JPH06224169A - Method for removing metal impurities in semiconductor wafer cleaning chemicals - Google Patents

Abstract

(57) [Summary] [Structure] Metal impurities contained in a small amount in hydrofluoric acid or buffer hydrofluoric acid 101 are deposited on and removed from the silicon wafer 104 by repeating the loading and unloading of the silicon wafer 104 into and from these chemicals. [Effect] Metal impurities in hydrofluoric acid and buffer hydrofluoric acid, which are difficult to remove by the conventional method, can be easily removed, and deterioration of element characteristics due to metal impurity contamination during cleaning of a semiconductor substrate is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing metal impurities in chemicals used for cleaning semiconductor wafers.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit manufacturing process, dilute hydrofluoric acid or buffer hydrofluoric acid is used as a wafer cleaning chemical before thin film formation. In hydrofluoric acid and buffer hydrofluoric acid, there is a problem that metal impurities, which are contained in a trace amount of several hundred ppt to several hundred ppb in the chemicals, easily adhere to the surface of the semiconductor wafer, and the semiconductor wafer is contaminated. It is necessary to remove a trace amount of metal impurities.

In the prior art, a silicon wafer or a piece of silicon is immersed in hydrofluoric acid or buffer hydrofluoric acid to deposit a trace amount of metal impurities in the liquid on the silicon surface to remove the metal impurities in the liquid. There is a method (JP-A-0
4-162627).

[0004]

It is known that copper (Cu) easily adheres to the silicon surface in hydrofluoric acid or buffer hydrofluoric acid.
Cu in buffer hydrofluoric acid can be removed efficiently, but other metal impurity elements such as iron (Fe) and chromium (Cr) do not adhere to the silicon surface so much. The method of immersing in the metal has a problem that these metal impurities cannot be removed efficiently. Heavy metal in hydrofluoric acid and buffer hydrofluoric acid adheres to the substrate surface during cleaning of the semiconductor substrate, deteriorating device characteristics. Although it is necessary, it has been difficult to reduce Cr and Fe to 10 ppb or less by the conventional technique.

An object of the present invention is to efficiently deposit metal impurities, particularly Cr and Fe, on the surface of a silicon wafer in order to remove metal impurities in hydrofluoric acid and buffer acid.

[0006]

In order to remove metal impurities in dilute hydrofluoric acid and buffer hydrofluoric acid, the method of the present invention for efficiently adhering metal impurities to a silicon wafer surface is
A silicon wafer is repeatedly put into and taken out from these chemicals, and metal impurities are attached to the surface of the silicon wafer when the wafer crosses the liquid surface.

[0007]

2 and 3 show Cr, Fe, Ni, Cu,
Dilute hydrofluoric acid (0.5% each containing 100 ppb of Zn)
% HF) and buffer hydrofluoric acid (NH ₄ F 15%, HF
0.3%) when the silicon wafer was dipped for 2 minutes, and when the silicon wafer was dipped for 2 minutes while taking the silicon wafer in and out 60 times These are the results measured by X-ray analysis. By loading and unloading the silicon wafer to and from hydrofluoric acid and buffer hydrofluoric acid, the amount of Cr and Fe deposited increases about 10 times compared to the case where the silicon wafer is only immersed, and N
It was confirmed by this experiment that the i, Cu, and Zn adhesion amounts increased 2 to 5 times.

As shown in FIG. 4, the present method uses a silicon wafer 3 on a liquid surface 2 of hydrofluoric acid or buffer hydrofluoric acid 1.
The electric field near the surface of the silicon wafer at the liquid surface caused by the difference between the surface potential φ _L in the liquid and the surface potential φ _A in the air attracts the metal impurities 4 in the liquid to the surface. It is an improved one. The surface potential of a silicon wafer is hydrofluoric acid,
In the buffer hydrofluoric acid solution, electrons are more likely to be released into the conductive solution than in the air, and the level is low (φ _L <φ _A ).
In the present invention, this potential gradient is generated by taking a silicon wafer in and out.

The electronegativities of Cr and Fe are 1.
66 and 1.83, and electronegativity of Cu is 1.90.
Since it is lower than that of, the adhesion of the silicon surface is less likely to occur, but φ _A −φ _L = 0.2-
A potential difference of about 0.3 eV occurs, and Cr, F
The amount of e deposited increases like Cu.

[0010]

Embodiment An embodiment of the present invention will be described with reference to FIG.

Buffer hydrofluoric acid (NH ₄ ) contaminated with Cr
(F17%, HF 0.3%) 101 is put in the Teflon tank 102. The Cr contamination amount is 100 ppb and the buffer hydrofluoric acid amount is 5 liters.

Five 6 inch silicon wafers 104 stored in the Teflon cassette 103 are put into and taken out of the container by moving the Teflon cassette 103 up and down. The top and bottom of the Teflon cassette 103 is immersed in buffer hydrofluoric acid 2
The cycle was repeated 500 times with a cycle of 5 seconds, 1 second for pulling, 1 second for holding in air, and 1 second for descending. Then, the silicon wafer 104 was taken out. The total processing time is 2500 seconds.

By the above treatment, Cr in the buffer hydrofluoric acid can be removed more efficiently than the conventional method in which five silicon wafers stored in the Teflon cassette are immersed in the buffer hydrofluoric acid for the same time.

FIG. 5 shows the Cr concentration in the buffer hydrofluoric acid after the removal of the Cr element in the buffer hydrofluoric acid by the method of the present invention shown in the above embodiment and the conventional method. The Cr concentration was measured by ICP analysis. In the conventional method of immersing the wafer, the Cr concentration is 95 ppb because the amount of Cr deposited on the silicon surface is small, whereas in the method of depositing / removing the wafer to deposit impurities on the silicon, the Cr concentration is 95 ppb. Was confirmed to be reduced to 10 ppb or less.

[0015]

The method of the present invention facilitates removal of metal impurities in hydrofluoric acid and buffer hydrofluoric acid, which are difficult to remove by conventional methods, and suppresses deterioration of device characteristics due to metal impurity contamination during semiconductor substrate cleaning. To be done.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the amount of metal impurities deposited on the surface of a silicon wafer in dilute hydrofluoric acid (0.5% HF).

FIG. 3: Buffer hydrofluoric acid (NH ₄ F 17%, HF0.3
FIG. 3 is a diagram showing the amount of metal impurities attached to the surface of a silicon wafer in (%).

FIG. 4 is a diagram showing a potential change on the surface of a silicon wafer at the liquid surface of buffer hydrofluoric acid.

FIG. 5: Method C of the present invention and C after treatment by conventional method
It is a figure which shows Cr concentration in the buffer hydrofluoric acid polluted with r.

[Explanation of symbols]

 101 buffer hydrofluoric acid 102 Teflon tank 103 Teflon cassette 104 silicon wafer

Claims (1)

[Claims] 1. A metal impurity contained in dilute hydrofluoric acid (HF) or buffer hydrofluoric acid (NH ₄ F + HF) used for cleaning a semiconductor wafer is immersed in these chemicals of a silicon wafer and The method for removing metal impurities in a semiconductor wafer cleaning chemical, characterized in that the metal impurities are adhered to and removed from the surface of the silicon wafer by repeating the removal of the above step.