A method for improving the surface morphology and surface flatness of wafer after single-side polishing

Abstract

The present invention discloses a method for changing the surface morphology and surface flatness of a wafer after single-sided polishing. The method comprises the following steps: (1) producing concentric circle adhesive according to the size of a ceramic disc; (2) preheating the ceramic disc and attaching the concentric circle adhesive to the surface of the ceramic disc; (3) attaching a suction cup pad to the surface of the ceramic disc with the concentric circle adhesive and applying pressure for pressing; (4) using the ceramic disc for single-sided polishing of the wafer to obtain wafers with different surface morphologies and surface flatness after polishing. The present invention changes the force applied to the wafer during single-sided polishing by attaching concentric circle adhesives with different inner diameters to the interlayer of the suction cup pad, thereby improving the surface morphology and surface flatness of the wafer after single-sided polishing. The present invention has strong practicality and can design adhesives with different inner diameters according to the required surface morphology and surface flatness. The process flow is simple, the cost is low, the effect is obvious, and it has good application prospects in the semiconductor field.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to a method for improving the surface morphology and surface flatness of a wafer after single-side polishing. Background Art

[0002] With the rapid development of integrated circuits, large-size silicon substrates have more advantages in reducing chip production costs, improving equipment production efficiency and reuse rate. At present, the use of 300mm diameter wafers to manufacture chips has become the mainstream. As the feature size decreases and the focal depth of the lithography machine becomes shorter, the uneven surface of the wafer will cause the lithography pattern to deform, affecting the chip performance and yield rate, so the wafer surface is required to be globally flat.

[0003] Chemical mechanical polishing (CMP) is the most common surface smoothing technology for semiconductor materials. It is a process that combines mechanical friction and chemical corrosion, and combines the advantages of both to obtain a relatively perfect wafer surface. Wafer CMP generally uses alkaline silica polishing liquid, which uses the chemical corrosion reaction of alkali and silicon to generate soluble silicates, and then removes the reaction products in time through the adsorption of small, soft, large specific surface area, negatively charged silica colloidal particles and the mechanical friction between the polishing cloth and the wafer, thereby achieving the polishing purpose of removing the surface damage layer and contaminants of the wafer. This process of chemical and mechanical interaction is the process of wafer CMP polishing. Wafer polishing is generally divided into three steps: the first step is rough polishing, that is, removing the surface damage layer remaining on the wafer surface; the second step is medium polishing, that is, further improving the surface flatness of the wafer and reducing the roughness; the third step is fine polishing, that is, "defogging", trimming the wafer surface to give it extremely high nano-morphological characteristics.

[0004] For rough polishing of wafers, due to the large amount of removal, the surface flatness and surface morphology are most affected. Currently, most wafers are attached to suction pads and fixed by suction pads for single-sided polishing. The suction pad adsorbs the wafer by a velvet layer with strong adsorption force, and the wafer is fixed by a plastic ring pressed on the velvet layer. The defect is that the velvet layer on the inner circle of the plastic ring is significantly thinner than the central area due to the compression molding of the plastic ring. This results in stronger mechanical friction in the center of the wafer than at the edge during polishing, and a larger amount of removal than at the edge, which ultimately leads to a concave surface morphology after polishing and poor surface flatness. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for improving the surface morphology and surface flatness of a wafer after single-side polishing.

[0006] The present invention is suitable for single-sided polishing of 12-inch wafers. By changing the inner diameter of the concentric circle adhesive backing of the suction cup pad, the contact position with the polishing cloth during the wafer CMP process is changed, thereby controlling the mechanical friction effect of the contact surface with the polishing cloth during the wafer CMP process, and obtaining different surface morphologies and surface flatness after polishing. The following technical solutions are specifically adopted:

[0007] A method for improving the surface morphology and surface flatness of a wafer after single-side polishing, which is applicable to single-side polishing of 12-inch wafers, comprises the following steps:

[0008] (1) According to the size of the ceramic plate, make concentric circle adhesive;

[0009] (2) preheating the ceramic plate and attaching the concentric circle adhesive to the surface of the ceramic plate;

[0010] (3) Attach the suction cup pad to the surface of the ceramic plate with concentric circle adhesive and apply pressure to press it;

[0011] (4) The ceramic disc is used for single-side polishing of the wafer, and wafers with different surface morphologies and surface flatness are obtained after polishing.

[0012] As a preferred technical solution of the present invention, in step (1), the concentric circle adhesive is made of a non-woven fabric substrate coated with acrylic adhesive on both sides. The thickness of the concentric circle adhesive is 0.05-0.25 mm, the outer diameter is 334 mm, and the inner diameter is 250-310 mm.

[0013] The thickness of the concentric circle adhesive may be, for example, 0.10 mm, 0.15 mm, 0.20 mm, etc. The inner diameter of the concentric circle adhesive may be, for example, 275 mm, 290 mm, 300 mm, 310 mm, etc. Preferably, the thickness of the concentric circle adhesive is 0.1-0.15 mm. The inner diameter of the concentric circle adhesive is 275-305 mm.

[0014] As a preferred technical solution of the present invention, in the step (2), the preheating temperature of the ceramic disk is 30-40°C, for example, 32°C, 34°C, 36°C, 38°C, etc. can be selected.

[0015] As a preferred technical solution of the present invention, in the step (3), the pressing pressure of the suction cup pad is 5-20kg, for example, 8kg, 12kg, 15kg, 18kg, etc. can be selected; the pressing time of the suction cup pad is 12-24h, for example, 13h, 15h, 18h, 20h, etc. can be selected.

[0016] Through the above method, the concentric circle adhesive changes the surface morphology of the suction cup pad, thereby affecting the mechanical friction between the wafer surface and the polishing cloth during the CMP process, and significantly improves the morphology and surface flatness of the wafer after CMP. At the same time, the process is simple, the cost is low, the effect is significant, and it has good application prospects.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention changes the mechanical action area during the single-sided polishing of the wafer by adding concentric circle adhesives of different thicknesses and inner diameters, which can significantly improve the surface morphology after polishing and enhance the surface flatness quality of the wafer.

[0019] (2) The method provided by the present invention can be widely used in CMP processing in which the wafer is fixed by a suction cup pad. The process flow is simple and the cost is low. The inner diameter size can be flexibly adjusted according to the processing requirements to obtain the required wafer surface morphology and excellent surface flatness. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the polishing principle diagram without adding back glue in the normal process.

[0021] Figure 2 This is a schematic diagram of the polishing principle of adding back glue in the present invention.

[0022] Figure 3 This is a photo of the ceramic disk with concentric circle adhesive in Example 1 of the present invention.

[0023] Figure 4 This is a photo of the ceramic plate after the suction cup pad is attached according to Example 1 of the present invention.

[0024] Figure 5 These are the wafer surface morphology test results obtained using normal processes.

[0025] Figure 6 The wafer surface morphology test results obtained in Example 1.

[0026] Figure 7 The wafer surface morphology test results obtained in Example 2.

[0027] Figure 8 These are the wafer surface flatness test results obtained by the normal process and Examples 1 and 2. DETAILED DESCRIPTION

[0028] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that many specific details are set forth in the following description to facilitate a full understanding of the present invention, but the following embodiments are only part of the embodiments of the present invention, and the present invention is not limited to these embodiments.

[0029] The present invention is applicable to single-side polishing of 12-inch wafers, and the specific steps are as follows:

[0030] (1) A non-woven fabric substrate is coated with acrylic adhesive on both sides to produce concentric circle adhesive with a thickness of 0.05-0.25 mm, an outer diameter of 334 mm, and an inner diameter of 250-310 mm.

[0031] (2) Preheat the ceramic plate to 30-40°C and attach the concentric circle adhesive to the surface of the ceramic plate.

[0032] (3) Attach the suction cup pad to the surface of the ceramic plate with concentric circles of adhesive backing and press it under a pressure of 5-20 kg for 12-24 hours.

[0033] (4) The ceramic disc is used for single-side polishing of the wafer, and wafers with different surface morphologies and surface flatness are obtained after polishing.

[0034] The concentric circle adhesive provided in the present invention changes the surface morphology of the suction cup pad, thereby affecting the mechanical friction between the wafer surface and the polishing cloth during the CMP process, and significantly improves the morphology and surface flatness of the wafer after CMP. At the same time, the process flow is simple, the cost is low, the effect is significant, and it has good application prospects.

[0035] Figure 1 and Figure 2 The following diagrams respectively show the polishing principle diagram of the normal process without adding back glue and the polishing principle diagram of the present invention with adding back glue. Figure 1 As shown, since the single-sided polishing pressurization method is center pressurization, in the normal process, the suction pad 2 is directly attached to the surface of the ceramic plate 1, and the mechanical friction in the middle is greater than that at the edge when polishing the wafer 3, resulting in high center removal and low edge removal after polishing. Figure 2 As shown, by adding concentric circle adhesive 4 between the suction pad 2 and the ceramic disk 1, since the adhesive has a certain thickness, the mechanical friction effect on the edge of the wafer 3 during polishing is greater than that in the middle, thereby offsetting the disadvantages of the center pressurization method, making the surface flatness of the wafer higher after polishing. The inner circle diameter of the concentric circle adhesive of the suction pad affects the position where the mechanical friction of the wafer increases. The smaller the inner diameter, the closer the wafer collapse position is to the center. The larger the inner diameter, the worse the adhesion between the suction pad and the ceramic disk, and the risk of falling off is likely to occur. The thickness of the concentric circle adhesive of the suction pad affects the center and edge removal rate. The larger the thickness, the higher the edge removal rate, and the greater the risk of fragments. The smaller the thickness, the smaller the edge removal rate, and the smaller the impact on the edge morphology. Therefore, the mechanical friction effect of the contact surface with the polishing cloth during the wafer CMP process can be controlled by adjusting the thickness and inner diameter of the concentric circle adhesive to obtain different surface morphologies and surface flatness after polishing.

[0036] Example 1

[0037] In this embodiment, the size of the wafer to be single-sided polished is 12 inches; the size of the ceramic disc used is 340 mm.

[0038] (1) Take 12 wafers to be single-sided polished and use the RPW3040i surface topography measuring instrument to measure the initial GBIR and topography of the wafer surface.

[0039] (2) A non-woven fabric substrate is coated with acrylic adhesive on both sides to produce concentric circle adhesive with a thickness of 0.1 mm, an inner diameter of 275 mm, and an outer diameter of 334 mm.

[0040] (3) After the ceramic plate is preheated to 35°C, attach the concentric circles of adhesive to the surface of the ceramic plate (such as Figure 3 ), and then attach the suction pad to the ceramic plate (as shown Figure 4 As shown), press at a pressure of 8 kg for 15 hours.

[0041] (4) Use the prepared ceramic disk to process 12 wafers normally on the SPM-15 single-sided polishing machine.

[0042] (5) After processing, use SPMC cleaning machine for cleaning and drying.

[0043] (6) After cleaning, the GBIR and morphology of the wafer surface after polishing are measured using the RPW3040i surface morphology measuring instrument.

[0044] Comparative Example

[0045] Take another 12 pieces and process them according to the normal process as a comparison. The processing process is as follows:

[0046] (1) The initial GBIR and morphology of the wafer surface were measured using the RPW3040i surface topography measuring instrument.

[0047] (2) Attach the suction pad to a ceramic plate that has not been preheated and leave it alone without pressure for 15 hours.

[0048] (3) 12 wafers were processed on a SPM-15 single-sided polishing machine using the prepared ceramic disk. The processing parameters are shown in Table 1.

[0049] (4) After processing, use SPMC cleaning machine for cleaning and drying.

[0050] (5) After cleaning, the GBIR and morphology of the wafer surface after polishing are measured using the RPW3040i surface morphology measuring instrument.

[0051] Table 1 Processing parameters of SPM-15 single-side polishing machine

[0052] Suction pad classification Polishing pressure Polishing time Throwing head speed Large disk speed Polishing liquid flow Normal process without adhesive 70kpa 12min 18r / min 22r / min 5L / min Example 1 70kpa 12min 18r / min 22r / min 5L / min Example 2 70kpa 12min 18r / min 22r / min 5L / min

[0053] Performance test 1: Surface morphology analysis

[0054] Normal process surface morphology test results are shown in Figure 5 , the surface morphology test results of Example 1 are shown in Figure 6 , surface flatness test results see Figure 8 As can be seen from the figure, the surface morphology of the wafer after normal process polishing is concave, with an average GBIR value of 2.8μm. The surface morphology of the wafer after polishing with the concentric circle adhesive added is changed to convex, with an average GBIR value of 2.1μm. The surface morphology of this embodiment is significantly changed, and the surface flatness is significantly improved.

[0055] The following table 2 corresponds to Figure 5-7 The coordinates of points along the diameter direction of a wafer surface after polishing are randomly selected in the normal process and the two embodiments.

[0056] Table 2

[0057]

[0058]

[0059]

[0060]

[0061] Example 2

[0062] In this embodiment, the size of the wafer to be single-sided polished is 12 inches; the size of the ceramic disc used is 340 mm.

[0063] (1) Take 12 wafers to be single-sided polished and use RPW3040i to measure the initial GBIR and morphology of the wafer surface.

[0064] (2) A non-woven fabric substrate is coated with acrylic adhesive on both sides to produce a backing adhesive with a thickness of 0.15 mm, an inner diameter of 303 mm, and an outer diameter of 334 mm.

[0065] (3) The ceramic plate is preheated to 37°C, the concentric circle adhesive is attached to the surface of the ceramic plate, the suction cup pad is attached to the ceramic plate, and pressed for 12 hours under a pressure of 12 kg.

[0066] (4) Use the prepared ceramic disk to process 12 wafers on the SPM-15 single-sided polishing machine.

[0067] (5) After processing, use SPMC cleaning machine for cleaning and drying.

[0068] (6) After cleaning, use RPW3040i to measure the GBIR and morphology of the polished wafer surface.

[0069] Performance test 2: Surface morphology analysis

[0070] Normal process surface morphology test results are shown in Figure 5 , the surface morphology test results of Example 2 are shown in Figure 7 , surface flatness test results see Figure 8 As can be seen from the figure, the surface morphology of the wafer after polishing with the normal process is concave, and the GBIR average value is 2.8μm. The surface morphology of the wafer after polishing with the concentric circle adhesive is changed to a "straight" shape, and the GBIR average value is 1.0μm. The surface morphology of this embodiment is significantly changed, and the surface flatness is significantly improved.

[0071] In summary, it can be seen from the embodiments and performance tests that the method provided by the present invention can change the surface flatness and surface morphology of the wafer after polishing, and within the preferred range of the present invention, it can effectively improve the surface flatness of the wafer after single-sided polishing, and at the same time obtain a more excellent surface morphology.

Claims

1. A method for improving the surface morphology and surface flatness of a wafer after single-side polishing, suitable for single-side polishing of 12-inch wafers. It is characterized in that The steps include: (1) According to the size of the ceramic plate, a concentric circle adhesive is produced. The concentric circle adhesive is made of a non-woven fabric substrate coated with acrylic adhesive on both sides. The thickness is 0.05-0.25 mm, the outer diameter is 334 mm, and the inner diameter is 250-310 mm; (2) Preheating the ceramic plate and attaching the concentric circle adhesive to the surface of the ceramic plate; (3) Attach the suction cup pad to the surface of the ceramic disk with concentric circle adhesive, apply pressure to press it, and by adding concentric circle adhesive between the suction cup pad and the ceramic disk, the mechanical friction effect on the edge during wafer polishing is greater than the mechanical friction effect in the middle; (4) The ceramic disc is used for single-sided polishing of the wafer. The mechanical friction between the contact surface between the wafer and the polishing cloth is controlled by adjusting the thickness and inner diameter of the concentric circle adhesive. After polishing, wafers with different surface morphologies and surface flatness are obtained.

2. The method for improving the surface morphology and surface flatness of a wafer after single-side polishing according to claim 1, It is characterized in that In the step (1), the thickness of the concentric circle adhesive is 0.1-0.15 mm.

3. The method for improving the surface morphology and surface flatness of a wafer after single-side polishing according to claim 1, It is characterized in that In the step (1), the inner diameter of the concentric circle adhesive is 275-305 mm.

4. The method for improving the surface morphology and surface flatness of a wafer after single-side polishing according to claim 1, It is characterized in that In the step (2), the preheating temperature of the ceramic disk is 30-40°C.

5. The method for improving the surface morphology and surface flatness of a wafer after single-side polishing according to claim 1, It is characterized in that In the step (3), the pressing pressure of the suction pad is 5-20 kg, and the pressing time of the suction pad is 12-24 hours.

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