JPH0562961A - Wafer cleaning method - Google Patents

Abstract

PURPOSE:To enable an insulating film excellent in insulating properties to be formed on the surface of a wafer by a method wherein the wafer is disposed inside a cleaning chamber keeping its surface horizontal, the cleaning chamber is exhausted after HF vapor is brought into enough contact with the surface of the wafer, the wafer is cleaned by feeding water vapor, and the chamber is exhausted after the cleaning of the wafer is finished. CONSTITUTION:A wafer 2 is disposed inside a cleaning chamber 1 keeping its surface substantially horizontal, HF vapor 4 is brought into enough contact with the surface of the wafer 2, and then the chamber 1 is exhausted. In succession, water vapor 4 is supplied to clean the wafer 2, the chamber 1 is exhausted to be of a normal pressure or a reduced pressure after a cleaning process is finished. The wafer 2 which is not subjected yet to oxidation pre-treatment executed for the formation of an insulating film on its surface and on whose surface a natural oxide film has been formed is used. By this setup, the surface of the wafer 2 can be uniformly cleaned, and an insulating film excellent in insulating properties can be formed on the surface concerned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer cleaning method.

[0002]

2. Description of the Related Art Cleaning used in a semiconductor process generally requires a high degree of cleaning. Among them, the cleaning performed before the oxidation treatment requires a particularly high degree of cleaning, and this degree of cleaning affects the yield of products. It has a big impact. The pre-oxidation cleaning of the silicon wafer includes a step of removing a natural oxide film formed on the surface of the silicon wafer.

A natural oxide film is formed by oxidizing the surface of a silicon wafer with oxygen in the atmosphere. Generally, since the natural oxide film is not formed in a clean atmosphere, impurities are incorporated in the film, which is preferable. Therefore, the pre-oxidation cleaning includes a step of removing the naturalized film to expose a clean silicon surface. In the conventional wafer cleaning method, a silicon wafer before oxidation treatment is vertically arranged in a cleaning chamber, and HF vapor is sufficiently brought into contact with the wafer surface to dissolve the natural oxide film on the surface to remove oxides or the like. Then, the solution is transferred to the surface of the silicon wafer and dropped to remove it. Then high-purity H ₂ O
The cleaning residue adhering to the wafer surface is washed away by bringing vapor into contact with the wafer surface, and finally heated high purity N
_A method is known in which _two gases are sprayed to dry a silicon wafer (JP-A-62-173720).

[0004]

In the conventional method for cleaning a wafer described above, while the HF solution after cleaning travels along the surface of the wafer and drops, impurities reattach to the wafer and the in-plane uniformity of the cleaning degree is poor. Therefore, there is a problem that the insulating film formed on the surface of the obtained wafer is likely to cause dielectric breakdown.

The present invention has been made to solve the above problems, and provides a wafer cleaning method capable of uniformly cleaning the wafer surface and forming an insulating film having excellent insulating properties on the surface. Is what you are trying to do.

[0006]

According to the present invention, when cleaning a wafer before oxidation treatment with HF vapor in advance, the wafer is arranged in the cleaning chamber so that its plane is substantially horizontal, A method for cleaning a wafer is provided, which comprises sufficiently contacting HF vapor with the surface of the wafer, then exhausting it, then supplying steam to clean it, and then exhausting the inside of the chamber to normal pressure or reduced pressure after cleaning. ..

In the present invention, the wafer is placed in the cleaning chamber so that its surface is substantially horizontal.
The cleaning chamber is for cleaning the wafer, and the wafer can be disposed substantially horizontally, and the HF vapor and the H ₂ O vapor can be sufficiently contacted with the disposed wafer surface. Cleaning products with H ₂ O vapor, HF
And be able to vent the rest of the H ₂ O vapor.

The above-mentioned wafer is one that has not been subjected to an oxidation treatment for forming an insulating film on the surface by an oxidation method, for example, a wafer on which a natural oxide film has been formed by oxygen in the atmosphere is used. .. The arrangement of the wafers in which the plane is substantially horizontal is for preventing re-deposition of the substance to be cleaned and removed on the surface of the wafer being cleaned.
Even if a solution of the substance to be cleaned and removed is generated by cleaning the wafer surface, the wafer surface can be prevented from flowing.

By suppressing this flow, the degree of cleaning of the wafer surface can be made uniform. In the present invention, HF vapor is sufficiently contacted with the surface of the wafer and then exhausted. The HF vapor is used for cleaning the wafer surface, and when it is brought into sufficient contact with the wafer surface, for example, a natural oxide film, impurities contained in the air contained in the natural oxide film, and the like are vaporized by a chemical reaction or the like. It can be changed to a substance that is easy to turn into. The conditions for bringing the HF vapor into contact with the wafer surface are usually a pressure of 1 to 10 kg / cm ² and a temperature of 20 to 60 ° C. The substance that is easily vaporized is, for example, SiF ₄ , and is removed together with unreacted HF vapor by exhausting the inside of the cleaning chamber under normal pressure or reduced pressure. The wafer processed by this HF vapor is
A small amount of residue remains on the surface. This residue is, for example, an oxide or a fluorine atom. Of these, the oxide reduces the insulating property of the oxide film formed on the wafer surface after cleaning.

In the present invention, water vapor is then supplied for cleaning, and then the chamber is evacuated to atmospheric pressure or reduced pressure. The water vapor is for cleaning the residue that reduces the insulating property of the wafer surface treated with the HF vapor, and can change the residue (oxide) into a substance that is easily vaporized. The conditions for contacting the wafer surface with water vapor are usually 1 to 10 kg / cm ^{2 at} a pressure and 20 to 6 at a temperature.
It is 0 ° C. The substance that is easily vaporized is SiF ₄ or the like, and can be removed by exhausting the inside of the cleaning chamber under normal pressure or reduced pressure.

Further, it is preferable to purge the inside of the chamber with N ₂ . After that, the wafer is taken out from the cleaning chamber and subjected to an oxidation treatment to form an oxide film having excellent insulating properties on the wafer surface.

[0012]

The substantially horizontal wafer arrangement suppresses the flow of the solution on the wafer surface even if a solution of the substance to be cleaned and removed occurs during wafer cleaning, and further vaporizes and exhausts the substance to be cleaned and removed. This prevents recontamination of the wafer surface.

[0013]

Embodiments of the present invention will be described with reference to the drawings.
In this embodiment, a silicon wafer having a native oxide film on its surface is cleaned by using the wafer cleaning apparatus shown in FIG. However, 1 is a chamber, 3 is a distributor, 4 is N ₂ gas or HF vapor or H ₂ O vapor, and 5 is H.
F steam inlet, 6 H ₂ O steam inlet, 7 exhaust port, 8
Is a fan blower, and 9 is a rotary pump. Also,
The volume of this chamber is 10 l.

A silicon wafer 2 having a natural oxide film is placed in a chamber 1, and N ₂ gas at 50 ° C. is introduced from a HF vapor introduction port 5 using a rotary pump 9 at a standard flow rate of 6 l / min for 1 minute. Then, the fan blower 8 evacuates and pre-purges. Next, a mixed gas of HF vapor and N ₂ gas at 50 ° C. is mixed from the HF vapor inlet port 5 using the rotary pump 9 at a flow rate of 4 liter / min (l / min) and 2 l / min in a standard state, respectively. Then, it is sprayed uniformly on the entire surface of the silicon wafer 2 having the natural oxide film through the distributor 3 at a pressure of ³ to 4 kg / cm ² for 50 seconds / interval, and the inside of the chamber 1 is exhausted using the fan blower 8. As a result, the natural oxide film on the surface of the silicon wafer 2 is processed.

Next, the N ₂ gas at 50 ° C. is fed to the loader pump 9
Is introduced from the H ₂ O vapor introducing port 6 at a standard flow rate of 6 l / min for 1 minute, and exhausted by the fan blower 8 to perform intermediate purging. Next, a mixed gas of H ₂ O vapor and N ₂ gas at 50 ° C. is supplied to the H ₂ O vapor inlet port 6 using the rotary pump 9.
Introduced at a standard flow rate of 2 l / min from
The wafer is uniformly sprayed on the entire surface of the wafer processed by the HF vapor through the distributor 3 at a pressure of 3 to 4 kg / cm ² for 1 minute, and a chamber 1 using a fan blower 8 is used.
Exhaust the inside.

Next, N ₂ gas at 50 ° C. is introduced from the H ₂ O vapor introducing port 6 at a standard flow rate of 6 l / min for 1 minute using a rotary pump and exhausted by a fan blower 8 to perform post-purging. Next wafer (P-type silicon 10)
To form a N-type impurity layer 11 as shown in FIG. 2, the upper Te by the thermal oxidation method to form a SiO ₂ film 12 of 70Å to form a polysilicon gate electrode 13 on the, SiO ₂ film For 12, the time until a constant current stress is applied from the polysilicon gate electrode 13 side to cause dielectric breakdown (constant current TD
DB) was measured. As a result, the constant current TDDB value is 304 seconds for the wafer after the intermediate purge (before the H ₂ O vapor treatment),
It was 348 seconds for the post-purged wafer, and it was confirmed that a good SiO ₂ film was formed on the post-purged wafer.

[0017]

According to the present invention, there is provided a wafer cleaning method capable of uniformly cleaning the surface of a wafer before the oxidation treatment and forming an insulating film having excellent insulating properties on the surface. You can

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a wafer cleaning apparatus manufactured in an embodiment of the present invention.

FIG. 2 is an explanatory diagram of dielectric breakdown measurement of a wafer cleaned by a wafer cleaning device manufactured in an example of the present invention.

[Explanation of symbols]

1 Chamber 2 Wafer 3 Distributor 4 HF or H ₂ O Steam 5 HF Steam Inlet 6 H ₂ O Steam Inlet 7 Exhaust 8 Fan Blower 9 Loader Pump

Claims (1)

[Claims] 1. When cleaning a wafer before oxidation treatment with HF vapor in advance, the wafer is placed in a cleaning chamber so that its plane is substantially horizontal, and the surface of the wafer is sufficiently contacted with HF vapor. After that, the wafer is evacuated, and then water vapor is supplied for cleaning, and after cleaning, the inside of the chamber is evacuated to normal pressure or reduced pressure.