Method for polishing a silicon wafer and method for manufacturing a silicon wafer

Abstract

A polishing method of a silicon wafer, which includes a step of performing a front-stage polishing process and a subsequent fine polishing process as a final polishing process, in the polishing method of the silicon wafer, the fine polishing process in the final polishing process includes: a fine slurry polishing process using a slurry having a density of 1 x 10 13 cm 3 above as the second polishing liquid; and a pre-polishing process performed before the fine slurry polishing process and using a slurry having a density of 1 x 10 10 cm 3 above as the second polishing liquid. A manufacturing method of a silicon wafer, which, after forming a notch portion in a peripheral portion of a single crystal silicon ingot grown by a Czochralski method, and then slicing to obtain a silicon wafer, performs a polishing treatment on the obtained silicon wafer by the above polishing method of a silicon wafer.

Description

Technical Field

[0001] This invention relates to a method for polishing silicon wafers and a method for manufacturing silicon wafers. Background Technology

[0002] The processes used to manufacture silicon wafers mainly include the single-crystal pulling process for producing single-crystal ingots and the processing steps for the produced single-crystal ingots. These processing steps typically include slicing, lapping, chamfering, etching, mirror polishing, and cleaning processes. Through these processes, silicon wafers with mirror-finished surfaces are manufactured.

[0003] The mirror polishing process involves multiple stages, including a two-sided polishing process (rough polishing) that polishes both sides of the silicon wafer simultaneously, followed by a final polishing process that mirrors a single side of the wafer. Typically, a polishing unit is used for the final polishing process, comprising a platform with a polishing pad on its surface and a polishing head that holds the silicon wafer. The single side of the silicon wafer, held by the polishing head, is pressed onto the polishing pad, while a polishing slurry (polishing paste) containing abrasive particles is supplied to the polishing pad, and the polishing head and platform rotate simultaneously. Thus, the single side of the silicon wafer is polished through chemical-mechanical polishing (CMP), a combination of the mechanical polishing action of the abrasive particles and the chemical polishing action of the alkaline solution, resulting in a mirror-like surface with excellent smoothness.

[0004] Here, in the final polishing process, polishing is performed in two or more stages, including one or more pre-polishing processes (performed in one or more pre-polishing units) and a fine polishing process (performed subsequently in a fine polishing unit).

[0005] Patent documents 1 and 2 describe a method in which, in the final polishing process, a rinsing solution is used for polishing after the slurry polishing. This method can suppress the accumulation of abrasive particles from the polishing slurry on the polishing head.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 11-243072

[0009] Patent Document 2: Japanese Patent Application Publication No. 2007-103703. Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] However, the method in Patent Document 1 has the following problems. Specifically, although ultrapure water is used as the rinsing fluid in Patent Document 1, if the slurry-like polishing fluid remaining on the polishing pad is diluted with ultrapure water, the pH of the polishing fluid drops to near neutral. This causes the abrasive particles to agglomerate instead of remain dispersed, and they easily adhere to the silicon wafer surface and remain there. The abrasive particles agglomerated in this polishing fluid interact with the silicon wafer surface due to the near-neutral pH, resulting in micro-scratches, damage, and other defects on the silicon wafer surface. Furthermore, if abrasive particles remain on the silicon wafer surface, pits will form on the silicon wafer surface during the cleaning process after removal from the polishing apparatus.

[0012] Furthermore, in the method of Patent Document 2, polishing with rinsing liquid is performed after slurry polishing in the front-end polishing process. Although it can suppress the accumulation of slurry abrasive particles on the polishing head used in the front-end polishing, it is not sufficient to counteract damage to the silicon wafer surface in the fine polishing process. For example, particles adhering during transport between polishing units and fine polishing slurry residue adhering to the fine polishing head can sometimes lead to the generation of LPD (lightpoint defect).

[0013] Therefore, the purpose of this invention is to provide a polishing method for silicon wafers and a manufacturing method for silicon wafers that can suppress the generation of LPD.

[0014] Solutions for solving technical problems

[0015] The main idea of ​​this invention is as follows:

[0016] (1) A method for polishing a silicon wafer, characterized in that it includes the following steps as the final polishing step:

[0017] In the front-end polishing process, a front-end polishing unit includes a first platform with a first polishing pad on its surface and a first polishing head. While supplying a first polishing liquid to the first polishing pad, the first platform and the silicon wafer are rotated while the silicon wafer, held by the first polishing head, is in contact with the first polishing pad, thereby polishing the surface of the silicon wafer; and

[0018] In the fine polishing process, following the preceding polishing process, a fine polishing unit is used, comprising a second platform with a second polishing pad on its surface and a second polishing head. While supplying a second polishing fluid to the second polishing pad, the second platform and the silicon wafer are rotated while the silicon wafer, held by the second polishing head, is in contact with the second polishing pad, thereby further polishing the surface of the silicon wafer.

[0019] In the silicon wafer polishing method, the fine polishing step in the final polishing process includes:

[0020] In the polishing process of the fine slurry, the abrasive grain density used is 1×10⁻⁶. 13 pcs / cm 3 The above polishing slurry is used as the second polishing slurry; and

[0021] The pre-polishing process is performed before the polishing process using slurry, and the density of the abrasive used is 1×10⁻⁶. 10 pcs / cm 3 The following polishing slurry is used as the second polishing slurry.

[0022] Among them, "the density of the abrasive particles is 1×10 10 pcs / cm 3 The polishing fluid described below as the second polishing fluid also includes polishing fluids that do not contain abrasive particles, such as pure water.

[0023] (2) The polishing method for silicon wafers according to (1) above, wherein the second polishing liquid used in the pre-polishing process is pure water.

[0024] (3) The polishing method for silicon wafers according to (1) or (2) above, wherein the pre-polishing process is performed in the range of 10 to 60 seconds.

[0025] (4) The polishing method for silicon wafers according to any one of (1) to (3) above, wherein the rotational speed of the second polishing head in the pre-polishing step is greater than the rotational speed of the second polishing head in the slurry polishing step.

[0026] (5) The polishing method for silicon wafers according to (4) above, wherein the rotational speed of the second polishing head in the pre-polishing process is more than 1.5 times the rotational speed of the second polishing head in the slurry polishing process.

[0027] (6) A method for manufacturing a silicon wafer, characterized in that, after obtaining a silicon wafer before polishing by slicing a single crystal silicon ingot grown by the Czochralski method, the silicon wafer before polishing is polished by the silicon wafer polishing method described in any one of (1) to (6) above.

[0028] Invention Effects

[0029] According to the present invention, a polishing method for silicon wafers and a manufacturing method for silicon wafers are provided that can suppress the generation of LPD. Attached Figure Description

[0030] Figure 1This is a flowchart illustrating the silicon wafer manufacturing process, including a silicon wafer polishing method according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram illustrating a single-sided polishing apparatus used in the fine polishing step of a silicon wafer polishing method according to an embodiment of the present invention.

[0032] Figure 3 A graph illustrating the evaluation results of an embodiment. Detailed Implementation

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0034] (Polishing methods for silicon wafers)

[0035] Figure 1 This is a flowchart illustrating the silicon wafer manufacturing process, including a silicon wafer polishing method according to an embodiment of the present invention. Figure 2 This is a schematic diagram illustrating a single-sided polishing apparatus used in the fine polishing step of a silicon wafer polishing method according to an embodiment of the present invention.

[0036] exist Figure 1 The preceding process (step S1) shown includes slicing, grinding, chamfering and etching processes.

[0037] Next, the silicon wafer shape is formed by double-sided polishing (DSP process) (step S2).

[0038] Next, the silicon wafers polished on both sides are fed into the cleaning (step S3) process.

[0039] These steps S1 to S3 can be performed in the same way as existing methods, so detailed descriptions are omitted.

[0040] Next, the cleaned silicon wafer is fed into a final polishing process that includes a front-end polishing process (step S4) and a fine polishing process (step S5). Furthermore, the front-end polishing process may include multiple stages, and the fine polishing process includes multiple stages as described below.

[0041] The front-end polishing process S4 can be performed using existing methods. Specifically, a polishing unit including a first platform with a first polishing pad on its surface and a first polishing head is used. While supplying the first polishing slurry to the first polishing pad, the first platform and the silicon wafer are rotated while the silicon wafer held by the first polishing head is in contact with the first polishing pad, thereby polishing the surface of the silicon wafer. Furthermore, as an example of the structure of the polishing unit used in the front-end polishing, the same polishing unit as the polishing unit used in the fine polishing described later can be used.

[0042] The fine polishing process (step S5) will be explained in detail later.

[0043] After the final polishing process, the silicon wafers are cleaned in the fine polishing process (step S5) and then inspected (step S7) to confirm the flatness of the silicon wafers, visible damage, and the presence of stains.

[0044] Subsequently, the silicon wafers are supplied to the final cleaning process (step S8) and then shipped after surface inspection (step S9).

[0045] Steps S7 to S9 can be performed in the same way as existing methods, so detailed explanations are omitted.

[0046] The final polishing step (step S5) in the above process will be described in detail below. First, refer to... Figure 2 This paper describes a single-sided polishing apparatus used in a silicon wafer polishing method according to an embodiment of the present invention. The single-sided polishing apparatus 100 includes: a rotating platform 10 with a polishing pad 12 attached thereon for polishing one side of a silicon wafer W; a polishing head 20 having a pad 22 and a retaining ring 24 disposed opposite to each other on the rotating platform 10, wherein the pad 22 serves as a retaining surface for the other side of the silicon wafer W, and the retaining ring 24 is mounted on the outer edge of the pad 22 on the retaining surface side; and a slurry supply unit 30 for supplying polishing slurry 32 to the polishing pad 12. The polishing slurry 32 may contain abrasive particles and etchant. Furthermore, the retaining ring 24 may be configured to have an inner diameter equal to or greater than the diameter of the silicon wafer W.

[0047] Furthermore, the polishing head 20 may include: a shaft portion 26 for raising, lowering, and rotating the polishing head 20; and a rotating frame portion 28 disposed at the lower end of the shaft portion 26, with a pad 22 mounted thereon. The single-sided polishing apparatus 100 may also include a platform rotation shaft 14 connected to the rotating platform 10 and used to rotate the rotating platform 10. Additionally, the shaft portion 26 and the platform rotation shaft 14 may be connected to a drive mechanism such as a motor (not shown).

[0048] In the fine polishing process (step S5), after the previous polishing process (step S4), a fine polishing unit (single-sided polishing device 100) including a second platform (rotating platform 10) with a second polishing pad (polishing pad 12) on its surface and a second polishing head (polishing head 20) is used. While supplying the second polishing liquid to the second polishing pad (polishing pad 12), the second platform (rotating platform 10) and the silicon wafer W are rotated while the silicon wafer W held by the second polishing head (polishing head 20) is in contact with the second polishing pad (polishing pad 12), thereby further polishing the surface of the silicon wafer W.

[0049] Here, the final polishing process (step S5) includes: a fine slurry polishing process (step S52), using abrasive grains with a density of 1×10⁻⁶. 13 pcs / cm 3 The above polishing slurry is used as the second polishing slurry; and the pre-polishing process (step S51) is performed before the fine slurry polishing process (step S52) and the density of the abrasive used is 1×10. 10 pcs / cm 3 The following polishing slurry is used as the second polishing slurry.

[0050] In the polishing process of the slurry (step S52), the polishing solution is preferably alkaline, and preferably contains water-soluble polymers and has a density of 5×10. 13 pcs / cm 3 The following is an alkaline aqueous solution containing abrasive particles. The polishing rate of this alkaline aqueous solution on silicon is preferably set to 5–20 nm / min. If it is 5 nm / min or higher, the polishing time to obtain the desired polishing amount will not increase, thus preventing productivity degradation, and the effect of removing defects formed on the silicon wafer surface in the preceding polishing process can be fully achieved. If it is 20 nm / min or lower, the etching effect of the alkali will not be excessive, and the roughness of the silicon wafer surface will not deteriorate. From the viewpoint of obtaining such a polishing rate, the aforementioned alkaline aqueous solution preferably contains ammonia, and preferably contains a water-soluble polymer. As a water-soluble polymer, one or more selected from hydroxyethyl cellulose (HEC), polyethylene glycol (PEG), and polypropylene glycol (PPG) are preferred. Furthermore, the viscosity of the aforementioned alkaline aqueous solution at the operating temperature (18–25°C) is preferably set to 1.5–5.0 mPa·s. When the viscosity is less than 1.5 mPa·s, the polishing slurry is prone to flow and may not achieve the desired etching rate. When the viscosity is above 5.0 mPa·s, even after cleaning after fine polishing, the polishing slurry may remain and adhere to the silicon wafer surface.

[0051] Abrasive grains can be made of materials such as ceramics like silica and alumina, monomers or compounds like diamond and silicon carbide, or polymers like polyethylene and polypropylene. However, for reasons such as low cost, good dispersibility in polishing slurry, and ease of controlling abrasive grain size, grains containing SiO2 particles are preferred. Furthermore, the type of SiO2 particles can be any of those produced by dry methods (combustion / arc method) or wet methods (precipitation / sol-gel method). The shape of the abrasive grains can be spherical, cocoon-shaped, etc.

[0052] The polishing time for the slurry polishing process (step S52) is preferably set to 60 to 900 seconds. Setting it to 60 seconds or more allows for thorough polishing of the silicon wafer, while setting it to 900 seconds or less prevents the surface roughness of the silicon wafer from becoming rough.

[0053] Next, on the other hand, in the pre-polishing process (step S51), the polishing solution is preferably neutral or alkaline, and the density of the abrasive grains is 1×10⁻⁶. 10 pcs / cm 3 The following applies. When the polishing slurry is an alkaline solution, the polishing rate for silicon is preferably set to 10 nm / min or less. This is because, at 10 nm / min or less, the surface roughness of the silicon wafer will not be rough, allowing for uniform polishing of the wafer surface. The polishing slurry is preferably pure water, more preferably ultrapure water. This is because it prevents the roughness of the silicon wafer from becoming rough. Alternatively, the polishing slurry can also be an alkaline solution. When the polishing slurry is alkaline, it is easier to remove particles remaining on the polishing head (especially the inner wall of the retainer ring). In this case, it is preferable to contain one or more bases selected from potassium hydroxide (KOH), sodium hydroxide (NaOH), tetramethylammonium (TMAH), and tetraethylammonium (TEAH), and water-soluble polymers may also be included. This protects the silicon wafer, preventing particles from re-adhering to the retainer ring or causing scratches. When the polishing slurry is pure water, the viscosity of the polishing slurry at 20°C is approximately 1 mPa·s. When the polishing slurry contains water-soluble polymers, the viscosity of the polishing slurry at the operating temperature (18–25°C) is preferably set to 5.0 mPa·s or less. This is because even if the viscosity exceeds 5.0 mPa·s, no further effect is obtained, and productivity deteriorates. The type of abrasive particles is the same as that described for the polishing slurry used in the fine polishing process described above.

[0054] The pre-polishing process (step S51) is preferably performed in the range of 10 to 60 seconds. By setting it to 10 seconds or more, particles accumulated on the polishing pad can be removed more reliably. On the other hand, by setting it to 60 seconds or less, the surface roughness of the silicon wafer can be prevented from becoming rough.

[0055] The rotational speed of the second polishing head in the pre-polishing step (step S51) is preferably greater than that of the second polishing head in the fine slurry polishing step (step S52). Specifically, the rotational speed of the second polishing head in the pre-polishing step (step S51) is preferably at least 1.5 times that of the second polishing head in the fine slurry polishing step (step S52). This is because increasing the mechanical action can further improve the removal of particles.

[0056] The effects of the silicon wafer polishing method of this embodiment will be explained below.

[0057] The inventors have discovered that the polishing head used in the fine polishing process, especially the inner wall of the retainer ring, accumulates microparticles, which can damage the surface of the silicon wafer during the fine polishing process and become the cause of LPD (Liquidity-Degradation).

[0058] In contrast, according to the silicon wafer polishing method of this embodiment, the final polishing process (step S5) includes a fine slurry polishing process (step S52), using abrasive grains with a density of 1×10⁻⁶. 13 pcs / cm 3 The above polishing slurry is used as the second polishing slurry; and the pre-polishing process (step S51) is performed before the fine slurry polishing process (step S52) and the density of the abrasive used is 1×10. 10 pcs / cm 3 The following polishing slurry is used as the second polishing slurry.

[0059] In this way, by performing a pre-polishing process (step S51) before the fine slurry polishing process (step S52), particles adhering to the polishing head (especially the inner wall of the retainer ring) of the fine polishing can be removed, thereby suppressing the generation of LPD caused by particles.

[0060] Here, the second polishing solution used in the pre-polishing process is preferably pure water. This is because it can prevent the roughness of the silicon wafer from becoming rougher.

[0061] Furthermore, as mentioned above, the pre-polishing process is preferably performed within the range of 10 to 60 seconds.

[0062] Furthermore, as mentioned above, the rotational speed of the second polishing head in the pre-polishing process is preferably greater than that of the second polishing head in the slurry polishing process. In particular, the rotational speed of the second polishing head in the pre-polishing process is preferably more than 1.5 times that of the second polishing head in the slurry polishing process.

[0063] (Methods for manufacturing silicon wafers)

[0064] In a method for manufacturing a silicon wafer according to one embodiment of the present invention, firstly, a single-crystal silicon ingot grown by the Czerklaussky method is sliced ​​to obtain a silicon wafer before polishing. The growth and slicing processes of the single-crystal silicon ingot can be performed in the same manner as existing methods.

[0065] Subsequently, the silicon wafer obtained before polishing is polished using the silicon wafer polishing method described in the above embodiments.

[0066] Thus, through the same mechanism as described above, it is possible to remove particles adhering to the polishing head (especially the inner wall of the retainer ring) during fine polishing, thereby suppressing the generation of LPD caused by particles. Example

[0067] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0068] To confirm the effectiveness of the present invention, a silicon wafer was polished using the methods of Examples 1 and 2, and an experiment was conducted to check and evaluate the number of LPDs. In Examples 1 and 2, a p-type silicon wafer with a diameter of 300 mm and a crystal orientation of (100) was used as the silicon wafer. Furthermore, the polishing apparatus used was as follows: Figure 2 The apparatus shown.

[0069] Example 1

[0070] After the silicon wafers that had undergone initial polishing were pre-polished, a fine polishing process was performed. Subsequently, the silicon wafers were cleaned and the LPD (Liquidity Limiting) was measured.

[0071] In the pre-polishing process, pure water without abrasive particles was used as the polishing fluid. The polishing time was set to 30 seconds, and the rotation speed of the polishing head was set to twice the rotation speed of the polishing head in the fine polishing process.

[0072] In the fine polishing process, an alkaline aqueous solution (using SiO2 as abrasive particles) was used, and the density of the abrasive particles was 5 × 10⁻⁶. 13 / cm 3 Use the polishing slurry. Set the polishing time to 180 seconds.

[0073] For LPD measurements, a KLA-Tencor Surfscan SP5 was used in DCN measurement mode to detect and count LPDs with dimensions larger than 35 nm. This measurement was performed on four silicon wafers, and the average LPD count was calculated.

[0074] • Example 1

[0075] Polishing was performed in the same manner as in Example 1, except that no pre-polishing process was performed.

[0076] Existing Example 2

[0077] No polishing was performed after the initial polishing process and before the fine polishing process. Instead, a polishing process identical to the pre-polishing process in Example 1 was performed after the fine polishing process. Otherwise, polishing was performed using the same method as in Example 1.

[0078] Show the evaluation results Figure 3 .like Figure 3 As shown in Example 1, compared with Existing Example 1 and Existing Example 2, LPD can be reduced.

[0079] Explanation of reference numerals in the attached figures

[0080] 100 - Single-sided polishing device, 10 - Rotary platform, 12 - Polishing pad, 14 - Platform rotation axis, 20 - Polishing head, 22 - Pad, 24 - Holder ring, 26 - Shaft section, 28 - Rotating frame section, 30 - Slurry supply section, 32 - Polishing slurry, W - Silicon wafer.

Claims

1. A method for polishing silicon wafers, characterized in that, This includes the following steps, which are performed as the final polishing step: In the front-end polishing process, a front-end polishing unit includes a first platform with a first polishing pad on its surface and a first polishing head. While supplying a first polishing liquid to the first polishing pad, the first platform and the silicon wafer are rotated while the silicon wafer, held by the first polishing head, is in contact with the first polishing pad, thereby polishing the surface of the silicon wafer; and In the fine polishing process, following the preceding polishing process, a fine polishing unit is used, comprising a second platform with a second polishing pad on its surface and a second polishing head. While supplying a second polishing fluid to the second polishing pad, the second platform and the silicon wafer are rotated while the silicon wafer, held by the second polishing head, is in contact with the second polishing pad, thereby further polishing the surface of the silicon wafer. In the silicon wafer polishing method, the fine polishing step in the final polishing process includes: In the polishing process of the fine slurry, the abrasive grain density used is 1×10⁻⁶. 13 pcs / cm 3 The above polishing slurry is used as the second polishing slurry; and The pre-polishing process is performed before the polishing process using slurry, and the density of the abrasive used is 1×10⁻⁶. 10 pcs / cm 3 The following polishing slurry is used as the second polishing slurry. The pre-polishing process and the polishing process with the fine slurry are performed in the same fine polishing unit. The pre-polishing process is performed by rotating the second platform and the silicon wafer while the silicon wafer is in contact with the second polishing pad.

2. The polishing method for silicon wafers according to claim 1, wherein, The second polishing liquid used in the pre-polishing process is pure water.

3. The polishing method for silicon wafers according to claim 1 or 2, wherein, The pre-polishing process is performed within the range of 10 to 60 seconds.

4. The polishing method for silicon wafers according to claim 1, wherein, The rotational speed of the second polishing head in the pre-polishing process is greater than that of the second polishing head in the fine slurry polishing process.

5. The polishing method for silicon wafers according to claim 4, wherein, The rotational speed of the second polishing head in the pre-polishing process is more than 1.5 times that of the second polishing head in the fine slurry polishing process.

6. A method for manufacturing a silicon wafer, characterized in that, After slicing a single-crystal silicon ingot grown by the Czerklaussky method to obtain a silicon wafer before polishing, the silicon wafer before polishing is polished by the silicon wafer polishing method described in claim 1.

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