Template assembly, polishing head, and wafer polishing method

Abstract

A template assembly is provided for single-sided polishing of a wafer. The template assembly includes a back pad having a radial profile with a PV value of 0.9 mm or less and a surface roughness Ra of 1.1 μm or less on a wafer supporting surface, and a guide ring portion fixed along an outer peripheral portion of the back pad. The template assembly can improve in-plane uniformity of edge flatness of a wafer after single-sided polishing.

Description

Technical Field

[0001] This invention relates to a template assembly, a grinding head, and a grinding method for wafers. Background Technology

[0002] The polishing of semiconductor wafers typically follows this process: after double-sided polishing (DSP), a second polishing and finishing polishing process is performed using single-sided polishing (CMP). In polishing using a single-sided polishing apparatus, a polishing head containing a template assembly for wafer support is primarily used. This template assembly has a back pad and a guide ring located on its outer periphery; the wafer is supported in the portion surrounded by the back pad and the guide ring. The wafer support surface is the back pad, which is pressurized during polishing, causing the wafer to slide into contact with the polishing pad (polishing cloth) attached to the platform for polishing.

[0003] Patent Document 1 describes a method for grinding a wafer in a single-sided grinding apparatus at a wafer rotation rate of 25 degrees / minute or more and 60 degrees / minute or less, thereby reducing the circumferential flatness deviation of the outer periphery of the wafer.

[0004] Patent document 2 describes a grinding method in which a multi-stage grinding process using a double-sided grinding device and a single-sided grinding device is employed, thereby preventing scratches from occurring in the final single-sided grinding stage.

[0005] Patent document 3 describes a manufacturing method for regenerated wafers, in which, after double-sided grinding, single-sided grinding is performed to reduce the thickness by less than 50 μm, thereby enabling the regeneration of a regenerated wafer suitable for 0.13 μm equipment processes.

[0006] Patent document 4 describes a grinding method that uses a wafer holding tool of a single-sided grinding device, wherein the thickness of the holding pad is 0.25~1.0 mm and the depth of the holding part is 40~150 μm.

[0007] Patent document 5 describes a polishing method that uses a retaining ring, which is a retaining ring for holding a substrate and pressing it against a polishing pad. The retaining ring has an inner ring and an outer ring. The radial thickness of the inner ring is 0.05 mm or more and 5 mm or less, and the surface roughness Ra of the bottom surface of the retaining ring is 1.6 μm or less.

[0008] Patent document 6 describes a grinding method that uses a retaining ring, which is a retaining ring of a single-sided grinding device, wherein the surface roughness Ra of the inner wall of the inner ring is ground to less than 30 microinches.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2021-091081

[0012] Patent Document 2: Japanese Patent Application Publication No. 2010-131683

[0013] Patent Document 3: Japanese Patent Application Publication No. 2001-358107

[0014] Patent Document 4: Japanese Patent Application Publication No. 2016-043446

[0015] Patent Document 5: Japanese Patent Application Publication No. 2016-155188

[0016] Patent Document 6: Japanese Patent Application Publication No. 2016-178304 Summary of the Invention

[0017] (a) Technical problems to be solved

[0018] Although efforts to improve the flatness of polished wafers have been ongoing, the requirements for wafer flatness are becoming increasingly stringent. In particular, there is a demand for further improvement in the circumferential uniformity of the flatness (edge ​​flatness) of the wafer's periphery.

[0019] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a template assembly for wafer support, a grinding head having the template assembly, and a grinding method for a wafer using the grinding head. The template assembly for wafer support is used for single-sided grinding of the wafer, which can improve the circumferential uniformity of edge flatness on the wafer after single-sided grinding such as CMP.

[0020] (II) Technical Solution

[0021] To achieve the above-mentioned objective, the present invention provides a template assembly for single-sided grinding of wafers and for supporting wafers. The template assembly for supporting wafers is characterized in that it includes a back pad and a guide ring fixed along the outer periphery of the back pad. The PV value of the radial shape profile of the back pad on the surface supporting the wafer is 0.9 mm or less, and the surface roughness Ra of the surface supporting the wafer is 1.1 μm or less.

[0022] Based on such template components, it is possible to improve the circumferential uniformity of the edge flatness of wafers after single-sided grinding and enhance the in-plane uniformity of flatness.

[0023] At this point, a grinding head can be obtained, which includes the template assembly described above in this invention, and a retaining ring disposed at a position corresponding to the guide ring portion.

[0024] Thus, it becomes a grinding head that can improve the circumferential uniformity of the edge flatness of a wafer after single-sided grinding.

[0025] At this point, a wafer polishing method can be obtained, which uses the polishing head of the present invention to polish the wafer while pressing it against the polishing pad.

[0026] According to this wafer grinding method, the circumferential uniformity of the edge flatness of the wafer after single-sided grinding can be improved, and the in-plane uniformity of the flatness can be enhanced.

[0027] (III) Beneficial Effects

[0028] As described above, the template assembly according to the present invention can improve the circumferential uniformity of the edge flatness of a wafer after single-sided grinding and enhance the in-plane uniformity of the flatness. Attached Figure Description

[0029] Figure 1 This is a cross-sectional schematic diagram of the grinding head.

[0030] Figure 2 Indicates the shape profile (PV value) of the back pad and the measurement direction.

[0031] Figure 3 This indicates the PV value of the back pad used in the embodiments and comparative examples.

[0032] Figure 4 Ra represents the surface roughness of the backing pad used in the embodiments and comparative examples.

[0033] Figure 5 The flatness evaluation results for the examples and comparative examples are shown. Detailed Implementation

[0034] The present invention will now be described in detail, but the invention is not limited to these examples.

[0035] As described above, there is a need to improve the circumferential uniformity of the edge flatness of wafers after single-sided grinding and to enhance the in-plane uniformity of the flatness. To address this problem, the inventors conducted meticulous research and discovered that the reduced (deteriorated) circumferential uniformity of the edge flatness of wafers after single-sided grinding such as CMP is due to insufficient wafer rotation. In the templates used in existing grinding heads, it was found that the backing pad has an undulating shape. Even with increased wafer rotation, this undulation is transferred to the wafer as a load distribution. In this state, the wafer is ground along with the grinding head, thus reducing (deteriorating) the circumferential uniformity of the wafer's edge flatness.

[0036] Therefore, the inventors conducted careful research focusing on the construction of a template assembly for wafer support, and found that the following template assembly can improve the circumferential uniformity of edge flatness and enhance the in-plane uniformity of flatness, thereby completing the present invention. The template assembly is a template assembly for wafer support used for single-sided grinding of wafers, and includes a back pad and a guide ring fixed along the outer periphery of the back pad. The PV value of the radial shape profile of the back pad on the surface supporting the wafer is 0.9 mm or less, and the surface roughness Ra of the surface supporting the wafer is 1.1 μm or less.

[0037] The following explanation is based on the accompanying drawings.

[0038] [Grinding head]

[0039] Figure 1 This is a cross-sectional schematic diagram showing a grinding head used in single-sided grinding of a wafer. (Example:) Figure 1 As shown, the grinding head 100 includes a template assembly 3 and a retaining ring 4 positioned corresponding to the guide ring portion 2 of the template assembly 3. The template assembly 3 is attached to the retaining ring 4 such that the retaining ring 4 is positioned corresponding to the guide ring portion 2. Thus, the outer periphery of the backing pad 1 is clamped between the retaining ring 4 and the guide ring portion 2. Furthermore, Figure 1 The grinding head 100 shown in the example also includes a back plate 7 and an upper flange assembly 6, which is disposed on the side of the retaining ring 4 opposite to the template assembly 3. The retaining ring 4 is fixed along the outer periphery of the upper flange assembly 6. The space surrounded by the back plate 7, the back pad 1 and the retaining ring 4 is called the fluid sealing part, namely the back pad pressurization part (fluid sealing part) 5.

[0040] [Template Components]

[0041] The wafer support template assembly 3 includes a back pad 1 and a guide ring portion 2 fixed along the outer periphery of the back pad 1. Regarding the back pad of the present invention, its radial shape profile PV (Peak-to-Valley) value on the surface supporting the wafer is 0.9 mm or less, and the surface roughness Ra of the surface supporting the wafer is 1.1 μm or less. With such a back pad, the contact resistance with the wafer increases, thus effectively promoting wafer rotation. As a result, the circumferential uniformity of edge flatness can be improved. Furthermore, the lower limit of the PV value of the radial shape profile on the surface supporting the wafer of the present invention is 0.0 mm or more, and the lower limit of the surface roughness Ra of the surface supporting the wafer is 0.0 μm or more.

[0042] As a backing pad, for example, a material is used where a layer of polyurethane foam is formed on a substrate layer such as a polyurethane foam sheet, a non-woven fabric sheet, or a PET (polyethylene terephthalate) film. Regarding the method for manufacturing the backing pad of the shape described above, for the roughness Ra, after forming the polyurethane foam on the substrate, the grit size of the diamond abrasive grains on the surface of the polishing wheel used to adjust the surface roughness is changed, thereby enabling the production of backing pads with different roughnesses. Furthermore, regarding the PV value of the shape profile, by changing the PET material, non-woven fabric sheet, or other materials used as the substrate, backing pads with different PV values ​​for the shape profile can be produced. By changing the manufacturing conditions of such backing pads, backing pads of various shapes can be obtained.

[0043] The shape of the back pad can be measured using known measuring devices. The PV value of the radial shape profile on the surface of the back pad supporting the wafer can be determined using a three-dimensional shape measuring machine. Figure 2 The radial shape profile indicated by the arrow is measured and calculated. The surface roughness Ra of the backing pad can be measured using a contact roughness measuring machine.

[0044] Example

[0045] The present invention will be specifically described below with examples and comparative examples, but these are not intended to limit the present invention.

[0046] (Template component)

[0047] A template assembly with a backing pad is prepared, the backing pad having various shapes. Comparative Example 1 is a conventionally used template assembly (existing product). Comparative Example 2 is a backing pad whose PV value does not meet the conditions of the present invention, and Comparative Example 3 is a backing pad whose surface roughness Ra does not meet the conditions of the present invention.

[0048] The shape of the backing pad of the template assembly was measured using a 3D shape measuring machine employing a laser probe. The template assembly was attached to a ceramic retaining ring, and the finished product was placed on a pedestal with the template side facing upwards. The measurement was performed using a Tokyo Precision XYZAX-SVA laser probe type 3D shape measuring machine. Figure 2 As shown, radial measurements are performed on the surface supporting the wafer in a full scan, thereby determining the PV (Peak-to-Valley) value of the radial shape profile with the surface as a reference. Figure 3 The PV value represents the radial shape profile of the back pad on the surface of the supporting wafer used in Examples 1, 2, and Comparative Examples 1-3.

[0049] The roughness of the backing pad was measured using a Mitutoyo SURFTEST SJ-410 contact roughness measuring machine. The measurement length was set to 400 μm, and a Gaussian filter (cutoff wavelength 80 μm, λs filter 2.5 μm) was used. Figure 4 Ra represents the surface roughness of the support wafer surface of the back pad used in Examples 1, 2, and Comparative Examples 1-3.

[0050] (Grinding process)

[0051] In the evaluation, 300 mm diameter silicon wafers that had undergone double-sided polishing and SC1 cleaning were used. The thickness of the wafers used was 775 μm. The number of wafers polished was set to 25 in each example and comparative example. The polishing process was performed as follows: a polishing pad made of urethane-impregnated nonwoven fabric was attached to a ceramic platform, and then a polishing slurry containing an alkaline aqueous solution (pH 11) of KOH groups containing silica-based abrasive particles was supplied to the polishing pad while the polishing head was rotated with the platform at 40 rpm to bring the wafer into contact. The polishing margin was set to 300 nm.

[0052] (Flatness evaluation)

[0053] The flatness of the polished wafers was measured. Flatness was measured using a KLA WaferSight 2+. For each wafer, the difference in ESFQR range before and after polishing (excluding the outer perimeter: EE = 2 mm) was calculated, and the average value of 25 wafers under each condition was calculated. The evaluation results are shown in Table 1. Figure 5 In addition, Table 1 also records the PV value of the radial shape profile on the surface of the back pad supporting the wafer, the surface roughness Ra of the surface of the back pad supporting the wafer, the polishing wheel grit number used to adjust the surface roughness of the back pad, and the substrate of the back pad.

[0054] [Table 1]

[0055]

[0056] As shown in Table 1, Figure 5 As shown, in Examples 1 and 2 using back pads that meet the conditions of the present invention, and in Comparative Examples 1 to 3 using back pads that do not meet the conditions of the present invention, the differences in ESFQR Range are significantly different. According to embodiments of the present invention, it is possible to obtain favorable results where the change in ESFQR Range of the wafer before and after grinding is smaller than that in the comparative examples. This favorable result is believed to be due to the effect of the rotation of the grinding head on promoting wafer rotation and suppressing the transfer of back pad shape.

[0057] Furthermore, the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any solution having a structure that is substantially the same as the technical concept described in the claims of the present invention and achieving the same effect is included within the technical scope of the present invention.

Claims

1. A template assembly for single-sided grinding of wafers and for wafer support, characterized in that, The template assembly for wafer support includes a back pad and a guide ring portion fixed along the outer periphery of the back pad. The PV value of the radial shape profile of the back pad on the surface supporting the wafer is less than 0.9 mm, and the surface roughness Ra of the surface supporting the wafer is less than 1.1 μm.

2. A grinding head, characterized in that, have: The template component as claimed in claim 1; and A retaining ring positioned corresponding to the guide ring portion.

3. A method for grinding a wafer, characterized in that, Using the grinding head as described in claim 2, the wafer is pressed against the grinding pad while being ground.

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