JPH07321080A - Method for cleaning silicon wafer - Google Patents

Abstract

PURPOSE:To provide a cleaning method to obtain a silicon wafer with high cleanness in which the adhesion of a metal is suppressed, even after the silicon wafer is cleaned by a cleaning liquid containing a sulfuric acid or hydrochloric acid. CONSTITUTION:After a silicon wafer is cleaned by a cleaning liquid containing a sulfuric acid or hydrochloric acid, for example, a mixture liquid (SPM) of sulfuric acid and hydrogen peroxide or a mixture liquid (HPM) consisting of hydrochloric acid, hydrogen peroxide and an ultra-pure water, it is treated with a water-soluble liquid containing hydrofluoric acid and nitric acid.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cleaning method for obtaining a highly clean silicon wafer used for manufacturing semiconductor devices.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have been highly integrated, it has been strongly desired to further clean the surface of a silicon wafer as a substrate. Contaminants such as fine particles and metal impurities adhere to the silicon wafer surface during the silicon wafer manufacturing process and semiconductor device manufacturing process.
Unless these removal measures are taken, various inconvenient problems are caused in the device manufacturing yield and the device performance.

The fine particles adhering to the surface of the silicon wafer cause disconnection or short circuit of the wiring of the device, or cause abnormal diffusion of dopant or abnormal oxide film thickness in the diffusion or oxidation process. On the other hand, metal impurities such as Fe and Cu diffuse inside the silicon oxide film and the silicon wafer in the heat treatment process, and reduce the dielectric breakdown voltage and the carrier lifetime. Therefore, in the silicon wafer maker and the device maker, various kinds of cleaning are performed to remove these contaminants attached to the silicon wafer. For example, a typical cleaning method called RCA cleaning heats a mixed solution of ammonia water, hydrogen peroxide solution, and ultrapure water (hereinafter abbreviated as APM) to 60 to 90 ° C. to remove fine particles and organic substances on a silicon wafer. After the removal, a mixed solution of hydrochloric acid, hydrogen peroxide solution and ultrapure water (hereinafter abbreviated as HPM) is added to 50
It is a cleaning method that is a combination of methods of removing metal impurities on a silicon wafer by heating to -100 ° C.
A mixed solution of sulfuric acid and hydrogen peroxide (hereinafter abbreviated as SPM)
The cleaning liquid heated to 80 to 150 ° C. is used for decomposing and removing organic substances such as photoresist or removing metal impurities.

After these cleanings, if the chemical solution component remains on the surface of the silicon wafer and advances to the next step, this has various adverse effects in the subsequent steps. For example, AP
Since the ammonia component in the M cleaning etches silicon, it causes the surface of the silicon wafer to be rough, and the acid components such as sulfuric acid and hydrochloric acid in the SPM cleaning and HPM cleaning cause the corrosion of the device in the subsequent process. Therefore, usually, after cleaning these, the silicon wafer is rinsed with ultrapure water in order to remove the chemical liquid component remaining on the surface of the silicon wafer.

However, there is a problem that it is difficult to completely remove the chemical liquid component adhering to the surface of the silicon wafer by only rinsing with ultrapure water. It is considered that this is because the surface of the silicon wafer is very active. Originally, SPM cleaning and HPM cleaning are effective cleaning for removing metal impurities on the surface of a silicon wafer, but the surface after these cleaning is contaminated with metal impurities due to adhered chemical liquid components. It has been clarified by the study of the present inventors that this is easily done. This means that when the cleaning tank is contaminated with metal in the ultrapure water rinse after the SPM cleaning or HPM cleaning, or after the cleaning, metal contamination such as ion implantation or plasma etching is likely to occur. The problem is that the metal easily adheres to the. SPM cleaning and HP
In the M cleaning, a thin natural oxide film is formed on the surface of the silicon wafer by hydrogen peroxide solution which is an oxidizing agent, but at the same time, chemical liquid components such as chlorine ions and sulfate ions adhere to the surface of the oxide film. These cannot be removed sufficiently by rinsing with ultrapure water. As a means for solving these problems, for example, a method of immersing an SPM-cleaned or HPM-cleaned silicon wafer in an aqueous solution containing hydrofluoric acid in the next step has been proposed. If metallic impurities having a low ionization tendency are present, they may adhere to the surface of the silicon wafer and cause reverse contamination.

[0006]

An object of the present invention is to treat chemical components remaining on the surface of a silicon wafer with a specific aqueous solution after cleaning with a cleaning liquid containing sulfuric acid or hydrochloric acid, and to remove the chemical components, thereby removing the following steps. An object of the present invention is to provide a cleaning method for obtaining a highly clean silicon wafer in which adhesion of metal impurities is suppressed.

[0007]

According to the present invention, a method for cleaning a silicon wafer and a method therefor are characterized in that after cleaning a silicon wafer with a cleaning solution containing sulfuric acid or hydrochloric acid, the silicon wafer is treated with an aqueous solution containing hydrofluoric acid and nitric acid. With respect to a silicon wafer that has been washed with.

The silicon wafer to which the cleaning method of the present invention is applied is generally used for manufacturing semiconductor devices, and its specifications are not particularly limited.

A typical example of the cleaning solution containing sulfuric acid in the present invention is an SPM cleaning solution used for removing organic substances such as resists and metal impurities, and a typical example of a cleaning solution containing hydrochloric acid is for removing metal impurities. H used
A PM cleaning liquid can be used. The SPM cleaning is performed by heating a mixed solution of sulfuric acid and hydrogen peroxide solution. The washing conditions are not particularly limited as long as the intended function is satisfied,
Generally, the composition is such that the volume ratio of sulfuric acid and hydrogen peroxide water is (4 ~
8) The range of 1 to 1 and the washing temperature of 80 to 150 ° C. are often used.

On the other hand, HPM cleaning is performed by heating a mixed solution of hydrochloric acid, hydrogen peroxide solution and ultrapure water. Similar to the SPM cleaning, the cleaning conditions are not particularly limited as long as the function is satisfied, and the composition is such that the volume ratio of hydrochloric acid, hydrogen peroxide solution, and ultrapure water is 1: (1-4) :( 5-). In the case of 10), the washing temperature is 50
The range of ℃ to 100 ℃ is generally used.

According to the present invention, a silicon wafer washed with a washing solution containing sulfuric acid or hydrochloric acid is immersed in an aqueous solution containing hydrofluoric acid and nitric acid in the next step to remove chemical components such as sulfate ions and chlorine ions on the surface of the silicon wafer. At the same time, it also prevents reverse contamination by metal impurities having a smaller ionization tendency than silicon such as copper.

Although the action of hydrofluoric acid is not clear, when the natural oxide film is etched, the above-mentioned chemical components adhering to the surface of the natural oxide film are also peeled off from the surface of the silicon wafer, and at the same time, the surface of the silicon wafer is hydrogenated by hydrogen fluoride. It is presumed that the adhesion of metal impurities is suppressed because it is terminated with and stabilized. Moreover, it is presumed that the solubility of metal impurities is improved by mixing nitric acid, and therefore the adhesion to the silicon wafer is suppressed, but in this case, sulfuric acid, which has the same metal solubility as nitric acid, does not exist at all. has no effect. Further, when hydrochloric acid is used, it is possible to obtain the same effect as nitric acid, but at that time, a trace amount of chlorine ions remaining on the surface of the silicon wafer easily causes metal contamination in the next step.

The concentration of hydrofluoric acid in the aqueous solution containing hydrofluoric acid and nitric acid is not particularly limited, but if it is too low, the controllability during liquid preparation will be poor, and if it is too high, the cost will be high, which is economical. Absent. Therefore, the concentration is preferably 0.5 to 20% by weight, more preferably 0.5 to 10% by weight.

The concentration of nitric acid in the aqueous solution containing hydrofluoric acid and nitric acid is preferably in the range of 0.1 to 20% by weight, more preferably 1.
A range of 0-10% by weight is adopted. If it is less than this concentration range, the effect of suppressing metal adhesion is low, and if it exceeds this concentration range, it is not economical.

The quality of the hydrofluoric acid and nitric acid used in the present invention is preferably as high as possible in order to avoid the problem that the silicon wafer is contaminated by the metal impurities in the chemicals. It is desirable to use commercial grade chemicals. For water, it is desirable to use ultrapure water for the same reason.

An example of the cleaning procedure in the present invention will be described below. After cleaning the silicon wafer with a cleaning liquid containing sulfuric acid or hydrochloric acid, first, ultrapure water rinsing is performed to wash out most of the chemical liquid components adhering to the surface of the silicon wafer. Rinsing with ultrapure water is performed under general conditions, for example, at a room temperature for 1 to 15 minutes by a method in which ultrapure water overflows from the cleaning tank. Then, the silicon wafer is immersed in a cleaning bath made of a fluororesin containing an aqueous solution containing hydrofluoric acid and nitric acid for processing. The remaining chemical solution component is removed by etching the natural oxide film. The processing temperature is not particularly limited, but as generally used for etching a natural oxide film,
Room temperature is sufficient.

Treatment with an aqueous solution containing hydrofluoric acid and nitric acid
Not only the immersion method but also the spray method and the spin method can be used. Further, not only batch type processing but also single wafer type processing can be performed. The processing time depends on the thickness of the natural oxide film formed by cleaning with a cleaning solution containing sulfuric acid or hydrochloric acid and the concentration of hydrofluoric acid in the processing solution.
A range of 1 to 10 minutes is sufficient for the above-mentioned hydrofluoric acid concentration.

After treating the silicon wafer with an aqueous solution containing hydrofluoric acid and nitric acid, excess chemical liquid adhering to the wafer surface is rinsed with ultrapure water and removed. An overflow method is generally used for the rinse, but a spray method may be used. Then, the silicon wafer is dried by a commonly used method such as spin drying. The silicon wafer cleaned by the method of the present invention is suppressed from being contaminated even if it contacts metal impurities in the next step.

[0019]

According to the cleaning method of the present invention, it is possible to obtain a highly clean silicon wafer in which adhesion of metal impurities to the surface of the silicon wafer is suppressed even after SPM cleaning or HPM cleaning. The cleaning method of the present invention is extremely useful in manufacturing semiconductor devices.

[0020]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the example, the plane orientation (100), the specific resistance 3 to 6
An Ω · cm n-type silicon wafer was used. The quantification of metal impurities adhering to the silicon wafer is performed by dissolving and recovering the adhering metal by moving droplets of an aqueous solution containing hydrofluoric acid, hydrogen peroxide solution, hydrochloric acid, and water on the wafer surface.
It was performed by measuring the liquid with an atomic absorption spectrometer. A standard solution for atomic absorption analysis was used as a metal source for contaminating the silicon wafer. Further, the concentrations of metal impurities contained in the chemicals such as hydrochloric acid, sulfuric acid, hydrofluoric acid, hydrogen peroxide solution, nitric acid used in the examples were all 10 ppb or less.

Example 1 A silicon wafer was pre-washed by immersing it in a 1 wt% hydrofluoric acid aqueous solution for 1 minute, and then 96 wt% sulfuric acid and 30 wt% hydrogen peroxide solution were mixed at a volume ratio of 4: 1. It was immersed in the above liquid at 120 ° C. and washed for 10 minutes. Then rinse with ultrapure water for 10 minutes,
It was immersed for 10 minutes in an aqueous solution containing 1 wt% hydrofluoric acid and 10 wt% nitric acid containing 100 ppb of Cu. Then 5 with ultrapure water
Analysis of Cu concentration adhering to the silicon wafer surface after rinsing for 5 minutes and drying was 8.0 × 10 ⁹ atoms / c
It was m ² .

Example 2 After prewashing in the same manner as in Example 1, 36% by weight of hydrochloric acid was added.
The silicon wafer was dipped in a liquid of 80% by mixing 30% by weight of hydrogen peroxide water and ultrapure water at a volume ratio of 1: 1 to 6, and washed for 10 minutes. After rinsing with ultrapure water for 10 minutes, it was immersed in an aqueous solution containing 1 wt% hydrofluoric acid and 10 wt% nitric acid for 10 minutes. After that, Fe adhered to the surface of the silicon wafer after rinsing with ultrapure water containing 50 ppb of Fe for 5 minutes and drying
When the concentration was analyzed, it was 8.0 × 10 ⁹ atoms / cm ² .

Comparative Example 1 After SPM cleaning in the same manner as in Example 1, rinsed with ultrapure water for 10 minutes and immersed in a 1 wt% hydrofluoric acid aqueous solution containing 100 ppb of Cu for 10 minutes. Then, the Cu concentration adhering to the surface of the silicon wafer after rinsing with ultrapure water for 5 minutes and drying was analyzed and found to be 1.2 × 10 ¹² atoms / cm ² .

Comparative Example 2 After washing with HPM in the same manner as in Example 2, the substrate was rinsed with ultrapure water for 10 minutes. After that, the concentration of Fe adhering to the surface of the silicon wafer after rinsing for 5 minutes with ultrapure water containing 50 ppb of Fe and drying was analyzed and found to be 8.8 × 10 ¹⁰ atoms / cm ² .

Claims (4)

[Claims] 1. A method of cleaning a silicon wafer, which comprises cleaning a silicon wafer with a cleaning solution containing sulfuric acid or hydrochloric acid, and then treating the silicon wafer with an aqueous solution containing hydrofluoric acid and nitric acid. 2. The method for cleaning a silicon wafer according to claim 1, wherein the concentration of nitric acid in the aqueous solution containing hydrofluoric acid and nitric acid is 0.1% by weight or more. 3. The method for cleaning a silicon wafer according to claim 1, wherein the cleaning liquid is a mixed liquid containing sulfuric acid or hydrochloric acid and hydrogen peroxide solution. 4. A silicon wafer cleaned by the method according to claim 1, 2 or 3.