Short pulse fiber laser for LTPS crystallization
Laser pulses from pulsed fiber lasers are directed to an amorphous silicon layer to produce a polysilicon layer comprising a disordered arrangement of crystalline regions by repeated melting and recrystallization. Laser pulse durations of about 0.5 to 5 ns at wavelength range between about 500 nm and 1000 nm, at repetition rates of 10 kHz to 10 MHz can be used. Line beam intensity uniformity can be improved by spectrally broadening the laser pulses by Raman scattering in a multimode fiber or by applying varying phase delays to different portions of a beam formed with the laser pulses to reduce beam coherence.
1. A method of processing a substrate, comprising:
producing an optical line beam based on repetitive laser pulses from a fiber laser at a repetition frequency between about 1 kHz and 1 MHz and having pulse durations less than about 25 ns; and
scanning at least one of a substrate that includes a silicon layer and the optical line beam so as to produce silicon crystal grains in the silicon layer such that the processed silicon layer has a mobility of at least about 5 cm 2 /V-sec.
2. The method of claim 1 , wherein the optical line beam pulses have spectral content between about 500 nm and 1000 nm.
3. The method of claim 1 , wherein the repetition frequency is between about 10 kHz and 1 MHz.
4. The method of claim 1 , wherein the repetition frequency is between about 70 kHz and 130 kHz.
5. The method of claim 1 , wherein the pulse durations are less than about 10 ns.
6. The method of claim 1 , wherein the pulse durations are less than about 1.5 ns.
7. The method of claim 1 , wherein the processed silicon layer has a mobility of at least about 50 cm 2 /V-sec.
8. The method of claim 1 , wherein the processed silicon layer has a mobility of at least about 100 cm 2 /V-sec.
9. The method of claim 1 , wherein the processed silicon layer has silicon crystal grains having an average grain size of between about 200 nm and 500 nm.
10. The method of claim 1 , wherein the processed silicon layer comprises randomly oriented silicon crystal grains having a grain size of between about 200 nm and 500 nm.
11. The method of claim 10 , wherein the substrate includes a transparent support having an a-Si layer on at least one surface.
12. The method of claim 1 , wherein the effective fluence is between about 20 mJ/cm 2 and 200 mJ/cm 2 .
13. The method of claim 1 , further comprising processing the laser pulses to produce spectrally enhanced pulses in which at least about 10% of the pulse energy is frequency shifted,and directing the spectrally enhanced pulses to the substrate.
14. The method of claim 13 , wherein the spectrally enhanced pulses are produced by Raman scattering, and at least about 25% of the pulse energy is frequency shifted.
15. The method of claim 14 , wherein the Raman scattering is produced by directing the laser pulses through a multimode optical fiber.
16. The method of claim 1 , further comprising applying a plurality of phase delays to respective portions of the repetitive laser pulses, and forming the line beam with the phase delayed optical pulses.
17. A method of processing a substrate, comprising:
producing an optical line beam based on repetitive laser pulses from a fiber laser at a repetition frequency between about 70 kHz and 130 kHz and having pulse durations less than about 25 ns; and
scanning at least one of a substrate that includes a silicon layer and the optical line beam so as to produce silicon crystal grains in the silicon layer such that the processed silicon layer has a mobility of at least about 5 cm 2 /V-sec.
18. A method of processing a substrate, comprising:
producing an optical line beam based on repetitive laser pulses from a fiber laser at a repetition frequency between about 1 kHz and 10 MHz and having pulse durations less than about 25 ns;
processing the laser pulses to produce spectrally enhanced pulses in which at least about 10% of the pulse energy is frequency shifted, and directing the spectrally enhanced pulses to the substrate; and
scanning at least one of a substrate that includes a silicon layer and the optical line beam so as to produce silicon crystal grains in the silicon layer such that the processed silicon layer has a mobility of at least about 5 cm 2 /V-sec.
19. The method of claim 18 , wherein the spectrally enhanced pulses are produced by Raman scattering, and at least about 25% of the pulse energy is frequency shifted.
20. The method of claim 19 , wherein the Raman scattering is produced by directing the laser pulses through a multimode optical fiber.
21. The method of claim 18 , wherein the optical line beam pulses have spectral content between about 500 nm and 1000 nm.
22. The method of claim 18 , further comprising applying a plurality of phase delays to respective portions of the repetitive laser pulses, and forming the line beam with the phase delayed optical pulses.
23. A method of processing a substrate, comprising:
producing an optical line beam based on repetitive laser pulses from a fiber laser at a repetition frequency between about 1 kHz and 10 MHz and having pulse durations less than about 25 ns;
applying a plurality of phase delays to respective portions of the repetitive laser pulses, and forming the line beam with the phase delayed optical pulses; and
scanning at least one of a substrate that includes a silicon layer and the optical line beam so as to produce silicon crystal grains in the silicon layer such that the processed silicon layer has a mobility of at least about 5 cm 2 /V-sec.
24. The method of claim 23 , wherein the optical line beam pulses have spectral content between about 500 nm and 1000 nm.
25. The method of claim 23 , wherein the repetition frequency is between about 70 kHz and 130 kHz.
26. The method of claim 23 , wherein the effective fluence is between about 20 mJ/cm 2 and 200 mJ/cm 2 .