface of two pieces of glass after polishing step B, serving as a comparative example.

[0034] Figure 5 This is a flowchart illustrating the steps.

[0035] Figure 6 This is a front view of the glass after polishing steps A and B in Example 1.

[0036] The numbers in the attached diagrams are as follows: 11 Upper polishing disc, 12 Lower polishing disc, 13 Upper polishing pad, 14 Lower polishing pad, 15 Internal gear ring, 16 External gear ring, 17 Planetary wheel, 18 Liquid guide hole, 19 Glass, 20 Base. Detailed Implementation

[0037] To address the issue of existing technologies failing to achieve a high level of flatness, this invention analyzes the causes and effects of each step in existing correction methods. Through statistical analysis and observation of the performance of processed glass 19, it was found that the front surface of glass 19 after double-sided chemical mechanical polishing generally exhibits a surface shape that is lower in the center and higher around the edges. In existing technologies, technicians only consider reducing the thickness difference between glass sections and removing excessively high portions of the glass surface during parameter adjustment, without considering the changes in the surface shape of glass 19 during each polishing correction. Therefore, even if a second or more flatness polishing correction is performed, without changing the trend of the glass front surface changing towards a lower center and higher edges, the height difference between the bottom center and the four corners is not reduced, and the flatness cannot be further improved. It may even lead to the accumulation of identical surface shapes, increasing the height difference between the bottom center and the four corners, thus worsening the flatness.

[0038] This invention further analyzes the reasons for the height difference between the center and the perimeter after polishing. In such cases... Figure 1In the double-sided polishing machine shown, the relative speed between the glass and the polishing pad is controlled by the inner gear ring 15, the outer gear ring 16, the upper polishing disc 11, and the lower polishing disc 12. On one hand, the planetary wheel 17 revolves and rotates within the polishing machine under the influence of the inner gear ring 15 and the outer gear ring 16, while the glass 19 also revolves and rotates within the planetary wheel 17. On the other hand, the upper polishing disc 11 and the lower polishing disc 12 rotate independently and rub against the surface of the glass 19. The superposition of these complex motion relationships results in different relative grinding speeds of the polishing pad on different parts of the glass 19. The faster the relative grinding speed of a certain part, the greater the grinding amount in a certain time, and therefore the lower the surface of that part. Ultimately, this results in the processed glass 19 having a surface shape that is lower in the center and higher around the edges, or vice versa. In summary, this invention concludes that for each polishing of glass, the motion relationship of the four rotating components of the double-sided polishing machine—upper polishing disc 11, lower polishing disc 12, inner gear ring 15, and outer gear ring 16—determines the direction of surface shape change during that polishing. Their actual rotational speed and processing pressure affect the overall polishing speed of the glass 19. Combined with the adjustment of processing time, this ultimately affects the degree of surface shape change of the glass 19—either a surface shape with a low center and high edges, or a surface shape with a high center and low edges.

[0039] The resulting surface finish is an unavoidable inherent effect of double-sided polishing machines, determined by their polishing principle. Eliminating this inherent effect would likely require extensive analysis and significant modifications to the polishing machine, resulting in substantial costs. This invention does not alter the structure or polishing principle of the machine. Instead, it utilizes the changes in glass surface finish produced by each polishing cycle, alternately applying polishing correction steps A and B to the front of the glass. Step A is a polishing correction step that produces a surface finish effect with a lower center and higher edges after a single polishing of one side of the glass. Step B is a polishing correction step that produces a surface finish effect with a higher center and lower edges after a single polishing of the front of the glass. Ultimately, the center is slightly lower, and the flatness of the glass surface is improved through the complementary effects of the two processes.

[0040] Based on the above concept, the present invention further analyzes the motion relationship, pressure and time parameter relationship of each rotating component of the polishing machine to form the surface shape of polishing step A and polishing step B, so as to achieve the complementarity of the surface shapes produced by the successive polishing steps and eliminate the technical problem of unsatisfactory flatness caused by the accumulation of the same surface shape in each polishing.

[0041] This invention uses a conventional double-sided polishing machine with the structure described in the background art for polishing. Through testing and analysis of different models of polishing machines, this invention concludes that, compared to directly changing the rotational speed, controlling the motion relationship of each rotating component by controlling the load speed ratio can more universally achieve the surface shape effects of polishing steps A and B on various models of double-sided polishing machines. The load speed ratio is the ratio of the rotational speed load between two rotating components. The rotational speed load is the ratio of the actual set rotational speed of a certain rotating component to the maximum rotational speed that component can achieve at that moment, given a fixed rotational speed of the lower plate. Through experiments and analysis, this invention concludes that when the load speed ratio of the upper polishing disc 11 to the lower polishing disc 12 is 50-80%, the load speed ratio of the inner gear ring 15 to the lower polishing disc 12 is 80-100%, and the load speed ratio of the outer gear ring 16 to the lower polishing disc 12 is 5-30%, and the lower polishing disc 12 rotates in the opposite direction to the other three components, the front of the glass 19 can achieve a single polishing process that produces a surface shape with a low center and high edges, as shown in the image. Figure 3 As shown; based on this, the present invention further studied the relationship between the polishing speed, time and the final surface shape, and found that the rotation speed of the lower polishing disc 12 is 10-50 rpm and the processing pressure is 20-50 g / cm. 2 The polishing time is 2-4 hours, ultimately resulting in glass 19 with a low center and high periphery surface on the front. Using the above parameters, the front of glass 19 can achieve this low center and high periphery surface effect after a single polishing. Conversely, when the load speed ratio of the upper polishing disc 11 to the lower polishing disc 12 is 50-80%, the load speed ratio of the inner gear ring 15 to the lower polishing disc 12 is 80-100%, and the load speed ratio of the outer gear ring 16 to the lower polishing disc 12 is 20-50%, and the lower polishing disc 12 rotates in the opposite direction to the other three, the front of glass 19 can achieve a high center and low periphery surface effect after a single polishing. Figure 4 As shown. Further adjustments are made with the polishing disc rotating at 5-30 rpm and the processing pressure at 10-30 g / cm. 2 The polishing time is 0.5-2 hours, which can produce a glass 19 with a high center and low perimeter on the front. That is, using the above parameters, the front of the glass 19 can produce a surface shape with a high center and low perimeter after a single polishing.

[0042] Furthermore, since a slight center-low and periphery-high surface profile is preferred for the mask substrate's glass 19 in downstream processes, this invention adjusts parameters so that the front surface of the glass 19, after surface pattern stacking, achieves a flatness of less than 0.5 μm and also exhibits a slight center-low and periphery-high surface profile. Further analysis of this invention suggests that the method of "first performing a single polishing correction to produce a center-high and periphery-low surface profile, then performing another single polishing correction to produce a center-low and periphery-high surface profile, ultimately resulting in a slightly lower center" removes more material from the glass 19 substrate than the method of "first performing a single polishing correction to produce a center-low and periphery-high surface profile, then performing another single polishing correction to produce a center-high and periphery-low surface profile, ultimately resulting in a slightly lower center." When processing defective glass 19 that is being reworked, its thickness is already within the standard range. Excessive material removal may cause the thickness of the glass 19 to fall below the standard, rendering it unusable; therefore, the former method has a narrower application range.

[0043] Therefore, this invention will describe a specific embodiment using the example of "polishing the front of the glass first in step A, then polishing in step B, ultimately making the center slightly lower." Figure 5 .

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0045] Example 1

[0046] This embodiment uses a double-sided polishing machine with the structure described in the background art to correct the flatness of glass 19. Four planetary wheels 17 are placed accordingly. The upper polishing pad 13 and lower polishing pad 14 are 2.5mm thick polyurethane coarse polishing pads. Before polishing, a polishing pad dresser is used to flatten the surface until the height difference between the highest and lowest points is within 30μm. In this embodiment, the height difference on the polishing pad surface after dressing is 15μm. Eight glass substrates 19 to be reworked, with a thickness difference within 50μm, are selected and placed in the through holes of the planetary wheels 17, with two substrates on each planetary wheel 17. The first set of polishing is performed, and the specific polishing correction steps are as follows:

[0047] Polishing Step A: Control parameters are as follows: the lower polishing disc 12 rotates at 35 rpm; the load speed ratio of the upper polishing disc 11 to the lower polishing disc 12 is 50%; the load speed ratio of the internal gear ring 15 to the lower polishing disc 12 is 90%; and the load speed ratio of the external gear ring 16 to the lower polishing disc 12 is 10%. The lower polishing disc 12 rotates in the opposite direction to the other three. Commercially available cerium oxide coarse polishing solution is used, with a pressure of 40 g / cm³. 2 Polishing for 2.5 hours.

[0048] Polishing Step B: The control parameters are set as follows: the rotation speed of the lower polishing disc 12 is 15 rpm; the load speed ratio of the upper polishing disc 11 to the lower polishing disc 12 is 50%; the load speed ratio of the internal gear ring 15 to the lower polishing disc 12 is 92%; and the load speed ratio of the external gear ring 16 to the lower polishing disc 12 is 22%. The rotation direction of the lower polishing disc 12 is opposite to that of the other three. The polishing fluid is commercially available cerium oxide coarse polishing fluid with a pressure of 25 g / cm³. 2 Polishing for 1.2 hours.

[0049] After polishing step A, the thickness difference of this batch of glass 19 was reduced to 10μm. After the second polishing step B, ... The flatness measuring machine determined that the front flatness of this batch of glass (19mm) was 0.1-0.5μm, with an average flatness of 0.470μm. For example... Figure 6 As shown, one piece of glass, after undergoing two complementary surface shaping processes, exhibits a very slight center-low and periphery-high shape, with a TIR (Taiwanese Indicator) of 0.469 μm on its front surface. This illustrates that combining polishing steps A and B can achieve a front surface flatness of less than 0.5 μm for glass 19.

[0050] In this embodiment, the maximum rotational speeds of each rotating component of the polishing machine are as follows: 20 rpm for the upper polishing disc 11, 50 rpm for the lower polishing disc 12, 30 rpm for the internal gear ring 15, and 20 rpm for the external gear ring 16, but are not limited to these speeds.

[0051] As a comparative example 1, only glass 19 underwent polishing correction step A, and the surface shape and flatness of the front side of glass 19 were measured: after polishing correction, the flatness of the front side of glass 19 was measured to be 0.6-1.0 μm, and the average flatness was 0.850 μm. Figure 3 As shown, the TIR (flatness index) of the front surface of one of the glass pieces is 0.857 μm, and the surface shape is lower in the center and higher around the edges. This indicates that the parameters of polishing step A can make the front surface of glass 19 have a lower center and higher edges, but polishing step A alone cannot make the flatness of the front surface of glass 19 below 0.5 μm.

[0052] As a comparative example 2, only glass 19 underwent polishing correction step B, and the surface shape and flatness of the front side of glass 19 were measured: the flatness of the front side of glass 19 was 0.6-1.0 μm, and the average flatness was 0.846 μm. Figure 4 As shown, the TIR (flatness index) of the front surface of one of the glass pieces is 0.875 μm, and the surface shape is higher in the center and lower around the edges. This indicates that the parameters of polishing step A can make the front surface of glass 19 have a higher center and lower edges, but polishing step B alone cannot make the flatness of the front surface of glass 19 below 0.5 μm.

[0053] Example 2

[0054] Using the double-sided polishing machine as described in Example 1, five planetary wheels 17 are placed on the machine. The upper polishing pad 13 and the lower polishing pad 14 are 3mm thick polyurethane coarse polishing pads, which are trimmed with a polishing pad dresser until the height difference of the polishing pad surface is 20μm. Fifty pieces of 6-inch glass 19 with a thickness difference within 50μm are selected and placed in the through holes of the planetary wheels 17, with 10 pieces of glass 19 placed on each planetary wheel 17, for the first set of polishing. The specific steps are as follows:

[0055] Polishing Step A: The control parameters are as follows: lower polishing disc 12 rotates at 30 rpm; the load speed ratio of upper polishing disc 11 to lower polishing disc 12 is 50%; the load speed ratio of internal gear ring 15 to lower polishing disc 12 is 85%; and the load speed ratio of external gear ring 16 to lower polishing disc 12 is 5%. The rotation direction of lower polishing disc 12 is opposite to that of the other three. Commercially available cerium oxide coarse polishing solution is used, with a pressure of 50 g / cm³. 2 Polishing time: 2 hours.

[0056] Polishing Step B: The control parameters are as follows: the lower polishing disc 12 rotates at 10 rpm; the load speed ratio of the upper polishing disc 11 to the lower polishing disc 12 is 50%; the load speed ratio of the internal gear ring 15 to the lower polishing disc 12 is 90%; and the load speed ratio of the external gear ring 16 to the lower polishing disc 12 is 20%. The lower polishing disc 12 rotates in the opposite direction to the other three. The polishing fluid is commercially available cerium oxide coarse polishing fluid with a pressure of 30 g / cm³. 2 Polishing for 1 hour.

[0057] The flatness of the glass substrate 19 before processing was measured by a flatness measuring machine to be approximately 2-5 μm. After two polishing operations, the average TIR (Temperature Intensity Reflectance) of the front side of the glass substrate 19, i.e., the average flatness, was measured to be 0.303 μm. This demonstrates that combining polishing steps A and S2 can achieve a flatness of less than 0.5 μm for the glass substrate 19.

[0058] As a comparative example 3, only polishing step A was performed on glass 19 for polishing correction, and the surface shape and flatness of the front side of glass 19 were measured: after polishing correction, the average TIR (i.e., average flatness) of the front side of glass 19 was measured to be 1.029 μm. This indicates that polishing step A alone cannot achieve a flatness of less than 0.5 μm on the front side of glass 19.

[0059] Example 3

[0060] Using the double-sided polishing machine as described in Example 1, four planetary wheels 17 are placed accordingly. The upper polishing pad 13 and the lower polishing pad 14 are flat polyurethane coarse polishing pads with a thickness of 3 mm. Eight glass substrates 19 to be reworked with a thickness difference within 50 μm are selected and placed in the through holes of the planetary wheels 17, with two substrates placed in each planetary wheel 17, for the first set of polishing. The specific steps are as follows.

[0061] Polishing Step A: The control parameters are as follows: lower polishing disc 12 rotates at 40 rpm; the load speed ratio of upper polishing disc 11 to lower polishing disc 12 is 50%; the load speed ratio of internal gear ring 15 to lower polishing disc 12 is 95%; and the load speed ratio of external gear ring 16 to lower polishing disc 12 is 15%. The rotation direction of lower polishing disc 12 is opposite to that of the other three. Commercially available cerium oxide coarse polishing solution is used, with a pressure of 30 g / cm³. 2 Polishing time: 3 hours.

[0062] Polishing Step B: The control parameters are as follows: lower polishing disc 12 rotates at 20 rpm; the load speed ratio of upper polishing disc 11 to lower polishing disc 12 is 50%; the load speed ratio of internal gear ring 15 to lower polishing disc 12 is 94%; and the load speed ratio of external gear ring 16 to lower polishing disc 12 is 24%. The rotation direction of lower polishing disc 12 is opposite to that of the other three. The polishing fluid is commercially available cerium oxide coarse polishing fluid with a pressure of 20 g / cm³. 2 Polishing for 1.5 hours.

[0063] After two polishing corrections, the average TIR (mean flatness) of the front side of glass 19 was measured to be 0.468 μm.

[0064] As a comparative example 4, only polishing step A was performed on glass 19 for polishing correction, and the surface shape and flatness of glass 19 were measured: after polishing correction, the average TIR (i.e., average flatness) of the front surface of glass 19 was measured to be 1.209 μm. This indicates that polishing step A alone cannot achieve a flatness of less than 0.5 μm on the front surface of glass 19.

[0065] Example 4

[0066] Considering that if the glass 19 substrate needs to be coated with a light-shielding film in subsequent processes, in addition to the flatness needing to be below 0.5μm, the surface roughness of the glass 19 substrate also needs to be below 1nm. Therefore, an additional fine polishing step can be added to reduce the roughness, further remove shallow scratches, and improve the roughness, so that the glass 19 substrate can better meet the requirements of subsequent processes.

[0067] Based on Example 1, a second polishing process is added. The second polishing process uses the same double-sided polishing machine as Example 1, except that the upper polishing pad 13 and the lower polishing pad 14 are polyurethane fine polishing pads.

[0068] The second polishing process involves fine polishing of the glass 19 using the aforementioned double-sided polishing machine. The lower polishing disc 12 rotates at 35 rpm. The load speed ratio of the upper polishing disc 11 to the lower polishing disc 12 is 50%, the load speed ratio of the internal gear ring 15 to the lower polishing disc 12 is 90%, and the load speed ratio of the external gear ring 16 to the lower polishing disc 12 is 10%. The lower polishing disc 12 rotates in the opposite direction to the other three. Commercially available cerium oxide polishing solution is used, with a pressure of 15 g / cm³. 2 Polishing time: 0.33 hours.

[0069] The final measured average flatness of the front side of glass 19 was 0.464 μm, the surface roughness Ra < 1 nm, and the surface shape was slightly lower in the center and higher around the edges. After cleaning, there were no obvious processing defects on the surface. This indicates that this step will not cause the flatness of the front side of glass 19 to deteriorate beyond the required range of 0.5 μm, and it can ensure that the surface roughness of glass 19 meets the requirements and meets the coating standard.

[0070] Example 5

[0071] Based on Example 2, a second polishing process is added. The second polishing process uses the same double-sided polishing machine as Example 2, except that the upper polishing pad 13 and the lower polishing pad 14 are polyurethane fine polishing pads.

[0072] The second polishing process involves using the aforementioned double-sided polishing machine to finely polish the glass 19. The control parameters are as follows: the lower polishing disc 12 rotates at 30 rpm; the load speed ratio of the upper polishing disc 11 to the lower polishing disc 12 is 50%; the load speed ratio of the internal gear ring 15 to the lower polishing disc 12 is 85%; and the load speed ratio of the external gear ring 16 to the lower polishing disc 12 is 5%. The lower polishing disc 12 rotates in the opposite direction to the other three. Commercially available cerium oxide polishing solution is used, with a pressure of 15 g / cm³. 2 Polishing time: 0.5 hours.

[0073] The final measured average flatness of the front side of glass 19 was 0.370 μm, and the surface roughness Ra < 1 nm. After cleaning, there were no obvious processing defects on the surface. This indicates that this step will not cause the flatness of the front side of glass 19 to deteriorate to the required range of 0.5 μm, and can ensure that the surface roughness of glass 19 meets the requirements and meets the coating standard.

[0074] Compared with the prior art, the present invention has the following advantages:

[0075] 1. During the glass flatness polishing correction process, controlling the change of the glass front surface shape in a single operation avoids the accumulation of a single surface shape, and the flatness can be achieved to below 0.5μm, resulting in a significant improvement in performance.

[0076] 2. By first polishing and correcting the surface with a lower center and higher edges, and then polishing and correcting the surface with a higher center and lower edges, the amount of material removed during the flatness correction process is reduced. This method has a wider range of applications, especially for reworked glass, which can minimize the risk of being scrapped due to excessively thin thickness after processing.

[0077] 3. After the fine polishing process, the flatness of the glass will not deteriorate beyond the required range, and the surface roughness can meet the requirements and achieve the coating standard.

[0078] 4. The method used in this invention is simple and can quickly achieve the target flatness, thus saving polishing fluid, reducing the wear of polishing pads, and reducing processing costs.

[0079] 5. When the amount of material to be removed is slightly large, the amount of material to be removed can be increased by polishing and correcting the surface shape multiple times, which can avoid deep scratches caused by direct grinding.

[0080] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A method for correcting the flatness of glass, characterized in that: The first stage of polishing the glass includes: The front surface of the glass is polished alternately in steps A and B; wherein, The polishing step A is a polishing correction step that produces a surface shape effect with a low center and high edges after polishing one side of the glass in one pass. The polishing step B is a polishing correction step that produces a surface shape effect with a high center and low periphery after polishing one side of the glass in one go. Both polishing steps A and B use a double-sided polishing machine to polish and correct the front side of the glass while simultaneously polishing the back side. The double-sided polishing machine includes an upper polishing disc, a lower polishing disc, an upper polishing pad, a lower polishing pad, an inner gear ring, an outer gear ring, and several planetary wheels; The upper polishing disc can rotate independently; The lower polishing disc can rotate independently; the lower polishing disc and the upper polishing disc are axially opposite and parallel; the upper polishing disc and the lower polishing disc can be moved away from or closer to each other. The upper polishing pad and the lower polishing pad respectively cover the opposite surfaces of the upper polishing disk and the lower polishing disk; The internal gear ring is located between the upper polishing disc and the lower polishing disc, with its rotation center line coinciding with the rotation center line of the lower polishing disc. It can rotate independently, and its diameter is smaller than that of the lower polishing disc. The outer ring is equipped with teeth. The outer ring of the planetary wheel has teeth, and the inside has through holes; several planetary wheels mesh with the outer ring teeth of the inner gear ring, but the planetary wheels do not contact each other; The outer gear ring can rotate independently, and its rotation center line coincides with the rotation center line of the inner gear ring. The inner ring is equipped with teeth that mesh with the planetary gear. In polishing step A, the load speed ratio of the upper polishing disc to the lower polishing disc is 50-80%, the load speed ratio of the internal gear ring to the lower polishing disc is 80-100%, and the load speed ratio of the external gear ring to the lower polishing disc is 5-30%, wherein the lower polishing disc rotates in the opposite direction to the upper polishing disc, the internal gear ring, and the external gear ring. In polishing step B, the load speed ratio of the upper polishing disc to the lower polishing disc is 50-80%, the load speed ratio of the internal gear ring to the lower polishing disc is 80-100%, and the load speed ratio of the external gear ring to the lower polishing disc is 20-50%, wherein the rotation directions of the lower polishing disc, the upper polishing disc, the internal gear ring, and the external gear ring are opposite.

2. The glass flatness correction method as described in claim 1, characterized in that: First perform polishing step A, then perform polishing step B.

3. The glass flatness correction method as described in claim 1, characterized in that: In polishing step A, the rotation speed of the lower polishing disc is 10-50 rpm.

4. The glass flatness correction method as described in claim 1, characterized in that: In polishing step B, the lower polishing disc rotates at a speed of 5-30 rpm.

5. The glass flatness correction method as described in claim 3, characterized in that: In polishing step A, the processing pressure is 20-50 g / cm. 2 Polishing time is 2-4 hours.

6. The glass flatness correction method as described in claim 4, characterized in that: The processing pressure in polishing step B is 10-30 g / cm. 2 Polishing time is 0.5-2 hours.

7. The glass flatness correction method as described in claim 1, characterized in that: Also includes: The glass is then polished a second time using a double-sided polishing machine. The lower polishing disc rotates at 10-50 rpm, the load speed ratio of the upper polishing disc to the lower polishing disc is 50-80%, the load speed ratio of the internal gear ring to the lower polishing disc is 80-100%, and the load speed ratio of the external gear ring to the lower polishing disc is 5-30%. The lower polishing disc rotates in the opposite direction to the upper polishing disc, internal gear ring, and external gear ring. The processing pressure is 10-30 g / cm². 2 Polishing time is 0.1-1 hour.

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