Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2002-06-14
2004-03-16
Spector, David N. (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S623000, C359S621000
Reexamination Certificate
active
06707614
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stage for specifying a shape of an irradiation surface onto which a laser beam is irradiated. Further, the present invention relates to a laser irradiation apparatus in which energy distribution of a laser beam is made uniform over a certain specific region. The present invention also relates to a method of making an energy distribution uniform, and to an optical system to realize the uniformity. Furthermore, the present invention relates to a method of making the energy distribution of a laser beam uniform over a certain specified region, and to a method of annealing a semiconductor film using the laser beam (the method is hereafter referred to as “laser annealing”). The present invention also relates to a method of manufacturing a semiconductor device, the semiconductor device having circuits structured by thin film transistors (hereafter referred to as “TFTs”), which includes a laser annealing process. For example, electro-optical devices, typically liquid crystal display devices, and an electronic equipment in which such an electro-optical device is mounted as a part, are all included in the category of the semiconductor devices. Namely, the term “semiconductor device” as used throughout the specification indicates general devices capable of functioning by utilizing semiconductor device characteristics, and electro-optical devices, semiconductor circuits, and electronics all fall under the category of semiconductor devices.
2. Description of the Related Art
Techniques for performing crystallization, or for increasing crystallinity, by performing laser annealing of amorphous semiconductor films or crystalline semiconductor films (semiconductor films that are not single crystal, but have crystallinity such as poly-crystallinity or micro-crystallinity), in other words non-single crystal semiconductor films formed on an insulating substrate such as glass have been undergoing widespread research recently. Films such as silicon films are often used as the semiconductor films.
Glass substrate are low cost, and can be easily made into large surface area substrates, compared with conventional quartz substrates, which are often used. This is because the above research is actively performed. Lasers can impart a high energy to only a non-single crystal semiconductor film, without causing much change in the temperature of a substrate, and therefore lasers are suitable for annealing semiconductor films formed on the glass substrates having low melting point temperature (the distortion temperature of generally available glass substrate is on the order of 600° C.).
Crystalline semiconductor films formed by laser annealing have high mobility. The manufacture of TFTs on a single glass substrate, used for driving pixels and used in driver circuits, by using the crystalline semiconductor films is therefore flourishing, along with the manufacture of active matrix liquid crystal electro-optical devices. The crystalline semiconductor films are made from many crystal grains, and therefore they are also referred to as polycrystalline semiconductor films.
In laser annealing, a method in which a laser beam of a pulse oscillation type excimer laser or the like having high output is formed by an optical system so as to have a square shape spot of several cm/square, or a linear shape with a length equal to or greater than 10 cm, on an irradiation surface, and then scanning of the laser beam is performed (the irradiation position of the laser beam is made to move relative to the irradiation surface) is preferably used because it has good productivity and is industrially superior.
In particular, if a linear shape laser beam (hereafter referred to as a linear shape beam) is used, then the laser beam can be irradiated over the entire irradiation surface by scanning only in a direction perpendicular to the longitudinal direction of the linear shape beam. This differs from a case of using a spot shape laser bean, with which it is necessary to scan forward and backward, left and right, and therefore high productivity can be obtained. Scanning in a direction perpendicular to the longitudinal direction is performed because that scanning direction has the best efficiency. Due to their high efficiency, linear shape beams formed by appropriate optical systems are being used mainly in laser annealing processes. Note that, within this specification, the direction of the long side of the linear shape beam is referred to as a longitudinal direction, while the short side is referred to as a transverse direction.
An example of an optical system for forming the shape of a laser beam into a linear shape on an irradiation surface is illustrated. The optical system shown in
FIG. 2
is an extremely general one. The optical system not only converts the shape of the laser beam into a linear shape on the irradiation surface, but at the same time it makes the energy distribution of the laser beam uniform. In general, optical systems for making the beam energy distribution more uniform are referred to as beam homogenizers. The optical system shown in
FIG. 2
is one of beam homogenizers.
Synthetic quartz may be used in all cases, for example, as the base material of the optical light system, provided that an excimer laser to be an ultraviolet light is used as a light source. This is true because a high transmissivity can be obtained. Further, there may be employed a coating material capable of obtaining a transmissivity of 99% or more with respect to the wavelength of the excimer laser used as a coating.
The side view of
FIG. 2
is explained first. A plane containing the light axis and parallel to the page of the side view is taken as a meridional plane, and a plane containing the light axis and perpendicular to the meridional plane is taken as a sagittal plane. The direction of the light axis changes here for cases in which it is necessary to bend the light path by using mirrors or the like due to the layout of the optical system, and it is assumed that the meridional plane and the sagittal plane also change at this time. A laser beam output from a laser oscillator
1201
is divided in a direction perpendicular to the sagittal plane by cylindrical lens arrays
1202
a
and
1202
b
. With this structure, there are four cylindrical lenses contained in the cylindrical lens array
1201
, and therefore four divisions are made. It is assumed that the number of cylindrical lenses contained in the cylindrical lens array
1202
b
is also four. The divided laser beams are made to mutually overlap in a certain plane by a cylindrical lens
1204
. It is not always necessary to use the two cylindrical lens arrays
1202
a
and
1202
b
; one cylindrical lens array may also be used. The advantages of using two cylindrical lens arrays are that the size of the linear shape beam can be changed, and that the width of the linear shape beam in the transverse direction can be made shorter.
The once again divided laser beams are bent at a right angle by a mirror
1207
, and then made to once again overlap on an irradiation surface
1209
by using a doublet cylindrical lens
1208
. The doublet cylindrical lens designates a lens structured by two cylindrical lenses. Uniformity of the energy distribution is thus formed in the transverse direction of the linear shape beam, and the width in the transverse direction of the linear shape beam is determined. The mirror
1207
is used in order to make the irradiation surface into a level surface, and is not always necessary.
The upper view of
FIG. 2
is explained next. The laser beam emitted from the laser oscillator
1201
is divided in a direction perpendicular to the meridional plane by the cylindrical lens array
1203
. There are seven lenses contained in the cylindrical lens array
1203
with this structure, and therefore the laser beam is divided into seven divisions. Two cylindrical lens arrays
1203
may also be used in order to change the length of the linear shape beam in the longitudinal direction. The laser bea
Costellia Jeffrey L.
Nixon & Peabody LLP
Semiconductor Energy Laboratory Co,. Ltd.
Spector David N.
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