Grinding pad for improving wafer edge uniformity and preparation method and application thereof

Abstract

The invention belongs to the technical field of wafer manufacturing, and relates to a grinding pad for improving wafer edge uniformity and a preparation method and application thereof.The grinding pad comprises a grinding layer and a buffer layer which are arranged in a stacked mode, the buffer layer is made of foaming polyurethane, and the grinding layer and the buffer layer are attached to each other through an adhesive. The preparation method comprises the steps that the surface of one side of the grinding layer is evenly coated with an adhesive, then the buffer layer made of the foaming polyurethane material is attached, and the grinding pad is obtained after drying. According to the polishing pad, the foaming polyurethane serves as the buffer layer, the defects of traditional non-woven fabric are overcome, meanwhile, the adhesive is adopted to be attached to the polishing layer and the buffer layer, the influence of the adhesive layer on the deformation characteristic of the buffer layer is considered, and the wafer edge uniformity is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of wafer manufacturing technology, and relates to a polishing pad for improving wafer edge uniformity, and more particularly to a polishing pad for improving wafer edge uniformity, its preparation method and application. Background Technology

[0002] Chemical mechanical polishing (CMP) is a key process for achieving global planarization of semiconductor wafers during manufacturing. Its polishing effect directly determines the surface quality of the wafer and the yield of subsequent chip manufacturing processes. The polishing uniformity of the wafer edge area is an important quality control point. Deviations in edge uniformity can lead to chip failure at the wafer edge, significantly reducing the effective utilization rate of the wafer. Therefore, the industry has imposed stringent requirements on the uniformity control capability of CMP polishing pads.

[0003] In existing technologies, commercial CMP polishing pads generally adopt a two-layer structure combining a polishing layer and a buffer layer, with clearly defined functions for each. The polishing layer directly polishes the wafer, and its material and surface structure determine the polishing rate of the wafer, making it the core functional layer of the polishing pad. The buffer layer mainly serves to evenly distribute pressure and absorb vibrations, adjusting the contact pressure distribution during the polishing process through its own deformation characteristics, making it a key structural layer for controlling the uniformity of wafer polishing.

[0004] Currently, most mainstream buffer layers are made of non-woven fabric. This material is a common choice in the industry due to its mature processing technology and low cost. However, it has inherent defects and cannot meet the high-precision wafer edge uniformity requirements. First, non-woven fabric has strong water absorption, while CMP polishing continuously uses polishing fluid containing water. The buffer layer absorbs the polishing fluid and expands significantly, causing the overall thickness of the polishing pad to continuously change with the polishing process. This results in irregular undulations on the surface, disrupting the stability of the polishing pressure and directly leading to inconsistent polishing amounts in different areas of the wafer. Second, non-woven fabric is relatively soft, with a compression ratio generally in the high range of 14% to 20%, resulting in large deformation. During polishing, to prevent wafer slippage, positioning rings are used to apply continuous limiting pressure to the polishing pad. This pressure causes significant local deformation of the buffer layer, leading to irregular fluctuations in the polishing contact pressure in the wafer edge area. This results in either insufficient or excessive edge polishing, ultimately maintaining a wafer polishing non-uniformity of 4.5% to 5%, highlighting the problem of poor edge uniformity.

[0005] Furthermore, existing methods for bonding the abrasive layer and the buffer layer mostly use double-sided adhesive. While convenient, double-sided adhesive has insufficient bonding strength with the buffer layer. Mechanical vibration and pressure during polishing can easily cause delamination between the two, compromising the structural stability of the abrasive pad and further exacerbating the deviation in polishing uniformity. If the adhesive type is changed, the impact of the adhesive layer on the deformation characteristics of the buffer layer must also be considered. Currently, no suitable bonding solution has been found in the industry.

[0006] Therefore, it is evident that providing a polishing pad that improves wafer edge uniformity, overcomes the defects of existing nonwoven buffer layers, and takes into account the influence of the adhesive layer on the deformation characteristics of the buffer layer has become a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a polishing pad for improving the uniformity of wafer edges, its preparation method and application, to overcome the defects of existing nonwoven buffer layers, while taking into account the influence of the adhesive layer on the deformation characteristics of the buffer layer.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a polishing pad for improving the uniformity of wafer edges, comprising a polishing layer and a buffer layer stacked together, wherein the buffer layer is made of foamed polyurethane, and the polishing layer and the buffer layer are bonded together by an adhesive.

[0009] The polishing pad provided by this invention uses foamed polyurethane as a buffer layer, which is not easily deformed under the pressure of the positioning ring. The contact pressure at the wafer edge is more uniform, and the amount of polishing removal from the center to the edge is more consistent. Compared with traditional non-woven fabric, polyurethane material does not absorb water but only absorbs water. It will not expand due to the moisture in the polishing liquid, thus ensuring that the overall thickness of the polishing pad is constant and there are no unevenness. It maintains polishing stability and ultimately reduces the wafer polishing non-uniformity from the traditional 4.5%~5% to 2%~3%, effectively improving the uniformity of the wafer edge.

[0010] Furthermore, the present invention uses an adhesive to bond the grinding layer and the buffer layer, which provides a strong bond and completely solves the delamination problem. Compared with traditional double-sided tape, the adhesive is very thin after drying, which does not adversely affect the deformation characteristics of the buffer layer, further ensuring the control of uniformity of the buffer pad.

[0011] Furthermore, this invention only changes the buffer layer in the polishing pad, indirectly improving the uniformity of the wafer edge, without significantly affecting the overall polishing rate of the wafer. The process is easy to implement and perfectly adapts to the existing production system.

[0012] Preferably, the compression ratio of the buffer layer is 9% to 16%, and more preferably 9% to 12%.

[0013] Preferably, the porosity of the buffer layer is 45% to 55%, more preferably 45% to 50%.

[0014] Preferably, the internal pores of the buffer layer are uniformly distributed in the horizontal direction.

[0015] Preferably, the thickness of the buffer layer is 3~63 mil.

[0016] Preferably, the adhesive comprises at least one of epoxy resin, polyurethane, acrylate or phenolic resin.

[0017] In a second aspect, the present invention provides a method for preparing an abrasive pad as described in the first aspect, the method comprising: uniformly coating an adhesive on one side surface of an abrasive layer, then bonding a buffer layer made of foamed polyurethane material, and drying to obtain the abrasive pad.

[0018] Thirdly, the present invention provides an application of the polishing pad as described in the first aspect, wherein the polishing pad is used in a chemical mechanical polishing production line for semiconductor wafers.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The polishing pad provided by the present invention uses polyurethane foam as a buffer layer. It is not easily deformed under the pressure of the positioning ring, the contact pressure of the wafer edge is more uniform, the amount of polishing removal from the center to the edge is more consistent, and compared with the traditional non-woven fabric, the polyurethane material does not absorb water but only gets wet. It will not expand due to the water in the polishing liquid, thus ensuring that the overall thickness of the polishing pad is constant and there is no undulation phenomenon. It continuously maintains the polishing stability and finally reduces the wafer polishing non-uniformity from the traditional 4.5%~5% to 2%~3%, effectively improving the wafer edge uniformity.

[0020] (2) The present invention uses an adhesive to bond the grinding layer and the buffer layer, which has a strong bonding force and completely solves the delamination problem. Compared with traditional double-sided tape, the adhesive is very thin after drying, which has no adverse effect on the deformation characteristics of the buffer layer, further ensuring the control of uniformity of the buffer pad.

[0021] (3) The present invention only changes the buffer layer in the polishing pad, which indirectly improves the uniformity of the wafer edge and does not significantly affect the overall polishing rate of the wafer. The process is easy to implement and perfectly adapts to the existing production system. Attached Figure Description

[0022] Figure 1 This is a cross-sectional micrograph of the foamed polyurethane buffer layer in the abrasive pad provided in Example 1.

[0023] Figure 2 This is a cross-sectional micrograph of the non-woven fabric buffer layer in the abrasive pad provided in Comparative Example 1.

[0024] Figure 3 These are diagrams of chemical mechanical polishing apparatuses for semiconductor wafers using the polishing pads obtained in Examples 1-6 and Comparative Examples 1-2. Detailed Implementation

[0025] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0026] One embodiment of the present invention provides a polishing pad for improving wafer edge uniformity, comprising a polishing layer and a buffer layer stacked together, wherein the buffer layer is made of foamed polyurethane, and the polishing layer and the buffer layer are bonded together by an adhesive.

[0027] The polishing pad provided by this invention uses foamed polyurethane as a buffer layer, which is not easily deformed under the pressure of the positioning ring. The contact pressure at the wafer edge is more uniform, and the amount of polishing removal from the center to the edge is more consistent. Compared with traditional non-woven fabric, polyurethane material does not absorb water but only absorbs water. It will not expand due to the moisture in the polishing liquid, thus ensuring that the overall thickness of the polishing pad is constant and there are no unevenness. It maintains polishing stability and ultimately reduces the wafer polishing non-uniformity from the traditional 4.5%~5% to 2%~3%, effectively improving the uniformity of the wafer edge.

[0028] Furthermore, the present invention uses an adhesive to bond the grinding layer and the buffer layer, which provides a strong bond and completely solves the delamination problem. Compared with traditional double-sided tape, the adhesive is very thin after drying, which does not adversely affect the deformation characteristics of the buffer layer, further ensuring the control of uniformity of the buffer pad.

[0029] Furthermore, this invention only changes the buffer layer in the polishing pad, indirectly improving the uniformity of the wafer edge, without significantly affecting the overall polishing rate of the wafer. The process is easy to implement and perfectly adapts to the existing production system.

[0030] In some embodiments, the compression ratio of the buffer layer is 9% to 16%, for example, it can be 9%, 10%, 11%, 12%, 13%, 14%, 15% or 16%, preferably 9% to 12%, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] Compared to the compression ratio of non-woven fabrics, which is as high as 14% to 20%, this invention reduces the compression ratio of the foamed polyurethane buffer layer to 9% to 16%, and further to 9% to 12%. This significantly reduces the deformation of the buffer layer, making it less prone to significant local deformation under the limiting pressure of the positioning ring. This fundamentally avoids the disruption of polishing contact pressure caused by deformation, thereby ensuring that the pressure is evenly transmitted on the wafer surface (especially the edge area) during the polishing process, and preventing insufficient or excessive polishing at the edges.

[0032] Specifically, the compression ratio directly reflects the hardness and elasticity of the buffer layer, and the calculation formula is: Compression Ratio = (T1 - T2) / T1 × 100%. Where T1 is the thickness of the buffer layer after 60 seconds of exposure to 30 kPa pressure from an unloaded state; T2 is the thickness of the buffer layer after 60 seconds of exposure to 180 kPa pressure from state T1. Following the above measurement method, the compression ratio is measured at multiple points on both sides of the buffer layer, and the average value of the compression ratio is calculated.

[0033] In some embodiments, the porosity of the buffer layer is 45% to 55%, for example, it can be 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54% or 55%, preferably 45% to 50%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] The aforementioned porosity range is well-matched to the polyurethane foam material, preserving the necessary vibration damping and pressure buffering functions of the buffer layer while avoiding the problems of excessively high porosity leading to an overly soft buffer layer and increased deformation, or excessively low porosity leading to an overly hard buffer layer and loss of pressure regulation. Simultaneously, this porosity range makes the internal structure of the buffer layer more adaptable to the polishing process requirements, enabling more stable transmission of polishing pressure, reducing localized deformation under the pressure of the positioning ring, ensuring uniform contact pressure at the wafer edge, and thus improving wafer edge uniformity.

[0035] In addition, the porosity of 45% to 55% and the compression ratio of 9% to 16% work together to constrain the physical properties of the foamed polyurethane buffer layer. This structurally avoids wafer edge grinding deviations caused by material deformation and uneven pressure distribution, while ensuring the stable performance of the buffer layer's non-absorbent properties, thereby maintaining a constant overall thickness of the grinding pad.

[0036] In some embodiments, the internal pores of the buffer layer are uniformly distributed in the horizontal direction, which effectively ensures that the polishing pressure is uniformly transmitted on the wafer contact surface, stabilizes the pressure regulation effect of the buffer layer from the structural level, and further improves the polishing uniformity of the wafer edge.

[0037] In some embodiments, the thickness of the buffer layer is 3 to 63 mil, for example, it can be 3 mil, 5 mil, 10 mil, 15 mil, 20 mil, 25 mil, 30 mil, 35 mil, 40 mil, 45 mil, 50 mil, 55 mil, 60 mil or 63 mil, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0038] The thickness unit mil mentioned above specifically refers to "milliinch".

[0039] In some embodiments, the adhesive comprises at least one of epoxy resin, polyurethane, acrylate or phenolic resin, for example, cyanoacrylate adhesive.

[0040] The aforementioned cyanoacrylate adhesive is a fast-drying adhesive, which is easy to apply and cures quickly. It can achieve rapid and uniform bonding between the grinding layer and the buffer layer, and is suitable for the industrial-scale batch production process of grinding pads without requiring significant adjustments to the existing preparation process.

[0041] In addition, the adhesive layer formed after the cyanoacrylate adhesive dries is extremely thin, which will not adversely affect the deformation characteristics and pressure regulation of the buffer layer, ensuring the normal buffering and vibration reduction function of the buffer layer under the pressure of the positioning ring, and ensuring the uniform transmission of polishing pressure.

[0042] Furthermore, the material properties of cyanoacrylate and polyurethane are compatible, resulting in strong adhesion that effectively resists mechanical vibration and pressure during the polishing process. This completely avoids the problem of easy delamination that is common with traditional double-sided adhesives. Moreover, after bonding, it will not react adversely with the buffer layer, nor will it change its non-absorbent and low-deformation physical properties, thus maintaining the overall stable performance of the polishing pad.

[0043] One embodiment of the present invention also provides a method for preparing the abrasive pad described in any of the above embodiments. The preparation method includes: uniformly coating an adhesive on one side surface of the abrasive layer, then attaching a buffer layer made of foamed polyurethane material, and drying to obtain the abrasive pad.

[0044] One embodiment of the present invention also provides an application of the polishing pad described in any of the above embodiments, wherein the polishing pad is used in a chemical mechanical polishing production line for semiconductor wafers.

[0045] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0046] Examples 1-6 This set of embodiments provides a polishing pad for improving wafer edge uniformity and its preparation method, including a polishing layer and a buffer layer stacked together. The buffer layer is made of polyurethane foam, and the internal pores are uniformly distributed in the horizontal direction. The polishing layer and the buffer layer are bonded to each other with cyanoacrylate adhesive.

[0047] The compression ratio, porosity, and thickness of the buffer layer in each embodiment are shown in Table 1 below.

[0048] Table 1 In all embodiments, the grinding layer is made of thermosetting polyurethane foam and has a thickness of 60 mil.

[0049] The method for preparing the abrasive pad in each embodiment includes: uniformly coating an adhesive on one side surface of the abrasive layer, then attaching a buffer layer made of foamed polyurethane, and drying it to obtain the abrasive pad.

[0050] Among them, the microscopic photograph of the cross-section of the foamed polyurethane buffer layer in the abrasive pad provided in Example 1 at a magnification of ×50 is shown in the image. Figure 1 .

[0051] Comparative Example 1 This comparative example provides an abrasive pad, except that the buffer layer is replaced with a 30mil thick nonwoven fabric (compression ratio of 20% and porosity of 80%). The rest of the structure and conditions are the same as in Example 1, so they will not be described in detail here.

[0052] Among them, the microscopic photograph of the cross-section of the non-woven fabric buffer layer at a magnification of ×50 is shown below. Figure 2 .

[0053] Comparative Example 2 This comparative example provides an abrasive pad, which is identical to Example 1 except that the abrasive layer and the buffer layer are bonded together with conventional double-sided adhesive. Therefore, it will not be described in detail here.

[0054] Performance testing according to Figure 3 The device structure utilizes the polishing pads obtained in the above embodiments and comparative examples for chemical mechanical polishing of semiconductor wafers. Specific polishing parameters include: flexible film pressure 3±1 psi, positioning ring pressure 8±2 psi, polishing disk rotation speed 90±3 rpm, and polishing fluid flow rate 200±50 m³ / min. The wafer polishing non-uniformity corresponding to the polishing pads obtained in each embodiment and comparative example is shown in Table 2 below.

[0055] Table 2 Furthermore, the polishing pads obtained in Examples 1-6 and Comparative Example 1 did not exhibit delamination during continuous polishing, while the polishing pad obtained in Comparative Example 2 did exhibit delamination.

[0056] In the table above, the formula for calculating non-uniformity is: (Max - Min) / 2 × Removal rate. Where Max is the maximum thickness value at the measurement point; Min is the minimum thickness value at the measurement point; and Removal rate is the grinding rate.

[0057] Therefore, the polishing pad provided by this invention uses foamed polyurethane as a buffer layer, which is not easily deformed under the pressure of the positioning ring, and the contact pressure at the wafer edge is more uniform. The amount of polishing removal from the center to the edge is more consistent. Moreover, compared with traditional non-woven fabric, polyurethane material does not absorb water but only absorbs water. It will not expand due to the moisture in the polishing liquid, thus ensuring that the overall thickness of the polishing pad is constant and there are no unevenness. It continuously maintains polishing stability and ultimately reduces the wafer polishing non-uniformity from the traditional 4.5%~5% to 2%~3%, effectively improving the uniformity of the wafer edge.

[0058] Furthermore, the present invention uses an adhesive to bond the grinding layer and the buffer layer, which provides a strong bond and completely solves the delamination problem. Compared with traditional double-sided tape, the adhesive is very thin after drying, which does not adversely affect the deformation characteristics of the buffer layer, further ensuring the control of uniformity of the buffer pad.

[0059] Furthermore, this invention only changes the buffer layer in the polishing pad, indirectly improving the uniformity of the wafer edge, without significantly affecting the overall polishing rate of the wafer. The process is easy to implement and perfectly adapts to the existing production system.

[0060] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A polishing pad for improving wafer edge uniformity, comprising a polishing layer and a buffer layer stacked together, characterized in that, The buffer layer is made of foamed polyurethane, and the abrasive layer and the buffer layer are bonded together by adhesive.

2. The polishing pad for improving wafer edge uniformity according to claim 1, characterized in that, The compression ratio of the buffer layer is 9% to 16%.

3. The polishing pad for improving wafer edge uniformity according to claim 2, characterized in that, The compression ratio of the buffer layer is 9% to 12%.

4. The polishing pad for improving wafer edge uniformity according to any one of claims 1 to 3, characterized in that, The porosity of the buffer layer is 45% to 55%.

5. The polishing pad for improving wafer edge uniformity according to claim 4, characterized in that, The porosity of the buffer layer is 45%~50%.

6. The polishing pad for improving wafer edge uniformity according to claim 5, characterized in that, The internal pores of the buffer layer are uniformly distributed in the horizontal direction.

7. The polishing pad for improving wafer edge uniformity according to any one of claims 1 to 3, characterized in that, The thickness of the buffer layer is 3~63 mil.

8. The polishing pad for improving wafer edge uniformity according to any one of claims 1 to 3, characterized in that, The adhesive comprises at least one of epoxy resin, polyurethane, acrylate or phenolic resin.

9. A method for preparing an abrasive pad as described in any one of claims 1 to 8, characterized in that, The preparation method includes: uniformly coating an adhesive on one side surface of the abrasive layer, then attaching a buffer layer made of foamed polyurethane, and drying it to obtain the abrasive pad.

10. An application of the abrasive pad as described in any one of claims 1 to 8, characterized in that, The polishing pad is used in the chemical mechanical polishing production line for semiconductor wafers.

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