JPH04291724A - Silicon wafer polishing method - Google Patents

Abstract

PURPOSE:To obtain a silicon wafer which does not generate any haze by supplying a nonionic surface-active agent having HLB value in the particular range or a particular anionic surface-active agent together with alkali colloidal silica or a powder silica polishing solution which is dispersed in water at the time of polishing a silicon wafer. CONSTITUTION:The nonionic surface-active agent used is required to have the HLB value of 13.0 or higher but under 20.0. As the anionic surface-active agent, suphonic acid salt type, sulfurnic acid ester salt type, calboxylic acid salt type and phosphoric acid ester salt type agent are used. When the surface-active agents are supplied together, the concentration thereof on the polisher is desirably 10ppm to 1wt.% aqueous solution in terms of the total amount of effective component of the solid matter of alkali colloidal silica or powder silica which is dispersed in water. The amount of coexistence of surface-active agents is desirably about 0.01 to 1.0wt times for the supplied amount of alkali colloidal silica or powder silica.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method that does not generate haze during mirror polishing of silicon wafers in the process of manufacturing semiconductors.

0002

[Prior Art and Problems to be Solved by the Invention] The mirror polishing process of silicon wafers for semiconductors includes a lapping process (a lapping process) in which cut strain layers and surface waviness that occur when the silicon ingot is cut into wafers are removed. There is a polishing process (precision polishing process) that finishes the wrapped silicon wafer that has undergone the lapping process to the desired surface precision. The polishing process is divided into a primary polishing process (primary polishing process) for finishing to a rough level of accuracy, and a final polishing process (final polishing process) for finishing to a desired surface accuracy. Further, the primary polishing process may be divided into two stages for the purpose of shortening working time and increasing efficiency, and in that case, the primary polishing process is called a primary polishing process and a secondary polishing process. The present invention relates to a polishing method during the aforementioned final polishing step.

[0003] The final polishing process is used to finish silicon wafers, which have generally been finished to a surface roughness of about 4 to 20 nm in the primary or primary and secondary polishing processes, to a desired surface roughness of 1 nm or less. A process in which a silicon wafer as a semiconductor substrate is completed through a final polishing process. In the actual final polishing process, multiple primary polishing silicon wafers are attached to a polishing block, and this polishing block is brought into close contact with soft artificial leather (polisher) glued on a rotary table by applying appropriate pressure. While the table is rotating, add alkaline colloidal silica with a pH of about 8 to 12, or disperse it in pure water and add an appropriate pH.
It is said that polishing is achieved by flowing a powdered silica dispersion liquid adjusted to H, and causing a mechanochemical action between the polishing liquid and the silicon wafer.

However, in the conventional polishing method using alkaline colloidal silica, a haze (a state in which impurities are attached in a cloudy manner) is generated on the surface of the silicon wafer at the end of final polishing, which is related to the fact that the silicon wafer is a brittle material. However, there was no easy way to remove it.

[0005] When powdered silica is used in the final polishing process, haze is less likely to occur, but a new step is required to uniformly disperse it in an aqueous solution, and furthermore, it precipitates if left standing, so it is necessary to constantly stir it. there were.

[0006] JP-A-2-125413 describes an anti-fogging device for semiconductor wafers, but it requires special equipment, and the introduction of new equipment increases the burden on the manufacturer, making it impractical. It is true. Japanese Patent Publication No. 61-2099
No. 09 and No. 61-209910 disclose a method for synthesizing colloidal silica for polishing silicon wafers, but the cost is high and furthermore, the prevention of haze, which is the gist of the present invention, is not improved in any way. do not have. Also, JP-A-6
2-285976, JP-A-1-297487, JP-A-63-272458, JP-A-63-272459, and JP-A-1-177969 do not have the haze prevention ability for the same reason. Also, USP No. 4169337,
Although the composition of an abrasive for silicon wafers is disclosed in US Pat. No. 3,170,273, it does not have any function of suppressing the occurrence of haze, and is therefore unsuitable for this purpose.

[0007]

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors have found that the HLB value is 13.0 or more and 20 or more.
．． less than 0 nonionic surfactant or sulfonate type,
Silicon wafers that do not generate haze by co-flowing a sulfate ester salt type, phosphate ester salt type, or carboxylate type anionic surfactant with alkaline colloidal silica or a powder silica polishing liquid dispersed in water during silicon wafer polishing. The present invention was completed based on the discovery that the following could be obtained.

That is, the present invention provides an HLB value of 13.0 or more and 20
．． less than 0 nonionic surfactant or sulfonate type,
Haze generation characterized by co-flowing a sulfate ester salt type, phosphate ester salt type or carboxylate type anionic surfactant with alkaline colloidal silica or a powder silica polishing liquid dispersed in water during silicon wafer polishing. The present invention provides a method for polishing silicon wafers that does not require the use of conventional silicon wafers.

In the present invention, co-current means that alkaline colloidal silica or powder silica polishing liquid dispersed in water is supplied during silicon wafer polishing.
At this time, in addition to the alkaline colloidal silica or the powder silica polishing liquid dispersed in water, a nonionic surfactant with an HLB value of 13.0 or more and less than 20.0, or a sulfonate type, sulfate ester salt type, or phosphate ester salt type is used. Alternatively, it refers to an operation in which a carboxylate type anionic surfactant is simultaneously supplied. In other words, this refers to the operation of creating a mixed state with a supply port of alkaline colloidal silica or powder silica polishing liquid from a separate tank, or providing a separate supply port and mixing on the polisher (inside the stock tank of alkaline colloidal silica or powder silica). No surfactant coexists).

Nonionic surfactants having an HLB value of 13.0 or more and less than 20.0 that can be used in the present invention include ethylene oxide adducts of nonylphenol, ethylene oxide adducts of paracumenylphenol, and carbon atoms of 12 to 1.
Ethylene oxide adduct of primary alcohol with about 3 carbon atoms, ethylene oxide adduct of secondary alcohol with about 12 to 13 carbon atoms, ethylene oxide adduct of beef tallow glyceride, block polymer of propylene oxide and ethylene oxide, propylene oxide and Examples include random polymers of ethylene oxide, but are not limited to those described above. However, it is necessary that the HLB value is within the above range. Further, the HLB value can be calculated using the following formula.

[0011]

[Math 1]

The anionic surfactants that can be used in the present invention include sulfonate type, sulfate ester salt type, carboxylate type, phosphate ester salt type, and the like. Examples of the sulfonate type include alkylsulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, sulfosuccinates, N-acylsulfonates, and the like. Examples of the sulfate ester salt type include alkyl sulfates, alkyl ether sulfates, alkylaryl ether sulfates, and alkylamide sulfates. As a carboxylate type, N
-acyl amino acid salt, alkyl ether carboxylate,
There are acylated peptide salts, etc. Examples of phosphoric acid ester salts include alkyl phosphates, alkyl ether phosphates, and alkylaryl ether phosphates. Note that any counterion may be used, but Na, K, Li, amine, ammonium, etc. are preferable.

[0013] The concentration on the polisher when the surfactant is co-flowed is 10 ppm to 10 ppm in total of the active ingredients of the above various surfactants based on the silica solid content of alkaline colloidal silica or powdered silica dispersed in water. A 1% by weight aqueous solution is good. In addition, the co-flow amount of surfactant is 0.0 with respect to the amount of alkaline colloidal silica or powder silica supplied.
Approximately 1 to 1.0 times the weight is preferable. At this time, it is preferable to control the aqueous surfactant solution used so that the concentration of the surfactant relative to the silica solid content of the alkaline colloidal silica or the powdered silica dispersed in water becomes the above concentration. However, co-current flow requires alkaline colloidal silica or powdered silica to be supplied, and use of a diluted surfactant alone should be avoided as it will cause fine scratches on the silicon wafer. Unless the diluted surfactant is used alone, the cocurrent condition is
It does not matter whether it is carried out during the entire polishing process or only at the end of the polishing process, but at the end of the polishing process, the diluted surfactant must be co-flowed, and the co-flow time must be at least 30 seconds. If this is not done, the desired effect will not be sufficient. When the above conditions are met, a good silicon wafer with suppressed haze formation can be obtained.

[0014] The alkaline colloidal silica used in the present invention preferably has a pH of 8.5 to 11.0, and has an average particle diameter of 7.0 or less, for example, as measured by the nitrogen adsorption method (BET method).
-100 mμ, and generally commercially available products can be used. For example, Adelite AT-30S
(Asahi Denka Kogyo Co., Ltd., average particle size 7 to 10 mμ, silica solid content 30% by weight), Adelite AT-30 (Asahi Denka Kogyo Co., Ltd., average particle size 10 to 15 mμ, silica solid content 30% by weight) ), Adelite AT-40 (Asahi Denka Kogyo (
Co., Ltd.), average particle size 15-20 mμ, silica solid content 40
weight%), Adelite AT-50 (Asahi Denka Kogyo Co., Ltd.),
Average particle size 20-30 mμ, silica solid content 50% by weight
), Adelite BT-55 (Asahi Denka Kogyo Co., Ltd., average particle size 30-50 mμ, silica solid content 50% by weight), Adelite BT-57 (Asahi Denka Kogyo Co., Ltd., average particle size 5)
0-70 mμ, silica solid content 50% by weight), Adelite BT-59 (Asahi Denka Kogyo Co., Ltd., average particle size 70-1
00 mμ, silica solid content 50% by weight), etc. are optimal.

[0015] The powdered silica dispersed in water can be any powdered silica that is generally used for polishing silicon wafers.

[0016]

[Examples] Various examples will be described below, but the present invention is not limited to the following examples.

Example 1 Adelite BT-55 (manufactured by Asahi Denka Kogyo Co., Ltd., average particle size 30-50 mμ, silica solid content 50%) was diluted to a silica concentration of 5.0% by weight. This diluted Adelite A
T-50 was supplied onto a polishing disk under the conditions described below, and the primary polished wafer that had undergone the primary polishing process was polished.

Polishing machine: LPH-15 improved machine manufactured by Lap Master Co., Ltd. Polishing machine diameter: 15 inches Processing pressure: 100g/cm2 Processing temperature: 30°C Processing fluid supply amount: 10 liters/hr Processing time: 1 hour Number of sheets processed: 1-sheet polisher: SUPREME RN-H Manufactured by Rodel Nitta Co., Ltd. During final polishing under the above conditions, 50 mol of ethylene oxide adduct of nonylphenol diluted to 50 ppm of active ingredient (HLB value 18.
2) was co-flowed for 1 hour at a rate of 1 liter/hr. After final polishing, the wafer surface was washed with ultrapure water for 1 minute, being careful not to dry it. After cleaning with ultrapure water, RCA cleaning with a hydrogen peroxide-ammonia solution at 80°C, followed by QDR (quick dump cleaning).
Dry with a spin dryer. After drying, halogen parallel light (ultra-high brightness inspection lighting device U) is used in the clean bench.
1H-1H (Intec Co., Ltd.) reflection was visually measured to observe the occurrence of haze. As a result of the measurement, the obtained silicon wafer was free of haze (haze-free).
, was in good condition.

Example 2 Ethylene oxide of nonylphenol flowing together 50
The method of Example 1 was followed except that the co-flow time of the diluted mol adduct (HLB value 18.2) was changed to 40 seconds just before the end of final polishing. The obtained silicon wafer was haze-free and good.

Example 3 The surfactant to be co-flowed was a 13 mol ethylene oxide adduct of paracumenylphenol (HLB value 14.6).
) and the active ingredient during co-current flow was changed to 20 ppm, but the method of Example 1 was followed. The obtained silicon wafer was haze-free and good.

Example 4 The method of Example 3 was followed except that the co-flow time of 13 mol of ethylene oxide adduct (HLB value 14.6) of paracumenylphenol (HLB value 14.6) was changed to 30 seconds just before the end of final polishing. Ta. The obtained silicon wafer was haze-free and good.

Example 5 Example 1 except that the co-current surfactant was changed to sodium lauryl sulfonate (sulfonate type anionic surfactant) and the active ingredient during co-flow was changed to 15 ppm.
According to the method of The obtained silicon wafer was haze-free and good.

Example 6 The procedure of Example 5 was followed except that the co-flow time of sodium lauryl sulfonate (sulfonate type anionic surfactant) was changed to 40 seconds just before the end of final polishing. The obtained silicon wafer was haze-free and good. Example 7 Powdered silica used for final polishing of silicon wafers was dispersed in distilled water to have a silica solid content of 3% by weight, and the pH was adjusted to 10.0 with aqueous ammonia. This processing liquid was constantly stirred to suppress the precipitation of powdered silica. Final polishing was performed by supplying this processing liquid at a rate of 15 liters/hr. For 40 seconds just before the end of final polishing, a block polymer of propylene oxide and ethylene oxide (HLB value 16.
The conditions of Example 1 were followed except that a nonionic surfactant (No. 6) was co-flowed at a rate of 1.5 liters/hr. The obtained silicon wafer had good haze-free properties.

Comparative Example 1 Adelite BT-55 (manufactured by Asahi Denka Kogyo Co., Ltd., average particle size 30-50 mμ, silica solid content 50% by weight) was diluted to a silica concentration of 5.0% by weight. This diluted Adelite BT-55 was supplied onto a polishing disk under the conditions described in Example 1, and the primary polished wafer that had undergone the primary polishing process was polished. This final polished silicon wafer was directly cleaned by the method of Example 1. The obtained silicon wafer has haze,
It was defective.

Comparative Example 2 Adelite BT-55 (manufactured by Asahi Denka Kogyo Co., Ltd., average particle diameter 30-50 mμ, silica solid content 50% by weight) was diluted to a silica concentration of 5.0% by weight. This diluted Adelite BT-55 was supplied onto a polishing disk under the conditions described in Example 1, and the primary polished wafer that had undergone the primary polishing process was polished. During final polishing, nonylphenol ethylene oxide 16
An aqueous solution prepared by diluting a mol adduct (a nonionic surfactant with an HLB value of 12.8) to 50 ppm of active ingredient was co-flowed at a rate of 1 liter/hr. After final polishing, a cleaning step was performed using the method of Example 1. The obtained silicon wafer had slight haze and was defective.

Comparative Example 3 Powdered silica used for final polishing of silicon wafers was dispersed in distilled water to give a solid silica content of 3% by weight, and the pH was adjusted to 10.0 with aqueous ammonia. This processing liquid was constantly stirred to suppress the precipitation of powdered silica. Final polishing was performed by supplying this processing liquid at a rate of 15 liters/hr. The cleaning method and the like were based on the conditions of Example 1. The obtained silicon wafer had haze and was defective.

[0027]

[Effect of the invention] A nonionic surfactant, or a sulfonate type, sulfate ester salt type, phosphate ester salt type, or carboxylate type anionic surfactant having an HLB value of 13.0 or more and less than 20.0 can be used by polishing a silicon wafer. Sometimes, by co-flowing with alkaline colloidal silica or powdered silica polishing solution dispersed in water, haze-free silicon wafer surfaces could be obtained without changing the conventional polishing process.

Claims (1)

[Claims] Claim 1: A nonionic surfactant, or a sulfonate type, sulfate ester salt type, phosphate ester salt type, or carboxylate type anionic surfactant having an HLB value of 13.0 or more and less than 20.0 is polished on a silicon wafer. A method for polishing a silicon wafer, which is sometimes co-current with an alkaline colloidal silica or a powder silica polishing liquid dispersed in water.