JPH04298038A - Wafer cleaning method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer manufacturing process, and more particularly to an improvement in a wafer cleaning method.

0002

[Prior Art] When there are contaminants on the surface of a semiconductor wafer,
They must be removed as they degrade its properties. Contaminants include foreign matter (garbage) and deposits such as heavy metals. In particular, heavy metals adhere strongly, so it is not easy to remove them. For example, there is an RCA cleaning method as a cleaning method for Si wafers, but in this method Cu,
It is known that although heavy metals such as Zn can be removed, Fe and Al remain.

[0003] As a method for reliably removing these, there is an etching method. For example, sulfuric acid-based etchant (mixture of H2SO4, H2O2, H2O) and ammonia-based etchant (NH4OH, H2O2, H2O) for GaAs
2O), etc., to remove several micrometers from the surface. However, when this method is used, undulations and pits occur on the surface and the flatness of the surface is lost.

Although there is a dry etching method using plasma or the like, the removal effect is small and there is a possibility that a strained layer may be generated on the surface.

As a method for removing deposits without damaging flatness or crystallinity, a method has been proposed in which a thermal oxide film is formed on the surface and then the oxide film is removed by heating the wafer in a vacuum (Saito et al. Others: Institute of Electronics, Information and Communication Engineers Technical Report, E
D-117, 1987, P43). This method uses MBE
It was devised as a pretreatment for (molecular beam epitaxial method) and is used for cleaning GaAs wafers. That is, the wafer is thermally oxidized at 450°C, and
An oxide film with a thickness of 0 Å (Angstrom) is formed and then heated to 750° C. or higher in vacuum to remove the oxide film. This method has been shown to have a remarkable removal effect, such as reducing the carbon concentration on the surface to one-third.

[0006]

The conventional etching method deteriorates the surface condition of the wafer as described above. Further, although the thermal oxide film removal method is excellent as a treatment immediately before epitaxial growth, it is difficult to apply to wafer manufacturing. The key is to perform heat treatment. In particular, if the wafer is exposed to high temperatures of 750° C. or higher, defects such as dislocations will be introduced into the wafer.

In compound semiconductors such as GaAs and InP,
Heating in vacuum evaporates As and P, forming a metamorphosed layer on the surface. Furthermore, processing in a vacuum does not have good productivity. Furthermore, when forming a thermal oxide film, the quality of the oxide film changes depending on the atmosphere, temperature, etc. The temperature at which it evaporates will also change, and reproducibility will be lost.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method that can be used at room temperature without deteriorating the surface condition.
An object of the present invention is to provide a wafer cleaning method that can remove deposits on the surface in a normal pressure atmosphere.

[0009]

[Means for Solving the Problems] The structure of the wafer cleaning method of the present invention for solving the above problems is such that, in the semiconductor wafer cleaning method, the wafer is held in an ozone atmosphere and an oxide film is formed on the surface of the wafer. After the wafer is formed, the oxide film is removed by immersion in a reducing solution, thereby removing foreign matter adhering to the wafer surface.

0010

[Operation] A method for forming an oxide film on the surface of a semiconductor wafer was carried out by keeping it at room temperature in an ozone atmosphere. Furthermore, the problem was solved by using a reducing solution such as hydrofluoric acid as a method for removing the oxide film. In addition to hydrofluoric acid, examples of reducing solutions include hydrochloric acid, nitric acid, sulfuric acid, and diluted solutions thereof. Furthermore, an alkaline solution with a pH of 12 or higher is effective because it dissolves As oxides in GaAs.

[0011]

EXAMPLE The following describes the method and results of an experiment in which an oxide film was formed on the surface of a GaAs wafer, the film was removed, and the concentration of residual heavy metals was measured.

The experimental sample was a 75 mmφ semi-insulating G
It is an aAs wafer, and the surface is mirror finished. This wafer was divided into four, one of which was left for initial surface contamination measurement, and the other three were used for cleaning experiments.

[0013] The ozone atmosphere was generated using an iozone device (manufactured by Iwasaki Electric Co., Ltd.). That is, when a wafer is placed in this apparatus, the wafer is irradiated with ultraviolet light of 15 mW and a wavelength of 245 nm. Therefore, ozone is generated near the wafer, oxidizes the wafer surface, and forms an oxide film. The oxide film thickness was measured using an ellipsometer. The film thickness of the initial sample was 12 Å. When the wafer was placed in the above apparatus and the film thickness formation time was maintained at 0 to 240 min, the film thickness was 12 to 210 Å.

[0014] This wafer was soaked in a dilute solution of hydrofluoric acid (HF:H
2O=50:1) for 2 minutes to remove the oxide film, and then washed with pure water for 5 minutes (flowing water at 1 l/min) and dried.

The oxide film thickness after cleaning was 7 to 9 Å, confirming that the oxide film was removed by the above treatment. After processing, the wafer surface had a good mirror surface with no waviness, cloudiness, pits, etc. observed.

The amount of heavy metals remaining on the surfaces of these wafers was measured. The measurement method is as follows.

First, an etching solution (ammonia-based) was applied (0.5 cc) onto the wafer surface, and after being held for a predetermined time, the solution was collected, and the concentration of heavy metals in the solution was measured by atomic absorption spectrometry.

[0018] The concentration of heavy metals in the etching solution was measured in advance, and the amount of adhered metals incorporated into the etching solution per unit area was calculated from the difference with the recovered solution and the area of the etching solution when applied to the surface. This was repeated until there was no difference between the recovered liquid and the etching liquid, and the data was integrated to determine the amount of surface adhesion. At this time, the metals measured were Cu, Cr, Fe, Z
It is n.

FIG. 1 is a diagram showing the experimental results of an embodiment of the present invention. That is, in the above experiment, the graph shows the oxide film thickness (Å) on the horizontal axis and the residual heavy metal concentration on the vertical axis.

In FIG. 1, the film thickness of each heavy metal is 10
The amount of adhesion decreases as the thickness increases up to 0 Å, and a removal effect is observed. When the film thickness becomes 100 Å or more, the amount of adhesion becomes approximately constant. At this time, the concentration of each heavy metal was reduced by one order of magnitude from the initial value, indicating that it was significantly removed.

According to this embodiment, heavy metal contamination on the surface of the semiconductor wafer can be removed, and an improvement in product yield can be expected.

[0022] As a method of generating the ozone atmosphere, a method using electric discharge may be used. As a method for removing the oxide film, a method in which the sample is held in the vapor of a reducing liquid may be used.

[0023] Also, the target semiconductor wafer is G
In addition to aAs, there are compound semiconductors such as InP, GaP, and InAs.

[0024]

According to the present invention, it is possible to easily obtain a wafer in which the amount of contaminant heavy metals attached is extremely small and the surface is free from cloudiness, waviness, pits, etc. and has a good surface condition. That is, according to the present invention, high-quality wafers can be obtained at a high yield, which can greatly contribute to improving economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between oxide film thickness and residual heavy metal concentration in an example of the present invention.

Claims (1)

[Claims] 1. A method for cleaning a semiconductor wafer, in which the wafer is held in an ozone atmosphere to form an oxide film on its surface, and then the wafer is immersed in a reducing solution to remove the oxide film. A wafer cleaning method characterized by removing attached foreign matter.