Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate
Reexamination Certificate
1999-02-22
2001-06-12
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
C438S680000
Reexamination Certificate
active
06245647
ABSTRACT:
RELATED APPLICATION
This application claims the priority of Japanese Patent Application No. 10-57481 filed on Feb. 23, 1998, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a method for fabrication of thin films. More specifically, the invention relates to a method for fabricating on a semiconductor substrate a thin film which is uniform in resistivity.
When a thin film such as a silicon semiconductor single crystal thin film having a specified resistivity is fabricated on a semiconductor substrate (hereinafter, referred to simply as “substrate” from time to time) such as a silicon semiconductor single crystal substrate, it is practiced to take the steps of, with the semiconductor substrate placed in a reaction vessel of vapor phase growth equipment, supplying a raw material gas for growth of a thin film as well as a dopant gas through a gas inlet provided in the reaction vessel, and increasing the temperature of the semiconductor substrate higher than the reaction temperature of the raw material gas, by which a thin film doped with dopant elements is deposited and formed on the semiconductor substrate.
As vapor phase growth equipment, conventionally, there have been available those called “hot wall” type in which the inside wall of the reaction vessel is not cooled but left at a temperature nearly equal to the substrate temperature, and those called “cold wall” type in which the inside wall of the reaction vessel is cooled so as to be kept lower than the substrate temperature.
In the hot wall type vapor phase growth equipment, because of the high inside-wall temperature of the reaction vessel, easily thermally-decomposable raw material gas for thin film growth and dopant gas, when introduced into the hot wall type reaction vessel, decompose before reaching the substrate surface, so that a substantial portion of the gases is deposited on the inside-wall surface of the reaction vessel, and thus consumed. Therefore, for the reason that the raw material gas for thin film growth and the dopant gas do not reach the substrate surface sufficiently, there have been issues that film thickness distribution of the thin film to be formed is difficult to control or resistivity distribution within the thin film becomes nonuniform and difficult to control. Whereas the issue of the control of film thickness distribution is beginning to be solved by using a reaction atmosphere under reduced pressure or other means, no effective solutions have been developed for the issue of resistivity distribution.
In the case of the cold wall type vapor phase growth equipment, on the other hand, it is known that because the inside-wall temperature of the reaction vessel is set to about 500° C., which is lower than the thermal decomposition temperature of the raw material gas for thin film growth, deposition of the thin film onto the inside wall of the reaction vessel is suppressed, which produces an effect of preventing losses of the raw material gas for thin film growth. However, attentions have not been paid at all hitherto to losses of the dopant gas due to its thermal decomposition at the inside wall of the reaction vessel. Accordingly, there has been an issue that the resistivity distribution of the thin film may become difficult to control due to any inappropriate setting of the inside-wall temperature of the reaction vessel.
Also, thermal decomposition of the dopant gas at the inside wall of the reaction vessel would cause dopant elements to be deposited on the inside wall of the reaction vessel. Therefore, if the thin film continues to be fabricated without removing the deposit by etching, the deposited dopant elements would be liberated from the inside-wall surface of the reaction vessel during the reaction and mixed into the thin film. This would lead, in some cases, to occurrence of the so-called memory effect that a higher than designed concentration level of dopant is taken into the growing thin film even if a specified level of dopant gas is introduced into the reaction vessel. This memory effect has been a factor that makes it difficult to control the resistivity distribution of thin films among different substrates.
SUMMARY OF THE INVENTION
The present invention having been achieved in view of these and other problems, an object of the invention is to provide a method which makes it possible to form a thin film uniform in resistivity distribution on a semiconductor substrate.
In a first aspect of the present invention, there is provided a thin film fabrication method for forming on a semiconductor substrate a thin film doped with dopant elements comprising steps of placing the semiconductor substrate in a reaction vessel of vapor phase growth equipment, and supplying a raw material gas for thin film growth as well as a dopant gas thereinto, wherein the thin film is formed while the inside wall of the reaction vessel is controlled to below a thermal decomposition temperature of the dopant gas.
Preferably, diborane is used as the dopant gas.
Preferably, the inside-wall temperature of the reaction vessel controlled to below the thermal decomposition temperature of the dopant gas is within a range of room temperature to 250° C., desirably, room temperature to 200° C.
Preferably, the inside wall of the reaction vessel is temperature controlled so that a region thereof opposite to a portion of the semiconductor substrate which ranges, along a direction of flow of the dopant gas supplied from one end of the reaction vessel, from an upstream-side end of the semiconductor substrate to at least an upstream-side {fraction (1/3 )} point of the substrate diameter, desirably, over an entire region just above the semiconductor substrate is controlled to below the thermal decomposition temperature of the dopant gas.
Preferably, the inside wall of the reaction vessel is set to a higher temperature in a pre-heat treatment process or etching process than a temperature during introduction of the dopant gas.
In a second aspect of the invention, there is provided a thin film fabrication method for forming on a semiconductor substrate a thin film comprising steps of placing the semiconductor substrate in a reaction vessel of vapor phase growth equipment and supplying diborane gas thereinto, wherein the thin film is formed while the inside wall of the reaction vessel is controlled to below a thermal decomposition temperature of the diborane gas.
The inventors of the present invention investigated and discussed a method for obtaining a uniform resistivity distribution of the thin film and achieved the present invention.
More specifically, carrying out basic researches to grasp fundamental issues, the inventors have clarified the thermal decomposition temperature of dopant gas and found out for the first time a temperature range that should be set for the inside wall of the reaction vessel.
With respect to diborane gas that is widely used as the p-type dopant gas for the fabrication of silicon semiconductor thin films, the inventors researched the temperature at which boron is deposited by thermal decomposition, and carried out the growth of a semiconductor thin film while controlling the inside-wall temperature of the reaction vessel below an appropriate temperature. As a result, the inventors have found out that diborane gas can be supplied sufficiently onto the substrate surface by suppressing the consumption of diborane gas at the inside wall of the reaction vessel, thus having invented a method for fabricating a silicon semiconductor thin film having a uniform resistivity distribution.
Consequently, in the present invention, by controlling the inside-wall temperature of the reaction vessel below the thermal decomposition temperature of the dopant gas, consumption of the dopant gas at the inside wall of the reaction vessel is suppressed so that the dopant gas can be supplied sufficiently onto the substrate surface.
The region where the inside-wall temperature of the reaction vessel is controlled to below the thermal decomposition temperature of the dopant ga
Akiyama Shoji
Habuka Hitoshi
Otsuka Toru
Elms Richard
Shin-Etsu Handotai & Co., Ltd.
Snider Ronald R.
Snider & Associates
Wilson Christian D.
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