Coherent light generators – Particular beam control device
Reexamination Certificate
2000-08-14
2003-05-13
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
C372S025000, C372S072000, C359S325000, C359S326000, C359S623000
Reexamination Certificate
active
06563843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for manufacturing a semiconductor device having a circuit constituted by a thin film and, or example, to a device for manufacturing an electro-optical device typified by a liquid display device and an electric device having the electro-optical device as a part. In this connection, in the present specification, a semiconductor device designates in general a device capable of functioning by the use of semiconductor characteristics and includes the above electro-optical device and electric device.
2. Description of the Related Art
In recent years, research and development have been widely conducted on the technologies for performing a laser annealing processing to an amorphous semiconductor film or a crystalline semiconductor film (semiconductor film which is not a single crystal but a polycrystal or a micro-crystal), that is, non-single crystal semiconductor film formed on an insulating substrate such as a glass substrate or the like to crystallize the non-single crystal semiconductor film or to improve its crystallinity. A silicon film is often used as the above semiconductor film.
A glass substrate has advantages that it is cheap and has good workability and is easy to make a large area substrate in comparison with a quartz substrate which has been conventionally used. This is because the above research and development have been carried out. Also, it is because the melting point of the glass substrate is low that a laser is widely used for crystallizing the semiconductor film. The laser can apply high energy only to a non-single crystal film without increasing the temperature of the substrate too much.
The crystalline silicon film is called a polycrystalline silicon film or a polycrystalline semiconductor film because it is made of many crystal grains. Since the crystalline silicon film subjected to a laser annealing processing has high mobility, a thin film transistor (hereinafter referred to as TFT) is formed by the use of the crystalline silicon film and, for example, is widely used for a monolithic liquid crystal electro-optical device having a glass substrate and TFTs for driving a pixel and for a driving circuit.
Also, a laser annealing method of transforming the high-power laser beam of a pulse oscillation such as an excimer laser into a square spot several cm square or a linear beam 10 cm or more in length at an irradiate surface by the use of an optical system and of scanning a semiconductor film with the laser beam (or moving a spot irradiated with the laser beam relatively to an irradiate surface) has been widely used because it increases mass productivity and is excellent in an industrial view point.
In particular, when a linear laser beam is used, the whole irradiate surface is irradiated with the linear laser beam only by scanning the irradiate surface in the direction perpendicular to the direction of the line of the linear laser beam, which therefore produces high mass productivity. In contrast to this, when a spot-like laser beam is used, the irradiate surface needs to be scanned with the laser beam in the back-and-forth direction and in the right-and-left direction. The irradiate surface is scanned with the linear laser beam in the direction perpendicular to the direction of the line of the linear laser beam because the direction is the most efficient scanning direction. The method of using the linear laser beam into which the laser beam emitted from the excimer laser of pulse oscillation is transformed by the use of a suitable optical system for the laser annealing processing has become a mainstream technology.
In
FIG. 1
is shown an example of the constitution of an optical system for transforming the cross section of the laser beam into a linear shape at an irradiate surface. This constitution is extremely ordinary and all the above optical systems are similar to FIG.
1
. This constitution not only transforms the cross section of the laser beam into the linear shape but also homogenizes the energy of the laser beam at the irradiate surface. In general, an optical system homogenizing the energy of the beam is called a beam homogenizer.
In the case where an excimer laser which is ultraviolet radiation is used as a light source, it is recommended that the base material of the above optical system be quartz because the quartz can produce a high transmittance. Also, it is recommended to use a coating capable of producing a transmittance of 99% or more to the wavelength of the excimer laser.
First, a side view in
FIG. 1
will be described. A laser beam emitted by a laser oscillator
101
is divided into the direction orthogonal to the direction of travel of the laser beam by cylindrical lens arrays
102
a
and
102
b.
The applicable direction is called a vertical direction in the present specification. When a mirror is arranged in the middle of the optical system, the above vertical direction is bent in the direction of the light bent by the mirror. In this constitution, the laser beam is divided into four portions. These divided laser beams are once unified to one laser beam by a cylindrical lens
104
. The unified laser beam is reflected by a mirror
107
and then is again focused on one laser beam at an irradiate surface
109
by a doublet cylindrical lens
108
. The doublet cylindrical lens means the one constituted by two cylindrical lenses. The doublet lens homogenizes the energy in the width direction of the linear laser beam and determines a length in the width direction of the laser beam.
Next, a top view will be described. The laser beam emitted by the laser oscillator
101
is divided by cylindrical lens arrays
103
into the direction orthogonal to the direction of travel of the laser beam and in the direction orthogonal to the vertical direction. The applicable direction is called a lateral direction in the present specification. When a mirror is arranged in the middle of the optical system, the above lateral direction is bent in the direction of the light bent by the mirror. In this constitution, the laser beam is divided into seven portions. These divided laser beams are once converged on one laser beam at the irradiate surface
109
by the cylindrical lens
105
. This homogenizes the energy in the length direction of the linear laser beam and determines the length of the linear laser beam.
The above lenses are made of synthetic quartz to respond to the excimer laser. Also, their surfaces are coated such that they well transmit the excimer laser, whereby the transmittance of one lens to the excimer laser is made 99% or more.
The linear laser beam transformed by the above constitution is applied to the non-single crystal silicon film while it is gradually shifted and superposed in the direction of the width of the linear laser beam to subject the whole surface of the non-single crystal silicon film to laser annealing to thereby crystallize the non-single crystal silicon film or to improve the crystallinity thereof.
Next, a typical method of forming a semiconductor film to be irradiated with the laser beam will be described.
First, a Corning 1737 substrate 0.7 mm thick and 5 inch square was prepared as a substrate. A SiO
2
film (silicon oxide film) having a thickness of 200 nm was formed on the substrate with a plasma CVD device and the amorphous silicon film (hereinafter referred to as “a-Si film”) having a thickness of 50 nm was formed on the surface of the SiO
2
film.
The substrate was heated at 500° C. in a nitrogen atmosphere for 1 hour to reduce the concentration of hydrogen in the film, whereby the resistance to laser of the film was remarkably improved.
A XeCl excimer laser L3308 (wavelength=308 nm, pulse width=30 ns) made by Ramda Corp. was used as a laser device. The laser device generates a pulse oscillation laser and has a capacity producing an energy of 500 mJ/pulse. The size of the laser beam is 10-30 mm (both in full width at half maximum) at the exit of the laser beam. The exit of the laser beam is defined, in the pres
Nguyen Tuan M
Robinson Eric J.
Robinson Intellectual Property Law Office P.C.
Semiconductor Energy Laboratory Co,. Ltd.
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