JPH09270393A - Laser light irradiation device - Google Patents

Abstract

(57) Abstract: In a laser light irradiation device for irradiating a line beam, the irradiation light intensity distribution of the line beam is flattened to prevent the formation of fine crystals in a low irradiation light intensity region and to prevent non-single crystal grains with large crystal grains. A crystalline semiconductor layer is obtained. A slit is provided in the vicinity of a substrate to be processed. Since the slit 20 blocks both end regions of the irradiation beam in which the light intensity of the line beam is reduced, only the light in the central region where the light intensity distribution is flat is applied to the substrate. In the irradiation area, recrystallization is uniformly and sufficiently performed, and it is possible to prevent fine crystal grains from being formed and remaining, resulting in insufficient crystallization. Good chemical annealing is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam irradiating device, and in particular, it is possible to irradiate a large area by linearly irradiating an irradiating laser with a lens optical system and scanning it. The present invention relates to a laser light irradiation device.

[0002]

2. Description of the Related Art In recent years, fine processing technology using laser light has been applied to the manufacture of semiconductor devices, and mass productivity and low cost have been realized. Further, as an image display device, a liquid crystal display device (LCD: liquid crystal display) is being put into practical use in the fields of OA equipment, AV equipment and the like because of its advantages such as small size, thinness and low power consumption. A thin film transistor (TFT) is used as a switching element for controlling the rewriting timing of image information in each pixel.
The active-matrix type with a large screen,
Since it enables high-definition moving image display, it is used for displays of various televisions, personal computers, and the like.

A thin film transistor is a field effect transistor (FET) formed by forming a semiconductor layer together with a metal layer on an insulating substrate.
stor). In the active matrix type LCD, the TFT is connected to one electrode of each capacitance for driving the liquid crystal formed between a pair of substrates sandwiching the liquid crystal. In the field of LCD as well, in manufacturing or modifying TFTs on an insulating substrate,
Laser processing technology is used.

In particular, an LCD using polycrystalline silicon (p-Si) as a semiconductor layer has been developed in place of amorphous silicon (a-Si) which has been widely used until now.
Annealing using a laser beam is used to form or grow Si crystal grains. Generally, p-Si has a higher mobility than a-Si, and the size of the TFT is reduced.
High definition is realized. Further, since the gate self-alignment structure achieves miniaturization and reduction in parasitic capacitance to achieve higher speed, a high-speed drive circuit is formed by forming an electrically complementary connection structure of n-ch TFTs and p-ch TFTs, that is, CMOS. be able to. Therefore, by integrally forming the drive circuit section and the display pixel section on the same substrate,
The manufacturing cost is reduced and the LCD module is downsized.

As a method of forming p-Si on an insulating substrate, there are recrystallization by annealing a-Si produced at a low temperature, solid phase growth method at a high temperature, and the like. In either case, since the treatment is performed at a high temperature of 900 ° C. or higher, an inexpensive soda glass substrate cannot be used as an insulating substrate in terms of heat resistance, and an expensive quartz glass substrate is required, resulting in cost reduction. It was hanging. In contrast,
Laser annealing is used to perform silicon recrystallization treatment at a relatively low temperature of 600 ° C. or lower, and as an insulating substrate,
A method using an inexpensive soda glass substrate has been developed. Such a process in which the temperature is set to 600 ° C. or lower in all steps of manufacturing the TFT substrate is called a low temperature process, and is an essential process for mass production of low-cost LCDs.

FIG. 5 is a conceptual diagram showing the structure of a laser light irradiation apparatus for performing such laser annealing. In the figure, (1) is a laser oscillation source, (2,11) is a mirror, (3,4,5,6) is a cylindrical lens,
(7, 8, 9, 12, 13) is a condenser lens, (10) is a slit in the line width direction, and (14) is a substrate to be processed having a non-single crystal semiconductor layer such as a-Si formed on its surface ( 20) for supporting stage 20). The laser light emitted from the laser oscillation source (1) is converted into parallel light with a flat intensity distribution in the vertical and horizontal directions by the condenser lens composed of the cylindrical lenses (3, 5) and (4, 6). Be transformed. This parallel light is converged in one direction by the lens (8, 9, 12, 13) as shown in FIG. 6, and is expanded in the other direction by the lens (7) as shown in FIG. The substrate to be processed (2
0) is irradiated. The stage (14) on which the substrate (20) to be processed is placed is scanned in the direction of the line width of the irradiation line beam, and high-throughput laser annealing is realized by large-area processing.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The distribution of the irradiation light intensity with respect to the position is as shown in FIG.
Although it has a flat property with a sharp edge with respect to the line width W, the light intensity distribution is lowered at both ends in the line length direction as shown in FIG. The shape was bad. That is, in the region of the substrate to be processed, which is within the range of the beam line width L1 in FIG. 9, the laser beam is uniformly irradiated with a sufficient intensity Ia, so that the recrystallization of the a-Si film is performed well. It is possible to form a p-Si film having a sufficiently large crystal grain size, but at both ends of the irradiation beam, within the L2 region where the light intensity is reduced and outside the L1 region, the intensity is larger than the intensity Ia. However, a sufficiently strong laser irradiation is not performed with a low intensity Ib.

Such a decrease in the intensity at both ends in the line length direction results from the large refraction of the shorter wavelength component of the frequency component light of the laser light having extremely large energy due to the resonance of the coherent light. It is considered that the intensity distribution became like this. In such a laser-irradiated region with insufficient strength, the recrystallized grain size does not become sufficiently large, and the grains are present in the film in a microcrystalline state. The film in this microcrystalline state again has a sufficient strength Ia.
Even if laser light irradiation is carried out, the crystallization does not proceed further and the grain size cannot be increased, so that it remains in the microcrystalline state.

For example, in the laser light irradiation device shown in FIG. 5, the line length of the line beam is 80 to 150 mm.
The degree is obtained, and the both ends of 5 mm are regions where the strength is reduced in FIG. On the other hand, the substrate (20) to be processed is 9
It is a mother glass substrate that contains 9 substrates corresponding to 1 LCD panel of 5 × 130 mm. By scanning the line beam multiple times, the laser beam is evenly distributed over the entire substrate, but with a low intensity once. In the area exposed to
The silicon layer is formed as a microcrystalline silicon layer, and even if the laser light irradiation is performed again with a predetermined overlap, the microcrystalline silicon remains as it is without increasing the grain size. That is, in one scanning of the beam line, a silicon layer made of fine crystal grains is formed in a band shape along the end portion of the scanning region.

As described above, a TFT made of p-Si having a low mobility without being sufficiently recrystallized has a sufficient O 2 content.
N current cannot be obtained. For this reason, when the line beam edge portion of the laser light irradiation hits the pixel portion, the ON current of the TFT in that region is lower than that in the other regions, and the contrast ratio is lowered. Further, when the edge portion of the line beam hits the drive circuit portion around the pixel portion, the ON resistance of the TFT increases, the operating speed decreases, and malfunction occurs. Especially in a large-screen, high-definition LCD, if the number of pixels increases,
Since the writing time to the pixel is shortened and the pulse width in the drive circuit section is also shortened, the decrease in ON current is a fatal defect.

Further, depending on the design of the lens optical system, the beam line width and the LC included in the mother glass substrate are included.
By matching the dimensions with the area that will be the D panel and matching the strip area that hits the edge of the beamline scan to the unused portion between the areas that will be the LCD panel, the above problems will be avoided. However, in this case, since the size of the LCD panel applied to the expensive laser irradiation device is determined from the beginning, it is not used for LCD panels of various sizes, which causes an increase in cost.

[0012]

The present invention has been made in order to solve this problem, and comprises an oscillation source of laser light and an optical system composed of a combination of a plurality of lenses for the laser light emitted from this oscillation source. In the laser light irradiation device that deforms the laser light linearly and irradiates the target object, the end portion in the line length direction of the linear laser light is blocked so as not to be irradiated to the target object. .

[0013] As a result, the target is not irradiated with the laser beam whose strength is lowered, and microcrystals are formed without sufficient recrystallization, so that the microcrystal grains can be enlarged. Instead, the problem that the mobility is lowered can be prevented. In particular, the blocking of the end portion of the laser light in the line length direction is performed by a slit provided close to the target object.

As a result, the light passing through the slit is
It has a uniform and sufficient intensity in all areas and has a clear linear ray at the boundary between the irradiation area and the non-irradiation area. It is possible to prevent the formation of.
Further, the slit has a configuration in which the size of the opening is variable.

As a result, there is no restriction due to the size of the substrate to be processed that can be used by the laser light irradiation device, the versatility is increased, and the running cost can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram showing the structure of a laser beam irradiation apparatus according to an embodiment of the present invention. In the figure, (1) is a laser oscillation source, (2, 11) is a mirror,
(3, 4, 5, 6) are cylindrical lenses, (7,
8, 9, 12, 13) are lenses, (10) is a slit in the line width direction, and (14) is a stage for supporting the substrate (20) to be processed. Further, a slit (30) in the line length direction is provided at a position close to the stage (14).

With this structure, the laser light emitted from the laser oscillation source (1) is emitted from the cylindrical lens (3
By the condenser lens composed of 5) and (4, 6), the output distribution of the intensity is transformed into flat light in the vertical and horizontal directions. As shown in FIG. 5, the parallel light is transmitted through the lenses (8, 9,
12 and 13) to form a line. Also,
In the other direction orthogonal to this, as shown in FIG. 2, the lens (7) extends in one direction, and
Both ends of the slit (30) are blocked, and the substrate (20) to be processed is irradiated. In this way, the line beam that is converged in one direction and extended and linearized in the other direction is processed substrate (20).
At the same time, the stage (14) on which the substrate (20) to be processed is placed moves in the line width direction of the irradiation line beam. By such scanning of the line beam, a large area can be processed, and laser annealing with high throughput can be realized.

In the present invention, as shown in FIG. 1, the slit (30) is arranged close to the substrate (20) to be processed.
As shown in FIG. 2, the slit (30) cuts off a predetermined line width at both ends of the line beam in which the laser beam is extended by the lens (7). This time,
The line length Lo of the line beam which passes through the slit (30) and is irradiated onto the substrate (20) to be processed is set to be equal to or less than the line length L1 of the flat portion of the irradiation intensity distribution shown in FIG.
The substrate (20) to be processed is irradiated with only the flat portion of the line beam intensity distribution. That is,
As shown in FIG. 3, the light intensity distribution of the laser beam applied to the substrate to be processed becomes flat with sharp edges in the range of the line length Lo, and its intensity becomes sufficiently large at Ia. There is.

Therefore, in the line beam with which the substrate (20) to be processed is irradiated, the boundary between the irradiation region and the non-irradiation region becomes clear, and a- formed on the substrate (20) in the irradiation region. Si is sufficiently annealed to be recrystallized and is formed into p-Si having high mobility and made of sufficiently large silicon crystal grains. Therefore, by sequentially scanning the substrate with a slight overlap, recrystallization is uniformly performed over the entire region.

Therefore, since the p-Si film formed on the mother glass substrate which is the substrate (20) to be processed is formed with sufficiently high mobility in all regions, the TFT made of this p-Si is formed. In the pixel portion, a sufficient ON current can be obtained, and in a high-definition, large-screen display, sufficient charge can be supplied even if the number of pixels increases and the writing time to the pixels becomes short. The contrast ratio is improved. Further, also in the driving circuit portion, since the response is high and the high speed operation can be performed, it is possible to perform driving with a short pulse width corresponding to a large screen and high definition.

The slit (30) is installed at a position sufficiently close to the substrate (20) to be processed. This is because the further the slit (30) is from the substrate (20) to be processed, the more the diffraction of the laser light becomes remarkable, and the diffracted light component again causes the low-intensity light to reappear at the end portion in the line length direction of the line beam. This is to prevent components from being produced. In the present embodiment, the slit (30) is used for processing the substrate (2
0) and are close to each other with a distance of about 30 cm.

Further, by using a slit having a variable opening size as the slit (30), the irradiation line length of the line beam can be freely adjusted. As a result, even if the size of the mother glass substrate that is the substrate to be processed (20) or the size of the area used for the LCD panel included in the mother glass substrate changes, the opening of the slit (30) is changed depending on the time. It can be handled by changing the size of the part. That is, since the same laser light irradiation device is applied to the manufacture of LCD panels of a plurality of sizes, an expensive laser light irradiation device can be used efficiently, and because of its high mass productivity and high manufacturing quality. On the contrary, the cost is reduced.

FIG. 4 is a schematic view of the essential parts of a laser beam irradiation apparatus according to another embodiment of the present invention. In this embodiment, the convex lens (7) for extending the laser beam in the line length direction in FIG. 1 and FIG. 2 is replaced with a concave lens (40). Also in this case, as in the case of FIG. 2, by providing the slits (30) for blocking predetermined line lengths at both ends of the light intensity distribution, a flat light intensity distribution having sharp edges as shown in FIG. 3 is obtained. Obtainable. Since the focus position is different from that in the case where the convex lens (7) is used, the position of the slit (30) and the size of the opening thereof need to be slightly changed in design, but the slit (4
The line length Lo of the line beam passing through 0) is set to be equal to or less than the line length L1 of the flat portion of the light intensity distribution of the line beam.

[0024]

As is apparent from the above description, according to the present invention, in a line beam laser light irradiation apparatus,
By blocking the area of low irradiation light intensity at the end of the line beam in the line length direction, the presence or absence of irradiation light in the irradiation area and non-irradiation area becomes clear, and a uniform irradiation light intensity distribution is obtained in the entire irradiation area. And sufficient annealing is performed. Accordingly, the crystal grain size of the non-single-crystal semiconductor layer can be made sufficiently large, and annealing can be completely prevented in the non-irradiation region, so that the formation of microcrystals due to insufficient annealing is avoided. For this reason, the fine crystal grains once formed by insufficient annealing do not progress crystallization even in the overlapping portion during the scanning of the subsequent line beam,
It is possible to prevent that the microcrystals remain as they are, the crystal grains in the region are small, and the mobility does not increase, and the large area annealing can be favorably performed.

Further, by using a slit capable of varying the size of the opening to block the low irradiation light intensity region,
Since the line length of the line beam can be freely controlled according to the size of the substrate to be processed and the scanning width can be adjusted, it is applied to the production of panels of various sizes, and the versatility is increased.
Running costs are reduced.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a laser light irradiation device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical system of the laser light irradiation apparatus according to the embodiment of the present invention.

FIG. 3 is a light intensity distribution chart of the laser light irradiation apparatus according to the embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical system of a laser light irradiation device according to another embodiment of the present invention.

FIG. 5 is a conceptual diagram of a conventional laser light irradiation device.

FIG. 6 is a configuration diagram of an optical system of a laser light irradiation device.

FIG. 7 is a configuration diagram of an optical system of a laser light irradiation device.

FIG. 8 is a light intensity distribution chart of the laser light irradiation device.

FIG. 9 is a light intensity distribution chart of a conventional laser light irradiation device.

[Explanation of reference numerals] 1 laser light oscillation source 2,7 mirror 3,4,5,6 cylindrical lens 7,8,9,12,13 lens 10,30 slit 14 stage 20 processed substrate 40 concave lens

Claims (3)

[Claims] 1. An oscillation source of laser light and an optical system composed of a combination of a plurality of lenses for irradiating the laser light emitted from the oscillation source, and the laser light is linearly deformed and applied to a target object. In the laser light irradiation device, the end portion of the linear laser light in the line length direction is blocked so that the target object is not irradiated with the laser light irradiation device. 2. The laser light irradiation apparatus according to claim 1, wherein the blocking of the end portion of the laser light in the line length direction is performed by a slit provided in the vicinity of the target object. 3. The laser light irradiation device according to claim 2, wherein the size of the opening of the slit is variable.