JP4212830B2 - Silicon crystallization method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon crystallization method.
[0002]
[Prior art]
The liquid crystal display device includes an active matrix driving circuit including TFTs. Further, the system liquid crystal display device includes an electronic circuit including a TFT in a peripheral region around the display region. Low-temperature poly-Si is suitable for forming TFTs of liquid crystal display devices and TFTs of electronic circuits in the peripheral region of the system liquid crystal display device. Further, low-temperature poly-Si is expected to be applied to a pixel driving TFT in an organic EL and an electronic circuit in a peripheral region in the organic EL. The present invention relates to a semiconductor crystallization method and apparatus using a CW laser (continuous oscillation laser) for making TFTs with low-temperature poly-Si.
[0003]
In order to form a TFT of a liquid crystal display device with low-temperature poly-Si, conventionally, an amorphous silicon film is formed on a glass substrate, and the amorphous silicon film on the glass substrate is irradiated with an excimer pulse laser to form the amorphous silicon. It was crystallized. Recently, a crystallization method has been developed in which an amorphous silicon film on a glass substrate is irradiated with a CW solid-state laser to crystallize the amorphous silicon.
[0004]
In silicon crystallization using an excimer pulse laser, the mobility is about 150 to 300 (cm ² / Vs), whereas in silicon crystallization using a CW laser, the mobility is 400 to 600 (cm ² / Vs). This is particularly advantageous in forming TFTs for electronic circuits in the peripheral region of the system liquid crystal display device.
[0005]
In crystallization of silicon, a silicon film is scanned with a laser beam. In this case, a substrate having a silicon film is mounted on a movable stage, and scanning is performed while moving the silicon film with respect to a fixed laser beam. As shown in FIG. 10, in the excimer pulse laser, for example, the beam spot X can be scanned with a laser beam of 27.5 cm × 0.4 mm, the beam width is 27.5 cm, and the scanning speed is 6 mm / s. The area scan speed is 16.5 cm ² / s.
[0006]
On the other hand, as shown in FIG. 11, in the CW solid-state laser, for example, when the laser power is 10 W, the width of the beam spot Y is about 400 μm, and scanning is performed at a scanning speed of 50 cm / s, effective crystallization is possible. Since the melt width is 150 μm at a beam spot of 400 μm, the area scan speed is 0.75 cm ² / s. As described above, crystallization using a CW solid-state laser can obtain high-quality polysilicon, but has a problem of low throughput.
[0007]
[Problems to be solved by the invention]
Crystallization with a CW solid-state laser can obtain high-quality polysilicon, but has a problem that the area scan speed is low and the throughput is not sufficiently increased.
[0008]
An object of the present invention is to provide a semiconductor crystallization method and apparatus capable of increasing the throughput even when a CW solid-state laser is used.
[0009]
[Means for Solving the Problems]
The silicon crystallization method according to the present invention irradiates an amorphous silicon film on a glass substrate with a laser beam emitted from a plurality of Nd: YVO4 continuous wave solid-state laser sources through a focus optical system, and melts and crystallizes the amorphous silicon film. A method of crystallizing silicon, wherein a plurality of the laser beams are irradiated onto the glass substrate without overlapping each other, and the amorphous silicon film is scanned in parallel with each other, and the melting marks overlap each other. At least one of the continuous-wave solid-state laser sources is provided with a beam expander, and the laser beam has its divergence angle adjusted by the beam expander, and The laser beam irradiation scan and the display area on the glass substrate That the performed by crossing the scan of the laser beam irradiation, the intensity of the irradiation of the laser beam with respect to the peripheral region, the display stronger than the intensity of the irradiation of the laser beam with respect to area, the scanning of the display region The speed is higher than the speed of the scan for the peripheral area, and in the area where the scan for the peripheral area side and the scan for the display area intersect, the scan for the display area is performed after the scan for the peripheral area. It is characterized by that.
[0010]
The semiconductor crystallization method according to the related inventions of the present invention, there a plurality of the laser beam emitted from the laser source is irradiated through the focusing optical system to the semiconductor film of the substrate, a semiconductor crystallization method of melt crystallizing the semiconductor film The plurality of laser beams are irradiated on the substrate without overlapping each other, and the semiconductor film is scanned in parallel with each other, and the melting marks are positioned so as to overlap each other.
[0011]
A semiconductor crystallization method according to a related invention of the present invention is a semiconductor crystallization method in which a semiconductor film on a substrate is irradiated with laser beams emitted from a plurality of laser sources through a focus optical system, and the semiconductor film is melt-crystallized. Thus, the plurality of beam spots formed by the laser beam emitted from the laser source overlap each other at least partially.
[0012]
A semiconductor crystallization apparatus according to a related invention of the present invention includes a plurality of laser sources, a focus optical system, and a synthesis optical system that guides a laser beam emitted from the plurality of laser sources to the focus optical system, The combining optical system includes a λ / 2 plate disposed after the first laser source, a beam expander disposed after at least one of the first and second laser sources, and the first and second laser sources. And a polarization beam splitter for synthesizing the laser beams emitted from.
[0013]
According to these structures, the irradiated beam spot can be enlarged by irradiating the amorphous semiconductor of the substrate with laser beams emitted from a plurality of laser sources through the focus optical system. Since the melt width is increased by increasing the beam spot, the area scan speed is increased even if the scan speed necessary for obtaining polysilicon having excellent quality is constant. Thus, high quality polysilicon can be obtained with high throughput.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments will be described with reference to the drawings.
[0015]
FIG. 1 is a schematic cross-sectional view showing a liquid crystal display device. The liquid crystal display device 10 is formed by inserting a liquid crystal 16 between a pair of opposed glass substrates 12 and 14. An electrode and an alignment film may be provided on the glass substrates 12 and 14. One glass substrate 12 is a TFT substrate, and the other glass substrate 14 is a color filter substrate.
[0016]
FIG. 2 is a schematic plan view showing the glass substrate 12 of FIG. The glass substrate 12 has a display area 18 and a peripheral area 20 around the display area 18. The display area 18 includes a large number of pixels 22. In FIG. 2, one pixel 22 is partially enlarged. The pixel 22 includes sub-pixel areas RGB of three primary colors, and a TFT 24 is formed in each sub-pixel area RGB. The peripheral region 20 has TFTs (not shown), and the TFTs in the peripheral region 20 are arranged more densely than the TFTs 24 in the display region 18.
[0017]
The glass substrate 12 of FIG. 2 constitutes a 15-inch QXGA liquid crystal display device, and has 2048 × 1536 pixels 22. 2048 pixels are arranged in the direction (horizontal direction) in which the sub-pixel areas RGB of the three primary colors are arranged, and the number of sub-pixel areas RGB is 2048 × 3. In the direction (vertical direction) perpendicular to the direction (horizontal direction) in which the sub-pixel areas RGB of the three primary colors are aligned, 1536 pixels are aligned. In the semiconductor crystallization described later, laser scanning is performed in the direction parallel to each side in the peripheral region 20, and laser scanning is performed in the direction of arrow A or arrow B in the display region 18.
[0018]
The reason is that TFTs are densely arranged in the directions of A and B, and TFTs are sparsely arranged in the direction perpendicular to A and B. Therefore, in mother glass close to a square, the directions of A and B are lasers. This is because the number of scans decreases and the throughput increases.
[0019]
FIG. 3 is a schematic plan view showing a mother glass 26 for making the glass substrate 12 of FIG. The mother glass 26 collects a plurality of glass substrates 12. In the example shown in FIG. 3, four glass substrates 12 are collected from one mother glass 26, but four or more glass substrates 12 can be collected from one mother glass 26.
[0020]
FIG. 4 is a diagram showing a process of forming the TFT 24 of the glass substrate 12 and the TFT of the peripheral region 20 of FIG. In step S1, an insulating film and an amorphous silicon film are formed on the glass substrate. In step S2, the amorphous silicon film is crystallized to become polysilicon. In step S3, necessary silicon portions such as silicon portions to be TFTs are left, unnecessary portions of the polysilicon and amorphous silicon films are removed, and TFT isolation is performed. In step S4, a gate electrode, a drain electrode, an interlayer insulating film, a contact hole, and the like are formed. In step S5, an insulating film or ITO film is further formed to complete the glass substrate 12. The ITO film becomes a pixel electrode constituting the pixel 22.
[0021]
FIG. 5 is a diagram showing the crystallization of an amorphous silicon film (semiconductor film) with a laser beam. An amorphous silicon film 36 is formed on the glass substrate 12 with an insulating film such as SiO ₂ interposed therebetween, and the glass substrate 12 is fixed to the XY stage 38 by a vacuum chuck or a mechanical stopper of the XY stage 38. The laser beam LB is applied to the amorphous silicon film 36, the XY stage 38 is moved in a predetermined direction, and scanning is performed. First, the amorphous silicon 36 in the peripheral region 20 of the glass substrate 12 is focused and irradiated with a laser beam to melt and solidify the amorphous silicon and crystallize it into polysilicon. Then, the amorphous silicon in the display region 18 of the glass substrate 12 is focused and irradiated with a laser beam to melt and solidify the amorphous silicon and crystallize it into polysilicon. The reason for this is that, when performing laser scanning with crossing, when crystallizing with strong laser light like the peripheral region and then crystallizing with weak laser light corresponding to the display area, the crystallinity of the crossing part is strong laser light However, in the reverse order, crystallization with strong laser light is insufficient. This is because light absorption is reduced when it is amorphous and well crystallized to some extent.
[0022]
Since the TFTs in the peripheral region 20 are arranged more densely than the TFTs 24 in the display region 18, high-quality polysilicon is required. Therefore, the laser scanning of the peripheral region 20 is performed at a relatively low scanning speed with a laser beam having a relatively high power, and the TFT 24 in the display region 18 may not be so high quality polysilicon. The scanning is performed at a relatively high scanning speed with a laser beam having a relatively low output (or a sub beam obtained by dividing the laser beam).
[0023]
FIG. 6 is a diagram showing a laser device 70 used for crystallizing the semiconductor in the peripheral region 20. The laser device 70 is used with the XY stage 38 of FIG. 5 for crystallization. The laser device 70 includes two laser sources (continuous oscillation (CW) laser oscillators) 71 and 72, a common focus optical system 73, and a laser beam LB emitted from the two laser sources 71 and 72 to the focus optical system 73. And a combining optical system 74 for guiding.
[0024]
The focus optical system 73 includes a substantially semi-cylindrical lens 75, a substantially semi-cylindrical lens 76 disposed so as to be orthogonal to the lens 75, and a convex lens 77. Due to the focus optical system 73, the beam spot of the laser beam LB becomes elliptical.
[0025]
The combining optical system 74 includes a λ / 2 plate 78 disposed after the first laser source 71, a beam expander 79 disposed after the second laser source 72, and the first and second laser sources 71. , 72 and a polarization beam splitter 80 for synthesizing the laser beam LB. Reference numeral 81 denotes a mirror.
[0026]
In this way, the laser beam LB emitted from the plurality of laser sources 71 and 72 is configured by the combining optical system 74, and the combined laser beam LB is irradiated to the amorphous semiconductor 36 of the glass substrate 12 through the focus optical system 73. Crystalline semiconductor 36 is crystallized. The beam expander 79 adjusts the divergence angle of the laser beam LB. That is, if the spread angles of the laser beams LB of the plurality of laser sources 71 and 72 vary, even if one laser beam LB is focused by the focus optical system 73, the other laser beam LB is not focused. Therefore, by adjusting the divergence angle of the laser beam LB by the beam expander 79, the two laser beams LB are brought into focus. The beam expander 79 may be disposed in the optical path of the other laser beam LB. Moreover, you may arrange | position to both the optical paths of two laser beams.
[0027]
The laser beam LB emitted from the first and second laser sources 71 and 72 is vertically linearly polarized light. The laser beam LB emitted from the first laser source 71 has a plane of polarization of 90 by the λ / 2 plate 78. Rotate the angle and become linearly polarized light. Therefore, the laser beam LB exiting from the first laser source 71 and passing through the λ / 2 plate 78 and the laser beam LB exiting from the second laser source 72 are introduced into the polarization beam splitter 80, and the two laser beams LB are Almost overlapped and headed toward the amorphous semiconductor 36. The state of the change in linearly polarized light is shown in more detail in FIG.
[0028]
Each laser beam LB passes through the focus optical system 73 to form an elliptical beam spot. As shown in FIG. 8, the beam spot of the combined laser beam LB is formed so that the beam spots of the individual laser beams LB overlap with each other, and becomes an eyebrow-shaped beam spot BS. This is achieved, for example, by slightly shifting any angle of the mirror 81. That is, the laser beams LB emitted from the plurality of laser sources 71 and 72 each form an elliptical beam spot, and the plurality of elliptical beam spots overlap with each other in the major axis direction.
[0029]
In the example, SiO ₂ was formed on the glass substrate 12 by plasma CVD to a thickness of 400 nm, and amorphous silicon 36 was formed thereon by plasma CVD to a thickness of 100 nm. The laser uses a continuous wave of a solid state laser of Nd: YV04. In one example, when a single laser source is used, a beam spot of 400 μm × 20 μm is formed at a laser power of 10 W. With a single laser source, an area scan of 200 cm ² / s can be achieved by scanning with a laser width of 400 μm and a scan speed of 50 cm / s. Of the laser irradiation width of 400 μm, the stripe-shaped portion of the amorphous semiconductor 36 having a width of 150 μm is well melted and crystallized to show a flow-type grain boundary. When a TFT is formed in a polysilicon region composed of this flow type crystal grain boundary, a high mobility characteristic having a mobility of 500 (cm ² / Vs) can be obtained.
[0030]
As shown in FIG. 6, the beam spot of the laser beam LB emitted from the two laser sources 71 and 72 and synthesized is 600 μm × 20 μm. When scanning with a laser power of 10 W, a spot width of 600 μm, and a scanning speed of 50 cm / s, the stripe-shaped portion of the amorphous semiconductor 36 having a width of 350 μm out of the laser irradiation width of 600 μm is particularly well melted and crystallized. A region showing the type of grain boundaries was obtained. The high quality crystallized 350 μm wide stripes were larger than twice the high quality crystallized 150 μm wide stripes using a single laser source. That is, by mutual heating of the two beam spots, the size of the beam spot and the effective melt width (the width crystallized with high quality) could be expanded.
[0031]
FIG. 7 is a view showing a modification of the laser device 70. The laser device 70A in FIG. 7 includes two units of optical systems. The optical system of each unit includes an optical member similar to the laser device 70 of FIG. The optical system of the first unit is shown with a suffix a added to the number representing the optical member of FIG. 6, and the optical system of the second unit is shown with a suffix b added to the number representing the optical member of FIG. . The beam expander 79 can be provided as appropriate.
[0032]
The two units of the optical system are arranged close to each other, and the beam spot BS formed by the two units of the optical system is arranged so as to be shifted in a direction perpendicular to and parallel to the scanning direction. In this configuration, the effective melt width regions of 350 μm were arranged such that the scan traces were overlapped by 50 μm, and the effective melt width was 650 μm.
[0033]
FIG. 9 is a diagram showing another example of a beam spot. Three beam spots BS are arranged so as to be shifted in a direction perpendicular to and parallel to the scanning direction. The three beam spots are shifted from each other in the scanning direction and irradiated onto the substrate without overlapping each other. However, the three beam spots scan the semiconductor film in parallel with each other, and the three beam spots overlap each other when viewed in the scanning direction, and are positioned so that their melt widths (melt widths) overlap each other. Also, three or more beam spots BS can be arranged so as to be shifted in a direction perpendicular to and parallel to the scanning direction.
[0034]
【The invention's effect】
As described above, the throughput can be increased even when the CW solid-state laser is used.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a liquid crystal display device.
2 is a schematic plan view showing the glass substrate of FIG. 1. FIG.
3 is a schematic plan view showing a mother glass for making the glass substrate of FIG. 2. FIG.
4 is a diagram showing a process of forming TFTs on a glass substrate and TFTs in a peripheral region in FIG. 2. FIG.
FIG. 5 is a diagram showing a semiconductor film being crystallized by a laser beam.
FIG. 6 is a diagram showing a laser device used for crystallization of a semiconductor in a peripheral region.
FIG. 7 is a view showing a modification of the laser device.
FIG. 8 is a diagram showing an example of a beam spot.
FIG. 9 is a diagram showing an example of a beam spot.
FIG. 10 is a diagram for explaining a conventional crystallization method using an excimer pulse laser.
FIG. 11 is a diagram for explaining a conventional crystallization method using a CW laser.
[Explanation of symbols]
12, 14 ... Glass substrate 16 ... Liquid crystal 18 ... Display area 20 ... Peripheral area 22 ... Pixel 24 ... TFT
26 ... Mother glass 30 ... CW laser oscillator 36 ... Amorphous silicon film 73 ... Focus optical system 74 ... Synthetic optical system 78 ... [lambda] / 2 plate 79 ... Beam expander 80 ... Polarizing beam splitter

Claims (1)

A silicon crystallization method of irradiating an amorphous silicon film on a glass substrate with a laser beam emitted from a plurality of Nd: YVO4 continuous wave solid-state laser sources through a focus optical system and melt-crystallizing the amorphous silicon film,
The plurality of laser beams are irradiated on the glass substrate without overlapping each other, and the amorphous silicon film is scanned in parallel with each other, and the melting marks are positioned so as to overlap each other,
At least one of the continuous wave solid laser sources is provided with a beam expander,
The divergence angle of the laser beam is adjusted by the beam expander,
Performing the scan of the laser beam irradiation on the peripheral area of the glass substrate and the scan of the laser beam irradiation on the display area of the glass substrate,
The scan speed for the display area is greater than the scan speed for the peripheral area,
The intensity of the laser beam irradiation on the peripheral area is stronger than the intensity of the laser beam irradiation on the display area,
In the region where the scan for the peripheral region side and the scan for the display region intersect, the scan for the display region is performed after the scan for the peripheral region.

Images