Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Amorphous semiconductor
Reexamination Certificate
2000-12-21
2003-06-03
Cuneo, Kamand (Department: 2829)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Amorphous semiconductor
Reexamination Certificate
active
06573162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for manufacturing a semiconductor device having a circuit structured with a thin film transistor. For example, the invention relates to an apparatus for manufacturing an electro-optical device, typically a liquid crystal display device, and the structure of electric equipment mounted with such an electro-optical device as a component. The present invention also relates to a method of fabricating the apparatus. Note that throughout this specification, the semiconductor device indicates general devices that may function by use of semiconductor characteristics, and that the above electro-optical device and electric equipment are categorized as the semiconductor device.
2. Description of the Related Art
In recent years, the technique of crystallizing and improving the crystallinity of a semiconductor film formed on an insulating substrate such as a glass substrate by laser annealing, has been widely researched. Silicon is often used as the above semiconductor film.
Comparing a glass substrate with a quartz substrate, which is often used conventionally, the glass substrate has advantages of low-cost and great workability, and can be easily formed into a large surface area substrate. This is why the above research is performed. Also, the reason for preferably using laser annealing for crystallization resides in that the melting point of a glass substrate is low. Laser annealing is capable of imparting high energy only to the semiconductor film without causing much change in the temperature of the substrate.
The crystalline semiconductor film is formed from many crystal grains. Therefore, it is called a polycrystalline semiconductor film. A crystalline semiconductor film formed by laser annealing has high mobility. Accordingly, it is actively used in, for example monolithic type liquid crystal electro-optical devices where thin film transistors (TFTs) are formed using this crystalline semiconductor film and fabricate TFTs for driving pixels and driver circuits formed on one glass substrate.
Furthermore, a method of performing laser annealing is one in which a pulse laser beam emitted from a excimer laser or the like, is processed by an optical system so that the laser beam thereof becomes a linear shape that is 10 cm long or greater or a square spot that is several cm square at an irradiated surface to thereby scan the laser beam (or relatively move the irradiation position of the laser beam to the irradiated surface). Because this method is high in productivity and industrially excellent, it is being preferably employed.
Different from when using a spot shape laser beam which requires a front, back, left, and right scan on an irradiated surface, when using the linear beam, the entire irradiated surface can be irradiated by the linear beam which requires only scanning at a right angle direction to the linear direction of the linear beam, resulting in the attainment of a high productivity. To scan in a direction at a right angle to the linear direction is the most effective scanning direction. Because a high productivity can be obtained, using the linear beam which is linear in the irradiated surface that is emitted from the pulse oscillation type excimer laser and processing it into a linear beam by an appropriate optical system for laser annealing at present is becoming mainstream.
Shown in
FIG. 1
is an example of the structure of an optical system for linearizing the shape of a laser beam on the irradiated surface. This structure is a very general one and all aforementioned optical systems conform to the structure of the optical system shown in FIG.
1
. This structure of the optical system not only transforms the shape of the laser beam in the irradiated surface into a linear shape, but also homogenizes the energy of the laser beam in the irradiated surface at the same time. Generally, an optical system that homogenizes the energy of a beam is referred to as a beam homogenizer.
If the excimer laser, which is ultraviolet light, is used as the light source, then the core of the above-mentioned optical system may be preferably made of, for example, entirely quartz. The reason for using quartz resides in that a high transmittance can be obtained. Further, it is preferable to use a coating in which a 99% or more transmittance can be obtained with respect to a wavelength of the excimer laser that is used.
The side view of
FIG. 1
will be explained first. Laser beam emitted from a laser oscillator
101
is split at a right angle direction to the advancing direction of the laser beam by cylindrical lens arrays
102
a
and
102
b.
The direction is referred to as a longitudinal direction throughout the present specification. When a mirror is placed along the optical system, the laser beams in the longitudinal direction will curve in the direction of light curved by the mirror. These laser beams in this structure are split into 4 beams. The split laser beams are then converged into 1 beam by a cylindrical lens
104
. Then, the converged laser beam are split again and reflected at a mirror
107
. Thereafter, the split laser beams are again converged into 1 laser beam at an irradiated surface
109
by a doublet cylindrical lens
108
. A doublet cylindrical lens is a lens that is constructed of 2 pieces of cylindrical lenses. Thus, the energy in the width direction of the linear laser beam is homogenized and the length of the width direction of the linear beam is also determined.
The top view of
FIG. 1
will be explained next. Laser beam emitted from the laser oscillator
101
is split at a right angle direction to the advancing direction of the laser beam and at a right angle direction to the longitudinal direction by a cylindrical lens array
103
. The right angle direction is called a vertical direction throughout the present specification. When a mirror is placed along the optical system, the laser beams in the vertical direction will curve in the direction of light curved by the mirror. The laser beams in this structure is split into 7 beams. Thereafter, the split laser beams are converged into 1 beam at the irradiated surface
109
by the cylindrical lens
108
. Thus, homogenization of the energy in the longitudinal direction of the linear beam is made and the length of the longitudinal direction is also determined.
The above lenses are made of synthetic quartz for correspondence to excimer laser. Furthermore, coating is implemented on the surfaces of the lenses so that the excimer laser will be well transmitted. Therefore, the transmittance of excimer laser through each lens is 99% or more.
By irradiating the linear beam linearized by the above structure of the optical system in an overlapping manner with a gradual shift in the width direction thereof, laser annealing is implemented to the entire surface of a semiconductor film to thereby crystallize the semiconductor film and thus its crystallinity can be enhanced.
A typical method of manufacturing a semiconductor film that is to become the object to be irradiated is shown next. First, for example, a 5 inch square Corning 1737 substrate having a thickness of 0.7 mm is prepared as the substrate. Then a 200 nm-thick SiO
2
film (silicon oxide film) is formed on the substrate and a 50 nm-thick amorphous silicon film is formed on the surface of the SiO
2
film. The substrate is exposed under an atmosphere containing nitrogen gas at a temperature of 500° C. for 1 hour to thereby reduce the hydrogen concentration in the film. Accordingly, the laser resistance in the film is remarkably improved.
The XeCl excimer laser L3308 (wavelength: 308 nm, pulse width: 30 ns) manufactured by Lambda Co. is used as the laser apparatus. This laser apparatus generates a pulse oscillation laser and has the ability to output an energy of 500 mJ/pulse. The size of the laser beam at the exit of the laser beam is 10×30 mm (both half-width). Throughout the present specification, the exit of the laser beam is defined as the perpendicular plane in the advan
Nakaya Tomoko
Tanaka Koichiro
Cuneo Kamand
Robinson Eric J.
Robinson Intellectual Property Law Office P.C.
Sarkar Asok Kumar
Semiconductor Energy Laboratory Co,. Ltd.
LandOfFree
Laser irradiation apparatus and method of fabricating a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laser irradiation apparatus and method of fabricating a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser irradiation apparatus and method of fabricating a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3103861