Polishing Slurry

Abstract

The present invention relates to a polishing slurry used for polishing an interlayer insulating film, which contains silica abrasive grains and an organic ammonium cation having a molecular weight of 155 or less.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2017-252453, the entire disclosure of which is incorporated herein by reference. [Technical field]

[0002] The present invention relates to a polishing slurry. [Background technology]

[0003] 2. Description of the Related Art Conventionally, a polishing slurry containing silica abrasive grains has been used as a polishing slurry for polishing an interlayer insulating film, which is an object to be polished (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2006-61995 Summary of the Invention [Problem to be solved by the invention]

[0005] Large abrasive grains tend to cause scratches on the workpiece, while small abrasive grains tend to reduce the polishing speed. Therefore, it is necessary for the abrasive grains to be of an appropriate size.

[0006] Here, the polishing slurry is subjected to dynamic loads (pressure, shear force, etc.) during transportation, polishing, etc., and the abrasive grains in the polishing slurry tend to aggregate. As a result, the abrasive grains become larger, which makes the workpiece more susceptible to scratches caused by polishing.

[0007] In view of the above problems, an object of the present invention is to provide a polishing slurry in which changes in the size of abrasive grains are suppressed. [Means for solving the problem]

[0008] The polishing slurry according to the present invention is used for polishing an interlayer insulating film, Silica abrasive grains; and an organic ammonium cation having a molecular weight of 155 or less. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the relationship between the molecular weight of organic ammonium cations and the growth rate of abrasive grains. [Diagram 2] A scaled version of Figure 1. [Diagram 3] 1 is a graph showing the relationship between the amount (parts by mass) of organic ammonium cations per 100 parts by mass of silica abrasive grains, the polishing rate, and the growth rate of the abrasive grains. [Figure 4] FIG. 13 is a graph showing the number of defects when the polishing slurries of Example 5 and Comparative Example 3 were used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, one embodiment of the present invention will be described.

[0011] The polishing slurry according to this embodiment is used to polish an interlayer insulating film. The interlayer insulating film may be a silicon oxide film, a silicon nitride film, a low-k film, or the like. The silicon oxide film may be a film containing SiO2 formed by plasma CVD using tetraethoxysilane (TEOS). The low-k film means a film having a lower relative dielectric constant than a silicon oxide film (SiO2 film).

[0012] The polishing slurry according to this embodiment contains silica abrasive grains and an organic ammonium cation having a molecular weight of 155 or less. The polishing slurry according to this embodiment further contains an alkali and water.

[0013] The polishing slurry according to this embodiment may be used for polishing after being diluted with water or the like, or may be used for polishing as is without being diluted.

[0014] The pH of the polishing slurry according to this embodiment is preferably 8 to 12, and more preferably 10 to 12. The polishing slurry according to this embodiment has a preferable pH by containing the above-mentioned alkali.

[0015] When the polishing slurry according to this embodiment is used for polishing as is without being diluted, it preferably contains 1.0 to 25 mass %, more preferably 5.0 to 20 mass %, and even more preferably 9.0 to 14 mass % of silica abrasive grains. Furthermore, when the polishing slurry according to this embodiment is used diluted (for example, when the components other than water are diluted to half their concentration), it preferably contains 1.5 to 40 mass %, more preferably 10 to 30 mass %, and even more preferably 20 to 26 mass % of silica abrasive grains.

[0016] The polishing slurry according to this embodiment contains the organic ammonium cation in an amount of preferably 0.1 to 1.0 part by mass, and more preferably 0.1 to 0.25 part by mass, per 100 parts by mass of the silica abrasive grains. The polishing slurry according to this embodiment has the advantage that by containing 0.1 parts by mass or more of the organic ammonium cation per 100 parts by mass of the silica abrasive grains, changes in the size of the abrasive grains are further suppressed. Furthermore, the polishing slurry according to this embodiment has the advantage that the polishing rate can be increased by containing 1.0 part by mass or less of the organic ammonium cation per 100 parts by mass of the silica abrasive grains.

[0017] The molecular weight of the organic ammonium cation is preferably 135 or less, more preferably 35 to 95, even more preferably 70 to 90, and even more preferably 75 to 90. The organic ammonium cation is represented by the following formula (1): In the following formula (1), R1 is H or a monovalent organic group, R2 is H or a monovalent organic group, R3 is H or a monovalent organic group, and R4 is H or a monovalent organic group, except for the case where R1, R2, R3, and R4 are all H. Examples of the monovalent organic group include an alkyl group, an allyl group, and an aromatic alkyl group. R1 is preferably a monovalent organic group having 3 or less carbon atoms or H. R2 is preferably a monovalent organic group having 3 or less carbon atoms or H. R3 is preferably a monovalent organic group having 3 or less carbon atoms or H. R4 is preferably a monovalent organic group having 3 or less carbon atoms or H. It is also preferred that R1 is a monovalent organic group having 3 or less carbon atoms or H, R2 is a monovalent organic group having 3 or less carbon atoms or H, R3 is a monovalent organic group having 3 or less carbon atoms or H, and R4 is a monovalent organic group having 3 or less carbon atoms or H. Examples of the organic ammonium cation include primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, and quaternary ammonium cations. The organic ammonium cation is preferably a quaternary ammonium cation. Examples of primary ammonium cations include ethylenediamine and spermine, which is also a secondary ammonium cation. Secondary ammonium cations include piperazine, piperidine, and the like. Examples of the quaternary ammonium cation include a tetramethylammonium cation, an ethyltrimethylammonium cation, and a tetraethylammonium cation.

[0018] [ka]

[0019] The organic ammonium cation is contained in the polishing slurry according to this embodiment by mixing the organic ammonium salt with other materials of the polishing slurry. Examples of the organic ammonium salt include organic ammonium hydroxide, organic ammonium halogen, and organic ammonium nitrate.

[0020] The silica abrasive grains are contained in the polishing slurry according to this embodiment as primary particles or as secondary particles formed by agglomeration of a plurality of primary particles. The silica abrasive grains include fumed silica abrasive grains and colloidal silica abrasive grains, with the fumed silica abrasive grains being preferred.

[0021] The alkali includes inorganic alkali agents which are inorganic substances. Examples of inorganic alkaline agents include potassium hydroxide, sodium hydroxide, and ammonia.

[0022] The polishing slurry according to this embodiment has the above-mentioned composition and therefore has the following advantages.

[0023] The polishing slurry according to this embodiment contains silica abrasive grains and an organic ammonium cation having a molecular weight of 155 or less. In such a polishing slurry, the change in the size of the abrasive grains is suppressed. The reason why such a polishing slurry has a suppressed change in the size of the abrasive grains is that the SiO - It is believed that the adsorption of the organic ammonium cation to the base causes a steric hindrance to the silica abrasive grains, making it difficult for the silica abrasive grains to aggregate together.

[0024] The polishing slurry according to the present invention is not limited to the above embodiment. The polishing slurry according to the present invention is not limited by the above-mentioned action and effect. Furthermore, the polishing slurry according to the present invention can be modified in various ways without departing from the gist of the present invention. EXAMPLES

[0025] Next, the present invention will be described more specifically with reference to examples and comparative examples.

[0026] (Test 1: Dynamic stability) Polishing slurries of the examples and comparative examples were prepared containing 800 ppm of a salt of an organic ammonium cation and a hydroxide shown in Table 1 below, 20.0 mass % of fumed silica, potassium hydroxide as an alkali, and water (pH: 11.0).

[0027] <Evaluation of dynamic stability> The dynamic stability was evaluated by continuously shaking (dynamic load) the polishing slurries of the examples and comparative examples with a shaker for 10 days and checking the growth of the abrasive grains in the polishing slurry. The shaking conditions are shown below. The growth rate of the abrasive grains was calculated using the following formula. The median diameter of the abrasive grains in the formula below was calculated using a laser diffraction / scattering type particle size distribution analyzer (LA-920) manufactured by Horiba, Ltd. The results are shown in Table 1 below and in Figures 1 and 2. Shaking method: reciprocating Shaking speed: 310 times / min Amplitude: 40mm Sample container capacity: 50mL Sample volume: 20mL Growth rate of abrasive grains (%) = (median diameter of abrasive grains after shaking / median diameter of abrasive grains before shaking-1) x 100

[0028] [Table 1]

[0029] As shown in Table 1 above and Figures 1 and 2, the polishing slurries of the examples had a smaller growth rate of abrasive grains than the polishing slurry of Comparison Example 1, which did not use an organic ammonium cation, and the polishing slurry of Comparison Example 2, which had an organic ammonium cation with a large molecular weight.

[0030] (Test 2: Polishing rate) A polishing slurry containing a salt of ethyltrimethylammonium cation and hydroxide, 20.0 mass % of fumed silica, potassium hydroxide as an alkali, and water was prepared (pH: 11.0, concentration of the salt: 200 ppm, 800 ppm, 2000 ppm). Then, immediately before polishing, the polishing slurry was diluted twice with water, and the diluted polishing slurry was used to polish a blanket wafer having a SiO2 film formed by plasma CVD using tetraethoxysilane (TEOS), and the polishing rate was calculated. The polishing conditions are shown below. Polishing machine: EPO222D (manufactured by Ebara Corporation) Polishing pressure: 35MPa Plate rotation speed: 60 min -1 Carrier rotation speed: 40 min -1 Slurry flow rate: 150mL / min Polishing time: 60min The removal rate was calculated by dividing the thickness reduction due to polishing by the polishing time. The thickness was measured using a nanospecAFT5100 manufactured by Nano-metrics. The results are shown in Figure 3.

[0031] As shown in FIG. 3, the polishing rate was higher as the amount of organic ammonium cation relative to the amount of silica abrasive grains was smaller.

[0032] (Test 3: Number of defects) A polishing slurry of Example 5 containing 500 ppm of a salt of ethyltrimethylammonium cation and hydroxide, 12.5 mass % of fumed silica, potassium hydroxide as an alkali, and water was prepared (pH: 11.0). Also, a polishing slurry of Comparative Example 3 was prepared in the same manner as the polishing slurry except that the salt was not used. The polishing slurry was used to polish a blanket wafer having a SiO2 film formed by plasma CVD using tetraethoxysilane (TEOS) (wafer area: 706.5 cm2). 2(Number of wafers: 20) The polishing conditions are as follows: Polishing machine: FREX (manufactured by Ebara Corporation) Head: G2 Polishing pressure CAP / RAP / OAP / EAR / RRP / PCP[hPa]:285 / 280 / 250 / 240 / 350 / 140 Head / Platen Rotation Speed ​​[min -1 ]: 60 / 61 Slurry flow rate: 200mL / min Polishing time: 60min Then, the number of defects on the wafer (defects / wafer) was measured. The number of defects was measured using a wafer surface inspection device (model name: LS6600) manufactured by Hitachi High-Technologies Corporation. The results are shown in Table 2 below and FIG.

[0033] [Table 2]

[0034] As shown in Table 2 and FIG. 4, the polishing slurry of Example 5 had a smaller number of defects than the polishing slurry of Comparative Example 3 which did not use an organic ammonium cation.

Claims

1. A polishing slurry comprising: It is used to polish the interlayer insulating film, Silica abrasive grains; Contains a salt of an organic ammonium cation having a molecular weight of 155 or less and a hydroxide, The pH is 8 to 12, The polishing slurry contains 0.1 to 1.0 part by mass of the organic ammonium cation per 100 parts by mass of the silica abrasive grains.

2. 2. The polishing slurry according to claim 1, wherein the silica abrasive grains are fumed silica abrasive grains.

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