JPH0562958A - Purity evaluation method of chemical liquid - Google Patents

Abstract

PURPOSE:To provide a chemical liquid purity evaluation method, where metal impurities less than 0.1ppb in concentration contained in chemical liquid can be analyzed, a pre-treatment process can be easily carried out in a short time, requiring no chemical liquid sampling. CONSTITUTION:A silicon wafer whose surface is cleaned is dipped into chemical liquid for a certain time, rinsed, and dried up, and metal impurities attached to the surface of the silicon wafer are analyzed. Or, metal impurities attached to the surface of a wafer are decomposed with hydrofluoric acid vapor, the decomposed substances are collected, metal impurities contained in the collected liquid are analyzed with a high sensitivity analyzer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical solution purity evaluation method, and more particularly to a chemical solution purity evaluation method for highly sensitive analysis of metal impurities in a chemical solution.

[0002]

2. Description of the Related Art As LSIs are highly integrated, it is important to highly purify materials used in manufacturing processes.
The purity of the chemical liquid (including pure water) used in the cleaning process for cleaning the wafer influences the final cleanliness of the wafer, and is therefore required to be particularly high in purity.
The concentration of metal impurities in a chemical solution used in the production of ultra-high-integrated devices in the future needs to be suppressed to 1 ppb or 0.1 ppb or less depending on the type of chemical solution or the element. Therefore, since the evaluation technique for controlling the purity requires sensitivity of one digit or more than the control concentration,
A sensitivity of 0.1 ppb or 0.01 ppb or less is required.

Conventionally, for the analysis of metal impurities in these chemical solutions, the chemical solution was sampled from a chemical solution tank into a sampling container and analyzed by a highly sensitive analyzer such as atomic absorption and ICP-MS. For most chemicals, it is difficult to introduce them directly into the analyzer due to the influence of the matrix.Before performing the pretreatment operation such as diluting with pure water or removing the matrix components by heating concentration, the analysis is performed. I was going.

[0004]

DISCLOSURE OF THE INVENTION In the prior art,
There were the following problems. 1) Sampling of the chemical solution from the chemical solution tank is not only complicated and easy to cause danger, but also causes contamination. 2) Possibility of elution of impurities from the sampling container itself 3) Dilution with pure water High-sensitivity analysis cannot be performed by analysis. 4) The heating concentration operation requires several hours, and there is a high possibility of contamination during the operation. Therefore, in the prior art, not only the operation is complicated and it takes a long time, but also it is necessary to strictly carry out the contamination control in order to perform the highly sensitive analysis of 0.1 ppb or less, and it is necessary for the analyst to have an advanced analysis technique. There was a problem that skill was required.

The object of the present invention is to solve the problems of the prior art, to analyze metallic impurities of 0.1 ppb or less in a chemical solution, to dispense with the sampling of the chemical solution, and to carry out a pretreatment operation in a short time and simply. Another object of the present invention is to provide a method for evaluating the purity of a chemical solution that can be used for

[0006]

In order to achieve the above object, in the purity evaluation method according to the present invention, after a silicon wafer whose surface has been cleaned is immersed in a chemical solution for a certain period of time,
It is washed with water and dried to analyze the metal impurities adhering to the surface of the wafer. Further, the metal impurities adhering to the wafer surface are decomposed by hydrofluoric acid vapor, the decomposed products are recovered by a recovery liquid, and the metal impurities in the recovery liquid are analyzed by a high sensitivity analyzer.

[0007]

Function As a cleaning liquid for manufacturing LSI, a mixed liquid of acid or alkali and hydrogen peroxide, or a chemical liquid such as hydrofluoric acid is used. When a silicon wafer is dipped in these chemicals, metal impurities adhere to the surface of the wafer.

For example, when a wafer is immersed in an ammonia-hydrogen peroxide mixture, a natural oxide film is formed on the surface of the wafer, but elements such as Al and Fe, which have a larger enthalpy of oxide formation than silicon, are contained in the natural oxide film. It attaches in the form of being taken in. Further, when the wafer is immersed in hydrofluoric acid, the natural oxide film on the surface is removed and the metal silicon surface is exposed, so Cu, which has a smaller ionization tendency than silicon, is formed.
Metals such as Au and Au are deposited and adhere to the wafer surface by the redox reaction.

It has been found that the concentration of adhesion on the wafer surface corresponds to the concentration in the chemical solution. Therefore, if the relationship between the concentration of impurities in the chemical solution and the concentration of adhesion to the wafer surface is determined, the concentration in the chemical solution can be determined by analyzing the concentration on the wafer surface.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a flow chart of an evaluation operation showing Embodiment 1 of the present invention. In this example, an example of evaluating the purity of an ammonia-hydrogen peroxide mixture solution is shown. The surface-cleaned wafer is immersed in a chemical solution as shown in FIG. In FIG. 2, a silicon wafer 1 is set on a wafer carrier 2 and immersed in an ammonia-hydrogen peroxide mixture solution 4 in a chemical solution tank 3. Soak for a certain period of time and wash with water
After drying, the concentration of metal impurities adhering to the wafer surface is analyzed. As a pretreatment operation for analysis, metal impurities adhering to the wafer surface are decomposed with hydrofluoric acid vapor, and the decomposed products are recovered with a recovery liquid, and the concentrations of Al and Fe in the recovery liquid are measured by a graphite furnace atomic absorption method (hydrofluoric acid Steam decomposition-atomic absorption method).

FIG. 3 shows the relationship between the concentrations of Al and Fe in the ammonia-hydrogen peroxide mixture, which are adhered to the wafer surface.
Shown in. In this case, the chemical composition is NH40H: H20.
2: H20 = 1: 1: 5, the chemical temperature was 70 ° C., and the immersion time was 10 minutes. There is a linear correlation between the two, and the concentration in the chemical solution can be easily obtained from the wafer surface concentration.

Al, F by hydrofluoric acid vapor decomposition-atomic absorption method
Since the lower limit of quantification of e is 2 × 10 9 and 1 × 10 9 atoms / square centimeter, the lower limit of quantification of these elements in the chemical solution in this method is 0.01 pp from FIG.
b, the analysis sensitivity satisfying the required level can be obtained.

The deposition density on the surface of the wafer varies depending on the immersion time, but it is reproducible if the immersion time is kept constant. Therefore, the immersion time may be arbitrary. The elements that can be analyzed by this method (elements that adhere to the wafer surface) are limited to those elements that have a larger enthalpy of oxide formation than silicon as described above, but in LSI manufacturing, they adhere to the wafer surface and deteriorate device characteristics. It is these elements that cause
It is only necessary to be able to analyze these elements in order to control the purity of the chemical solution.

In this method, the wafer dipping operation, which corresponds to the chemical solution sampling of the prior art, is a normal operation, and the problem that has been a conventional problem in sampling can be solved. Also,
The time required for the analysis pretreatment (hydrofluoric acid vapor decomposition) is 5
Within minutes / sample, the pretreatment time could be shortened to tens of minutes, and the contamination could be greatly reduced.

(Embodiment 2) FIG. 4 is a flow chart of an evaluation operation showing Embodiment 2 of the present invention. In this example,
An example of the purity evaluation of hydrofluoric acid will be shown. Same as Example 1 except that the chemical solution for immersing the wafer is changed to hydrofluoric acid.

FIG. 5 shows the relationship between the Cu concentration in hydrofluoric acid and the wafer surface adhesion concentration. In this case, the chemical composition is HF:
H20 = 1: 49, the chemical temperature is room temperature, and the wafer immersion time is 10 minutes.

The lower limit of determination of Cu in the hydrofluoric acid vapor decomposition method is 5
Since it is × 10 8 atoms / square centimeter, the lower limit of quantification of Cu in the chemical solution by this method is 0.1 from FIG.
Since it is ppb, the analysis sensitivity that can satisfy the required level can be obtained.

[0019]

As described above, according to the method for evaluating the purity of a chemical solution of the present invention, the sampling of the chemical solution from the chemical solution tank, which has been a problem in the past, becomes unnecessary, and the processing time is required even in the pretreatment operation of the analysis. Was reduced to 5 minutes / sample, which was 1/10, which was several tens of the conventional value, and the contamination was significantly reduced.

[Brief description of drawings]

FIG. 1 is a flowchart of an evaluation operation showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of the first embodiment.

FIG. 3 is an explanatory diagram of the first embodiment.

FIG. 4 is a flow chart diagram of an evaluation operation showing a second embodiment of the present invention.

FIG. 5 is an explanatory diagram of the second embodiment.

[Explanation of symbols]

 1 Silicon wafer 2 Wafer carrier 3 Chemical bath 4 Ammonia-hydrogen peroxide mixture

Claims (2)

[Claims] 1. A method for evaluating the purity of a chemical solution, which comprises immersing a surface-cleaned silicon wafer in a chemical solution for a certain period of time, washing with water, and then drying, and analyzing metal impurities adhering to the surface of the wafer. 2. The metal impurities adhering to the wafer surface are decomposed by hydrofluoric acid vapor, the decomposed products are recovered by a recovery liquid, and the metal impurities in the recovery liquid are analyzed by a high sensitivity analyzer. Item 1. A method for evaluating the purity of a chemical solution according to Item 1.