KR100830750B1 - Method for cleaning silicon wafer - Google Patents

Abstract

The present invention discloses a silicon wafer cleaning method. The silicon wafer cleaning method according to the present invention includes a first step of cleaning a silicon wafer surface using ozone water to which megasonic is applied; A second step of cleaning the silicon wafer surface with diluted HF; A third step of cleaning the surface of the silicon wafer cleaned by dilute hydrofluoric acid using ozone water to which Megasonic is applied; And a fourth step of cleaning the surface of the silicon wafer cleaned by ozone water using a dilute alkali aqueous solution. In some cases, the first step may be omitted.

According to the present invention, unlike the conventional RCA cleaning method because it does not use hydrogen peroxide can reduce the waste water treatment cost according to the dehydrogen peroxide process, and because the cleaning process is carried out at room temperature, energy saving is possible, and using a diluted cleaning solution cleaning solution There is a saving effect and excellent cleaning effect for all contaminants such as fine particles, organic impurities, and metal impurities without damaging the wafer surface.

Silicon Wafer, Clean, RCA, SC-1, SC-2, DHF, Dilute Ammonia Water, Ozone Water

Description

Method for cleaning silicon wafer {Method for cleaning silicon wafer}

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to.

1 is a process flow diagram illustrating a silicon wafer cleaning method in accordance with a preferred embodiment of the present invention applied to a bare silicon wafer fabrication process.

2 is a graph showing fine particles on the surface of a silicon wafer after cleaning an 8-inch bare silicon wafer polished by chemical mechanical polishing (CMP) according to Comparative Examples and Examples 1 and 2, and showing the results. .

3 is a graph and a table showing the results of measuring roughness of the surface of the silicon wafer after cleaning the 8-inch bare silicon wafer polished by CMP according to SC-1, Examples 2 and 3;

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of cleaning a silicon wafer used as a substrate of a semiconductor device, and more particularly, to a method of cleaning a semiconductor wafer using ozone water and dilute hydrofluoric acid.

The silicon wafer is contaminated by various contaminants during a wafer manufacturing process or a semiconductor process for device integration. Representative contaminants include fine particles, organic contaminants, metal contaminants, and the like. Such contaminants cause a decrease in the production yield of semiconductor devices. Therefore, in the manufacture of bare silicon wafers, after the mirror polishing process using chemical mechanical polishing (CMP), and in the manufacturing of semiconductor devices, the cleaning process is performed after the unit semiconductor process in which a lot of contaminants are generated. Needs to be controlled to an appropriate level.

In recent years, the number of cleaning processes has increased due to the large diameter of silicon wafers and the reduction of design rules, and the amount of chemicals used in the cleaning process has been continuously increasing. As a result, the production cost of semiconductor devices is increasing, and enormous costs are required for treating a large amount of chemicals emitted in the cleaning process.

Silicon wafer cleaning methods widely used to date include RCA cleaning, Sulfuric acid peroxide mixture (SPM) cleaning, and Dilute HF (DHF) cleaning, and each cleaning method is selectively used depending on the type of contaminants to be cleaned. do.

RCA cleaning is a high temperature wet process that uses high concentrations of strong acids and strong base chemicals, usually RCA standard clean-1 (SC-1) and standard clean-2 (SC-2). It consists of steps.

SC-1 is a cleaning process that proceeds at a temperature of about 75 to 90 degrees using a mixture of ammonia water, hydrogen peroxide and ultrapure water (DI water), and simultaneously oxidizes the wafer surface with hydrogen peroxide and fine etching of the wafer surface with ammonia water. It is a cleaning process that repeatedly proceeds to remove organic contaminants and metal impurities (Au, Ag, Cu, Ni, Cd, Zn, Co, Cr, etc.) from the wafer surface. SC-2 is a cleaning process that proceeds at a temperature of about 75 to 85 degrees using a mixture of hydrochloric acid, hydrogen peroxide, and ultrapure water, and alkali ions (Al ^{3 +} , Fe ^{3 +} , Mg ^{2 +} ), Al (OH) _3. , Fe (OH) ₃ , Mg (OH) ₂ , Zn (OH) ₂ and the like, and a washing process for removing residual contaminants not removed from SC-1.

However, RCA cleaning method can achieve high efficiency in terms of removing contaminants, while wastewater treatment costs are high because the dehydrogen peroxide process is applied to wastewater treatment, and the washing process must be carried out at high temperature. Due to the use of the cleaning solution has a problem that takes a lot of process costs.

SPM cleaning is a cleaning process using a mixed solution of sulfuric acid and hydrogen peroxide. It is effective in removing heavy organic contaminants such as photoresist resin and makes the surface of the wafer hydrophilic, which makes it easy to wet other cleaning solutions. There is this. However, there is a disadvantage in that a large amount of sulfur residues remain after the cleaning process.

The DHF cleaning method is a cleaning step using dilute hydrofluoric acid diluted with hydrofluoric acid in ultrapure water, and is effective for removing unnecessary silicon oxide film formed on the surface of a silicon wafer. In addition, the DHF cleaning method has the advantage of removing fine particles and metal contaminants in the process of removing the silicon oxide film. For reference, the fine particles are lifted off in the process of etching the silicon oxide film by hydrofluoric acid, and the metal impurities are simultaneously removed together with the oxide film while being trapped in the silicon oxide film.

However, the DHF cleaning method has a problem of facilitating adhesion of fine particles by hydrophobicizing the surface of the silicon wafer. Therefore, after cleaning with DHF, it is necessary to hydrolyze the silicon wafer surface to prevent recontamination by fine particles.

In this regard, Korean Patent Laid-Open Publication No. 2003-56224 discloses a method of hydrophilizing a surface of a wafer using ozone water after wafer cleaning using dilute hydrofluoric acid. However, the hydrophilization treatment with ozone water alone is not sufficient to prevent the adhesion of fine particles. In addition, Japanese Laid-Open Patent Publication No. 2004-327878 discloses a method of hydrophilizing a surface of a wafer by adding a surfactant to dilute hydrofluoric acid and performing a cleaning process. However, since surfactants are a source of organic contaminants, there is a disadvantage that a separate cleaning process is required to remove the surfactants.

The present invention was devised to solve the above-mentioned problems of the prior art, it is possible to reduce the waste water treatment costs according to the progress of the dehydrogen peroxide process by eliminating the use of hydrogen peroxide, the removal of fine particles and metals using dilute hydrofluoric acid After removing the contaminants at the same time, the surface of the silicon wafer is hydrophilized to prevent reattachment of the fine particles, and the fine etching of the silicon wafer using a dilute alkaline aqueous solution maximizes the cleaning effect while preventing the adhesion of the fine particles during the cleaning process. It is an object of the present invention to provide a method for cleaning a silicon wafer.

According to an aspect of the present invention, there is provided a method of cleaning a silicon wafer, the method comprising: (a) a first step of cleaning a silicon wafer surface using ozone water to which megasonic is applied; (b) a second step of cleaning the silicon wafer surface with diluted HF; (c) a third step of cleaning the surface of the silicon wafer cleaned by dilute hydrofluoric acid using ozone water to which Megasonic is applied; And (d) a fourth step of cleaning the surface of the silicon wafer cleaned with ozone water using a dilute alkali aqueous solution.

In the present invention, in the first step, organic contaminants remaining on the surface of the silicon wafer are removed, and in the second step, the oxide film on the surface of the silicon wafer is etched by dilute hydrofluoric acid while the fine particles are lifted off and captured on the oxide film. In the third step, a chemical silicon oxide film is formed on the surface of the silicon wafer by ozone to perform a hydrophilization treatment, and in the fourth step, electrostatic repulsion of the surface of the silicon wafer and the fine particles is performed. The surface of the silicon wafer is finely etched while the re-attachment of the fine particles is prevented to remove the fine particles and contaminants not removed in the second step.

When the cleaning method according to the present invention is applied to cleaning a silicon wafer after a semiconductor process that does not cause organic contaminants, the first step may be omitted.

Preferably, the ozone concentration of ozone water used in the first and third steps is 1 to 30 ppm.

Preferably, the hydrofluoric acid content of the dilute hydrofluoric acid is 0.1 to 1 vol%.

Preferably, the alkali concentration of the diluted aqueous alkali solution is 0.001 to 0.1 vol%.

Preferably, the pH of the diluted alkali aqueous solution is 9 to 11.

Preferably, the alkali contained in the diluted aqueous alkali solution is NH ₄ OH, KOH, NaOH, TMAH (Tetra-Methyl Ammonium Hydroxide) or a mixed solution thereof.

Preferably, the first, third and fourth steps are performed at a temperature of 20 to 60 degrees, and the second step is performed at a temperature of 20 to 30 degrees.

The present invention described above may be applied after the mirror polishing process using CMP during the manufacturing process of the bare silicon wafer and after the unit semiconductor process in which the contaminants are derived during the semiconductor device manufacturing process.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms or words used in this specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors should properly introduce the concept of terms in order to best explain their invention. It should be interpreted as meanings and concepts in accordance with the technical spirit of the present invention based on the principle that it can be defined. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various equivalents that may be substituted for them at the time of the present application It should be understood that there may be water and variations.

1 is a process flow diagram illustrating a silicon wafer cleaning method in accordance with a preferred embodiment of the present invention applied to a bare silicon wafer fabrication process.

Referring to FIG. 1, first, a mirror polished silicon wafer is immersed in ozone water to which megasonic is applied using CMP (S10). Here, ozone water is obtained by dissolving ozone in ultrapure water. Then, organic contaminants and some fine particles remaining on the surface of the silicon wafer are removed by the chemical action of ozone contained in megasonic and ozone water. At the same time, ozone and silicon on the silicon wafer surface react with each other to form a chemical silicon oxide film on the silicon wafer surface.

Megasonic to be applied to ozone water is a high frequency ultrasonic wave of 1 MHz or more, and has an excellent ability to remove fine particles physically adsorbed on the surface of a silicon wafer. In addition, unlike ultrasonic, there is no cavitation effect, so the physical effect on the silicon wafer is small.

Preferably, the ozone concentration of the ozone water is 1 to 30 ppm, the temperature is 20 to 60 degrees, and the immersion time of the silicon wafer is 1 to 5 minutes. If the ozone concentration of the ozone water is less than 1 ppm, the effect of removing the desired organic pollutants cannot be expected. If the ozone concentration exceeds 30 ppm, the increase in the cleaning effect is not large compared to the increase in the ozone concentration. If the temperature of the ozone water is less than 20 degrees, the activity of ozone is lowered and the cleaning effect is lowered. If the temperature of the ozone water is higher than 60 degrees, the concentration of ozone is reduced and the cleaning effect is lowered. In addition, if the immersion time of the silicon wafer is less than 1 minute, the desired cleaning effect cannot be obtained. If the immersion time exceeds 5 minutes, the cleaning is almost completed. Therefore, it is preferable to maintain the immersion time for more than 5 minutes from the viewpoint of throughput. Not.

Subsequently, the silicon wafer is immersed in dilute hydrofluoric acid to etch the silicon oxide film on the silicon wafer surface (S20). In the process of etching the silicon oxide film, the fine particles present in the silicon wafer are lifted off and at the same time, various metal impurities trapped in the silicon oxide film are removed. As a result, the contamination level of the silicon wafer is drastically reduced.

Preferably, in the step S20, the hydrofluoric acid concentration of the dilute hydrofluoric acid is 0.1 to 1 vol%, the temperature is maintained at 20 to 30 degrees, the immersion time of the silicon wafer is 1 to 5 minutes. If the hydrofluoric acid concentration is less than 0.1 vol%, the desired silicon oxide film etching effect cannot be obtained. If the hydrofluoric acid concentration exceeds 1 vol%, the etching effect of the silicon oxide film is not large compared to the increase in the hydrofluoric acid concentration, so that the profit of increasing the hydrofluoric acid concentration is not large. . In addition, if the temperature of the dilute hydrofluoric acid solution is less than 20 degrees, there is a disadvantage in that a separate equipment for cooling the hydrofluoric acid solution is needed. not big. If the immersion time of the silicon wafer is less than 1 minute, the desired silicon oxide film etching effect cannot be obtained. If the immersion time of the silicon wafer is 5 minutes or more, the etching of the silicon oxide film is mostly completed. It is not desirable from the throughput point of view of the process.

On the other hand, when the silicon oxide film is etched and removed from the surface of the silicon wafer by dilute hydrofluoric acid, the surface of the silicon wafer is hydrophobic. In this case, since the fine particles are easily attached by the electrostatic action, the present invention is subjected to the hydrophilization treatment of the silicon wafer in a subsequent process.

That is, the silicon wafer is immersed once again in ozone water to which megasonic is applied (S30). Then, while microparticles remove fine particles from the surface of the silicon wafer, a chemical silicon oxide film is formed on the surface of the silicon wafer by ozone to hydrophilize the surface of the silicon wafer. Accordingly, it is possible to prevent the fine particles from adhering to the surface of the silicon wafer due to the action of the electrostatic repulsive force.

Preferably, the ozone concentration of the ozone water is 1 to 30 ppm, the temperature is 20 to 60 degrees, and the immersion time of the silicon wafer is 1 to 5 minutes. The reason for setting the numerical range is substantially the same as in step S10.

Next, the silicon wafer is immersed in dilute ammonia water, which is a kind of dilute alkaline aqueous solution, to fine-etch the surface of the silicon wafer (S40). This step is to remove contaminants that could not be removed in the cleaning step using dilute hydrofluoric acid. Here, the fine etching is not a wide range of etching to remove the entire chemical silicon oxide film formed in the step S30, but a thickness of several times to remove contaminants adsorbed on the top of the chemical oxide film or trapped in the chemical oxide film. It means that the chemical oxide film is finely etched. Therefore, it is preferable that the density | concentration of the alkali contained in dilute alkali aqueous solution is adjusted suitably in consideration of this point. As the S40 step proceeds, the contamination level of the silicon wafer becomes even lower.

On the other hand, since the surface of the silicon wafer immersed in dilute alkaline aqueous solution is hydrophilized by ozone water, it is possible to prevent the fine particles removed in the process of the S40 step to be reattached to the silicon wafer by the electrostatic action. Silicon wafers have a negative zeta potential regardless of the pH of the solution being immersed, and most fine particles have a negative zeta potential in alkaline solutions and a positive zeta potential in acid solutions. Since the cleaning solution used is an alkaline solution, both the silicon wafer and the fine particles have a zeta potential of negative (-), thereby generating an electrostatic repulsion force.

Preferably, the pH of the diluted ammonia water is 9 to 11, the temperature is 20 to 60 degrees, the concentration of alkali is 0.001 to 0.1 vol%, and the immersion time is 1 to 5 minutes. When the pH of the diluted alkali solution is less than 9, the repulsive force between the silicon wafer and the fine particles is small, so that it is difficult to effectively block the adhesion of the fine particles, and when the pH exceeds 11, the alkali concentration increases to increase the repulsive force of the fine particles and the silicon wafer. This is advantageous in terms of preventing reattachment of the fine particles, but there is a problem in that the surface of the silicon wafer is excessively etched to increase the surface roughness. If the alkali concentration is less than 0.001 vol%, the etching effect is not large, so it is difficult to remove contaminants such as fine particles from the surface of the silicon wafer, and if the alkali concentration exceeds 1 vol%, the chemical silicon oxide film formed in step S30 Etching can proceed excessively, damaging the silicon wafer and deepening the surface roughness of the silicon wafer surface. In addition, when the temperature of the diluted alkali aqueous solution is less than 20 degrees, the etching rate is delayed, which is undesirable from the viewpoint of throughput, and when the temperature of the diluted alkaline aqueous solution exceeds 60 degrees, the etching rate is increased, which may damage the surface of the silicon wafer. In addition, if the immersion time of the silicon wafer is less than 1 minute, it is difficult to expect a desired fine etching effect, and if the immersion time of the silicon wafer exceeds 5 minutes, the silicon wafer may be damaged by excessive etching, which is not preferable in terms of throughput.

Meanwhile, the dilute ammonia water used in step S40 may be replaced with another dilute alkaline aqueous solution known to be capable of etching the chemical silicon oxide film. For example, the diluted ammonia water may be replaced with a KOH solution, NaOH solution, TMAH solution, or a mixture thereof diluted with ultrapure water.

Optionally, after the step S40, the silicon wafer rinsing with ultrapure water may be further performed, and the silicon wafer may be dried when the cleaning process is completed.

Experimental Example

In order to confirm the effect of the present invention, the present inventors assumed Examples 1 to 3 as described below, and after cleaning the silicon wafer, the degree of fine particle contamination and surface roughness of the surface were measured. The silicon wafer to be used as a sample was an 8-inch silicon wafer whose mirror polishing process was completed by a CMP process using a slurry. The contamination level of this silicon wafer exceeded the measurement range of the fine particle measuring equipment.

The washing liquid and washing conditions used were as follows.

(a) ozone water washing step (ozone concentration: 30 ppm, washing time: 5 minutes, temperature: room temperature)

(b) dilute hydrofluoric acid washing step (concentration: 1 vol%, washing time: 5 minutes, temperature: room temperature)

(c) dilute ammonia washing step (concentration: 0.01 vol%, washing time: 5 minutes, temperature: room temperature)

In Example 1, the ozone water washing step, the dilute hydrofluoric acid washing step, the ozone water washing step, and the drying step were sequentially performed. However, megasonic was not used in the two ozone water washing steps. For Example 1 the fine particle level measured above 0.12 μm was “2127 particles / wafer”.

Example 2 was subjected to the cleaning process in the same order as in Example 1, but applied a megasonic of 1MHz (550W) in two ozone water washing steps. As a result, the measured fine particle level of 0.12um or more was reduced by 1/10 compared to Example 1.

Example 3 proceeds with the cleaning process in the same order as in Example 2, but further proceeds with the washing step using dilute ammonia before proceeding to the drying step. As a result, the measured fine particle level of 0.12 um or more was "12 wafers", and the contamination level was lower than that of Examples 1 and 2.

2 is a graph showing the above experimental results. Referring to FIG. 2 and the fine particle measurement results described above, by applying megasonic in the ozone water cleaning step, the contamination level of the silicon wafer could be reduced to 1/10 level (2127 to 200), and after the cleaning step by dilute hydrofluoric acid. In the state that the surface of the wafer is hydrophilized using ozone water applied to megasonic, the cleaning step is performed using dilute ammonia water to reduce the contamination level of the silicon wafer once again to a level of 1/10 or less (200 to 12). It can be confirmed that.

On the other hand, according to the experimental example described above, even though the pre-cleaning process was carried out at a room temperature level (25 degrees), the cleaning effect was excellent, so it is not necessary to proceed with the cleaning process at high temperature conditions such as RCA cleaning, and energy saving is also possible compared to the conventional. You can see that.

3 is a graph and a table showing the roughness of the silicon wafer surface after applying the cleaning process according to SC-1 and Examples 2 and 3 to the above-described silicon wafer samples.

Referring to the drawings, it can be seen that the silicon wafer cleaning method according to the present invention does not significantly affect the fine roughness of the silicon wafer compared to the cleaning method according to SC-1. Rather, compared with the cleaning method according to SC-1 it can be confirmed that the surface roughness is improved to the equivalent level or more. Therefore, it can be seen that the cleaning method according to the present invention can effectively remove contaminants without damaging the surface of the silicon wafer.

Meanwhile, the above-described preferred embodiment of the present invention will be described in detail in the case of cleaning the silicon wafer after the CMP mirror polishing process in the manufacturing process of the bare silicon wafer. However, the present invention is naturally applicable to those skilled in the art to which the present invention pertains even after the unit semiconductor process in which various contaminants are derived during a semiconductor device manufacturing process using a silicon wafer.

Accordingly, the term silicon wafer should be interpreted to include both a bare silicon wafer having no device structure stacked thereon and a silicon wafer having a device structure stacked thereon by application of a semiconductor device integration process.

On the other hand, when the silicon wafer cleaning method according to the present invention is applied after the semiconductor process in which organic contaminants are not derived during the semiconductor device manufacturing process, step S10 for removing the organic contaminants may be omitted.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

According to the present invention, unlike the RCA cleaning method because it does not use hydrogen peroxide can reduce the waste water treatment cost according to the dehydrogen peroxide process, energy saving is possible because the cleaning process is carried out at room temperature, reducing the cleaning solution by using a diluted cleaning solution In addition, the cleaning effect is excellent for all contaminants such as fine particles, organic impurities, and metal impurities without damaging the wafer surface.

Claims (16)

(a) a first step of cleaning a silicon wafer surface using ozone water to which Megasonic is applied; (b) a second step of cleaning the silicon wafer surface with diluted HF; (c) a third step of cleaning the surface of the silicon wafer cleaned by dilute hydrofluoric acid using ozone water to which Megasonic is applied; And (d) a fourth step of cleaning the surface of the silicon wafer cleaned with ozone water using a dilute alkali aqueous solution. The method of claim 1, The ozone concentration of the ozone water used in the first step and the third step is 1 to 30 ppm, the silicon wafer cleaning method. The method of claim 1, The hydrofluoric acid concentration of the dilute hydrofluoric acid used in the second step is 0.1 to 1 vol% silicon wafer cleaning method. The method of claim 1, The method of cleaning the silicon wafer, characterized in that the alkali concentration of the diluted aqueous alkali solution used in the fourth step is 0.001 to 0.1 vol%. The method of claim 1, Silicon wafer cleaning method, characterized in that the pH of the diluted aqueous alkali solution used in the fourth step is 9 to 11. The method of claim 1, The dilute alkali aqueous solution is diluted KOH, NaOH, NH ₄ OH, TMAH or a silicon wafer cleaning method, characterized in that a mixed solution thereof. The method of claim 1, Wherein the first, third and fourth steps are performed at a temperature of 20 to 60 degrees. The method of claim 1, The second step is a silicon wafer cleaning method, characterized in that proceeds at a temperature of 20 to 30 degrees. (a) a first step of cleaning the silicon wafer surface with diluted HF; (b) a second step of cleaning the surface of the silicon wafer cleaned by dilute hydrofluoric acid using ozone water to which Megasonic is applied; And (c) a third step of cleaning the surface of the silicon wafer cleaned with ozone water using a dilute alkali aqueous solution. The method of claim 9, The ozone concentration of the ozone water used in the first step is 1 to 30 ppm characterized in that the silicon wafer cleaning method. The method of claim 9, The hydrofluoric acid concentration of the dilute hydrofluoric acid used in the second step is 0.1 to 1 vol% silicon wafer cleaning method. The method of claim 9, The method of cleaning the silicon wafer, characterized in that the alkali concentration of the diluted aqueous alkali solution used in the third step is 0.001 to 0.1 vol%. The method of claim 9, The method of cleaning a silicon wafer, characterized in that the pH of the diluted aqueous alkali solution used in the third step is 9 to 11. The method of claim 9, The dilute alkali aqueous solution is a method of cleaning a silicon wafer, characterized in that the diluted KOH, NaOH, NH ₄ OH, KMAH or a mixed solution thereof. The method of claim 9, And the first and third steps are performed at a temperature of 20 to 60 degrees. The method of claim 9, The second step is a silicon wafer cleaning method, characterized in that proceeds at a temperature of 20 to 30 degrees.

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