Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2000-08-10
2003-05-20
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S619000
Reexamination Certificate
active
06567219
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. For example, the present invention relates to a device for manufacturing an electrooptical device typified by a liquid display device and the constitution of an electric device having. the electrooptical 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 electrooptical 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 electrooptical device having a glass substrate on which TFTs for driving a pixel and for a driving circuit are formed.
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 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.
The side view is explained first. A laser beam leaving from a laser oscillator
101
is partitioned in a direction perpendicular to the movement direction of the laser beam by cylindrical array lenses
102
a
and
102
b
. This direction is referred to as a vertical direction throughout this specification. There are four partitions with this structure. The partitioned laser beams are once collected into a single laser beam by a cylindrical lens
104
. This is then reflected by a mirror
107
, and once again condensed into one laser beam on an irradiation surface
109
by a doublet cylindrical lens
108
. The doublet cylindrical lens refers to a lens composed of two cylindrical lenses. The linear laser beam is thus given energy uniformity in the width direction, and the length of the width direction is thus determined.
The top view is explained next. The laser beam leaving from the laser oscillator
101
is partitioned in a direction perpendicular to the movement direction of the laser beam, and perpendicular to the vertical direction, by a cylindrical array lens
103
. This direction is referred to as a horizontal direction throughout this specification. There are seven partitions with this structure. The laser beams are next made into a single beam on the irradiation surface
109
by the cylindrical lens
104
. The linear laser beam is thus given energy uniformity in the longitudinal direction, and the length is thus determined.
The above lenses are manufactured by synthetic quartz in order to respond to the excimer laser. Further, coating of the lens surface is performed so as to make it very transmissive to the excimer laser. The transmissivity of the excimer laser by one lens thus becomes equal to or greater than 99%.
By performing laser annealing on the entire surface of a non-single crystal silicon film by irradiating the linear laser beam, processed by the above constitution, while gradually shifting it in the width direction, crystallization can be performed and crystallinity can be increased.
A model method of manufacturing a semiconductor film which becomes an irradiation object is shown next. First, a 5 inch diagonal Corning 1737 substrate having a thickness of 0.7 mm is prepared. A SiO
2
film (silicon oxide film) of 200 nm thickness is deposited on the substrate by using a plasma CVD apparatus, and an amorphous silicon film (hereafter referred to as an a-Si film) of 50 nm thickness is formed on the surface of the SiO
2
film.
The substrate is heated for 1 hour at a temperature of 500° C. in a nitrogen atmosphere, decreasing the hydrogen concentration within the films. The laser resistance of the film is thus significantly increased.
A Lambda Corp. XeCl excimer laser (wavelength 308 nm, pulse width 30 nm) L3308 is used as a laser apparatus. The laser apparatus is a pulse emission type, and possesses the capability of delivering energy of 500 mJ/pulse. The size. of the laser beam is 10×30 mm (both values are half-widths) at the exit of the beam. The shape of a laser beam generated by an excimer laser is generally a rectangular shape, and expressed as an aspect ratio, is in the range of approximately 3 to 5. The strength of the laser beam shows a Gaussian distribution, in which its strength increases as it approaches the center. The size of the laser beam is transformed into a 125 mm×0.4 mm linear laser beam having a uniform energy distribution by an optical system possessing the structure shown in FIG.
1
.
According to experiments performed by the applicant of the present invention, when the laser is irradiated on the above semiconductor film, the overlap pitch is most suitable at approximately {fraction (1/10)} of the width (half width) of the linear laser beam. The uniformity of crystallinity within the film is thus increased. In the above example, the half width is 0.4 mm, and therefore the pulse frequency of the excimer laser is set to 30 h
Costellia Jeffrey L.
Hindi Omar
Nixon & Peabody LLP
Semiconductor Energy Laboratory Co,. Ltd.
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