Source: http://www.google.com/patents/US20030183875?dq=7,403,220
Timestamp: 2018-01-20 14:25:51
Document Index: 215775584

Matched Legal Cases: ['art 3003', 'art 3003', 'art 3012', 'art 3013', 'art 3016', 'art 3012', 'art 3023', 'art 3023', 'art 3033', 'art 3033', 'art 3042', 'art 3042', 'art 3062', 'art 3063', 'art 3064', 'art 3064', 'art) 253', 'art) 253', 'art 172', 'art) 182', 'art) 182', 'art) 160', 'art) 160']

Patent US20030183875 - Semiconductor device and semiconductor device production system - Google Patents
It is a problem to provide a semiconductor device production system using a laser crystallization method capable of preventing grain boundaries from forming in a TFT channel region and further preventing conspicuous lowering in TFT mobility due to grain boundaries, on-current decrease or off-current...http://www.google.com/patents/US20030183875?utm_source=gb-gplus-sharePatent US20030183875 - Semiconductor device and semiconductor device production system
Publication number US20030183875 A1
Application number US 10/330,025
Also published as US6933527, US7176490, US7538350, US20050161742, US20070120127
Publication number 10330025, 330025, US 2003/0183875 A1, US 2003/183875 A1, US 20030183875 A1, US 20030183875A1, US 2003183875 A1, US 2003183875A1, US-A1-20030183875, US-A1-2003183875, US2003/0183875A1, US2003/183875A1, US20030183875 A1, US20030183875A1, US2003183875 A1, US2003183875A1
Inventors Atsuo Isobe, Koji Dairiki, Hiroshi Shibata, Chiho Kokubo, Tatsuya Arao, Masahiko Hayakawa, Hidekazu Miyairi, Akihisa Shimomura, Koichiro Tanaka, Shunpei Yamazaki, Mai Akiba
Original Assignee Atsuo Isobe, Koji Dairiki, Hiroshi Shibata, Chiho Kokubo, Tatsuya Arao, Masahiko Hayakawa, Hidekazu Miyairi, Akihisa Shimomura, Koichiro Tanaka, Shunpei Yamazaki, Mai Akiba
Patent Citations (47), Referenced by (76), Classifications (25), Legal Events (6)
US 20030183875 A1
wherein the channel region is formed on a projection part of an underlying insulation film having a rectangular or stripe-like step form, and extends in a lengthwise direction of the projection part; and
wherein the source region and the drain region are respectively formed over a step of the projection part and a depression part of the underlying insulation film.
wherein the channel region is formed on upper surface of the step and at least one of the source and drain regions is formed on the step and extends beyond the one edge of the step so that a part of the at least one of the source and drain regions is formed on the first surface.
wherein the channel region is formed on upper surface of the protrusion and at least one of the source and drain regions is formed on the protrusion and extends beyond the one edge of the protrusion so that a part of the at least one of the source and drain regions is formed on the first surface.
8. A semiconductor device production system comprising:
an optical system for focusing laser light oscillated from the laser oscillator such that a laser beam thereof is made into a linear form;
first means for moving an irradiation position of the laser light focused;
second means for forming an insulation film having a stripe-formed projection part on a substrate;
third means for forming a semiconductor film on the insulation film;
fourth means for storing pattern information of the insulation film;
fifth means for defining a scanning route of the laser beam from the pattern information with reference to a marker formed on the substrate in a manner including a projection part of the semiconductor film and controlling the first means to move the laser beam according to the scanning route thereby enhancing crystallinity of the semiconductor film; and
sixth means for patterning the semiconductor film enhanced in crystallinity to form an island on the projection part of the insulation film.
9. A semiconductor device production system comprising:
fifth means for defining a scanning route of the laser beam from the pattern information and a width of the laser beam in a direction perpendicular to a scanning direction of the laser beam with reference to a marker formed on the substrate in a manner including a convex part of the semiconductor film, and controlling the first means to move the laser beam according to the scanning route thereby enhancing crystallinity of the semiconductor film; and
10. A semiconductor device production system comprising:
second means for storing pattern information inputted;
third means for forming an insulation film having a stripe-formed projection part on a substrate according to the pattern information;
fourth means for forming a semiconductor film on the insulation film;
fifth means for reading pattern information of the semiconductor film formed;
sixth means for storing pattern information read out;
seventh means for defining a scanning route of the laser beam from the pattern information stored in the second means or pattern information stored in the sixth means with reference to pattern information stored in the second means, pattern information stored in the sixth means and position information of a substrate obtained from a thickness of the semiconductor film formed in a manner including a projection part of the semiconductor film, and controlling the first means to move the laser beam according to the scanning route thereby enhancing crystallinity of the semiconductor film; and
eighth means for patterning the semiconductor film enhanced in crystallinity to form an island on the convex part of the insulation film.
11. The semiconductor device production system according to claim 8, wherein the laser light is irradiated in a low pressure atmosphere or noble gas atmosphere.
12. The semiconductor device production system according to claim 9, wherein the laser light is irradiated in a low pressure atmosphere or noble gas atmosphere.
13. The semiconductor device production system according to claim 10, wherein the laser light is irradiated in a low pressure atmosphere or noble gas atmosphere.
14. The semiconductor device production system according to claim 8, wherein the laser light is to be outputted using one or a plurality of lasers selected from a YAG laser, a YVO4 laser, a YLF laser, a YAlO3 laser, a glass laser, a ruby laser, an alexandorite laser, a Ti:sapphire laser and an Nd:YVO4 laser.
15. The semiconductor device production system according to claim 9, wherein the laser light is to be outputted using one or a plurality of lasers selected from a YAG laser, a YVO4 laser, a YLF laser, a YAlO3 laser, a glass laser, a ruby laser, an alexandorite laser, a Ti:sapphire laser and an Nd:YVO4 laser.
16. The semiconductor device production system according to claim 10, wherein the laser light is to be outputted using one or a plurality of lasers selected from a YAG laser, a YVO4 laser, a YLF laser, a YAlO3 laser, a glass laser, a ruby laser, an alexandorite laser, a Ti:sapphire laser and an Nd:YVO4 laser.
17. The semiconductor device production system according to claim 8, wherein the laser light is to be outputted using a slab laser.
18. The semiconductor device production system according to claim 9, wherein the laser light is to be outputted using a slab laser.
19. The semiconductor device production system according to claim 10, wherein the laser light is to be outputted using a slab laser.
20. The semiconductor device production system according to claim 8, wherein the laser light is in continuous oscillation.
21. The semiconductor device production system according to claim 9, wherein the laser light is in continuous oscillation.
22. The semiconductor device production system according to claim 10, wherein the laser light is in continuous oscillation.
23. The semiconductor device production system according to claim 8, wherein the laser light is a second harmonic.
24. The semiconductor device production system according to claim 9, wherein the laser light is a second harmonic.
25. The semiconductor device production system according to claim 10, wherein the laser light is a second harmonic.
26. The semiconductor device production system according to claim 8, wherein the fifth means uses a charge coupled device.
Meanwhile, the present inventors have found that the direction of a stress caused in the semiconductor film has close bearing on the position and direction of grain boundaries in the course of crystallizing the semiconductor film by laser light irradiation. FIG. 1 shows a TEM sectional view taken in a direction perpendicular to a scanning direction of laser light when continuous oscillation laser light is irradiated at a scanning speed of 5 cm/sec to a 200-nm amorphous semiconductor film. In FIGS. 1A, 10a, 10 b and 10 c are crystal grain boundaries having a random width thereof in a direction perpendicular to the scanning direction.
[0055]FIG. 1B typically shows a TEM sectional image shown in FIG. 1A. As shown in FIG. 1B, there can be seen rises on the semiconductor film 102 at between the grain boundary 10 a and the grain boundary 10 b and between the grain boundary 10 b and the grain boundary 10 c. The present inventors have considered that this is because of possible stress application of from a vicinity of grain boundary toward a crystal grain center in a direction parallel with the substrate.
[0070]FIG. 1A is a view typically showing a TEM sectional image, and 1B is a sectional view of a crystallized semiconductor film;
[0071]FIG. 2 is a perspective view explaining a structure and manufacturing method of a semiconductor device of the invention;
[0072]FIG. 3 is a perspective view explaining a structure and manufacturing method of a semiconductor device of the invention;
[0073]FIGS. 4A and 4B are vertical sectional views explaining the detail of a crystallization process of the invention;
[0074]FIG. 5 is a perspective view explaining a structure and manufacturing method of a semiconductor device of the invention;
[0075]FIGS. 6A and 6B are perspective views explaining a structure and manufacturing method of a semiconductor device of the invention;
[0076]FIG. 7 is an arrangement view showing one form of a laser irradiation apparatus to be applied to the invention;
[0077]FIGS. 8A, 8B, 8C and 8D are views showing a manner that laser light is being irradiated to a semiconductor film;
[0078]FIGS. 9A, 9B and 9C are views of an island formed by patterning the crystallized semiconductor film;
[0079]FIGS. 10A and 10B are views showing a structure of a TFT formed by using an island shown in FIG. 9A;
[0080]FIG. 11 is a figure showing a flowchart of a production system of the invention;
[0081]FIG. 12 is a view of a laser irradiation apparatus;
[0082]FIG. 13 is a view of a laser irradiation apparatus;
[0083]FIGS. 14A, 14B, 14C, 14D, 14E and 14F are longitudinal sectional views explaining a manufacturing method of a semiconductor device of the invention;
[0084]FIG. 15 is a top view explaining the detail of a crystallization process of the invention;
[0085]FIG. 16 is a top view explaining a fabrication method of a semiconductor device of the invention;
[0086]FIG. 17 is a top view explaining a fabrication method of a semiconductor device of the invention;
[0087]FIG. 18 is a longitudinal sectional view explaining a manufacturing method of a semiconductor device of the invention;
[0088]FIG. 19 is a equivalent circuit diagram corresponding to the top view shown in FIG. 17;
[0089]FIGS. 20A and 20B are top views explaining a fabrication method of a semiconductor device of the invention;
[0090]FIGS. 21A, 21B and 21C are longitudinal sectional views explaining the detail of a crystallization process of the invention;
[0091]FIG. 22A, 22B and 22C are longitudinal sectional views explaining a method of forming an underlying insulation film and amorphous semiconductor film of the invention;
[0092]FIGS. 23A, 23B and 23C are longitudinal sectional views explaining a method of forming an underlying insulation film and amorphous semiconductor film of the invention;
[0093]FIG. 24 is an external view of a display panel;
[0094]FIG. 25 is a top view explaining a structure of a pixel part of the display panel;
[0095]FIGS. 26A, 26B, 26C, 26D, 26E, 26F and 26G are views showing examples of semiconductor devices;
[0096]FIGS. 27A, 27B, 27C and 27D are views showing examples of projectors;
[0097]FIGS. 28A, 28B, 28C and 28D are views showing a method for forming an insulation film having a concavo-convex;
[0098]FIGS. 29A, 29B and 29C are views showing a method for forming an insulation film having a concavo-convex;
[0099]FIGS. 30A and 30B are views showing forms of insulation films having a concavo-convex;
[0100]FIGS. 31A, 31B, 31C and 31D are views showing a method for forming an insulation film having a concavo-convex;
[0101]FIGS. 32A, 32B and 32C are views of an island formed by patterning the crystallized semiconductor film;
[0102]FIGS. 33A and 33B are views showing forms of insulation films having a concavo-convex;
[0103]FIGS. 34A and 34B and 34C and 34D are a top view and sectional views of a TFT formed by using the insulation film shown in FIG. 13B;
[0104]FIGS. 35A, 35B, 35C and 35D are views showing a method for manufacturing a semiconductor device using the invention;
[0105]FIGS. 36A, 36B and 36C are views showing a method for manufacturing a semiconductor device using the invention;
[0106]FIGS. 37A, 37B and 37C are views showing a method for manufacturing a semiconductor device using the invention;
[0107]FIG. 38 is a view showing a method for manufacturing a semiconductor device using the invention;
[0108]FIGS. 39A, 39B, 39C, 39D and 39E show views showing a method for crystallizing the semiconductor film;
[0109]FIGS. 40A and 40B are views showing an energy density distributions of laser beam;
[0110]FIGS. 41A and 41B are views showing energy density distributions of laser beam;
[0111]FIG. 42 is a view showing an energy density distribution of laser beam;
[0112]FIG. 43 is a view of an optical system;
[0113]FIGS. 44A, 44B and 44C are views of optical systems;
FIGS. 45 is a view showing an energy density distribution in a center-axis direction of a superposed laser beam;
[0115]FIG. 46 is a view showing a relationship between a center-to-center distance of laser beam and an energy difference; and
[0116]FIG. 47 is a view showing an output energy distribution in a center-axis direction of laser beam.
Meanwhile, the wavelength of a continuous oscillation laser beam is desirably 400-700 nm in consideration of an light absorption coefficient of amorphous semiconductor film. Such a wavelength band of light is to be obtained by extracting the second or third harmonic of a basic wave by the use of a wavelength changer device. The wavelength changer device is applied by ADP (ammonium dihydrogenphosphate), Ba2NaNb15O5 (barium sodium niobate), CdSe (selenium-cadmium), KDP (potasium dihydrogenphosphate), LiNbO3 (lithium niobate), Se, Te, LBO, BBO, KB5 or the like. Particularly, LBO is desirably used. In a typical example, used is the second harmonic (532 nm) of an Nd:YVO4 laser oscillator (basic wave: 1064 nm). Also, for laser oscillation mode, applied is a single mode as a TEM00 mode.
[0127]FIG. 4 explains such a crystallization process by a vertical sectional view. As shown in FIG. 4A, after forming a first insulation film 9102, second insulation films 9103-9105 and amorphous semiconductor film 9106 on the substrate 9101, crystallization is carried out by irradiating a laser beam 9107 as shown in FIG. 4B. It is considered that, in the crystallization, cool-down and solidification first begin at the boundary of between the first insulation film 9102 and the sidewall of second insulation films 9103-9105. Crystallization begins at that point to cause crystal growth toward the above of convex part (projection part). On the convex part (projection part), the first and second insulation films are layered to have a greater thermal capacity and hence a lower cooling rate as compared with the other region, making possible to crystal growth with a greater grain size. In the stepped region, a pulling force acts toward the direction of crystal growth. Due to the geometrical factor, strain concentrates to accumulate internal stress.
[0132]FIG. 7 shows a structural example of a laser processing apparatus applicable for crystallization. FIG. 7 illustrates, in front and side views, a construction of laser processing apparatus having a laser oscillator 9301, a shutter 9302, high change mirrors 9303-9306, a slit 9307, cylindrical lenses 9308, 9309, a table 9311, drive means 9312, 9313 to move the table 9311 in X-Y directions, control means 9314 to control the drive means, information processing means 9315 to send signals to the laser oscillator 9301 and control means 9314 according to a previously stored program, and so on.
Next, as shown in FIG. 8A, laser light is irradiated to the semiconductor film 102 to form a semiconductor film (post-LC) 103 enhanced in crystallinity. The laser light has an energy density decreasing in, a vicinity of an edge of the laser beam 104. Consequently, grain size is smaller in the vicinity of the edge to cause a rise region (ridge) along a grain boundary. For this reason, there is a necessity to avoid an overlap between the edge of a path of a laser beam 104 of laser light and the region to be made into a channel region or the convex flat surface of semiconductor film 102.
[0195]FIG. 19 shows equivalent circuits of a single channeled n-channel TFT 9630 or p-channel TFT 9631 and of a multi-channeled n-channel TFT 9632. The multi-channeled n-channel TFT 9632 has a plurality of channels provided in parallel between source and drain regions to form one transistor. By providing channel regions in parallel, the current flowing between the channels is normalized. By the transistor of this structure, characteristic variation can be reduced between a plurality of elements.
[0198]FIG. 20A shows a stage that an amorphous silicon film 9207 is formed on a second insulation film 9203, 9204 to crystallize it by a continuous-oscillation laser beam 9205. 9210-9212 shown by the one-dot chain line overlapped with the second insulation film 9203, 9204 denotes a region where a TFT active layer is to be formed.
[0203]FIG. 21 is a vertical sectional view showing the process. In FIG. 21A, a first insulating film 9402 is formed of silicon oxide nitride having 100 nm on a glass substrate 9401. A silicon oxide film is formed on that, and formed by photolithography into a second insulation film 9403-9405 having a rectangular pattern. An amorphous silicon film 9406 is formed in a thickness of 150 nm on that.
[0220]FIG. 25 is an example showing a configuration of one pixel of the pixel region 9902 that has TFTs 9801-9803. These are respectively switching, resetting and driving TFTs to control the light-emitting element or liquid-crystal element provided in the pixel.
[0224]FIG. 26A is an example of a television receiver completed by applying the invention, which is constructed with a housing 3001, a support base 3002, a display part 3003 and the like. The TFTs fabricated according to the invention is to be applied to the display part 3003. Thus, the invention can complete a television receiver.
[0225]FIG. 26B is an example of a video camera completed by applying the invention, which is constructed with a main body 3011, a display part 3012, a voice input part 3013, an operation switch 3014, a battery 3015, an image receiving part 3016 and the like. The TFTs fabricated according to the invention is to be applied to the display part 3012. Thus, the invention can complete a video camera.
[0226]FIG. 26C is an example of a notebook personal computer completed by applying the invention, which is constructed with a main body 3021, a housing 3022, a display part 3023, a keyboard 3024 and the like. The TFTs fabricated according to the invention is to be applied to the display part 3023. Thus, the invention can complete a personal computer.
[0227]FIG. 26D is an example of a PDA (Personal Digital Assistant) completed by applying the invention, which is constructed with a main body 3031, a stylus 3032, a display part 3033, an operation button 3034, an external interface 3035 and the like. The TFTs fabricated according to the invention is to be applied to the display part 3033. Thus, the invention can complete a PDA.
[0228]FIG. 26E is an example of an audio reproducing apparatus completed by applying the invention, specifically a vehicular audio apparatus, which is constructed with a main body 3041, a display part 3042, an operation switch 3043, 3044 and the like. The TFTs fabricated according to the invention is to be applied to the display part 3042. Thus, the invention can complete an audio apparatus.
[0229]FIG. 26F is an example of a digital camera completed by applying the invention, which is constructed with a main body 3051, a display part A 3052, an eyepiece 3053, an operation switch 3054, a display part B 3055, a battery 3056 and the like. The TFTs fabricated according to the invention is to be applied to the display part A 3052 and display part B 3055. Thus, the invention can complete a digital camera.
[0230]FIG. 26G is an example of a cellular phone completed by applying the invention, which is constructed with a main body 3061, a sound output part 3062, a voice input part 3063, a display part 3064, an operation switch 3065, an antenna 3066 and the like. The TFTs fabricated according to the invention is to be applied to the display part 3064. Thus, the invention can complete a cellular phone.
[0231]FIG. 27A is a front-type projector including a projector unit 2601 and a screen 2602. FIG. 27B is a rear-type projector including a main body 2701, a projector unit 2702, a mirror 2703 and a screen 2704.
[0233]FIG. 27D is a view showing one example of structure of the light-source optical system 2801 in FIG. 27C. In this embodiment, the light-source optical system 2801 is constructed with a reflector 2811, a light source 2812, lens arrays 2813, 2814, a polarization converter element 2815 and a focus lens 2816. Incidentally, the light-source optical system shown in FIG. 27D is one example and not especially limited to. For example, it is possible for the practitioner to properly provide an optical system, such an optical lens, a film having polarizing effect, a film for phase difference adjustment or IR film, on the light-source optical system.
Then, a semiconductor film is formed covering the first insulation film 251 and convex part (projection part) 253. Because in the embodiment the convex part (projection part) has a thickness of 30 nm-300 nm, the semiconductor film is desirably given a film thickness of 50- 200 nm, herein 60 nm. Incidentally, in case an impurity is mixed between the semiconductor film and the insulation film, there is a possibility that bad affection is exerted to the crystallinity of semiconductor film to increase the characteristic and threshold voltage variation of the TFT fabricated. Accordingly, the insulation film and the semiconductor film are desirably formed continuously. For this reason, in this embodiment, after forming an insulation film comprising the first insulation film 251 and the convex part (projection part) 253, a silicon oxide film is formed in a small thickness on the insulation film, followed by continuously forming a semiconductor film 256 without exposure to the air. The thickness of silicon oxide film, although properly set by the designer, was given 5 nm-30 nm in this embodiment.
[0255]FIG. 32A shows a TFT structure of this embodiment. In FIG. 32A, an insulation film 152 having striped convex parts (projection parts) 151 is formed on a substrate 150. A plurality of islands 153 are formed, isolated from one another, on the top surfaces of the convex parts (projection parts) 151. A gate insulation film 154 is formed in a manner contacting with the islands 153. Incidentally, although the gate insulation film 154 in FIG. 32A is formed exposing the regions, to be made into impurity regions, of the island, it may be formed covering the entire island 154.
[0261]FIG. 33A shows an embodiment on an insulation film form of the invention. In FIG. 33A, an insulation film 171 is formed on a substrate 170 wherein the insulation film 171 has a plurality of convex parts (projection parts) 172. The convex part 172 is rectangular in form as viewed from the above. All the convex parts (projection parts) have respective rectangular longer or shorter sides in a direction parallel with a scanning direction of laser light shown by the arrow.
[0263]FIG. 33B shows an embodiment on an insulation film form of the invention. In FIG. 33B, an insulation film 181 is formed on a substrate 180. The insulation film 181 is formed with a rectangular convex part (projection part) 182 having slit-like openings as viewed from the above. In the convex part (projection part) 182, the slit has a longer or shorter side in parallel with a scanning direction of laser light shown by the arrow. Explanation is now made on an example of a TFT structure formed by using the insulation film having slit-like openings shown in FIG. 33B.
[0264]FIG. 34A shows a top view of the TFT of this embodiment. As shown in FIG. 34A, this embodiment used an insulation film having a rectangular convex part (projection part) 160 having therein slit-like openings. A semiconductor film is formed covering the convex part (projection part) 160. Laser light is scanned, in a direction shown by the arrow, along a direction of a longer axis of the slit-like opening to crystallize the semiconductor film. Then, the semiconductor film is patterned to form an island 161 having an opening formed in the upper surface of the convex part (projection part).
In this embodiment, channel regions .164 are formed in plurality and the channel regions are isolated from each other. Accordingly, by increasing the channel width of the channel region, the heat generated by driving the TFT can be efficiently dissipated while securing on-current.
In crystallizing the amorphous semiconductor film, by using a continuous oscillatable solid laser and a second to fourth harmonic of basic wave, an increased grain size of crystal can be obtained. Typically, desirably used is the second harmonic (532 nm) or third harmonic (355 nm) of an Nd:YVO4 laser (basic wave: 1064 nm). Specifically, the laser light emitted from a continuous-oscillation YVO4 laser is changed into a harmonic by a nonlinear optical device to obtain a l0W-output laser light. Meanwhile, there is a method that an YVO4 crystal and a nonlinear optical device are inserted in a resonator to emit a higher harmonic. Preferably, laser light is formed by an optical system into a rectangular or elliptic form on irradiation plane, which is irradiated to a subject to be worked. The energy density, in this case, requires approximately 0.01-100 MW/cm2 (preferably 0.1-10 MW/cm2). For irradiation the semiconductor film is moved at a speed of approximately 10-2000 cm/s relatively to laser light.
[0321]FIG. 40A shows an example of a laser beam form on a subject to be processed in the case that laser light is oscillated from a plurality of laser oscillators without a slit. The laser beam shown FIG. 40A is elliptic in form. Incidentally, in the invention, the laser beam form of laser light oscillated from the laser oscillator is not limited to the elliptic. The laser beam form is different depending on a laser kind and can be formed by an optical system. For example, the laser light emitted from an XeCl excimer laser (wavelength 308 nm, pulse width 30 ns) L3308 by Lambda is rectangular in form having 10 mm×30 mm (each, width at half maximum in beam profile). The laser light emitted from a YAG laser is circular in form if a rod is cylindrical and rectangular in form if it is a slab type. By further forming such laser light by an optical system, a desired size of laser light can be formed.
[0322]FIG. 40A shows an laser light energy density distribution in a major-axis Y-direction of the laser beam. The laser light, whose laser beam is elliptic, has an energy density distribution increasing toward an elliptic center O. In this manner, the laser beam shown in FIG. 40A has an energy density in a center axis direction following the Gaussian distribution, wherein the region is narrow where energy density is to be determined uniform.
[0323]FIG. 40B shows a laser beam form when the laser light having a laser beam of FIG. 40A is combined together. Although FIG. 40B shows the case that four laser-light laser beams are superposed together to form one linear laser beam, the number of laser beams superposed is not limited to that.
[0325]FIG. 40B shows a laser-light energy density distribution in a center-axis y-direction of a combined laser beam. The laser beam of FIG. 40B corresponds to a region satisfying an energy density of 1/e2 of a peak value in the energy density of FIG. 40A. Energy density is added on in the overlapped areas of the uncombined laser beams. For example, adding the energy densities E1 and E2 together of the overlapped beams as shown in the figure, it becomes nearly equal to a peak value E3 of beam energy density. Thus, energy density is flattened between the elliptic centers O.
[0328]FIG. 41 shows an energy density distribution, determined by computation, on B-B′ and C-C′ in FIG. 40B. Note that FIG. 41 is with reference to the region satisfying an energy density of 1/e2 of a peak value of an uncombined laser beam. When the uncombined laser beam assumably has a length in minor axis direction of 37 μm and a length in major axis direction of 410 am and a center-to-center distance of 192 μm, the energy densities on B-B′ and C-C′ have respective distributions as shown in FIGS. 41A and FIG. 41B. Although the one on B-B′ is somewhat smaller than the one on C-C′, these can be considered to be substantially the same in magnitude. The combined laser beam, in a region satisfying an energy density of 1/e2 of a peak value of an uncombined laser beam, can be considered as linear in form.
[0329]FIG. 42A shows an energy distribution of a combined laser beam. The region shown at 361 is a region where energy density is assumed uniform while the region shown at 362 is a region having a low energy density. In FIG. 42, it is assumed that the laser beam has a length in a center axis direction of WTBW while the region 361 having an assumed uniform energy density has a length in a center axis direction of Wmax. As WTBW increases greater as compared to Wmax, the ratio of the region 362 uneven in energy density not to be used in crystallizing a semiconductor film increases relatively to the region 361 having an assumed uniform energy density to be used in crystallization. The semiconductor film irradiated only by the region 362 uneven in energy density has fine crystals, thus being not well in crystallinity. Consequently, there arises a necessity to define a layout of scanning route and insulation-film concavo-convex such that the region of semiconductor film to be made into an island is not superposed with the region irradiated with only the laser beam region 362. This restriction increases furthermore as the ratio of region 362 to region 361 increases. Accordingly, it is effective to use a slit to prevent only the region 362 uneven in energy density from being irradiated to the semiconductor film formed on the insulation-film convex part (projection part), in respect of decreasing the restriction occurring upon providing a layout of scanning route and insulation-film concavo-convex.
[0333]FIG. 43 shows an optical system for combining four laser beams into one laser beam. The optical system of FIG. 43 has six cylindrical lenses 417-422. The four portions of laser light entering in a direction of the arrows are respectively incident on the four cylindrical lens 419-422. The two portions of laser light formed by the cylindrical lenses 419, 421 are again formed in their laser beam form by the cylindrical lens 417, and then irradiated to a subject to be processed through a slit 424. On the other hand, the two portions of laser light formed by the cylindrical lenses 420, 422 are again formed in their laser beam form by the cylindrical lens 418, and then irradiated to the subject to be processed 423 through the slit 424.
[0336]FIG. 43 shows the example to combine four laser beams together. In this case, there are provided four cylindrical lenses respectively corresponding to four laser oscillators and two cylindrical lenses corresponding to the four cylindrical lenses. The number of laser beams to be combined is not limited to the above, i.e. the number of laser beams to be combined may be 2 or greater and 8 or smaller. In the case of combining laser beams in the number of n (n=2, 4, 6, 8), there are provided cylindrical lenses in the number of n respectively corresponding to the laser oscillator in the number of n as well as cylindrical lenses in the number of n/2 corresponding to the relevant cylindrical lenses in the number of n. In the case of combining laser beams in the number of n (n 32 3, 5, 7), there are provided cylindrical lenses in the number of n respectively corresponding to the laser oscillator in the number of n as well as cylindrical lenses in the number of (n+1)/2 corresponding to the relevant cylindrical lenses in the number of n.
The laser light having a laser beam in an elliptic form has an energy density distribution perpendicular to a scanning direction following the Gaussian distribution. Consequently, the ratio of a low energy density region to the entire is higher as compared to the laser light having a rectangular or linear laser beam. Accordingly, in the invention, the laser beam of laser light is desirably rectangular or linear comparatively uniform in energy density distribution..
[0345]FIG. 44A shows an example of a laser oscillator structure of a slab type. The slab-type laser oscillator of FIG. 24A has a rod 7500, a reflection mirror 7501, an output mirror 7502 and a cylindrical lens 7503.
[0347]FIG. 44B shows a slab-type laser oscillator structure different from that showed in FIG. 44A. In FIG. 44B, a cylindrical lens 7504 is added to the laser oscillator of FIG. 44A to control a laser beam length by the cylindrical lens 7504.
[0350]FIG. 44C shows an embodiment of a cylindrical lens form. 7509 is a cylindrical lens of this embodiment fixed by a holder 7510. The cylindrical lens 7509 has a form that a cylindrical surface and a rectangular flat surface are opposed to each other, wherein the two generating lines of the cylindrical surface and the two sides of the opposed rectangle are all in parallel with one another. The two surfaces, formed by the two lines of cylindrical surface and the parallel two lines, intersect with the rectangular flat surface at an angle greater than 0 degree and smaller than 90 degrees. In this manner, the two surfaces formed with the two parallel sides intersect with the rectangular flat surface at an angle of smaller than 90 degrees, whereby the focal length can be shortened as compared to that at 90 degrees or greater. This can further reduce the form of laser beam and approximate it to a linear form.
[0354]FIG. 45 shows an energy density distribution of each laser beam in a center axis direction by the solid line and an energy density distribution of a combined laser beam by the dotted line. The energy density value of a laser beam in a center axis direction of a laser beam generally follows the Gaussian distribution.
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U.S. Classification 257/347, 257/E29.295, 257/E21.413, 257/E27.111, 257/E29.293
International Classification H01L21/20, H01L27/12, H01L29/786, H01L21/336, H01L21/84, H01L21/77
Cooperative Classification H01L29/78603, H01L29/78675, H01L27/1281, H01L29/66757, H01L21/2022, H01L27/1296, H01L29/78696
European Classification H01L29/66M6T6F15A2, H01L27/12T30B2B, H01L21/20D, H01L27/12T30J, H01L29/786S, H01L29/786A, H01L29/786E4C2