Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
1998-12-22
2001-06-19
Le, Vu A. (Department: 2824)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S150000, C438S151000, C438S166000, C438S487000
Reexamination Certificate
active
06248606
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor chips for display, and more particularly to a method of thermally treating a semiconductor thin film with laser irradiation.
2. Description of Related Art
Liquid crystal display devices which are designed in a large size and with high minuteness and in which polycrystal silicon thin film transistors are used as switching elements have been developed with much hope. In order to mass-produce liquid crystal displays with polycrystal silicon thin film transistors in a large size and with high minuteness, it is indispensable to establish a low-temperature process in which low-price glass substrates are usable. A technique that a laser beam is irradiated onto a semiconductor thin film of amorphous silicon or the like to form high-quality polycrystal silicon on a glass substrate having a low melting point has been greatly expected as a method to perform the low-temperature process.
FIG. 1
is a schematic diagram showing a previous paper suggested laser beam irradiation method. A semiconductor chip
101
for display which is a target to be processed has such a laminating structure that a semiconductor thin film
103
is formed on a transparent insulating substrate
102
. In this method, a laser beam
105
is irradiated onto a predetermined sectioned area
104
which is provided on the semiconductor thin film
103
. In the conventional method, the output power of the laser beam is limited to a small level, and thus the maximum area which can be irradiated with one-shot laser irradiation of laser is limited to a narrow area about 100 &mgr;m
2
. Accordingly, when a semiconductor thin film
103
having a large area is required to be processed to satisfy a requirement for a large-scale picture, the laser beam is irradiated onto the whole semiconductor thin film while scanning the laser beam
105
or shifting the laser-irradiation area stepwisely. That is, it has been hitherto considered important to increase the energy density of the laser beam rather than to narrow the laser-irradiation area down. With increase of the energy density, a semiconductor thin film of amorphous silicon or polycrystal silicon having relatively small grain size is perfectly melted to increase its grain size. In this method, however, an irradiation time per chip increases and thus manufacturing throughput is reduced. Furthermore, the scanning of the irradiation of the laser beam causes temperature difference to occur locally, and thus causes increase in variability of crystal grain size. Therefore, wide variations occur in electrical characteristics of the thin film transistors such as mobility, a threshold voltage, etc.
The above point will be described in detail with reference to FIG.
2
.
In the method as described above, the semiconductor thin film
103
having a large area is crystallized by irradiating a laser beam onto a small area while scanning the laser beam as shown in FIG.
2
. Accordingly, non-uniformity of crystallization occurs at an overlap area
106
between a laser shot and a next laser shot, so that the electrical characteristics of thin film transistors formed at the overlap area
106
are uneven. For example, the overlap area
106
is subjected to the laser irradiation several times, whereas the other areas are subjected to the laser irradiation only once, so that the heating temperature for the semiconductor thin film is also locally uneven.
In addition to the method as described above, various laser irradiation systems have been hitherto proposed. For example, in a method of manufacturing a semiconductor device as disclosed in Japanese Laid-open Patent Application No. Sho-60-245124, a laser pulse having wavelength of 150 nm to 350 nm is irradiated at an energy density of 200 to 500 mJ/cm
2
to promote crystallization of a semiconductor thin film. In this system, an amorphous area and a crystal area coexist on a substrate, and thin film transistors are integrated over the two areas. Accordingly, the electrical characteristics of the thin film transistors vary between both the amorphous area and the crystal area, and thus controllability is lost.
Furthermore, in a method of manufacturing a semiconductor memory as disclosed in Japanese Laid-open Patent Application No. Hei-3-273621, a laser annealing treatment is performed on a memory-cell basis (microarea in several tens &mgr;m order), and non-irradiated areas remain in between memory cells. Therefore, it is impossible to irradiate a laser beam onto a large-scale circuit at the same time.
Still furthermore, in a method of manufacturing a liquid crystal display device as disclosed in Japanese Laid-open Patent Application No. Hei-5-66422, for crystallization of a semiconductor thin film, a one (single) shot of laser pulse is irradiated onto each of areas on which a horizontal scanning circuit and a vertical scanning circuit respectively will be formed. In this case, it is necessary to make crystallized areas continuous, and thus the crystal particle size is dispersed at a linking boundary between the laser-irradiated areas.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of manufacturing semiconductor chips for display in which semiconductor thin films having a large size can be mass-produced to have uniform particle size with shortening a heat-treatment time.
In order to attain the above object, a method of manufacturing semiconductor chips for display comprises a step of forming a semiconductor thin film on an insulating substrate, a step of processing the semiconductor thin film to form an integrated thin film transistors in a sectioned area for one chip and a step of forming pixel electrodes in the sectioned area to form a picture (frame), wherein the processing step contains a step of irradiating a laser pulse to the sectioned area by a single shot exposure to perform a batch heat-treatment on the semiconductor thin layer for one chip. At the laser-irradiation step, the semiconductor thin film is crystallized with the batch heat-treatment, or the semiconductor thin film is doped with impurities and then the impurities are activated with the batch heat-treatment. If necessary, the laser-irradiation step as described above may be performed after the semiconductor thin film is doped with the impurities, whereby the crystallization of the semiconductor thin film and the activation of the impurities are performed at the same time.
In the laser-irradiation step, a one-shot laser pulse may be successively irradiated onto each of plural sectioned areas which are beforehand provided on an insulating substrate. In this case, a one-shot laser pulse is irradiated onto an individual sectioned area except for a separation band which is provided between neighboring sectioned areas. When the individual sectioned area is rectangular, a laser pulse having a rectangular section which conforms to the shape of the sectioned area may be irradiated by one shot.
As a condition for laser irradiation, a one-shot laser pulse may be irradiated for a pulse time which is set to 40 nanoseconds or more. In this case, the batch heat-treatment can be performed to control crystallization of the semiconductor thin film in a state where the temperature of the insulating substrate is increased to the room temperature or more, or decreased to the room temperature or less. Furthermore, if the semiconductor thin film is beforehand formed at a thickness which is smaller than the absorption depth of the laser pulse, the crystallization or activation can be perfectly performed.
If necessary, a one-shot laser pulse may be irradiated through a microlens array to selectively concentrate the laser pulse on a portion of the semiconductor thin film, which corresponds to the element area of an individual thin film transistor. Furthermore, the one-shot laser pulse irradiation may be performed while controlling the cross-section intensity distribution of the laser pulse so that the irradiation energy density increases from the centra
Hayashi Hisao
Ino Masumitsu
Kunii Masafumi
Minegishi Masahiro
Nishihara Shizuo
Le Vu A.
Lebentritt Michael S.
Sonnenschein Nath & Rosenthal
Sony Corporation
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