JPS5837982B2 - Surface treatment method for Group 3-5 compound semiconductors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a protective film on the surface of a IIJ-V compound semiconductor wafer in the same container immediately after cleaning.

Conventionally, a 1V group compound semiconductor wafer cut from an ingot has been completed as a substrate for crystal growth by the following procedure.

That is, a wafer cut from an ingot is subjected to mechanical polishing or mechanochemical polishing to make its surface mirror-finished.

After this, the wafer removed from the polishing jig is cleaned of the wax used to fix the wafer to the polishing jig by reflux cleaning, boiling cleaning, or ultrasonic cleaning with an organic solvent such as acetone or trichlene, and then using nitrogen gas, etc. Blow dry with inert gas.

These wafers are then stored in an alcohol-filled container or dry box or simply a wafer container.

The stored wafers are taken out as needed and subjected to the next processing.

For example, when a gallium arsenide wafer is used as a substrate for epitaxial growth, the surface is etched by dipping it in a sulfuric acid-based chemical etching solution to obtain a clean surface, and then the wafer is set in a growth apparatus.

Although the conventional wafer processing method has been described above, this conventional wafer processing method has the following drawbacks.

First, the work is complicated because each process is independent;
It takes time too.

Second, the cleaned wafer surface is often exposed to air between steps because the steps are independent.
Microscopic dust particles in the air adhere to the surface and cause contamination.

This deposit adversely affects subsequent processing, such as a crystal growth step.

Third, the wafer surface is susceptible to damage due to complicated processing operations.

Fourth, conventional chemical surface etching processes have significant drawbacks as described below.

That is, when using the wafer as a substrate for crystal growth, the surface of the wafer is heated 10 to 10 times before being set in the growth apparatus.
Although the etching is approximately 0 μm, the periphery of the wafer surface, which had been mirror-polished by this process, inevitably sag.

Even if this etching process is performed carefully and while stirring the etching solution, the width of 2 to 8 mm from the periphery of the wafer is rounded compared to the center, and when looking at the wafer as a whole, the wafer is flat. It is damaged.

This poor flatness is a major hindrance in various subsequent processes, such as the epitaxial growth process, exposure of photoresist using a mask, and device fabrication processes that require high uniformity of the epitaxial film layer within the wafer. This ultimately causes a deterioration in the effective area utilization rate per wafer.

The method according to the present invention eliminates all of the above-mentioned drawbacks, makes it possible to reduce time by processing a large number of wafers at the same time, and is a novel m- This is a method for processing group (2) compound semiconductor wafers.

According to the present invention, it is possible to eliminate the disadvantages of conventional methods, such as: (1) contamination after wafer cleaning with organic solvents, (2) damage to the wafer surface, (2) complexity of each process, and (4) surface sag due to etching of the wafer surface. 3. According to the present invention, a wafer after mechanical and chemical polishing is cleaned with an organic solvent and then a protective film is immediately formed on the clean surface in the same equipment, so that the wafer is not contaminated and the surface is protected from damage. It is from.

Furthermore, the operations for performing these steps in series within the same device are extremely simple.

In the present invention, even when a ■-■ group compound semiconductor wafer is used as a substrate for crystal growth, the conventional etching treatment using sulfuric acid-based chemicals is not performed.

As a result of studies conducted by the present inventors, it has been found that the conventional etching process is not necessarily necessary.

In the case of a wafer on which a protective film has been formed by the processing method of the present invention, the flatness of the wafer surface is such that, for example, epitaxial growth can be performed simply on the surface from which the protective film has been removed, compared to the specularity immediately after mechanical and chemical polishing. It is in very good condition, comparable to the other examples.

A protective film formed by treating a wafer that has been cleaned with an organic solvent with an aqueous solution of sodium hypochlorite, hydrogen peroxide, or pure water is an oxide film on the wafer.

For example, in the case of gallium arsenide wafers, the surface is transformed into gallium arsenite, and it is well known that this transformed layer is mechanically hard and provides protection from damage and the outside air.

Therefore, a protective film formed by treatment with an aqueous solution of sodium hypochlorite, hydrogen peroxide solution, or pure water is characterized in that it transforms the wafer surface into a compound that is less susceptible to mechanical damage.

Therefore, this protective film is effective as passivation for protecting devices processed and provided on the wafer surface, and may be subjected to the processing method of the present invention for this purpose.

In the processing method of the present invention, the protective film can be more easily formed by increasing the temperature of the wafer in the container after it has been cleaned and dried.

The heater that raises the temperature of the wafer is preferably an explosion-proof type.

The thickness of this protective film can be changed at the time of its formation, for example, by appropriately selecting the processing temperature and processing time.

A feature of the present invention is that all the steps up to the formation of any protective film are performed continuously in the same apparatus while keeping the surface clean.

This will be explained in detail below using examples.

The figure shows an example of an apparatus used to implement the present invention.

A potassium arsenide wafer 2 to be used as a substrate for vapor phase growth is placed on a wafer support 3 and housed in a stainless steel container 1 whose inner surface is coated with fluororesin.

Thereafter, a fluororesin-coated lid 6 equipped with a pipe 4 and a valve 5 for introducing an organic solvent is closed, and trichlorethylene is introduced from the pipe 4 to fill the container until it overflows from the pipe 7.

At this time, valves 8 and 9 are closed, and valve 10 is left open.

The container is filled with trichlorethylene, and with the valve 5 closed, the temperature inside the container is brought to about 60° C. using the heater 11.

After cleaning in a heated state for about 20 minutes, open the valve 8 to discharge the trichlorethylene in the container, close the valve 8 again, and introduce new trichlorethylene from the pipe 4.
Wash again with heat.

After performing this operation two to three times as necessary, the same operation is repeated to perform acetone cleaning and alcohol cleaning as necessary.

Thereafter, the valves 5 and 10 are closed, the valves 8 and 9 are opened, and nitrogen gas for drying is introduced from the pipe 12 to sufficiently dry the inside of the container.

After drying, close valves 8 and 9 and close valves 5 and 1.
0 is opened, and an aqueous solution of 0.3N sodium hypochlorite is introduced from pipe 4, and the container is filled until it overflows from pipe 7.

With the valve 5 closed, the temperature inside the container is brought to about 70° C. using the heater 11.

After processing for about 5 minutes, valves 8 and 9 are opened, and with valve 10 closed, pure water is introduced from pipe 12, quickly replacing the sodium hypochlorite, and washing the wafer 2 and the inside of the container with water. .

Note that in the case of only hydrogen peroxide solution and pure water, the treatment temperature must be high and the treatment time must be lengthened.

When the treatment temperature exceeds 100° C. and is less than about 400° C., the solution is not filled into the container.

In this case, valves 9 and 10 are closed, valves 5 and 8 are opened, and the vapor of the solution is introduced from pipe 4 to cause the vapor to react with the wafer in the container for processing.

Regardless of which solution was used for processing, turn off the power to the heating heater, and when the wafer temperature drops to about 50°C or less, introduce nitrogen gas for drying through the pipe 12 instead of pure water introduced through the pipe 12. Dry the inside of the container and the wafer thoroughly.

The lid 6 was opened and the processed wafer was taken out.

A uniform deteriorated layer is formed on the wafer, and the wafer is stored as is.

The number of substrates required for vapor phase growth is taken out of the storage container, the oxide film of the altered layer is removed by another predetermined method, and the substrates are immediately inserted into the growth apparatus.

When crystal growth was performed, the epitaxial growth layer had no irregularities due to abnormal growth, and the film thickness was very uniform and there was little surface sagging around the wafer, so the effective utilization rate within the wafer surface was over 95%. Met.

This is the result of a reduction in the number of dust particles adhering to the surface and less damage to the surface compared to the case of using a wafer processed through conventional processes.

Furthermore, the absence of surface sag improves uniformity and simplifies the processing method.

Although examples have been shown above using the apparatus shown in the figure, the method of the present invention is not particularly limited to the shape of the apparatus shown in the figure, and the method of the present invention is not limited to the shape of the apparatus shown in the figure. It has at least one inlet through which an active gas can be introduced, and can be filled with such an organic solvent, reactive liquid, reactive vapor, or dry inert gas, and can sequentially replace these liquids, vapors, or gases. The cleaning of the wafer and the formation of the protective film may be performed continuously in the same container using a container that can raise the temperature and has at least one discharge port that can be heated.

[Brief explanation of the drawing]

The figure is an explanatory diagram mainly showing a cross section of an example of an apparatus used for carrying out the present invention. In the figure, 1 is a container body for carrying out a series of steps according to the present invention, 2 is a ■-■ group compound semiconductor wafer processed according to the present invention, 3 is a wafer support stand, 4, 7 and 12 are pipes. Reference numeral 6 indicates a lid of the container, and reference numerals 5, 8, 9, and 10 indicate valves for controlling various gases, vapors, and liquids. Reference numeral 11 is a heater for heating the wafer support stand 3, and arbitrarily controls the temperature inside the container.

Claims (1)

[Claims] Im-V group compound semiconductor wafer A step of cleaning with an organic solvent, a step of drying in a clean inert gas atmosphere, and a step of contacting the wafer surface with an aqueous solution of sodium hypochlorite, hydrogen peroxide solution, or pure water. ■-v characterized in that the step of providing a protective film consisting of a metamorphosed layer on the surface of the container is carried out in the same container as successive steps.
A method for surface treatment of group compound semiconductors.