JP2715086B2 - Method for forming thermal oxide film on semiconductor wafer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a thermal oxide film on a semiconductor wafer.

[Conventional technology]

Generally, semiconductor wafers such as silicon wafers
During the fabrication of such a semiconductor device, the formation of a thermal oxide film on a semiconductor wafer is repeated many times.

Conventionally, to form a thermal oxide film on the surface of a semiconductor wafer, for example, a silicon wafer, the silicon wafer is mounted on a processing jig (boat) made of a heat-resistant material and placed in a furnace tube in an electric furnace. Then, the thermal oxidation treatment is performed.

The control of the film thickness is performed after calculating according to the type and temperature of the atmosphere, and when the thermal oxide film reaches a desired film thickness, it is pulled out of the furnace, directly lowers the temperature of the silicon wafer to room temperature, and then directly. Alternatively, a simple cleaning process is performed, and then the process proceeds to the next step.

[Problems to be solved by the invention]

However, according to the above-described conventional method for forming a thermal oxide film, the semiconductor wafer 1 is made to have a very small size as shown in FIG. 4 due to the environment inside and outside the furnace tube, the operation of taking the semiconductor wafer into and out of the furnace, and the like. When the thermal oxide film 3 is formed by the thermal oxidation process in a state where the dust 2 easily adheres and the dust 2 adheres, the dust 2 is firmly bonded to the semiconductor wafer 1 and becomes a so-called “burned” state. As a result, it cannot be easily removed.

The dust 2 on the semiconductor wafer 1 adversely affects a subsequent process, causing a problem at the time of mask alignment in a lithography process, and deteriorating characteristics and quality of a device to be formed.

Accordingly, an object of the present invention is to provide a method for forming a thermal oxide film on a semiconductor wafer that can clean the thermal oxide film.

[Means for solving the problem]

In order to solve the above-mentioned problem, the present invention provides a method for removing a surface of a thermal oxide film to a desired thickness by wet etching after forming a thermal oxide film thicker than a desired thickness in a thermal oxidation process of a semiconductor wafer. Then, the etching solution is washed and removed, and then the surface of the thermal oxide film is washed with a chemical solution containing an aqueous solution of hydrogen peroxide and containing an acid or alkali having no etching property.

[Action]

In the above means, wet etching is performed with a solution containing a fluoride ion such as hydrofluoric acid capable of etching a thermal oxide film. By this etching, dust that has been burned to the surface can be removed by removing the thermal oxide film.

Therefore, it is necessary that the solution used for the etching has a sufficient etching performance to remove the thermal oxide film.

After wet etching the thermal oxide film to the desired thickness,
The etchant remaining on the semiconductor wafer is removed by cleaning with pure water or the like. This is performed in order to prevent a thermal oxide film from being removed more than necessary if an etchant is mixed with the chemical solution in the subsequent chemical solution cleaning.

Chemicals used for chemical cleaning include hydrochloric acid-hydrogen peroxide water-water, ammonia water-hydrogen peroxide water-water, sulfuric acid-hydrogen peroxide water and other non-etching acids or alkalis. A clean chemical solution is used. The aqueous hydrogen peroxide plays a role in adjusting the pH of an acid or alkali mixed therein. That is, the mixed liquid plays a role of an oxidizing agent or a reducing agent. Hydrochloric acid, ammonia water, sulfuric acid, and the like that are mixed have little ability to etch a thermal oxide film. However, when the semiconductor wafer is exposed to such a strong acid or alkali, the surface thereof is activated, which tends to cause inconveniences such as adsorption of gas or the like after the treatment of the present invention or adsorption of dust in the air. Therefore, by mixing the aqueous hydrogen peroxide, these effects can be suppressed and dust can be effectively removed.

Of the dust removed during the etching, relatively small dust may be adsorbed or remain due to high surface activity after the end of the etching. These dusts can hardly be removed by washing such as water washing after etching. In the chemical cleaning according to the present invention, dust can be lifted and removed by repeating reductive oxidation very slightly on the surface of the thermal oxide film. As a result, the thermal oxide film is not substantially etched.

These etching, cleaning, and chemical cleaning must be performed as a series of operations. This is because dust remaining on the surface after etching cannot be easily removed by a chemical cleaning or the like after long exposure to air.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

In the thermal oxidation treatment of the silicon wafer 10, first, the first
As shown in the figure, a thermal oxide film (silicon oxide film) 11 is formed thicker than a desired film thickness, and then the silicon wafer 10 is placed in a clean solution containing fluoride ions capable of etching the thermal oxide film 11. After immersion, the surface of the thermal oxide film 11 was wet-etched to a desired thickness as shown in FIG.
By this etching, dust 12 adhered to the surface of thermal oxide film 11 was substantially removed.

Thereafter, the silicon wafer 10 is taken out, the etchant is removed from the surface of the silicon wafer 10 by washing with water or the like, and then a chemical solution that repeats the reduction oxidation of the thermal oxide film 11 very slightly, for example, hydrochloric acid-hydrogen peroxide water-water, ammonia water- The substrate is washed with a hydrogen peroxide solution-water, a sulfuric acid-hydrogen peroxide solution, etc., and as shown in FIG. 3, relatively small dust 12 is removed before proceeding to the next step.

Here, the dust of the unprocessed silicon wafer A after the thermal oxidation treatment, the silicon wafer B after the etching treatment was removed by washing the etching liquid, and the etching liquid after the etching treatment was removed by cleaning, and then the silicon wafer C subjected to the chemical cleaning treatment When the numbers were compared, they were as shown in Table 1.

The number of dust was 50 silicon wafers (100 m diameter)
The average value of m) was measured by a dedicated dust counter.

Therefore, when the etching solution is cleaned after the etching process, it has an effect on removing relatively large dust, but has little effect on the removal of relatively small dust. Then, when a chemical cleaning treatment was performed, the effect was also exhibited in removing relatively small dust, and it was found that a cleaner thermal oxide film surface could be obtained.

Separately from this, when only cleaning with a chemical solution was performed without performing etching treatment, there was no significant change in the dust amount, and it was also confirmed that the effect was small.

In the above embodiment, the method of forming a thermal oxide film on a silicon wafer has been described. However, the present invention is not limited to this, and can be applied to, for example, the formation of a thermal oxide film on a germanium wafer or other semiconductor wafers.

〔The invention's effect〕

As described above, according to the method for forming a thermal oxide film of the present invention, relatively large dust that has been baked on the surface is removed by wet etching together with the surface of the thermal oxide film, and the thermal oxide film is removed. Unnecessary removal is prevented by cleaning and removing the etchant, and a relatively small dust adsorbed or remaining due to the high surface activity after the etching is completed, and the surface of the thermal oxide film is repeatedly reduced and oxidized very slightly. On the other hand, while removal by lifting due to cleaning, the adsorption of gas etc. or the adsorption of dust in the air after a series of operations such as etching, cleaning and removal, and chemical cleaning treatment are the causes of surface activation by hydrogen peroxide in the chemical. Since this is prevented by the suppression, a semiconductor wafer having a clean thermal oxide film can be obtained.

[Brief description of the drawings]

1 to 3 show one embodiment of the present invention.
FIGS. 2, 2 and 3 are cross-sectional views of the silicon wafer after a thermal oxidation process, an etching process, and a chemical cleaning process, respectively, and FIG. 4 is a cross-sectional view of the silicon wafer according to the conventional method. 10 ... silicon wafer, 11 ... thermal oxide film, 12 ... dust

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-272541 (JP, A) JP-A-59-125662 (JP, A) JP-A-50-3782 (JP, A)

Claims (1)

(57) [Claims] In a thermal oxidation treatment of a semiconductor wafer, after forming a thermal oxide film thicker than a desired film thickness, the surface of the thermal oxide film is removed to a desired film thickness by wet etching, and then the etching solution is washed. A method for forming a thermally oxidized film on a semiconductor wafer, comprising removing, and then cleaning the surface of the thermally oxidized film with a chemical solution containing an acid or an alkali having a non-etching property and containing a hydrogen peroxide solution.