JPH05166777A - Washing of semiconductor wafer - Google Patents

Abstract

PURPOSE:To simplify a washing process without lowering a washing effect of a semiconductor wafer in order to prevent generation of complex contamination by using liquid constituting of hydrogen fluoride, hydrochrolic acid, hydrogen peroxide water and pure water. CONSTITUTION:By means of a washing device with an automatic quantitative mixer, 0.68l of hydrofluoric acid (HF 50%), for instance, 0.34l of hydrochloric acid (HCl 36%), 0.34l of hydrogen peroxide water (H2O3 30%) and 33.64l of ultra-pure water are mixed so as to be uniform for being guided into a washing tank. 50 sheets of silicon wafers are loaded on a wafer carrier for being dipped into a washing liquid for 3min at a room temperature. Later, the wafers are dipped into an ultra-pure water washing tank being made to overflow for 20min for performing pure water linse followed by taking out the wafer for drying with isopropyl alcohol vapor. According to this method, a washing process is shortened so as to exclude complex contamination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer cleaning method. More specifically, the present invention relates to a method of cleaning a semiconductor wafer in a semiconductor wafer manufacturing process.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, cleaning of a wafer substrate at the time of inputting, pre-cleaning of a thermal oxidation process, pre-cleaning of a CVD process, or cleaning of a semiconductor wafer for removing phosphorus glass has been conventionally performed by (1). NH ₄ OH + H ₂ O ₂
+ H ₂ O mixed solution immersion treatment (1: 1: 5, 80 ° C, 10
Min), (2) pure water rinse, (3) HF + H ₂ O immersion treatment (containing 1% HF), (4) pure water rinse, (5) HCl +
Immersion treatment of H ₂ O ₂ + H ₂ O mixture (1: 1: 6, 80
So-called RCA cleaning method (W. Kern et.al .: RCA R), in which (6) pure water rinsing and (7) drying are successively performed
eveiw, 31 , p.187, 1970), based on the mixing ratio of each processing solution, the immersion time, the heating temperature, and (1) above.
In general, a cleaning method that is appropriately selected and used according to the process, such as changing the order of the cleaning treatments with the cleaning liquids of (2) and (3), is used.

Here, (1) NH ₄ OH + H ₂ O ₂ + H
_{The 2} O mixed solution is effective in removing foreign substances such as organic substances and heavy metals, and (3) HF + H ₂ O is effective in removing foreign substances adhering to the substrate surface at the same time as removing the oxide film. ) HCl + H ₂ O ₂ + H ₂ O mixture is said to be effective in removing heavy metals.

In the prior art, one cleaning step is divided into seven steps as described above. Since each cleaning solution is composed of an independent cleaning tank, the equipment becomes large, and the interval between processings is large. In addition, it is indispensable to remove the cleaning liquid by rinsing with pure water, which is a problem in improving productivity. Furthermore, it is necessary to move the semiconductor wafer from the cleaning tank to the next cleaning tank, and the semiconductor wafer may be contaminated at this time, or foreign substances that have reattached to the semiconductor wafer in the cleaning tank may move to the next cleaning tank. Then, there is a problem such as so-called compound contamination (cross contamination) that contaminates other semiconductor wafers.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a method for cleaning a semiconductor wafer, which does not reduce the cleaning effect on the semiconductor wafer, simplifies the cleaning process and does not cause complex contamination. To do.

[0006]

The above object can be achieved by a method for cleaning a semiconductor wafer, characterized in that a cleaning liquid composed of hydrogen fluoride, hydrochloric acid, hydrogen peroxide solution and pure water is used.

[0007]

The cleaning method of the present invention uses the above-mentioned cleaning solution comprising hydrogen fluoride, hydrochloric acid, hydrogen peroxide solution and pure water (hereinafter referred to as the cleaning solution of the present invention) to (1) to the cleaning solution of the present invention. Basically, the semiconductor wafer can be cleaned by the dipping treatment of the semiconductor wafer, (2) rinsing with pure water and (3) drying.

[0008]

EXAMPLE In the present invention, hydrofluoric acid (HF + H ₂ O) is diluted with pure water, and the content of hydrogen fluoride (HF) used in a normal cleaning step is, for example, 0. 5-
A solution prepared by adding a small amount of hydrochloric acid (HCl) and hydrogen peroxide solution (H ₂ O ₂ ) to a solution prepared to about 10%, preferably about 0.2 to 1% is used as a cleaning solution. The amount of hydrochloric acid added is about 0.0001 to 0.02% by volume, and the amount of hydrogen peroxide solution added is 0.001 to 0.02%.
It may be about 5% by volume. Specifically, for example, when preparing a cleaning liquid having a total volume of 30 liters, hydrochloric acid is added in an amount of about 0.01 to 0.5 liters and hydrogen peroxide solution is added to 0.1 to 1 so as not to exceed the above range of addition amount. It is preferable to add about 1 liter.

Here, the hydrogen fluoride in the cleaning liquid is effective in removing the oxide film on the semiconductor substrate, especially the natural oxide film and the surface foreign matter, while the hydrochloric acid and the hydrogen peroxide solution are gold,
It is effective in removing copper, chromium, sodium and other metallic foreign substances. If the added amount of hydrochloric acid in the cleaning liquid is less than 0.0001% by volume, the effect of removing metallic foreign matters cannot be obtained, and if added in excess of 0.02% by volume, the ratio of hydrochloric acid to hydrogen fluoride in the cleaning liquid increases. However, it affects the effect of removing the oxide film by hydrogen fluoride, which is not preferable. On the other hand, if the amount of hydrogen peroxide solution added is less than 0.001% by volume, the effect of removing metallic foreign matters cannot be obtained, and if it is added in excess of 0.05% by volume, no further effect is obtained and it is uneconomical. is there.

In the cleaning method of the present invention, (1) the immersion treatment of the semiconductor wafer in the cleaning liquid of the present invention differs in the immersion time, the added amount of hydrochloric acid and hydrogen peroxide solution, etc. depending on the steps after cleaning. It is carried out by appropriately adjusting the amount so as not to exceed the range.

Regarding the immersion temperature, it may be heated as in the conventional case. However, in the present invention, a sufficient cleaning effect is obtained at room temperature and heating is not necessary. sharp concentration change of H ₂ O ₂ in the washing liquid is a cleaning liquid common problem containing _{H 2 O 2 (H 2 O} 2
It is preferable to carry out at room temperature (room temperature) without concentration decrease). Next, (2) pure water rinsing and (3) drying are the same as in the conventional method, and the pure water rinsing is not particularly limited as long as the cleaning liquid is sufficiently removed, and the drying is usually performed. Spin drying that has been performed may be used, and in that case, an inert gas atmosphere such as dry nitrogen may be used.

As the semiconductor wafer to which the cleaning method of the present invention can be applied, a silicon substrate semiconductor,
It can be effectively used for a gallium-arsenic substrate semiconductor and a sapphire substrate or a substrate in which silicon is deposited on a sapphire substrate.

As the cleaning process to which the cleaning method of the present invention can be applied, cleaning of the wafer substrate at the time of introduction, pre-cleaning of the thermal oxidation process, pre-cleaning of the diffusion process, pre-cleaning of the CVD process, phosphorus glass removal, It can be used for pre-cleaning of the epitaxial growth process and the like, and for the cleaning process before the metal wiring process.

Further, at present, the miniaturization of LSIs has progressed, the junction depth in silicon has become shallow, and an alkaline cleaning solution having a function of slightly dissolving silicon cannot be used. Therefore, cleaning with hydrofluoric acid and acid alone is not possible. Even if a sufficient cleaning effect is not obtained, a sufficient cleaning effect can be obtained.

The present invention will be described in more detail below.

Example 1 0.68 hydrofluoric acid (HF concentration 50%) prepared for commercial semiconductor manufacture using a cleaning device equipped with an automatic quantitative mixer
Liter, hydrochloric acid (HCl concentration 36%) 0.34 liters, hydrogen peroxide solution (H ₂ O ₂ concentration 30%) 0.34 liters, and ultrapure water 33.64 liters are uniformly mixed and washed. Then, 50 silicon wafers having a diameter of 6 inches were loaded in a Teflon wafer carrier and immersed in a cleaning liquid at room temperature for 3 minutes. After immersion treatment,
2 in the ultrapure water cleaning tank that overflows the wafer
Immersion was carried out for 0 minutes to rinse with pure water, after which the wafer was taken out and IPA (isopropyl alcohol) vapor dried.

Comparative Example 1 Ammonia water (NH ₄ OH concentration 30%) prepared for commercial semiconductor production was used by using a cleaning device equipped with an automatic quantitative mixer.
%) 5 liters, hydrogen peroxide water (H ₂ O ₂ concentration 30%)
5 liters and 25 liters of ultrapure water are uniformly mixed and introduced into a cleaning tank, 50 Teflon wafer carriers with 6-inch diameter silicon wafers are loaded and immersed in a cleaning solution at 80 ° C. for 10 minutes. Processed. After the immersion treatment, the wafer is immersed in an ultrapure water cleaning tank in which the wafer is overflowing for 20 minutes to perform pure water rinse, and then 4.4 liters of hydrochloric acid (HCl concentration 36%) and hydrogen peroxide solution (H ₂ O ₂ Concentration 30%) 4.4 liters and ultrapure water 2
6.2 liters were mixed so as to be uniform, introduced into another cleaning tank, and immersed in a cleaning liquid at 80 ° C. for 10 minutes. After the immersion treatment, the wafer is immersed in an ultrapure water cleaning tank in which it overflows for 20 minutes to rinse it with pure water, and then 0.35 liters of hydrofluoric acid (HF concentration 50%) and 35 liters of ultrapure water are uniformly added. The mixture was mixed so as to be, and introduced into another cleaning tank, and immersed in the cleaning liquid at 23 ° C. for 3 minutes. After the immersion treatment, the wafer was immersed in an ultrapure water cleaning tank for overflowing for 20 minutes to rinse it with pure water, and then the wafer was taken out and IPA (isopropyl alcohol) vapor dried.

Example 2 A wafer substrate lifetime was measured by the following steps using a silicon wafer having a diameter of 6 inches, a P type, a substrate specific resistance of 8 to 12 Ω, and a plane crystal orientation <100>.

(A) ... Cleaning according to Example 1 (b) ... Thermal oxidization, oxide film thickness 200 Å The lifetime was measured by the following method.
The number of measurement points is 5 (pieces / wafer) × 3 wafers. The results are shown in Figure 1.

Lifetime Measurement The minority carrier lifetime is an important property to know the quality of crystals as it corresponds to impurities and structures and structural defects that make deep energy levels. The measurement method (here, the photoconductive decay method) irradiates the wafer with a short light pulse of several μsec by Xe discharge or infrared laser to generate excess carriers in the crystal, and measures the decay of this photocurrent with an oscilloscope. / E is measured as the life time.

Comparative Example 2 In the process of Example 2, the lifetime was measured in the same manner as in Example 2 except that (a) was used as the cleaning method of Comparative Example 1. The number of measurement points is 5 (pieces / wafer) × 3 wafers. The results are shown in Figure 2.

[0022]

As described above, the semiconductor wafer cleaning method characterized by using the cleaning solution of hydrogen fluoride, hydrochloric acid, hydrogen peroxide solution and pure water according to the present invention is applied to hydrofluoric acid diluted with pure water. By adding a small amount of hydrochloric acid and hydrogen peroxide solution, one cleaning step, like the conventional RCA cleaning method, has seven fine steps.
Since only three steps are required, productivity can be improved, complex contamination can be eliminated, and a higher cleaning effect can be obtained.

[Brief description of drawings]

FIG. 1 is a lifetime measurement result created by a process using the cleaning method of the present invention. The vertical axis represents the lifetime time and the horizontal axis represents the number of measurement points.

FIG. 2 is a lifetime measurement result created by a process using a conventional cleaning method. The vertical axis is the number of measurement points,
The horizontal axis is the number of measurement points.

Claims (1)

[Claims] 1. A method for cleaning a semiconductor wafer, which comprises using a cleaning liquid composed of hydrogen fluoride, hydrochloric acid, hydrogen peroxide solution and pure water.