Electric heating – Metal heating – By arc
Reexamination Certificate
2002-10-25
2004-03-02
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
Reexamination Certificate
active
06700096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser processing apparatus and a laser irradiation method for crystallizing a semiconductor substrate, a semiconductor film or the like using a laser light or for performing activation after ion implantation, a semiconductor device formed by using the laser apparatus and a manufacturing method thereof, an electronic equipment using the semiconductor device, and a production system of the semiconductor device using the laser apparatus.
2. Description of the Related Art
In recent years, a technique of forming a TFT over a substrate has greatly progressed, and its application and development for active matrix semiconductor display device has been advanced. In particular, since a TFT using a polysilicon film has higher field-effect mobility than a TFT using a conventional amorphous silicon film, it enables high speed operation. Therefore, although the pixel is conventionally controlled on a driving circuit provided outside the substrate, it is possible to control the pixel on the driving circuit formed over the same substrate.
Incidentally, as the substrate used in the semiconductor device, a glass substrate is regarded as important in comparison with a single crystal silicon substrate in terms of the cost. Since a glass substrate is inferior in heat resistance and is susceptible to heat-deformation, in the case where a polysilicon TFT is formed on the glass substrate, laser annealing is used for crystallization of the semiconductor film in order to avoid heat-deformation of the glass substrate.
Characteristics of laser annealing are as follows: it can greatly reduce a processing time in comparison with an annealing method using radiation heating or conductive heating; and it hardly causes thermal damage to the substrate by selectively and locally heating a semiconductor or the semiconductor film.
Note that the laser annealing method here indicates a technique of recrystallizing the damaged layer formed over the semiconductor substrate or the semiconductor film, and a technique of crystallizing the amorphous semiconductor film formed on the substrate. Also, the laser annealing method here includes a technique applied to leveling or surface reforming of the semiconductor substrate or the semiconductor film. A laser oscillation apparatus applied is a gas laser oscillation apparatus represented by an excimer laser or a solid laser oscillation apparatus represented by a YAG laser. It is known as the apparatus which performs crystallization by heating a surface layer of the semiconductor by irradiation of the laser light in an extremely short period of time of about several ten nanoseconds to several hundred microseconds.
Lasers are roughly divided into two types: pulse oscillation and continuous oscillation, according to an oscillation method. In the pulse oscillation laser, an output energy is relatively high, so that mass productivity can be increased assuming the size of a beam spot to be several cm
2
or more. In particular, when the shape of the beam spot is processed using an optical system and made to be a linear shape of 10 cm or more in length, it is possible to efficiently perform irradiation of the laser light to the substrate and further enhance the mass productivity. Therefore, for crystallization of the semiconductor film, the use of a pulse oscillation laser is becoming mainstream.
However, in recent years, in crystallization of the semiconductor film, it is found that grain size of the crystal formed in the semiconductor film is larger in the case where the continuous oscillation laser is used than the case where the pulse oscillation laser is used. When the crystal grain size in the semiconductor film becomes large, the mobility of the TFT formed using the semiconductor film becomes high and variation of the TFT characteristics due to a grain boundary is suppressed. Therefore, a continuous oscillation laser is recently attracting attention.
However, since the maximum output energy of the continuous oscillation laser is generally small in comparison with that of the pulse oscillation laser, the size of the beam spot is small, which is about 10
−3
mm
2
. Accordingly, in order to treat one large substrate, it is necessary to move a beam irradiation position on the substrate upward and downward, and right and left, it results in increasing the processing time per one substrate. Thus, processing efficiency is poor and it is an important object to improve the processing speed of the substrate.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems, and therefore it is an object of the present invention to provide a continuous oscillation laser apparatus, a laser irradiation method, and a method of manufacturing a semiconductor device using the continuous oscillation laser apparatus, which can enhance a processing efficiency in comparison with the conventional example.
The laser apparatus of the present invention includes: a first means for controlling an irradiation position of each laser light on an object to be processed; a plurality of second means (laser oscillation apparatuses) for oscillating laser lights; a third means (optical system) for having beam spots of the laser lights oscillated from the plurality of laser oscillation apparatuses partially overlap each other on the object to be processed; and a fourth means for controlling the oscillation by each of the plurality of second means and also controlling the first means so that the beam spots of the laser lights cover a position determined in accordance with data (pattern information) concerning a shape of a mask.
It should be noted here that the position determined in accordance with the mask data means a portion of a semiconductor film to be obtained by performing patterning after crystallization. With the present invention, in accordance with the mask, the fourth means grasps a portion of the semiconductor film formed on an insulating surface that should be left on a substrate after the patterning. In addition, a portion to be scanned with the laser lights is determined so that at least the portion to be obtained by performing the patterning is crystallized, and the first means is controlled so that the beam spots strike the portion to be scanned. In this manner, the semiconductor film is partially crystallized. That is, with the present invention, the laser lights are not scanned and irradiated onto the entire surface of the semiconductor film but are scanned so that at least an indispensable portion is crystallized. With the construction described above, it becomes possible to save a time taken to irradiate the laser lights onto a portion to be removed through the patterning after the crystallization of the semiconductor film.
With the present invention, in order to realize the construction described above, after the formation of the semiconductor film, prior to the crystallization using the laser lights, a marker is given to the semiconductor film using a laser light. Then, a position, at which the laser lights should be scanned, is determined based on a mask with reference to the position of the marker.
With the construction described above, it becomes possible to shorten a time taken to irradiate the laser lights and also to improve a speed at which a substrate is processed.
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paten
Akiba Mai
Hiroki Masaaki
Ohtani Hisashi
Shiga Aiko
Tanaka Koichiro
Costelia Jeffrey L.
Heinrich Samuel M.
Nixon & Peabody LLP
Semiconductor Energy Laboratory Co,. Ltd.
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