KR20070018689A - Silicon wafer cleaning method - Google Patents

Abstract

A method of cleaning a silicon wafer, comprising: a first cleaning step of immersing a silicon wafer having finished surface mirror polishing in an aqueous solution of a nonionic surfactant, a second cleaning step of immersing the finished wafer in a dissolved ozone aqueous solution; And a third cleaning step of immersing the wafer after the second cleaning step in an aqueous solution containing ammonia and hydrogen peroxide, and performing each of the above steps in succession.

Description

Silicon wafer cleaning method {SILICON WAFER CLEANING METHOD}

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the washing process performed to the silicon wafer which finished the mirror polishing process of this invention,

FIG. 2 is a diagram showing the number of particles detected in a wafer after cleaning of Example 1 and Comparative Example 1. FIG.

The present invention relates to a method for cleaning a silicon wafer. This application claims priority with respect to Japanese Patent Application No. 2005-231430 for which it applied on August 10, 2005, and uses the content here.

In the mirror polishing process of a silicon wafer, the surface of the silicon wafer attached to the holding tool is pressed to a polishing cloth attached on a rotating platen at a predetermined pressure, and the polishing slurry is supplied between the polishing cloth and the wafer surface. The surface of the wafer is polished into a mirror surface shape by rotating the rotating surface plate. Usually, a slurry in which SiO ₂ fine particles and other abrasive particles are suspended in a weak alkaline liquid is used, and a polymer component such as cellulose is contained to reduce haze and LPD and to maintain wettability. .

After the mirror polishing process, the silicon wafer is cleaned to remove contaminants such as particles, organic contaminants, and metal impurities present on the surface. RCA method is generally used widely in the cleaning of the silicon wafer after mirror polishing (for example, Non Patent Literature 1; Shimura Fumiozer, `` Semiconductor Silicon Crystal Engineering '', Maruzen, Inc., issued September 30, 2015) , p. 125 to p. 127). The RCA method consists of two steps of washing with (1) a high pH alkaline mixture (hereinafter referred to as SC-1) and (2) a low pH acid mixture (hereinafter referred to as SC-2) based on hydrogen peroxide. . By combining and washing these mixed liquids, contaminants can be efficiently removed from the substrate surface.

However, the polymer component contained in the polishing slurry used in the mirror polishing process remains on the surface of the silicon wafer after the mirror polishing process, and in the RCA cleaning shown in Non-Patent Document 1, the SC-1 mixture is included in the polishing slurry. Since the polymer component causes a reaction such as dehydration condensation to form a derivative of the polymer component, and the derivative is fixed on the wafer surface, even if the SC-2 cleaning is performed after the SC-1 cleaning, the derivative adhered on the wafer surface is removed. It could not be removed and the wafer surface cleanliness could not be sufficiently increased.

An object of the present invention is to provide a method for cleaning a silicon wafer having excellent cleaning ability.

This invention is an improvement of the washing | cleaning method performed after mirror-polishing the surface of a silicon wafer, as shown in FIG. The characteristic constitution is the 1st cleaning process which immerses the silicon wafer which finished mirror polishing, in the nonionic surfactant aqueous solution, the 2nd cleaning process which immerses the wafer which finished this 1st cleaning process in dissolved ozone aqueous solution, and The 3rd cleaning process which immerses the wafer which finished the 2nd cleaning process in the aqueous solution containing ammonia and hydrogen peroxide is included, and each process is performed continuously.

In the cleaning method described above, the first and third cleaning steps are successively performed on the silicon wafer after the mirror polishing process in this order, so that the polishing slurry used in the mirror polishing process remaining on the wafer surface in the first cleaning step is performed. Organic contaminants present on the surface of the polymer and the wafer contained in the wafer are removed, and in the second cleaning step, the organic contaminant that cannot be removed in the first cleaning step or the surfactant used in the first cleaning step is decomposed and removed. In the 3 cleaning process, since organic contaminants and metal impurities are removed, a wafer of high cleanliness can be obtained.

In the said washing | cleaning method, the washing | cleaning method whose surfactant concentration of the nonionic surfactant aqueous solution used by a 1st washing process is 0.001-10 weight% may be sufficient.

In the above washing method, a washing method in which the ozone concentration of the dissolved ozone aqueous solution used in the second washing step is 1 to 20 ppm may be used.

The cleaning method of the silicon wafer of this invention performs a 1st cleaning process-a 3rd cleaning process continuously to the silicon wafer which finished mirror polishing, and the polishing slurry used by the mirror polishing process which remains on the wafer surface in a 1st cleaning process is carried out. Organic contaminants present on the surface of the polymer and the wafer contained in the wafer, and the surfactants used in the first cleaning step and the organic contaminants that could not be removed in the first cleaning step in the second cleaning step are decomposed and removed. Since organic contaminants and metal impurities are removed in the cleaning process, a high clean wafer can be obtained.

EMBODIMENT OF THE INVENTION Next, preferred embodiment for implementing this invention is described based on drawing.

The object in the washing | cleaning method of this invention is a silicon wafer after mirror-polishing the surface. On the surface of the silicon wafer after this mirror polishing process, not only contaminants such as particles, organic contaminants and metal impurities, but also components contained in the polishing slurry used for mirror polishing process remain.

The cleaning method of the silicon wafer of this invention includes the 1st cleaning process 11-the 3rd cleaning process 13, as shown in FIG. 1, and each process is performed continuously.

First, in the 1st washing | cleaning process 11, the silicon wafer which finished mirror-polishing processing is immersed in the nonionic surfactant aqueous solution. As a result, the cleaning and removal effect of the polymer component or organic contaminants remaining on the wafer surface is obtained. In this 1st washing | cleaning process 11, the nonionic surfactant aqueous solution which melt | dissolved the nonionic surfactant which does not generate | occur | produce with a wafer surface in ultrapure water is used. When a cationic surfactant other than a nonionic surfactant, anionic surfactant, etc. are used for the aqueous solution used at this 1st washing | cleaning process 11, silicon and surfactant will react and the wafer surface will become rough. Occurs. The surfactant concentration of the nonionic surfactant aqueous solution used in the 1st washing | cleaning process 11 is 0.001 to 10 weight%, Preferably it is 0.1 to 3.0 weight%, More preferably, it is 0.2 weight%. If the concentration of the surfactant is less than 0.001% by weight, organic contaminants remaining on the surface of the wafer cannot be sufficiently removed. If the concentration of the surfactant exceeds 10% by weight, the surfactant adheres to the surface of the wafer in a large amount, and is subsequently attached. It becomes difficult to remove all the surfactants.

The nonionic surfactant aqueous solution of the 1st washing | cleaning process 11 is maintained in the temperature range of room temperature-95 degreeC. In particular, the cleaning and removal effect of the organic contaminants remaining on the wafer surface is suitable by increasing the temperature of the nonionic surfactant aqueous solution at a high temperature of 80 to 95 ° C. in the above temperature range. The time for immersing the silicon wafer in the nonionic surfactant aqueous solution is 1 to 10 minutes, preferably 2 to 5 minutes. When the immersion time is less than 1 minute, it cannot be said that the cleaning removal of organic contaminants is sufficient, and even after 10 minutes, the cleaning effect does not change and is inefficient.

Examples of nonionic surfactants dissolved in an aqueous solution of nonionic surfactants include glycerin fatty acids such as sorbitan fatty acid esters such as sorbitan monolaurate and sorbitan sesquiisostearate, glycerin monooleate, and glycerin monoisostearate. Polyglycerol fatty acid esters such as esters, diglyceryl monooleate, decaglyceryl diisostearate, polyoxyethylene sorbitan aliphatic esters such as polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monolaurate, poly Polyoxyethylene glycerine fatty acid esters such as polyoxyethylene sorbitan fatty acid esters such as oxyethylene sorbitol tetraoleate, polyoxyethylene glyceryl monooleate, polyethylene glycol fatty acid esters such as polyoxyethylene monoisostearate, Polyoxyethylene polyoxy, such as polyethyleneglycol difatty acid ester, such as polyoxyethylene diisostearate, polyoxyethylene alkyl ether, such as polyoxyethylene oleyl ether, and polyoxyethylene-1- polyoxypropylene-4- alkyl ether Polyoxyethylene castor oil and hardened castor oil, such as a propylene alkyl ether, polyoxyethylene castor oil, and polyoxyethylene hardened castor oil (40E.O.), are mentioned.

Next, in the 2nd cleaning process 12, the wafer which completed the above-mentioned 1st cleaning process 11 is immersed in dissolved ozone aqueous solution. Thereby, the effect of decomposition and removal of the surfactant used in the 1st washing | cleaning process 11 and the organic contaminant which was not removed in the 1st washing | cleaning process 11 is obtained. In addition, since metal impurities such as Cu and Ni present on the wafer surface are oxidized, it can be easily removed in the subsequent third cleaning step 13. The ozone concentration of the dissolved ozone aqueous solution is 1 to 20 ppm, preferably 5 to 20 ppm. If ozone concentration is less than 1 ppm, the effect in this 2nd washing | cleaning process 12 is not acquired. The upper limit is set to 20 ppm because of the viewpoint of member selection such as a cleaning device.

The dissolved ozone aqueous solution in the 2nd washing | cleaning process 12 is used at the temperature of about room temperature. Moreover, you may use the dissolved ozone aqueous solution cooled to about 15 degreeC, and the dissolved ozone aqueous solution heated to about 50 degreeC. The cooled dissolved ozone aqueous solution is easy to increase the ozone concentration in the aqueous solution, and thus is used when using extremely high purity ultrapure water, which is difficult to increase the ozone concentration in the aqueous solution. Since the oxidizing power becomes high compared with the oxidizing power at room temperature, the heated dissolved ozone aqueous solution is used when it is desired to increase the oxidizing power without changing the ozone concentration. The time for immersing the silicon wafer in the dissolved ozone aqueous solution is 1 to 10 minutes, preferably 2 to 5 minutes. When the immersion time is less than 1 minute, it cannot be said that the cleaning removal of organic contaminants is sufficient, and even after 10 minutes, the cleaning effect does not change and is inefficient.

Next, in the 3rd cleaning process 13, the wafer which finished the 2nd cleaning process 12 is immersed in the aqueous solution containing ammonia and hydrogen peroxide. As a result, the effect of removing particles remaining on the wafer surface is obtained. Organic contaminants can be removed by the strong oxidation of hydrogen peroxide and the dissolution of ammonia. In addition, Group 1B, Group 2B, and other metal impurities such as Au, Ag, Cu, Ni, Cd, Zn, Co, Cr, and other metal impurities are removed by a compound formation reaction with ammonia. The aqueous solution containing ammonia and hydrogen peroxide in the third washing step 13 may use a Sc-1 mixed liquid used for RCA washing. The aqueous solution containing ammonia and hydrogen peroxide in the 3rd washing | cleaning process 13 is used at the temperature of 75-80 degreeC. The time to immerse a silicon wafer in the aqueous solution containing ammonia and hydrogen peroxide is 1 to 20 minutes, Preferably it is 2 to 5 minutes. If the immersion time is less than 1 minute, it cannot be said that the cleaning removal of the particle component is sufficient, and the cleaning effect does not change even after more than 20 minutes, resulting in an inefficient and roughening of the wafer surface.

Thus, by performing the said 1st washing | cleaning process 11-the 3rd washing | cleaning process 13 continuously in this order, the particle | grains, organic contaminants, and metal impurities which remain in the surface of the silicon wafer which finished mirror-polishing processing can be removed. have.

In addition, when rinse cleaning by pure water is performed between the first washing steps 11 to 3 washing steps 13, the generation of the residual nonionic surfactant on the wafer surface and the dissolved ozone aqueous solution Since the unevenness of the oxidized film due to the introduction of OH groups into the oxide film formed by the oxidized film cannot be sufficiently exerted the cleaning effect of the subsequent cleaning process, the first cleaning process (11) to the third cleaning process (13). Needs to be done continuously.

The order of the 1st washing | cleaning process 11-the 3rd washing | cleaning process 13 in the washing | cleaning method of this invention is reversed, for example, the 3rd washing | cleaning process 13, the 1st washing | cleaning process 11, and 2nd When the cleaning is carried out in the order of the washing step 12, the polymer component contained in the polishing slurry is reacted with a dehydration condensation reaction by an aqueous solution containing ammonia and hydrogen peroxide in the third washing step to form a derivative of the polymer component. Since this derivative is fixed to the wafer surface, even if the first cleaning step and the second cleaning step are performed after this third cleaning step, the derivative cannot be removed and the cleaning effect of the cleaning method of the present invention is obtained. You won't lose. Moreover, if the 1st washing process 11 and the 2nd washing process 12 are reversed, and it wash | cleans in order of the 2nd washing process 12 and the 1st washing process 11, in the 1st washing process 11, Since the surfactant to be used remains on the wafer surface and cannot be sufficiently removed even after the third cleaning step 13 is performed, the cleaning effect of the cleaning method of the present invention is not obtained. Therefore, in the washing | cleaning method of this invention, each process of the 1st washing process 11-the 3rd washing process 13 needs to be performed continuously in this order.

Moreover, in the washing | cleaning method of this invention, following the 3rd washing | cleaning process 13, you may perform washing | cleaning which immerses a wafer in the acid-mixed liquid of low pH. As an acid mixture liquid of the low pH used here, the liquid mixture of hydrochloric acid and hydrogen peroxide solution is mentioned. Hydrochloric acid and by the mixed solution of the hydrogen peroxide solution wherein the alkaline ions of the insoluble matter in an aqueous solution containing ammonia and hydrogen peroxide used in the cleaning step and the Al ^{3 +,} Fe ^{2 +,} it is possible to remove cations such as Mg ^{+ 2.}

Example 1

Next, the Example of this invention is described in detail with a comparative example.

<Example 1>

In the period from June 2001 to January 2005, the following cleaning was continued for 1,320,000 silicon wafers finished with mirror polishing fabricated at a rate of 30,000 sheets / month.

First, a nonionic surfactant (manufactured by Wako Pure Pharmaceuticals, product name NCW) was dissolved in ultrapure water to prepare an aqueous solution having a concentration of 0.2% by weight, and the silicon wafer was placed in an aqueous solution of nonionic surfactant heated to 90 ° C. Immersion was maintained for 3 minutes. Subsequently, a dissolved ozone aqueous solution having an ozone concentration of 20 ppm was prepared, and the silicon wafer was immersed in the dissolved ozone aqueous solution maintained at room temperature and held for 3 minutes. Next, an aqueous solution containing 1.2% by weight of ammonia and 2.6% by weight of hydrogen peroxide was prepared, and the silicon wafer was immersed in an aqueous solution containing ammonia and hydrogen peroxide heated at 80 ° C. and held for 3 minutes. The cleaned wafers were dried after pure rinsing.

Comparative Example 1

In the period from December 2000 to May 2001, the following cleaning was continued with respect to 180,000 silicon wafers which finished mirror-polishing processing manufactured on the same conditions as Example 1 at a rate of 30,000 sheets / month.

An aqueous solution containing 1.2% by weight of ammonia and 2.6% by weight of hydrogen peroxide was prepared, and the silicon wafer was immersed in an aqueous solution containing ammonia and hydrogen peroxide heated to 80 ° C. and held for 3 minutes. The cleaned wafers were dried after pure rinsing.

Comparative test 1

About the silicon wafer which finished cleaning of Example 1 and the comparative example 1, arbitrary fixed ranges of the wafer surface were measured using the particle counter (made by ADE company, product name CR80), and the particle | grains exceeding 0.12 micrometer in size were detected. . The number of particles detected in the wafer which finished cleaning of Example 1 and the comparative example 1 is shown in FIG. 2, and the average value, the maximum value, and the minimum value of the particle number detected in the wafer which finished cleaning of Example 1 and Comparative Example 1 are shown in Table 1. .

As can be clearly seen in FIG. 2 and Table 1, the number of detected particles of more than 0.12 占 퐉 is greatly reduced in the wafer after cleaning in Example 1, compared to the wafer after cleaning in Comparative Example 1, and the cleaning of the present invention is greatly reduced. It can be seen that the cleanliness of the wafer can be improved by the method.

The cleaning method of the present invention can be applied not only to silicon wafers subjected to mirror polishing, but also to applications for cleaning glass substrates used in liquid crystal displays and the like.

As mentioned above, although preferred Example of this invention was described, this invention is not limited to these Examples. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit of the invention. The invention is not limited by the foregoing description, but only by the appended claims.

Claims (3)

As a cleaning method performed after mirror-polishing the surface of a silicon wafer, A first cleaning step of immersing the silicon wafer after the mirror polishing process in an aqueous solution of a nonionic surfactant; A second cleaning step of immersing the silicon wafer having finished the first cleaning step in a dissolved ozone aqueous solution; A third cleaning step of immersing the silicon wafer after the second cleaning step in an aqueous solution containing ammonia and hydrogen peroxide, A method for cleaning a silicon wafer, wherein the first to third cleaning steps are performed continuously. The washing | cleaning method of Claim 1 whose surfactant concentration of the nonionic surfactant aqueous solution used by a said 1st washing process is 0.001-10 weight%. The washing method according to claim 1, wherein the ozone concentration of the dissolved ozone aqueous solution used in the second washing step is 1 to 20 ppm.

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