Patent Number: 
Section: claims

1. A laser irradiation apparatus comprising:a substrate stage;a substrate over the substrate stage, a semiconductor film being formed over the substrate; anda laser oscillator which irradiates the semiconductor film with a laser beam,wherein the semiconductor film is irradiated with the laser beam at an incident angle θ, andwherein the incident angle θ satisfiesθ≧arctan(w/(14×D)), (w=(w1+w2)/2),where w1 indicates a beam width of the laser beam irradiated onto the semiconductor film,w2 indicates a beam width of the laser beam at the semiconductor film after reflected by a back surface of the substrate, andD indicates a thickness of the substrate. 2. The laser irradiation apparatus according to claim 1, wherein the semiconductor film is crystallized by the laser beam. 3. The laser irradiation apparatus according to claim 1, wherein an energy distribution of the laser beam is uniformed by using long focal length cylindrical lenses at or near an irradiation plane. 4. The laser irradiation apparatus according to claim 1, wherein the laser beam is linear in shape at or near an irradiation plane. 5. The laser irradiation apparatus according to claim 1, wherein the laser beam has a wavelength of 350 nm or more. 6. The laser irradiation apparatus according to claim 1, wherein the laser beam has a wavelength of 400 nm or more. 7. The laser irradiation apparatus according to claim 1, wherein the laser beam is the second harmonic of one kind selected from the group consisting of a YAG laser, a YVO4 laser, a YLF laser, a YAIO3 laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and a glass laser. 8. A laser irradiation apparatus comprising:a substrate stage;a substrate over the substrate stage, a semiconductor film being formed over the substrate;a laser oscillator which irradiates the semiconductor film with a laser beam; anda mirror configured to adjust a direction of the laser beam,wherein the semiconductor film is irradiated with the laser beam at an incident angle θ after reflected by the mirror, andwherein the incident angle θ satisfiesθ≧arctan(w/(14×D)), (w=(w1+w2)/2),where w1 indicates a beam width of the laser beam irradiated onto the semiconductor film,w2 indicates a beam width of the laser beam at the semiconductor film after reflected by a back surface of the substrate, andD indicates a thickness of the substrate. 9. The laser irradiation apparatus according to claim 8, wherein the semiconductor film is crystallized by the laser beam. 10. The laser irradiation apparatus according to claim 8, wherein an energy distribution of the laser beam is uniformed by using long focal length cylindrical lenses at or near an irradiation plane. 11. The laser irradiation apparatus according to claim 8, wherein the laser beam is linear in shape at or near an irradiation plane. 12. The laser irradiation apparatus according to claim 8, wherein the laser beam has a wavelength of 350 nm or more. 13. The laser irradiation apparatus according to claim 8, wherein the laser beam has a wavelength of 400 nm or more. 14. The laser irradiation apparatus according to claim 8, wherein the laser beam is the second harmonic of one kind selected from the group consisting of a YAG laser, a YVO4 laser, a YLF laser, a YAIO3 laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and a glass laser. 15. A laser irradiation apparatus comprising:a substrate stage which is inclined from a horizontal direction;a substrate over the substrate stage, a semiconductor film being formed over the substrate; anda laser oscillator which irradiates the semiconductor film with a laser beam,wherein the semiconductor film is irradiated with the laser beam at an incident angle θ, andwherein the incident angle θ satisfiesθ≧arctan(w/(14×D)), (w=(w1+w2)/2),where w1 indicates a beam width of the laser beam irradiated onto the semiconductor film,w2 indicates a beam width of the laser beam at the semiconductor film after reflected by a back surface of the substrate, andD indicates a thickness of the substrate. 16. The laser irradiation apparatus according to claim 15, wherein the semiconductor film is crystallized by the laser beam. 17. The laser irradiation apparatus according to claim 15, wherein an energy distribution of the laser beam is uniformed by using long focal length cylindrical lenses at or near an irradiation plane. 18. The laser irradiation apparatus according to claim 15, wherein the laser beam is linear in shape at or near an irradiation plane. 19. The laser irradiation apparatus according to claim 15, wherein the laser beam has a wavelength of 350 nm or more. 20. The laser irradiation apparatus according to claim 15, wherein the laser beam has a wavelength of 400 nm or more. 21. The laser irradiation apparatus according to claim 15, wherein the laser beam is the second harmonic of one kind selected from the group consisting of a YAG laser, a YVO4 laser, a YLF laser, a YAIO3 laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and a glass laser. 22. A laser irradiation apparatus comprising:a substrate stage;a substrate over the substrate stage, a semiconductor film being formed over the substrate; anda laser oscillator which irradiates the semiconductor film with a laser beam,wherein the semiconductor film is irradiated with the laser beam at an incident angle θ, andwherein the incident angle θ satisfiesθ≧arctan(w/(2×D)), (w=(w1+w2)/2),where w1 indicates a beam width of the laser beam irradiated onto the semiconductor film,w2 indicates a beam width of the laser beam at the semiconductor film after reflected by a back surface of the substrate, andD indicates a thickness of the substrate. 23. The laser irradiation apparatus according to claim 22, wherein the semiconductor film is crystallized by the laser beam. 24. The laser irradiation apparatus according to claim 22, wherein an energy distribution of the laser beam is uniformed by using long focal length cylindrical lenses at or near an irradiation plane. 25. The laser irradiation apparatus according to claim 22, wherein the laser beam is linear in shape at or near an irradiation plane. 26. The laser irradiation apparatus according to claim 22, wherein the laser beam has a wavelength of 350 nm or more. 27. The laser irradiation apparatus according to claim 22, wherein the laser beam has a wavelength of 400 nm or more. 28. The laser irradiation apparatus according to claim 22, wherein the laser beam is the second harmonic of one kind selected from the group consisting of a YAG laser, a YVO4 laser, a YLF laser, a YAIO3 laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and a glass laser. 29. A laser irradiation apparatus comprising:a substrate stage;a substrate over the substrate stage, a semiconductor film being formed over the substrate;a laser oscillator which irradiates the semiconductor film with a laser beam; anda mirror configured to adjust a direction of the laser beam,wherein the semiconductor film is irradiated with the laser beam at an incident angle θ after reflected by the mirror, andwherein the incident angle θ satisfiesθ≧arctan(w/(2×D)), (w=(w1+w2)/2),where w1 indicates a beam width of the laser beam irradiated onto the semiconductor film,w2 indicates a beam width of the laser beam at the semiconductor film after reflected by a back surface of the substrate, andD indicates a thickness of the substrate. 30. The laser irradiation apparatus according to claim 29, wherein the semiconductor film is crystallized by the laser beam. 31. The laser irradiation apparatus according to claim 29, wherein an energy distribution of the laser beam is uniformed by using long focal length cylindrical lenses at or near an irradiation plane. 32. The laser irradiation apparatus according to claim 29, wherein the laser beam is linear in shape at or near an irradiation plane. 33. The laser irradiation apparatus according to claim 29, wherein the laser beam has a wavelength of 350 nm or more. 34. The laser irradiation apparatus according to claim 29, wherein the laser beam has a wavelength of 400 nm or more. 35. The laser irradiation apparatus according to claim 29, wherein the laser beam is the second harmonic of one kind selected from the group consisting of a YAG laser, a YVO4 laser, a YLF laser, a YAIO3 laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and a glass laser. 36. A laser irradiation apparatus comprising:a substrate stage which is inclined from a horizontal direction;a substrate over the substrate stage, a semiconductor film being formed over the substrate; anda laser oscillator which irradiates the semiconductor film with a laser beam,wherein the semiconductor film is irradiated with the laser beam at an incident angle θ, andwherein the incident angle θ satisfiesθ≧arctan(w/(2×D)), (w=(w1+w2)/2),where w1 indicates a beam width of the laser beam irradiated onto the semiconductor film,w2 indicates a beam width of the laser beam at the semiconductor film after reflected by a back surface of the substrate, andD indicates a thickness of the substrate. 37. The laser irradiation apparatus according to claim 36, wherein the semiconductor film is crystallized by the laser beam. 38. The laser irradiation apparatus according to claim 36, wherein an energy distribution of the laser beam is uniformed by using long focal length cylindrical lenses at or near an irradiation plane. 39. The laser irradiation apparatus according to claim 36, wherein the laser beam is linear in shape at or near an irradiation plane. 40. The laser irradiation apparatus according to claim 36, wherein the laser beam has a wavelength of 350 nm or more. 41. The laser irradiation apparatus according to claim 36, wherein the laser beam has a wavelength of 400 nm or more. 42. The laser irradiation apparatus according to claim 36, wherein the laser beam is the second harmonic of one kind selected from the group consisting of a YAG laser, a YVO4 laser, a YLF laser, a YAIO3 laser, a ruby laser, an alexandrite layer, a Ti:sapphire layer, and a glass laser.