JP2008211093A - Laser annealing method or laser annealing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser annealing method or a laser annealing device for realizing polycrystalline uniformly in a large area, by connecting an anneal region of semiconductor film, such as amorphous Si. <P>SOLUTION: The laser annealing method includes a step (a) of dividing a semiconductor film formed on a substrate virtually into two or more regions of predetermined width and melting and crystallizing the semiconductor film on the substrate, by scanning the each region with long-length laser beam in a width direction; and a step (b) of scanning a border region of adjoining regions in the lateral direction with a short-length laser beam shorter than that of long-length laser beam and performing re-crystallization by melting. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser annealing apparatus and a laser annealing method, and more particularly to a laser annealing apparatus and a laser annealing method capable of crystallizing a semiconductor film such as an amorphous silicon (Si) film or a polycrystalline Si film having a small grain size.

In a liquid crystal display device or the like, polycrystallization is performed by irradiating an amorphous Si film formed on a glass substrate with laser light. Word when the electron mobility in the amorphous Si is at most ^{1 cm} 2 / Vs, for example, the electron mobility in the polycrystalline Si crystallization in excimer laser also reaches about 100cm ² / Vs~200cm ² / Vs It has been broken. The mobility of charge carriers in the polycrystalline Si film depends on the size of the grains in the polycrystal. When laser annealing is performed on a polycrystalline Si film having a small grain size and the grain size is increased, the mobility of charge carriers can be improved. Hereinafter, laser annealing of the amorphous Si film will be mainly described without limiting meaning.

  The output of the pulsed excimer laser is about 300 W, for example. The output light of the excimer laser is shaped into a long beam having a length of about 32 cm to 37 cm, for example, in accordance with the dimensions of the display device, and irradiated onto the amorphous Si film. The amorphous Si film irradiated with the excimer laser beam melts and crystallizes. A wide area can be crystallized by irradiating pulsed laser light one after another and scanning in the beam short direction.

  JP-T-2000-505241 discloses that a strip-shaped region of an amorphous silicon film is irradiated with an excimer laser beam using a mask having an opening pattern to completely melt and re-solidify the irradiated region. Two particle trains grow explosively (laterally) from both borders to the center of the region, shift the irradiation region below the width of the particle train, and crystallize by irradiating the next excimer laser light It is reported that when one of the grain rows is partially melted, the previously grown crystal grain rows become longer during re-solidification.

  In WO 2004/040628, when an amorphous silicon film is irradiated with a long excimer laser beam, a relatively large crystal grain grows to some extent from the width direction edge of the long laser beam irradiation region, and in an inner region thereof By irradiating with a long excimer laser beam that scans in the short direction, less than the width of the crystal grain, in which small microcrystal grains grow and medium size crystal grains are randomly distributed on the outside We report that large lateral crystal grains with the <110> direction aligned in the scanning direction can be obtained.

  Even if the long laser beam is scanned in the short direction to crystallize the stripe region, the width of the stripe region (the length of the long laser beam) is limited. In order to crystallize a large area, it is necessary to further crystallize the region adjacent to the stripe region.

  In Japanese Patent Laid-Open No. 2002-43245, the long laser beam continuously decreases in energy at the end portion to form a slope portion. The region crystallized in the slope portion of the first shot is the center portion in the second shot. Even when irradiated with high energy, it is reported that the crystallinity is worse than the region crystallized with high energy in the first shot and the carrier mobility is reduced, and the end of the long laser beam is shielded by a light shielding film. A method is proposed in which crystallization is performed by scan annealing, and then the light-shielding film is removed and the uncrystallized region is crystallized.

Special Table 2000-505241 WO 2004/040628 JP 2002-43245 A

  An object of the present invention is to provide a laser annealing method or a laser annealing apparatus capable of connecting a anneal region of a semiconductor film and crystallizing a wide area uniformly.

According to one aspect of the present invention,
(A) A process of virtually dividing a semiconductor film formed on a substrate into a plurality of regions having a predetermined width, and scanning the long laser beam in the width direction in each region to melt and crystallize the semiconductor film on the substrate When,
(B) melting and recrystallizing a boundary region between adjacent regions of the plurality of regions by scanning a short laser beam shorter than the long beam in the width direction;
A laser annealing method is provided.

According to another aspect of the invention,
A table on which a substrate on which a semiconductor film is formed can be mounted and driven in translation;
A long laser beam optical system disposed above the table and capable of irradiating a semiconductor film on the substrate with a long laser beam;
A short laser beam optical system disposed above the table and capable of irradiating a semiconductor film on the substrate with a short laser beam shorter than the long beam;
A laser annealing apparatus is provided.

  A boundary region between a plurality of crystallization regions by a long laser beam can be recrystallized by a short laser beam having a very narrow slope portion at the end in the length direction. Since the short laser beam only recrystallizes the boundary region, it can be made small, and a compact and lightweight imaging lens can be used.

  Although the output of the excimer laser is high, the length of the long beam is about 40 cm at most. In order to crystallize a semiconductor film having an area larger than 40 cm in width, it is necessary to virtually divide the semiconductor film into a plurality of regions and crystallize by scanning a long beam in the short direction in each region. For example, in order to form an amorphous silicon film on a glass substrate of 730 mm × 920 mm and crystallize the entire surface (multiple), a long laser beam with a length of 365 mm is formed, and a laser with a 730 mm width divided into two regions. It will anneal. Since the slope portion where the energy decreases exists at the end portion in the longitudinal direction of the long laser beam, the crystallinity of the boundary region between the plurality of regions is deteriorated. With the increase in size of liquid crystal display devices, the size of glass substrates is also increasing. The boundary area also tends to increase. The demand for crystallinity improvement in the boundary region of the laser annealing region will become stronger in the future.

  It is said that for the lateral growth, it is preferable that the intensity change at the edge of the laser beam is steep. If the change in beam intensity is slow, microcrystals are generated and lateral growth is hindered. An optical system that forms an image of a long laser beam uses a cylindrical lens having an image forming action in the short direction. In this method, an image of a mask having openings or slits is reduced and exposed in the width direction, and the width of the slope portion in the short direction can be set to about 2 μm. When an XY axis is assumed in the substrate plane, a cylindrical lens having an imaging action in the X direction does not have an imaging action in the Y direction. Even if a mask having an opening is used, it is difficult to increase the resolution in the Y direction. At the end in the Y direction, a slope portion where the beam intensity decreases is formed with a width of about 2 mm. Even if the technology advances in the future, it will be impossible to make the width of the slope portion less than 1 mm or less as long as a cylindrical lens is used. Therefore, it is necessary to assume that the long laser beam has a slope portion of 1 mm or more at the end in the length direction.

  In order to connect the laser annealing regions, it is desired that the width of the slope portion at the end in the Y (length) direction is about 2 μm or less. Considering that the width of the slope portion is 2.2 μm or less. For example, when the imaging optical system performs 1/5 reduction exposure, in order to form an image of a long laser beam of 10 μm × 365 mm, the opening of the mask becomes 50 μm × 1825 mm. In order to efficiently crystallize a large area, the length of the long laser beam is required to be at least 20 cm. Even if the length is 20 cm, the length of the mask opening is 1 m when the exposure is reduced by 1/5. The imaging lens must be larger than this aperture size. If a spherical lens having a resolution of 2.2 μm or less in both the X direction and the Y direction is to be produced, it becomes a very large high-precision lens, which is technically and cost impractical. A realistic long laser beam must use a cylindrical lens. For this reason, a slope part exists in an elongate direction edge part, and the crystallinity of a slope part is inferior.

  The term “spherical lens” is used in contrast to a cylindrical lens having a focal length only in one direction, and means a lens having a focal length in both XY directions. An aspheric lens is also called a spherical lens.

  Embodiments of the present invention will be described below with reference to the drawings.

  1A and 1B are plan views of a glass substrate schematically showing a laser annealing method according to a basic embodiment. 1C and 1D are cross-sectional views of the glass substrate corresponding to FIGS. 1A and 1B.

  As shown in FIGS. 1A and 1C, for example, a silicon film 2 is formed on a glass substrate 1 of X: 920 mm × Y: 730 mm. The silicon film deposited at a low temperature is initially amorphous. As shown in FIG. 1A, a 365 mm long beam LB of an excimer laser is made parallel to the Y direction, laser scanning S1 is performed in the -X direction, and the upper half of the substrate is crystallized. Next, the long beam is moved in the -Y direction, turned back, and laser scanning S2 is performed in the X direction to crystallize the lower half of the substrate. Although most of the amorphous silicon film 2 is crystallized uniformly, a thin stripe region 3 with poor crystallinity is generated corresponding to the slope portion at the end of the long beam LB. Two stripe regions 3 are collectively indicated by 3t. In addition, although the case where one long beam was reciprocated and the silicon film was crystallized was explained, as shown in S1 and S2 in FIG. 1A, a plurality of long beams are scanned in the scanning (X) direction. They may be spaced apart and scanned in the X direction in parallel. Although the case where the upper crystallization region and the lower crystallization region are in contact with each other is shown, the end portions may be overlapped or slightly separated. Instead of the amorphous silicon film, a polycrystalline silicon film having small crystal grains may be crystallized into larger crystal grains.

  As shown in FIG. 1B, laser scanning S3 of the central stripe region 3t is performed using a short laser beam SB that covers the width of the stripe region 3t having poor crystallinity at the center. Assuming that the width of the region 3 having poor crystallinity is 2 mm and the two regions are in contact with each other to form the region 3t having a width of 4 mm, it is sufficient that the length of the short laser beam is 5 mm. For example, the size may be about 5 mm in length and about 10 μm in width. The mask opening size in the case of 1/5 reduction exposure is 25 mm × 50 μm. An imaging lens having a diameter of about 30 mm can be used. With such a lens, a highly accurate spherical lens can be made relatively easily. The width of the slope portion is 2.2 μm or less in both the length direction and the width direction. Even if the absorption coefficient has changed due to crystallization, the semiconductor film in the irradiated region, including the region 3 with poor crystallinity, is completely melted by performing laser scanning at an energy intensity that can completely melt the irradiated region. Recrystallize.

  It is considered that the length of the short laser beam is increased to 10 mm so as to cope with the case where the length of the slope portion of the long laser beam is increased or the adjacent crystallized regions are slightly separated. In the case of 1/5 reduction projection, the opening length of the mask is 50 mm. A lens diameter of about 55 mm is sufficient. Consider overlapping slope portions of adjacent crystallization regions. The width of the slope portion can be reduced to about 2 mm. About 3 mm is sufficient for the length of the short laser beam. In the case of 1/5 reduction projection, the opening length of the mask is 15 mm. A lens diameter of about 20 mm is sufficient. A lens with higher accuracy can be easily created. Thus, the length of the short laser beam will be in the range of 3 mm to 10 mm, and the diameter of the high precision spherical lens will be in the range of 20 mm to 55 mm.

As shown in FIG. 1D, recrystallization is performed with a short laser beam LB having a narrow slope portion, and the region 3t having poor crystallinity in the center portion disappears. Since the regions 3 on both sides are located at the edge of the substrate, they are not used in the display region of the liquid crystal display device and may be left as they are. Of course, the regions 3 at both ends may be recrystallized. Short-length laser beam SB is, the area is small, low energy required, may be formed by excimer laser, for example, a laser diode pumped Nd: YAG, Nd: YVO 2 harmonic of such ₄ (2 [omega ), A solid-state laser having a wavelength of 527 nm to 532 nm can also be used.

  2A and 2B show a long beam projection optical system. Excimer laser light emitted from a pulsed excimer laser light source 11 such as an XeCl excimer is incident on a homogenizer 13 via a zoom lens system 12 to form a uniform energy distribution. The excimer laser light having a uniform energy distribution is reduced in the short direction by a one-way zoom lens system 14, the long direction is converted into parallel rays, and the short direction is formed by an imaging optical system 15 that forms an image of the mask 16. A long beam 18 is projected on the projection surface 17. As the long beam projection optical system, a known one can be used, and various modifications can be made.

  FIG. 2C shows a short beam projection optical system. For example, the laser light emitted from the pulse oscillation Nd: YAG harmonic solid-state laser light source 21 has its energy distribution made uniform by the homogenizer 23 via the zoom lens system 22 and illuminates the mask 26 via the zoom lens system 24. . The image of the aperture of the mask 26 is reduced and projected as a short beam 28 on the projection surface 17 by the imaging optical system 25 using a spherical lens. Assuming that an image having a length of 5 mm is formed by 1/5 reduction projection, the lens diameter of the imaging optical system constituted by a spherical lens is about 30 mm. The mask 26 has an opening having a length of 25 mm and a width of 50 μm, for example.

  Note that, in both the long beam projection optical system and the short beam projection optical system, the intensity distribution in the X direction in the beam width direction and the Y direction in the beam length direction within a plane (XY plane) perpendicular to the optical axis (Z axis). Although a configuration in which a homogenizer for homogenizing each is provided is shown, the homogenizer in the X direction in the beam width direction can be omitted.

  2D and 2E show energy distributions in the width direction and the length direction of the long laser beam 18. As shown in FIG. 2D, the width direction has a uniform strength portion of about 10 μm and slope portions of about 2 μm on both sides thereof. As shown in FIG. 2E, the length direction has a uniform strength portion of, for example, 365 mm and slope portions of about 2 mm on both sides thereof.

  2F and 2G show energy distributions of the short laser beam 28 in the width direction and the length direction. As shown in FIG. 2F, the width direction has a uniform strength portion of about 10 μm and slope portions of about 2 μm on both sides thereof. As shown in FIG. 2G, the length direction has, for example, a uniform strength portion of 5 mm and slope portions of about 2 μm on both sides thereof.

  In addition, although the case where the long laser beam is configured by excimer laser light and the short laser beam is formed by solid laser light such as a YAG harmonic laser has been described, the long laser beam may be formed by solid laser beam. it can. Since solid laser beams are difficult to increase in energy, the number of connections will be higher. If the connection part of the long laser beam can be connected with a short laser beam with good crystallinity, an all-solid-state laser annealing apparatus is also possible.

  FIG. 3A is a perspective view schematically showing a configuration of a laser annealing apparatus and an annealing method, and FIGS. 3B and 3C are plan views schematically showing modifications.

  As shown in FIG. 3A, the long beam optical system 10 and the short beam optical system 20 are disposed above the XY stage 30. The long beam optical system 10 includes an excimer laser light source 11, a variable attenuator 19, a homogeneous optical system 13, a direction changing mirror M1, and a long beam projection optical system 6. The homogenous optical system 13 is shown in a configuration that only performs homogenization in the length (Y) direction of a long beam. However, as shown in FIGS. 2A and 2B, homogenization in two directions orthogonal to the optical axis is performed. Also good. The long beam projection optical system 6 constitutes an imaging system with a cylindrical lens. The short beam optical system 20 includes an LD-excited solid-state laser light source 21, a variable attenuator 29, a homogeneous optical system 23, a direction changing mirror M2, and a short beam projection optical system 7. Although the homogenous optical system 23 is shown with a configuration that performs homogenization only in the length (Y) direction of the short beam, homogenization in two directions orthogonal to the optical axis may be performed as shown in FIG. 2C. The short beam projection optical system 7 forms an imaging system with a spherical lens. The short beam optical system 20 is arranged at a certain distance from one end of the long beam optical system 10 in the scanning direction rearward.

  A glass substrate 31 on which an amorphous silicon film is deposited is placed on the XY table 30, and laser annealing is performed by the long beam optical system 10 to perform crystallization. In the first first scan S1, the short beam optical system 20 is not driven. When the second scan S2 is performed after finishing the first scan and turning back, the short beam optical system 20 defines a boundary region between the crystallized region 33 by the first scan and the crystallized region 34 by the second scan or a region including an adjacent edge. Will follow-up scanning. The semiconductor film is melted and recrystallized including the region having poor crystallinity at the edge of the region crystallized by the long beam. Various modifications are possible as long as the boundary region connecting the stripe-shaped regions laser-annealed by the long beam optical system 10 is laser-annealed again by the short beam optical system 20. Laser annealing scanning of the long beam optical system 10 may be performed as long as the entire surface of the substrate can be laser annealed.

  FIG. 3B shows a modification in which folding scanning is performed from the lower side to the upper side of the substrate. A first scan S1 is performed on the lower part of the substrate, and the second scan S2 is performed by folding back upward. A case where the end portions of the long beam scanning region are overlapped is shown. In order to make the lens of the short beam optical system small, it is preferable to overlap the scanning region end of the long beam optical system to reduce the width of the region having poor crystallinity. The imaging lens system of the short beam optical system can be constituted by a spherical lens having a diameter of 5 mm or less.

  FIG. 3C shows a case where the two long beam optical systems 10a and 10b are arranged while being shifted in the scanning direction and the end portions are overlapped for scanning. The short beam optical system 20 further scans the boundary region with poor crystallinity from the rear and laser anneals.

  As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these. It will be apparent to those skilled in the art that various modifications, substitutions, improvements, combinations, and the like can be made.

1A and 1B are plan views of a glass substrate schematically showing a laser annealing method according to a basic embodiment, and FIGS. 1C and 1D are cross-sectional views of the glass substrate corresponding to FIGS. 1A and 1B. 2A and 2B are two-way side views showing the long beam projection optical system, FIG. 2C is a side view showing the short beam projection optical system, and FIGS. 2D and 2E are width directions of the long laser beam 18. FIGS. 2F and 2G are graphs showing the energy distribution in the width direction and the length direction of the short laser beam 28. FIG. FIG. 3A is a perspective view schematically showing a configuration of a laser annealing apparatus and an annealing method, and FIGS. 3B and 3C are plan views schematically showing a laser annealing method of a modification.

Explanation of symbols

1 substrate,
2 semiconductor film,
3 Regions with poor crystallinity,
6 Long beam projection optics,
7 Short beam projection optical system 10 Long beam optical system,
11 Pulsed excimer laser light source,
12 Zoom lens system,
13 Homogenizer,
14 one-direction zoom lens system,
15 imaging optical system,
16 mask,
17 Projection plane,
18 Long beam,
19 Variable attenuator,
20 Short beam optical system,
21 LD pumped solid state laser light source,
22 Zoom lens system,
23 Homogenizer,
24 Zoom lens system,
25 Imaging optics,
26 Mask 26,
28 Short beam,
29 Variable attenuator,
M mirror,

Claims (16)

(A) A process of virtually dividing a semiconductor film formed on a substrate into a plurality of regions having a predetermined width, and scanning the long laser beam in the width direction in each region to melt and crystallize the semiconductor film on the substrate When,
(B) melting and recrystallizing a boundary region between adjacent regions of the plurality of regions by scanning a short laser beam shorter than the long beam in the width direction;
A laser annealing method comprising:   2. The laser annealing method according to claim 1, wherein the long laser beam is an excimer laser beam or a solid laser beam.   3. The laser annealing method according to claim 1, wherein the short laser beam is a solid laser beam.   The laser annealing method according to claim 1, wherein a length of the short laser beam is 3 mm to 10 mm. The step (a)
(A1) a laser annealing step of scanning a long laser beam in the width direction to crystallize one of the plurality of regions;
(A2) a step of moving the position of the long laser beam to one of the adjacent regions and performing a return scanning;
The laser annealing method according to claim 1, comprising: The step (a)
(A3) a laser annealing step in which a plurality of long laser beams are arranged on a plurality of adjacent regions while being shifted in the width direction of the long laser beam and scanned in the width direction to crystallize the plurality of regions;
And (b-1) a step of scanning the boundary region of the plurality of regions with the short laser beam, melting, and recrystallizing,
The laser annealing method according to any one of claims 1 to 4, further comprising:   The laser annealing method according to claim 1, wherein the semiconductor film is an amorphous silicon film. A table on which a substrate on which a semiconductor film is formed can be mounted and driven in translation;
A long laser beam optical system disposed above the table and capable of irradiating a semiconductor film on the substrate with a long laser beam;
A short laser beam optical system disposed above the table and capable of irradiating a semiconductor film on the substrate with a short laser beam shorter than the long beam;
An apparatus for laser annealing.   9. The laser annealing apparatus according to claim 8, wherein the long laser beam optical system has an imaging lens system composed of a cylindrical lens, and the short laser beam optical system has an imaging optical system composed of a spherical lens.   10. The laser annealing apparatus according to claim 9, wherein the imaging lens system of the short laser beam optical system is constituted by a spherical lens having a diameter of 20 mm to 55 mm.   The long laser beam optical system is an optical system that projects a long laser beam having a slope portion of 1 mm or more in a length direction end portion, and the short laser beam optical system has a width of a slope portion at a length direction end portion. The laser annealing apparatus according to any one of claims 8 to 10, which is an optical system that projects a short laser beam of 2.2 µm or less.   The laser annealing apparatus according to any one of claims 8 to 11, wherein a length of the long laser beam is 20 cm or more and a length of the short laser beam is 5 mm or less.   The laser annealing apparatus according to any one of claims 8 to 12, wherein the long laser beam is an excimer laser beam or a solid laser beam.   The laser annealing apparatus according to any one of claims 8 to 13, wherein the short laser beam is a solid-state laser beam.   The long laser beam optical system includes a plurality of long laser beam irradiation systems, and when the table is driven in translation, a plurality of long laser beams emitted from the plurality of long laser beam irradiation systems on adjacent areas. 15. The laser according to claim 8, wherein the short laser beam optical system is an optical system capable of following scanning a boundary region between the adjacent regions with a short laser beam. Annealing equipment.   The laser annealing apparatus according to claim 15, wherein the plurality of long laser beam irradiation systems are arranged so as to be shifted in a width direction of the long laser beam.

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