cw laser anneal of polycrystalline silicon: Crystalline structure, electrical properties

Abstract

0.4-μm-thick polycrystalline silicon deposited in a low-pressure CVD reactor was implanted with B to a dose of 5×1014/cm2 and then irradiated in a cw laser scanning apparatus. The laser annealing produced an increase in grain size from ∼500 Å to long narrow crystals of the order of ∼25×2 μ, as observed by TEM. Each grain was found to be defect free and extended all the way to the underlying Si3N4. Electrical measurements show 100% doping activity with a Hall mobility of about 45 cm2/V sec, which is close to single-crystal mobility at the same carrier concentration. Thermal annealing produces material with an average grain size of 1000 Å and a resistivity higher by a factor of 2.2 than that obtained with the laser anneal. Laser annealing performed after a thermal anneal reduces the resistivity to approximately the same value obtained by laser annealing only.

Femtosecond laser irradiation-induced infrared absorption on silicon surfaces

“…Therefore, as the pulse number or pulse energy increases, the NIR absorptance decreases after reaching a maximum value. The silicon amorphous structure goes back to silicon crystalline structure under the influence of laser irradiation [15][16][17][18][19][20][21][22][23][24][25][26]. The silicon structure can be changed back and forth between crystalline and amorphous by controlling the experimental conditions.…”

“…On the one hand, amorphous silicon-related papers of laser irradiation mainly concentrated on the application of the laser-annealing effect, i.e., amorphous silicon became silicon crystalline or micro/nanostructured silicon for better optoelectronics applications [15][16][17][18][19][20][21][22][23][24][25][26]. On the other hand, amorphous silicon and lattice distortions could be formed with the femtosecond laser irradiation [27][28][29][30][31].…”

Crystalline Silicon Thin Film Solar Cells

“…5). First results on this method date back to the late 1970ies (Gat et al, 1978;Colinge et al, 1982). At these times laser crystallization was performed for applications in microelectronics.…”

“…The only available well suited lasers were argon ion lasers emitting green light at 514 nm wavelength with a total power of up to 15 W. Typically a circular Gaussian beam with diameter in the 40 µm range was scanned across the sample. At a scanning rate of 12.5 cm/s already in 1978 grains 2x25 µm in size were produced (Gat et al, 1978). Due to the high thermal conductivity of the wafer substrate a rather high power density is needed for melting and crystallization in this case.…”

Application of Modified Rapid Thermal Annealing to Doped Polycrystalline Si Thin Films Towards Low Temperature Si Transistors.

“…The detailed activation processes are furnace annealing, rapid thermal annealing, excimer laser annealing, etc. [15][16][17][18] In conventional furnace annealing, the processing is performed at 500 to 600 o C. Rapid thermal annealing (RTA) is processed around or below 1000 o C in nitrogen. Rapid thermal annealing and excimer laser annealing is proven to be more efficient than thermal annealing in terms of time and thermal budget in the LTPS process maps.…”