A CMP process for reducing the occurrence rate of silicon wafer polishing mist

Abstract

The present invention relates to a CMP process for reducing the incidence of polishing fog on silicon wafers, including processes of wax coating and attachment, rough polishing, medium polishing, fine polishing, stripping, and dewaxing and cleaning. By adjusting process conditions such as polishing pressure, medium and fine polishing time, and polishing liquid flow rate during different cloth times of the polishing cloth, the insufficient ability to repair the damaged layer in the middle and late stages of the cloth time is compensated: the medium and fine polishing cloth times are both 80h. Before 50h of the cloth time, the consistent CMP process is adopted: the medium polishing pressure is 2.2 - 2.4 kg / cm<supgt;2< / supgt>, the medium polishing liquid flow rate is 1.9 - 2.1 L / min, the fine polishing liquid flow rate is 0.4 - 0.6 L / min, the medium polishing time is 8 - 12 min, the fine polishing time is 7 - 9 min, and the rotational speeds of the polishing head and the platen are 35 - 45 rpm; after 50h of the cloth time, the medium polishing pressure is increased to 2.5 - 2.7 kg / cm<supgt;2< / supgt>, the medium polishing liquid flow rate is increased to 2.4 - 2.6 L / min, the fine polishing liquid flow rate is increased to 0.7 - 0.9 L / min, the medium polishing time is extended to 15 - 17 min, the fine polishing time is extended to 9 - 11 min, the rotational speeds of the rough polishing head and the platen are 55 - 65 rpm, and the rotational speeds of the medium and fine polishing heads and the platen are 35 - 45 rpm. By improvement, the incidence of polishing fog is reduced, and high polishing quality is maintained throughout the entire cloth time cycle without reducing the service life of the polishing cloth.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor substrate polishing sheets, and in particular relates to a CMP process for reducing the occurrence rate of silicon wafer polishing mist. Background Art

[0002] Semiconductor polishing wafers are the basic materials for various electronic products. With the increasingly severe market competition and the rapid development of IC towards high integration and high performance, the requirements for the polishing quality of device substrates are getting higher and higher. Silicon wafer polishing mist is one of the important parameters for high-quality polishing, especially for the evaluation of silicon wafer fine polishing quality.

[0003] Chemical mechanical polishing (CMP) is a process that uses a series of chemical reactions between a slurry made of a mixture of tiny abrasive particles and a chemical solution and the workpiece surface to change the chemical bonds on the workpiece surface, generate a low shear strength product that is easy to remove, and then remove a very thin layer of material from the workpiece surface through the mechanical action of a polymer polishing pad, thereby obtaining a high-precision, low-roughness, non-damaged smooth surface. It is not only an irreplaceable interlayer planarization method in ULSI chip multi-layer wiring, but also the most effective method for silicon wafer processing to ultimately obtain nano-level ultra-smooth and non-damaged surfaces.

[0004] The general production and processing flow of silicon wafer polishing is: wax coating → rough polishing → medium polishing → fine polishing → peeling → dewaxing and cleaning. Medium and fine polishing are used to remove the damaged layer in the rough polishing process to achieve surface finish. However, as the polishing time increases, the polishing cloth wears more and more seriously, the ability to repair the damaged layer gradually weakens, and the occurrence rate of polishing mist increases. In order to maintain high polishing quality throughout the entire polishing cycle, it is urgent to adjust the existing single polishing process to compensate for the ability to repair the damaged layer in the middle and late stages of the polishing process. Summary of the invention

[0005] The present invention is directed to the above-mentioned technical problems. By improving the polishing process, during different polishing times of the polishing cloth, the insufficient ability of the damaged layer to repair in the middle and late stages of the polishing process is compensated by adjusting the polishing pressure, polishing time, polishing liquid flow rate and other process conditions, thereby reducing the occurrence rate of polishing mist and maintaining high polishing quality throughout the entire polishing cycle without reducing the service life of the polishing cloth.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The CMP process for reducing the occurrence rate of silicon wafer polishing mist provided by the present invention comprises the following steps:

[0008] (1) Waxing and attaching: Place the silicon wafer to be treated on a wax coating machine, with a rotation speed of 1700-2500 rpm, a wax coating amount of 0.7-1.2 mL, and a baking temperature of 80-120°C;

[0009] (2) Rough polishing: polishing the silicon wafer treated in step (1), with a polishing head speed of 50-65 rpm, a fixed plate speed of 50-65 rpm, a rough polishing pressure of 3.5-4.5 kg / cm2, a rough polishing liquid flow rate of 1.8-2.5 L / min, and a pH value of 10.5-11.2;

[0010] (3) Middle polishing: The fabrication cycle is 80 hours. The process conditions before 50 hours of fabrication are as follows: Middle polishing pressure 2.2~2.5kg / cm 2 , polishing liquid flow rate 1.9 ~ 2.1L / min, medium polishing time 8 ~ 12min, polishing head speed 35 ~ 45rpm, fixed plate speed 35 ~ 45rpm; after 50h of polishing, the medium polishing pressure is increased to 2.5 ~ 2.7kg / cm 2 , the polishing liquid flow rate is increased to 2.4-2.6L / min, and the polishing time is extended to 15-17min;

[0011] (4) Fine polishing: The polishing cycle is 80 hours. The process conditions before 50 hours are as follows: polishing liquid flow rate 0.4-0.6 L / min, fine polishing time 7-9 min, polishing head speed 35-45 rpm, fixed plate speed 35-45 rpm; after 50 hours, the polishing liquid flow rate is increased to 0.7-0.9 L / min, and the polishing time is extended to 9-11 min.

[0012] (5) Peeling and dewaxing: In pure water flow mode, use a peeling knife to manually peel and dewax.

[0013] Preferably, in the CMP process for reducing the occurrence rate of silicon wafer polishing mist provided by the present invention, the coarse polishing liquid contains SiO2 with a mass fraction of 20-21%, a pH of 11-12, and a particle size of 60-100nm; the medium polishing liquid contains SiO2 with a mass fraction of 8.5-9.7%, a pH of 10.1-10.5, and a particle size of 62-82nm; the fine polishing liquid contains SiO2 with a mass fraction of 6-9%, a pH of 10-11, and a particle size of 60-80nm.

[0014] Preferably, in the CMP process for reducing the occurrence rate of silicon wafer polishing mist provided by the present invention, in step (5), during stripping, the pure water flow rate is 1.5 to 2.5 L / min.

[0015] Preferably, in the CMP process for reducing the occurrence rate of silicon wafer polishing mist provided by the present invention, in step (5), when dewaxing and cleaning are performed, 4-level pure water, 1-level HF, 1-level pure water, 2-level SC-1, and 1-level pure water are used in sequence for cleaning, with a pure water flow rate of 5 to 20 L / min, an HF concentration of 10 to 20%, and an SC-1 temperature of 40 to 70°C.

[0016] Preferably, in the CMP process for reducing the occurrence rate of silicon wafer polishing fog provided by the present invention, in step (3), the process conditions before 50 hours of preparation are as follows: polishing head speed 40 rpm, fixed plate speed 40 rpm, polishing pressure 2.5 kg / cm 2 , polishing liquid flow rate 2.0L / min, intermediate polishing time 10min; after 50h of polishing, the intermediate polishing pressure is increased to 2.6kg / cm 2 , the flow rate of medium polishing liquid is increased to 2.5L / min, and the medium polishing time is increased to 16min.

[0017] Preferably, in the CMP process for reducing the occurrence rate of silicon wafer polishing mist provided by the present invention, in step (4), the process conditions before 50 hours of preparation are as follows: polishing head speed 40 rpm, fixed plate speed 40 rpm, fine polishing liquid flow rate 0.5 L / min, fine polishing time 8 min; after 50 hours of preparation, the fine polishing liquid flow rate is increased to 0.8 L / min, and the fine polishing time is increased to 10 min.

[0018] The present invention is based on the fact that the fine polishing cloth gradually wears out as the use time increases, the thickness of the fluff layer decreases, the pore size increases, and the ability to repair the damaged layer on the surface of the silicon wafer becomes weaker. During the medium polishing and fine polishing process, the single polishing condition used in the entire polishing process in the prior art is abandoned, and the polishing pressure, polishing liquid flow, polishing time, polishing head and fixed plate speed are adjusted in different polishing cycles. Through experimental verification, after polishing using the CMP process of the present invention, the maximum fog occurrence rate in the entire polishing cycle is 5.40%, which is much lower than the maximum fog occurrence rate of 33.24% when a single polishing condition is used in the prior art.

[0019] In addition, the improved process of the present invention is simple, and does not require any improvement to the polishing equipment and the polishing liquid, and is highly innovative and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the changes in rotation speed (A), polishing pressure (B), polishing time (C) and polishing liquid flow rate (D) during the intermediate polishing and fine polishing process in the CMP process of the present invention;

[0021] Figure 2 The results of the distribution time correlation and fog occurrence rate under the single CMP process conditions in the prior art;

[0022] Figure 3 This is the result of the distribution time correlation and fog occurrence rate in the present invention. DETAILED DESCRIPTION

[0023] The implementation of the present invention is described in detail below in conjunction with the drawings and embodiments of the present invention. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0024] Example

[0025] The CMP process for reducing the occurrence rate of silicon wafer polishing mist provided in this embodiment includes the following steps:

[0026] (1) Waxing

[0027] Place the silicon wafer to be treated on a wax coating machine, with a speed of 2000 rpm, a wax coating volume of 1 mL, and a baking temperature of 100°C;

[0028] (2) Rough polishing

[0029] The silicon wafer treated in step (1) is roughly polished at a polishing head speed of 50-65 rpm, a platen speed of 50-65 rpm, and a rough polishing pressure of 4 kg / cm 2 , coarse throwing liquid flow rate 2.1L / min, pH value 10.5~11.2;

[0030] (3) Middle throw

[0031] The polishing cycle is 80 hours. The process conditions before 50 hours are as follows: polishing head speed 40 rpm, fixed plate speed 40 rpm, polishing pressure 2.5 kg / cm 2 , polishing liquid flow rate 2.0L / min, intermediate polishing time 10min; after 50h of polishing, the intermediate polishing pressure is increased to 2.6kg / cm 2 , the polishing liquid flow rate is increased to 2.5L / min, and the polishing time is extended to 16min.

[0032] (4) Fine polishing

[0033] The polishing cycle is 80h. Before 50h of polishing, the process conditions are as follows: polishing head speed 40rpm, fixed plate speed 40rpm, fine polishing liquid flow rate 0.5L / min, fine polishing time 8min; after 50h of polishing, the fine polishing liquid flow rate is increased to 0.8L / min, and the fine polishing time is increased to 10min.

[0034] In the above three polishings, the coarse polishing liquid contains 20-21% SiO2 by mass, pH 11-12, and a particle size of 60-100nm; the medium polishing liquid contains 8.5-9.7% SiO2 by mass, pH 10.1-10.5, and a particle size of 62-82nm; the fine polishing liquid contains 6-9% SiO2 by mass, pH 10-11, and a particle size of 60-80nm.

[0035] (5) Peeling and wax removal

[0036] Stripping: When stripping, the pure water flow rate is 1.5-2.5L / min, and the stripping knife is used for manual stripping and dewaxing and cleaning;

[0037] For dewaxing and cleaning, use grade 4 pure water, grade 1 HF, grade 1 pure water, grade 2 SC-1, and grade 1 pure water in sequence, with a pure water flow rate of 5 to 20 L / min, HF concentration of 10 to 20%, and SC-1 temperature of 40 to 70°C.

[0038] In the above-mentioned medium polishing and fine polishing process, the speed, pressure, polishing time and polishing liquid flow rate change with the cloth time cycle. Figure 1 The polishing head speed and the fixed plate speed are the same, and the entire polishing cycle is maintained at 40rpm; the pressure, polishing time and polishing liquid flow rate are all changed in the 50th polishing cycle, and the first 50 polishing cycles are lower than the last 30 polishing cycles.

[0039] Comparative Example

[0040] The conventional CMP process conditions are adopted: wax coating, rough polishing, stripping and wax removal and cleaning are the same as those in the embodiment.

[0041] During the intermediate polishing and fine polishing process, the polishing conditions remained unchanged during the entire 80-hour period: polishing head speed 40rpm, fixed plate speed 40rpm, intermediate polishing pressure 2.5kg / cm2, intermediate polishing liquid flow 2.0L / min, fine polishing liquid flow 0.5L / min, intermediate polishing time 10min, fine polishing time 8min. The fog occurrence rate was counted.

[0042] Results Analysis

[0043] Figure 2 The results of the distribution time correlation and fog occurrence rate under the single CMP process conditions in the prior art are shown; Figure 3 The results of the correlation between the distribution time and the fog occurrence rate in the present invention are shown in Figure 2. The results show that after the CMP process of the present invention is used for polishing, the maximum fog occurrence rate in the entire distribution time period is 5.40% ( Figure 3 ), which is much lower than the highest fog occurrence rate of 33.24% when using a single polishing condition in the prior art ( Figure 2 ).

[0044] The preferred embodiments of the present invention have been specifically described above, but the present invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A CMP process for reducing the occurrence rate of silicon wafer polishing mist, characterized in that: The steps include: (1) Waxing and attaching: Place the silicon wafer to be treated on a wax coating machine, with a rotation speed of 1700-2500 rpm, a wax coating amount of 0.7-1.2 mL, and a baking temperature of 80-120°C; (2) Rough polishing: The silicon wafer treated in step (1) is polished at a polishing head speed of 50 to 65 rpm, a platen speed of 50 to 65 rpm, and a rough polishing pressure of 3.5 to 4.5 kg / cm 2 , the flow rate of rough throwing liquid is 1.8~2.5L / min, and the pH value is 10.5~11.2; (3) Middle polishing: The fabrication cycle is 80 hours. The process conditions before 50 hours of fabrication are as follows: Middle polishing pressure 2.2~2.5kg / cm 2 , polishing liquid flow rate 1.9 ~ 2.1L / min, medium polishing time 8 ~ 12min, polishing head speed 35 ~ 45rpm, fixed plate speed 35 ~ 45rpm; after 50h of polishing, the medium polishing pressure is increased to 2.5 ~ 2.7kg / cm 2 , the polishing liquid flow rate is increased to 2.4-2.6L / min, and the polishing time is extended to 15-17min; (4) Fine polishing: The polishing cycle is 80 hours. The process conditions before 50 hours are as follows: polishing liquid flow rate 0.4-0.6 L / min, fine polishing time 7-9 min, polishing head speed 35-45 rpm, fixed plate speed 35-45 rpm; after 50 hours, the polishing liquid flow rate is increased to 0.7-0.9 L / min, and the polishing time is extended to 9-11 min. (5) Peeling and dewaxing: In pure water flow mode, use a peeling knife to manually peel and dewax.

2. The CMP process for reducing the occurrence rate of silicon wafer polishing mist according to claim 1, characterized in that: in, The coarse polishing liquid contains 20-21% SiO2 by mass, pH 11-12, and particle size 60-100nm; the medium polishing liquid contains 8.5-9.7% SiO2 by mass, pH 10.1-10.5, and particle size 62-82nm; the fine polishing liquid contains 6-9% SiO2 by mass, pH 10-11, and particle size 60-80nm.

3. The CMP process for reducing the occurrence rate of silicon wafer polishing mist according to claim 1, characterized in that: in, In step (5), during the stripping process, the pure water flow rate is 1.5 to 2.5 L / min.

4. The CMP process for reducing the occurrence rate of silicon wafer polishing mist according to claim 1, characterized in that: in, In step (5), when dewaxing and cleaning are performed, grade 4 pure water, grade 1 HF, grade 1 pure water, grade 2 SC-1, and grade 1 pure water are used in sequence for cleaning, with a pure water flow rate of 5 to 20 L / min, an HF concentration of 10 to 20%, and an SC-1 temperature of 40 to 70°C.

5. The CMP process for reducing the occurrence rate of silicon wafer polishing mist according to claim 1, characterized in that: in, In step (3), the process conditions before 50 hours of polishing are as follows: polishing head speed 40 rpm, fixed plate speed 40 rpm, polishing pressure 2.5 kg / cm 2 , polishing liquid flow rate 2.0L / min, intermediate polishing time 10min; after 50h of polishing, the intermediate polishing pressure is increased to 2.6kg / cm 2 , the flow rate of medium polishing liquid is increased to 2.5L / min, and the medium polishing time is increased to 16min.

6. The CMP process for reducing the occurrence rate of silicon wafer polishing mist according to claim 1, characterized in that: in, In step (4), the process conditions before 50 hours of polishing are as follows: polishing head speed 40 rpm, fixed plate speed 40 rpm, fine polishing liquid flow rate 0.5 L / min, fine polishing time 8 min; after 50 hours of polishing, the fine polishing liquid flow rate is increased to 0.8 L / min, and the fine polishing time is increased to 10 min.

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