Influence of hydrogen on the structure and surface morphology of pulsed ArF excimer laser crystallized amorphous silicon thin films

Effect of hydrogen on surface texturing and crystallization of a-Si:H thin film irradiated by excimer laser

“…The spike height at 1 or 100 pulses almost linearly increase with increasing of fluence. According to reference [17], the spike heights at 1 pulse are close to the experimental results. The average spike height of laser irradiated dehydrogenated aSi thin films (prepared by thermal annealing at 80 hours) at 0.4 J/cm 2 and 100 pulses is around 58 nm.…”

“…2.1, beyond the capillary waves formed by solidifying of the molten layer, hydrogen should play an important role in formation of the spikes. It is showed that the hydrogen atoms combine to form H 2 gas, and then diffuse into the ambient medium and leave the blister regions after laser processing [17]. However, a more complex process could occur, i.e., the combined hydrogen molecules may explode when the laser energy is high enough; subsequently, the released pressure drives the upper liquid silicon layer to move upwards while the surrounding liquid silicon flows to the explosion position.…”

“…Two different nucleation scenarios-a moving liquid/solid Si interface can be unstable with respect to nucleation of c-Si [20] and small crystallites can nucleate in a-Si during heating phase prior to melting [21]-had been made to explain why explosive crystallization occurs. Second, an observation by Mathe et al [17] showed that hydrogen slows down the crystallization process because more energy density is needed to crystallize a given depth when hydrogen is present. Largegrained polycrystallites are generated at the hydrogen depletion region near the surface, and fine-grained ones are located at hydrogen contained area underneath.…”

“…2.1 Hydrogen effect on nanosecond laser-induced surface texturing on a-Si:H Mathe et al [17] showed that the surface roughness caused by single-pulse irradiation on a-Si:H could be almost two orders of magnitude larger than that of non-hydrogenated a-Si, and mentioned that the movement of H 2 gas bubbles generated by the combination of H atoms and molecules in the ambient medium is responsible for the surface roughness.…”

“…Therefore, the feasibility of nanosecond laserinduced surface texturing and crystallization of a-Si:H becomes of interest. Many research groups focused on excimer laser induced crystallization on non-or low-hydrogen a-Si thin films [15,16], and Mathe et al [17] reported the effect of hydrogen on surface roughness and crystallization of aSi:H thin films by single-pulse irradiation of excimer laser. However, there is no work showing a sharp spiked surface on the a-Si:H thin film after multiple excimer laser pulses irradiation, and how hydrogen plays a role in the laser-induced surface texturing and crystallization is still not clear.…”