JPS5838929B2 - It's hard to see how it's going to turn out. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a vapor-phase grown multilayer thin film having a thin layer region with high impurity concentration, and particularly to a manufacturing method characterized by mixing an impurity gas into a carrier gas in a pulsed manner. It is.

BACKGROUND OF THE INVENTION Methods for manufacturing vapor-grown multilayer thin films having thin regions of high impurity concentration and the resulting vapor-grown multilayer thin films are of great importance for a variety of electronic devices.

For example, when manufacturing non-volatile semiconductor memory,
It is necessary to add an extremely small amount of impurity such as tungsten or molybdenum to the interface between the silicon oxide film and the alumina film formed on the semiconductor surface, the amount of which is about 1 to 2 atomic layers.

Also, high performance in-butt diodes are comprised of a multilayer structure having a narrow high impurity concentration region on the order of 00 to 0.05 microns in width in an epitaxial layer on the order of 10 microns.

When forming such a narrow high impurity concentration region, it would be very convenient if it could be realized as an industrial production method to add impurities in a pulsed manner during epitaxial growth.

Naturally, in addition to these applications, there are many cases where pulsed addition of impurities is required.

An important feature of the method of adding impurities in a pulsed manner or the equipment used to realize the same is that the amount of added impurities and the addition time can be adjusted, and the changeover at the start or end of addition can be quickly performed.

Methods for adding impurities are well known in the art and are carried out as follows.

A part of the gas pipe connected to the reactor containing the sample to be added with impurities is used as a T-shaped part, and a valve is installed in the branch pipe, and by opening and closing this valve, the doping gas containing the added impurity is introduced and stopped. This is a method of doing this.

At this time, the amount of impurities added is adjusted by adjusting the impurity concentration in the doping gas or the gas flow rate.

However, in such a conventional impurity addition apparatus, when attempting to add impurities in a pulsed manner, it is difficult to adjust the amount of added impurities due to the following drawbacks.

This is because when adding impurities in a pulsed manner, it is necessary to make the time from the start of introduction of the impurity gas to the stop of introduction sufficiently short, but when the valve is opened to introduce the doping gas, there is no flow until then. Since the gas flows suddenly, it takes time to adjust to the desired flow rate, and crystals may grow to a certain thickness before the flow rate setting is completed, which is an unsatisfactory addition of impurities, but there is no way to do it. In some cases, the valve must be closed in order to stop the gas supply, making it difficult to adjust the amount of impurities added with good reproducibility.

In view of this, the present invention provides a method of adding impurities in a pulsed manner, which eliminates the drawbacks of the conventional methods, thereby creating an ideal vapor-grown multilayer with a predetermined high impurity concentration thin layer region. The purpose is to manufacture thin films.

The method of the present invention will be explained in detail below with reference to the drawings.

The figure shows an embodiment embodying the present invention.

An outlet 2 of the pipe 1 is connected to the reactor, and a carrier gas carrying impurity gases is introduced through an inlet 3.

A three-way valve 4 is provided in the middle of the pipe 1.

The exhaust port 2 and the inlet port 3 are always in a conductive state, and the gas from the branch port 5 is opened and closed by opening and closing the valve 4.

Impurity gas is stored in a gas container 6, and a valve 4
It is guided into the reactor by opening the .

The amount of impurity added is determined by the volume of the gas container 6, the pressure inside the container, or the concentration of impurity gas.

The method of adding impurity gas in a pulsed manner is as described below.

First, connect the cylinder that stores the impurity gas to the introduction lower,
Impurity gas is allowed to flow through valves 8 and 9.

The valve 8 is a valve having the same structure as the valve 4,
The valve is always in a conductive state between 7 and 10, and can only be connected to or disconnected from the branch pipe 11.

Here, the valve 4 is closed and the valve 8 is opened to introduce the impurity gas into the gas container 6.

At this time, while watching the pressure gauge 12, the pressure regulating valve 9 is operated so that the pressure reaches a predetermined value higher than the pressure inside the reactor.

After this, valve 8 is closed. When adding impurities, the valve 4 is opened and the pressure inside the gas container 6 becomes equal to the pressure of the carrier gas, and the impurity gas is released.

After releasing the gas, the valve 4 is closed and the valve 8 is opened again to return the pressure inside the gas container 6 to the set value, thereby preparing for the next addition.

The amount added can be arbitrarily adjusted by changing the volume of the gas container 6, the pressure in the gas container 6 before releasing the gas, or the concentration of the introduced impurity gas.

The addition time is carried out by changing the time for discharging from the gas container, and can be arbitrarily set by selecting an appropriate regulator 13 that includes a nozzle for regulating the gas discharging rate.

When it is necessary to add in a sufficiently narrow pulse, a nozzle with a large inner diameter may be used.

Examples in which the method of the present invention is applied to the manufacture of semiconductor nonvolatile memories and the manufacture of imbat diodes will be described below.

Example 1: When applied to the production of semiconductor nonvolatile memory.

The apparatus shown in the figure is connected to a CVD apparatus for depositing an alumina film, and tungsten fluoride (WF) is used as an impurity gas.
6) Hydrogen gas was used as a carrier gas.

The gas container 6 is installed so that the volume between the valve 4 and the valve 8 is 10 -, and the internal pressure is set to 1.10 atmospheres.

The nozzle 13 was selected to be able to complete discharge in 0.1 seconds under these conditions.

After placing a silicon wafer on which an oxide film has been formed in advance in the CVD equipment and heating it to 800°C, valve 4 is opened and WF6 is introduced into the CVD equipment using carrier gas (hydrogen).
Gas was introduced, and valve 4 was closed again one second after opening.

Immediately thereafter, an alumina film was formed by CVD.

When the silicon wafer was taken out and examined to see if it had a memory effect, it was found that sufficiently good memory properties were obtained, and it was confirmed that a necessary and sufficient amount of tungsten was present at the interface between the oxide film and the alumina film.

Example 2: Application to production of gallium arsenide impact diode The apparatus shown in the figure was connected to an epitaxial vapor phase growth apparatus for gallium arsenide, and hydrogen gas containing hydrogen sulfide at a concentration of 1% was used as the impurity gas.

A gas container was installed so that the volume between bubble 4 and bubble 8 was 100 liters, and the pressure inside was maintained at 1.10 atm.

The nozzle 13 was equipped so that the impurity gas could be completely discharged in 8 seconds under these conditions.

During the epitaxial growth of gallium arsenide, the valve 4 was opened and closed again after 3.5 seconds.

When the epitaxially grown gallium arsenide wafer was taken out and the impurity concentration distribution was shown by the C-V method, the width was 0.
．． 1 micron, peak concentration 2 x 1017cfrL'
It was confirmed that a multilayer epitaxial structure with sufficiently good characteristics as an in-butt diode was formed.

As described above, the present invention is applied to the CVD method to form a thin layer containing a high concentration of tungsten between a silicon oxide film and an alumina film provided on a silicon crystal surface.
The present invention was applied to the vapor phase epitaxial growth method of gallium arsenide to produce a gallium arsenide multilayer crystal having a thin layer containing a high concentration of sulfur.

However, it goes without saying that the method of the present invention is not limited to these materials, and can be applied to methods for producing thin films and crystals using gas phase reactions in general.

[Brief explanation of drawings]

The figure is a diagram for explaining the present invention in detail, and shows one embodiment of an apparatus used to embody the method of the present invention. 1 is the pipe through which the carrier gas flows, 2 is its outlet, 3
indicates an inlet, and 4 is a valve provided in the middle. 5 is a branch pipe branching from valve 4, 6 is an impurity gas container, 7 is an impurity gas inlet, 8 is a valve, 9 is a pressure regulator, 10 is an outlet, 11 is a branch pipe of valve 8, 12 is a A pressure gauge is used to determine the pressure in the gas container 6, and 13 is a discharge rate regulator including a nozzle that determines the impurity gas discharge rate.

Claims (1)

[Claims] 1 Connect the pipe through which the carrier gas is to flow and the impurity gas container through a valve so that the impurity gas can be mixed into the carrier gas, and with this valve closed, the impurity gas is allowed to flow at a pressure higher than that of the carrier gas. A gas phase having a thin layer region with high impurity concentration, characterized in that the impurity gas is mixed into the carrier gas in a pulsed manner by filling an impurity container until the pressure is reached and then opening and closing the valve. Method for producing grown multilayer thin films.