Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
1998-11-20
2001-03-20
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S406000, C438S458000
Reexamination Certificate
active
06204101
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device represented by a thin-film transistor. More particularly, the present invention relates to a method of manufacturing a semiconductor device using a silicon thin film having crystallinity which is formed on a glass substrate or a quartz substrate.
2. Description of the Related Art
Up to now, there have been known thin-film transistors using a silicon film. The thin-film transistor is structured using a silicon film (several hundreds to several thousands Å in thickness) formed on a glass substrate or a quartz substrate.
The reason why the glass substrate or the quartz substrate is used is to employ the thin-film transistor for an active matrix liquid-crystal display unit.
Under existing circumstances, in the case of using the glass substrate, a general technique is that the thin-film transistor is formed using the amorphous silicon film. In the case of using the quartz substrate, a technique in which the crystalline silicon film obtained through a heat treatment is used has been put to practical use.
Compared with the thin-film transistor using the amorphous silicon film, the thin-film transistor using a crystalline silicon film enables high-speed operation of two digits or more to be performed. Hence, a peripheral drive circuit of the active matrix liquid-crystal display unit, which has been conventionally made up of an IC circuit externally attached hereto can be formed of a thin-film transistor on the glass substrate or the quartz substrate.
The above structure is very advantageous in the downsizing of the overall device or simplification of a manufacturing process. Also, the structure leads to reduction of the manufacturing costs.
As a technique by which a crystalline silicon film is obtained through a heating treatment, there has been known a technique disclosed in Japanese Patent Unexamined Publication No. Hei 6-232069. According to the technique, a metal element (for example, nickel) that promotes the crystallization of silicon is introduced into an amorphous silicon film so that the crystalline silicon film is obtained through a heat treatment at a lower temperature than a conventional one.
Using that technique, an inexpensive glass substrate as can be used as a substrate, and the crystalline silicon film as obtained can provide crystallinity which can be practically used over a wide area.
However, because the metal element is contained in the film and the control of its introduced amount is subtle, it is proved that there arise problems on the reproducibility and the stability (electric stability of the obtained device).
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to provide a technique by which the concentration of metal elements in a crystalline silicon film obtained by using metal elements that promote the crystallization of silicon is lowered.
In order to solve the above problem, according to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: intentionally introducing metal elements that promote crystallization of silicon in an amorphous silicon film to crystalize said amorphous silicon film through a first heat treatment; and conducting a second heat treatment in an atmosphere containing halogen elements therein to intentionally remove said metal elements; wherein said first heat treatment and said second heat treatment are conducted by identical heating means.
In the above method, it is important that the first heat treatment and the second heat treatment are conducted by the identical heating means. This is because in the case where the first heat treatment for diffusing the metal elements in the silicon film to conduct crystallization and the second heat treatment for removing the metal elements diffused in the silicon film are conducted through an identical method, the removal of the metal elements is carried out more effectively.
For example, in the case of using nickel as the metal elements, conducting the first heat treatment through a heating by a heater, and conducting the second heat treatment through heating by an infrared ray lamp (RTA: rapid thermal annealing), it is proved that the effect of removing nickel from the silicon film is lower than that in the case of using the heater in both of the heating methods.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: holding metal elements that promote crystallization of silicon in contact with a front surface or a rear surface of an amorphous silicon film; conducting a first heat treatment on said amorphous silicon film to crystallize at least a part of said amorphous silicon film; and conducting a second heat treatment in an atmosphere containing halogen elements on the silicon film to intentionally remove said metal elements, wherein the first heat treatment and the second heat treatment are conducted by the identical heating means.
As metal elements that promote crystallization of silicon, there can be used one kind or a plurality of kinds selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au.
In particular, the use of Ni (nickel) is most preferable from the viewpoint of its effect and reproducibility.
As an atmosphere containing halogen elements therein, there can be used one kind of gas or a plurality of kinds of gases selected from HCl, HF, HBr, Cl
2
, F
2
and Br
2
being added to the atmosphere containing one kind of gas or a plurality of gases selected from Ar, N
2
, He and Ne. In this example, halogen elements function to remove the metal elements.
Also, as an atmosphere containing halogen elements therein, there can be used oxygen and one kind of gas or a plurality of kinds of gases selected from HCl, HF, HBr, Cl
2
, F
2
and Br
2
being added to the atmosphere containing one kind of gas or a plurality of gases selected from Ar, N
2
, He and Ne.
Oxygen has a function to suppress the surface of the silicon film from being roughened by action of halogen elements since oxygen forms the oxide film on the surface of the silicon film simultaneously during the process of removing the metal elements.
The heat treatment for removing the metal elements can be conducted at a temperature of 450 to 1050° C.
With intentional introduction of the metal elements represented by nickel, the amorphous silicon film is crystallized through the first heat treatment. Then, the second heat treatment is conducted in the atmosphere containing halogen elements, to thereby remove the metal elements intentionally introduced from the film. In this situation, the first heat treatment and the second heat treatment may be conducted by the identical means.
The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.
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Koyama Jun
Miyanaga Akiharu
Teramoto Satoshi
Yamazaki Shunpei
Elms Richard
Fish & Richardson P.C.
Lebentritt Michael S.
Semiconductor Energy Laboratory Co,. Ltd.
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