JPH07193035A - Method for recovering impurity elements on the surface of a silicon wafer - Google Patents

Abstract

PURPOSE:To provide a method, which can safely recover elements in a short time without contaminating environment in order to analyze the impurity elements on the surface of a silicon wafer and can recover the impurity element such as Cu, whose ionization tendency is smaller than Si. CONSTITUTION:The droplet of solution 3 comprising fluoric acid, hydrogen peroxide and water or these materials and hydrochloric acid is moved on the analyzing region of a silicon wafer 2. Thus, impurity elements are dissolved and recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of recovering an impurity element for analyzing an impurity element on the surface of a silicon wafer.

[0002]

2. Description of the Related Art As the degree of integration of semiconductor devices increases, it is strongly desired to improve the cleanliness of the surface of a silicon wafer which is a substrate. Contaminants such as metal impurities and fine particles adhere to the surface of a silicon wafer during the manufacturing process of silicon wafers and semiconductor devices, but these cause various inconvenient problems in the device production yield and device performance. In particular, when the metal impurities adhere to the surface of the silicon wafer, they diffuse into the thermal oxide film and the inside of the silicon wafer in the heat treatment process, and reduce the dielectric breakdown voltage and the minority carrier lifetime. Therefore, in order to prevent such problems,
It is necessary to accurately control the extremely small amount of impurity element attached to the surface of the silicon wafer.

As a recovery method for analyzing the impurity element on the surface of the silicon wafer, a method of dissolving the impurity element by rolling the droplets of the solution in the analysis region of the silicon wafer and moving the solution uniformly has been proposed. . Compared with the vapor phase decomposition method in which the vapor of hydrofluoric acid is conventionally used as a method for recovering impurity elements to spray silicon wafers to recover impurities, this method is simpler in equipment and operation and requires less processing time. Moreover, since the dissolved solution is handled as a small amount of droplets, there is an advantage that the risk of environmental pollution is small. The movement of the droplets on the silicon wafer is an operation that is necessary both in the hydrofluoric acid vapor decomposition method and in the case of recovering the decomposed product containing the impurity element by droplets such as ultrapure water after the decomposition.

Regarding the composition of the solution, an aqueous solution containing hydrofluoric acid is generally used in both the liquid droplet moving method and the vapor phase decomposition method. However, with hydrofluoric acid alone, metals such as Cu and Ag having a smaller ionization tendency than Si are
Since it has a strong affinity with i, it is difficult to dissolve and recover the entire amount in the decomposition liquid.

[0005]

An object of the present invention is to be able to recover impurity elements on the surface of a silicon wafer safely in a short time and without polluting the environment.
An object of the present invention is to provide a method capable of recovering an impurity element such as u having a smaller ionization tendency than Si with a high recovery rate.

[0006]

According to the present invention, droplets of a solution containing hydrofluoric acid, hydrogen peroxide and water, or a solution of these and hydrochloric acid are moved within an analysis region of an impurity element on a silicon wafer to remove impurities. The present invention relates to a method for recovering impurities, which comprises recovering an element by dissolution.

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

The solution used in the present invention is hydrofluoric acid, hydrogen peroxide and water, or a mixture of these and hydrochloric acid.
This solution is C, which has a smaller ionization tendency than Si.
As a result of the study, it was revealed that the effect of recovering the impurity element such as u is great. The action of this solution is presumed as follows. That is, on the surface of the silicon wafer in contact with the dissolution liquid, the formation of the silicon oxide film by the hydrogen peroxide solution and the etching by the hydrofluoric acid proceed in parallel, and the impurity element attached to the surface is dissolved in the dissolution liquid together with the silicon oxide film. To do. It is considered that hydrochloric acid suppresses redeposition on the silicon wafer by further increasing the solubility of these impurity elements in the solution.

There is no particular limitation on the concentration range of each chemical in the solution, but the concentration of hydrofluoric acid, hydrogen peroxide and hydrochloric acid in the solution is in the range of 0.5% by weight to 20% by weight, preferably 1% by weight. The range from 10 to 10% by weight is suitable. If it is lower than this range, it takes a long time to etch the oxide film and dissolve the impurity element, which is not efficient. On the other hand, although a liquid having a concentration higher than this range can be used without any problem, it is preferable to use a liquid having the above concentration range in consideration of handling safety.

The quality of the hydrofluoric acid, hydrogen peroxide and hydrochloric acid used in the present invention is preferably as high as possible in order to avoid the inconvenience of contaminating the silicon wafer with the impurity elements contained therein. It is desirable to use electronic grade chemicals. Also for water, it is desirable to use ultrapure water for the same reason.

An example of the method for recovering the impurity element in the present invention will be described below. First, hydrofluoric acid, hydrogen peroxide and ultrapure water, or a solution containing them and hydrochloric acid is prepared. To prepare the solution, it is sufficient to mix these chemicals at room temperature and stir. A fixed amount of this solution is dispensed with a micropipette and dropped on the surface of the silicon wafer to be measured.
The dropping amount is preferably 100 μl to 1 ml. If the amount is less than this, it takes time to move the surface of the silicon wafer due to the small amount of liquid, and there is a part that remains after moving, which lowers reliability. On the other hand, if the amount is larger than this, the concentration of the recovered impurity element in the solution becomes low, and the detection sensitivity decreases.

In the method of the present invention, it is necessary to efficiently collect the impurity element by moving the droplets of the dissolution liquid evenly by a method such as rolling or sliding in the analysis region on the silicon wafer. The movement of the droplet may be performed while holding the vacuum tweezers holding the silicon wafer by hand and inclining it, but this method tends to cause inconveniences such as dropping the droplet from the silicon wafer by inclining the silicon wafer too much. Therefore, from the viewpoint of work efficiency, it is desirable to use a silicon wafer holding stand that prevents drops from dropping even if the silicon wafer is tilted too much or to automate the movement by a machine. As such a method, a known method can be used. For example, a silicon wafer is mounted on a horizontal stage, and while the stage is magnetically levitated, the droplets held on the silicon wafer are held by a droplet holder while rotating or moving in a horizontal plane. There is a method of moving the wafer surface in the radial direction. (Japanese Patent Laid-Open No. 1-302836) In addition, there is a method in which a droplet of ultrapure water is moved over the entire surface of the silicon wafer by inclining the silicon wafer together with the holding table. (JP-A-4-3445)

The surface temperature of the silicon wafer on which the droplets of the solution are to be moved is preferably around room temperature, and the analysis accuracy will be lowered if the temperature is higher or lower than this. That is, when the surface temperature of the silicon wafer is high, a part of the decomposition liquid is evaporated during movement and the impurities in the liquid are concentrated, so that the analysis value becomes higher than the actual value. On the other hand, when the temperature is low, the water content in the air is cooled, condensed on the silicon wafer and added to the solution, and the impurities are diluted, so that the analysis value becomes lower than the actual value.

The number of times the droplets are moved (the number of times the droplets are moved evenly throughout the predetermined analysis region) may be insufficient to dissolve the impurity element only once. Is. Usually, a method of scanning the surface of the silicon wafer evenly twice or more with the dropped solution is adopted.

The scanning time for one time is not limited because it varies depending on the amount of the solution to be dropped on the silicon wafer. For example, when 1 ml is dropped on a 4-inch wafer, the accuracy of the moving operation is maintained and the solution during the moving is kept. From the viewpoint of prevention of evaporation and the like, 3 minutes to 10 minutes is suitable.

After moving the dissolving solution to dissolve the impurity element, the whole amount of the dissolving solution is sucked with a micropipette and transferred to a clean Teflon container, and this solution is analyzed by an atomic absorption spectrometer or a plasma emission spectroscopic mass spectrometer. Measure the concentration of impurity elements. Impurity elements that can be recovered by the method of the present invention include metallic elements such as Fe, Ni, Zn, Cu, and Al.

[0017]

According to the method for recovering the impurity element of the present invention, the impurity element on the surface of the silicon wafer can be recovered safely in a short time without polluting the environment.
Further, an impurity element such as Cu having a smaller ionization tendency than Si can be recovered at a high recovery rate. Therefore, it is extremely useful for controlling contamination of silicon wafers in the semiconductor device manufacturing process.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the example, the plane orientation (100) and the specific resistance 3
An n-type silicon wafer of ˜6 Ω · cm was used, and a standard solution for atomic absorption spectrometry was used as a contamination source of impurity elements. The quantification of the impurity element recovered from the silicon wafer was performed by atomic absorption spectrometry.

Example 1 A silicon wafer was washed with a 1% by weight aqueous solution of hydrofluoric acid, and a certain amount of Cu-added ultrapure water was dispensed into a micropipette and evenly dropped on the entire surface of the silicon wafer evenly. After that, the silicon wafer is slowly heated on a hot plate to evaporate the water, thereby producing a Cu-contaminated silicon wafer having a Cu concentration of 2.2 × 10 ¹² atoms / cm ^{2 on} the silicon wafer. The wafer was held on a fluororesin wafer holder as shown with the measurement surface facing upward. Next, hydrofluoric acid, hydrogen peroxide and ultrapure water were mixed to prepare a solution having a concentration of 5% by weight, and 1 ml of this solution was dispensed into a micropipette.
It was dripped at almost the center of the contaminated silicon wafer. Then, at room temperature, the silicon wafer was tilted together with the wafer holding table to roll the droplets of the solution, and the solution was moved over the entire surface twice for 5 minutes, and then the entire amount of this solution was collected again with a micropipette. Analysis of Cu in the solution recovered by atomic absorption spectrometry showed that it was 2.1 in terms of the amount attached to the silicon wafer.
The concentration was × 10 ¹² atoms / cm ² , and the recovery rate was 98%.

Example 2 A Cu-contaminated silicon wafer having the same Cu concentration as in Example 1 was prepared, and a solution containing 5% by weight of hydrofluoric acid and hydrogen peroxide, hydrogen peroxide, and ultrapure water. 100 μl
Was dropped onto a contaminated silicon wafer, and Cu was recovered in the same manner as in Example 1. Atomic absorption spectrometric analysis of the recovered solution revealed that the Cu concentration in the decomposed solution was 2.0 × 10 ¹² atoms / cm ^{2 in} terms of silicon wafer attachment amount, and the recovery rate was 90%.

Comparative Example A Cu-contaminated silicon wafer having the same Cu concentration as in Example 1 was prepared, and 100 μl of a solution containing 5 wt% hydrofluoric acid and ultrapure water was dropped onto the contaminated silicon wafer. Cu was recovered in the same manner as in Example 1. Atomic absorption analysis of the recovered solution revealed that the Cu concentration in the solution was 1.2 × 10 ¹² atoms / c in terms of silicon wafer attachment amount.
m ² and the recovery rate was 55%.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a holding base for a fluororesin silicon wafer used in an example of the present invention.

[Explanation of symbols]

 1 ... Fluororesin silicon wafer holder 2 ... Silicon wafer 3 ... Solution

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[Procedure amendment]

[Submission date] April 21, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

After moving the dissolution liquid to dissolve the impurity element, the whole amount of the dissolution liquid is sucked with a micropipette and transferred to a clean Teflon container, and this liquid is then analyzed by an atomic absorption spectrometer or
The concentration of the impurity element is measured with an inductively coupled plasma mass spectrometer. Impurity elements that can be recovered by the method of the present invention include metallic elements such as Fe, Ni, Zn, Cu, and Al.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

Example 1 A silicon wafer was washed with a 1% by weight aqueous solution of hydrofluoric acid.
After that, a certain amount of Cu-added ultrapure water was put into a micropipette.
Collect and spread evenly over the entire surface of the silicon wafer little by little.
Dropped without. Then hot play the silicon wafer
By slowly heating it on the
The Cu concentration on the silicon wafer is 2.2 × 10¹²original
Child / cm²Cu-contaminated silicon wafer of
On a wafer holder made of fluororesin as shown in the figure
It was held face-up. Next, hydrofluoric acid and hydrogen peroxide,salt
acidAnd ultrapure water are mixed so that each concentration is 5% by weight.
Prepare a solution and use this solution100 μlA micro pipette
And drop it on the center of the contaminated silicon wafer.
Defeated Then, at room temperature, the silicon wafer
Tilt the holding table to roll the droplets of the solution, and then twice in 5 minutes
After moving the entire surface, use a micropipette to remove this liquid again.
The amount was recovered. C in the solution recovered by atomic absorption spectrometry
When u analysis is performed, the amount of adhesion to the silicon wafer is converted
2.1 x 10 ¹²Atom / cm²And the recovery rate is 98%
Met.

Claims (2)

[Claims] 1. An impurity element characterized in that a droplet of a solution containing hydrofluoric acid, hydrogen peroxide and water is moved in an impurity element analysis region on the surface of a silicon wafer to dissolve and recover the impurity element. Recovery method. 2. A droplet of a solution containing hydrofluoric acid, hydrogen peroxide, hydrochloric acid, and water is moved within an impurity element analysis region on the surface of a silicon wafer to dissolve and recover the impurity element. Method of recovering impurity elements.