Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2000-10-13
2002-04-16
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S066000, C257S350000, C257S351000, C257S627000
Reexamination Certificate
active
06373075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique by which a crystalline silicon film having a monocrystal-like region or a substantially monocrystal-like region is formed on a substrate having an insulating surface made of glass or the like. Also, the present invention relates to a technique by which a thin-film semiconductor device represented by a thin-film transistor is formed by using the crystalline silicon film.
2. Description of the Related Art
In the recent years, attention has been directed to a technique by which a thin-film transistor is constituted by using a thin-film silicon semiconductor film (a thickness of about several hundred to several thousand Å) which is formed on a substrate having a glass substrate or an insulating surface. What the thin-film transistor is applied to with the most expectancy is an active matrix type liquid-crystal display unit.
The active matrix type liquid-crystal display unit is structured such that liquid crystal is interposed between a pair of glass substrates and held therebetween. Also, it is structured such that a thin-film transistor is disposed on each of pixel electrodes which are arranged in the form of a matrix of several hundred x several hundred. Such structures require a technique by which the thin-film transistor is formed on a class substrate.
In the formation of the thin-film transistor on the glass substrate. it is necessary to form a thin-film semiconductor constituting thethin-film transistor on the glass substrate. For the thin-film semiconductor formed on the glass substrate, an amorphous silicon film formed through the plasma CVD technique or the low pressure thermal CVD technique is generally utilized.
Under existing circumstances, the thin-film transistor using the amorphous silicon film is practically used. However, in order to obtain display with a higher image quality, there is demanded a thin-film transistor utilizing a silicon semiconductor thin film (called “a crystalline silicon film”) with a crystalline property.
Techniques disclosed in Japanese Patent Unexamined Publication No. 6-232059 and Japanese Patent Unexamined Publication No. 6-244103 made by the present applicant have been well known as a method of forming the crystalline silicon film on the glass substrate. The techniques disclosed in those publications are that a crystalline silicon film is formed on a glass substrate through a heat treatment under a heating condition which can be withstood by the class substrate, that is, approximately at 550° C. for 4 hours, by utilizing a metal element that promotes the crystallization of silicon.
However, the crystalline silicon film obtained by the method using the above-mentioned techniques is not available to a thin-film transistor that constitutes a variety of arithmetic operating circuits. memory circuits or the like. This is because its crystalline property is insufficient and a characteristic as required is not obtained.
As the peripheral circuits of the active matrix type liquid-crystal display unit or the passive type liquid-crystal display unit, there are required a drive circuit for driving a thin-film transistor disposed in a pixel region, a circuit for dealing with or controlling a video signal, a memory circuit for storing a variety of information etc.
Of those circuits, the circuit for dealing with or controlling a signal and the memory circuit for storing a variety of information are required to provide a performance equal to that of an integrated circuit using a known monocrystal wafer. Hence, when those circuits are to be integrated using the thin-film semiconductor formed on the glass substrate, the crystalline silicon film having the crystalline property equal to that of monocrystal must be formed on the class substrate
As a method of enhancing the crystalline property of the crystalline silicon film, there have been proposed that the obtained crystalline silicon film is subjected to a re-heating treatment or to the irradiation of a laser beam. However, it has been proved that, even though the heat treatment or the irradiation of a laser beam is repeatedly conducted, it is difficult to dramatically improve the crystalline property.
Also, a technique in which a monocrystal silicon thin film is obtained by using the SOI technique has now been researched. However, since the monocrystal silicon substrate cannot be utilized for the liquid-crystal display unit, the above technique cannot be applied directly to the liquid-crystal display unit. In particular, in the case of using a monocrystal wafer, it is difficult to apply the SOI technique to the liquid-crystal display unit having a large area a demand of which is expected to increase in the future because of a limited substrate area.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems, and theretore an object of the present invention is to provide a technique in which a monocrystal or monocrystal-like region is formed on a substrate having an insulating surface, in particular, on a glass substrate, and a thin-film semiconductor device represented by a thin-film transistor is formed by using that region.
In order to solve the above-mentioned problems, according to one aspect of the present invention, there is provided a method of manufacturing a semiconductor, comprising the steps of:
forming a first semiconductor film on a substrate having an insulating surface;
applying an energy to said first semiconductor film to crystallize said first semiconductor film;
patterning said first semiconductor film to form a region that forms a seed crystal;
etching said seed crystal to selectively leave a predetermined crystal surface in said seed crystal;
covering said seed crystal to form a second semiconductor film; and
applying an energy to said second semiconductor film to conduct a crystal growth from said seed crystal in said second semiconductor film.
In the above-mentioned structure, a silicon film is typically used for the first and second semiconductor films. Also, in general, an amorphous silicon film formed through the CVD technique is used for the silicon film.
The reason why the predetermined crystal surface is selectively left is to conduct the crystal growth so as to produce crystal more approximating monocrystal. Leaving the predetermined crystal surface may be achieved by using etching means having a selectivity with respect to the predetermined crystal surface. For example, using an etchant resulting from mixing H
2
O of 63.3 wt %. KOH of 23.4 wt % and isopropanol of 13.3 wt % together, a (100) tace can be selectively left, as a result of which the seed crystal covered with the (100) face can be selectively left.
Also, a (111) face can be selectively left by etching in a gas phase using hydrazine (N
2
H
4
). Specifically, the (111) face can be left by dry etching using CIF
3
and N
2
H
4
as an etching gas.
Further, as a method of applying the energy in the above-mentioned structure, one or plural kinds of methods selected from a heating method, a laser beam irradiation method and an intense light beam irradiation method can be used simultaneously or gradually. For example, a laser beam can be irradiated while heating, a laser beam can be irradiated after heating, heating and the irradiation of a laser beam can be alternately conducted, or heating can be conducted after the irradiation of a laser beam. Also, the laser beam may be replaced by an intense light beam.
In the case where the silicon film is used as a semiconductor film, and an energy is applied to the film to crystallize the silicon film, it is useful to use a metal element that promotes the crystallization of silicon. For example, when an amorphous silicon film formed by the plasma CVD technique or the low pressure thermal CVD technique is to be crystallized by heating, a heat treatment at a temperature of 600° C. or higher for 10 hours or longer is required. However, in the case of using a metal element that promotes the crystallization of silicon, the effect equal to or more th
Miyanaga Akiharu
Teramoto Satoshi
Yamazaki Shunpei
Semiconductor Energy Laboratory Co,. Ltd.
Tran Minh Loan
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