We compare two types of laser ablation for ARC removal on polished and textured surfaces. Selective ablation with limited impact on the underlying substrate is performed with short wavelength picosecond sources working at relatively low repetition rate (<200 kHz). By adapting wavelength and fluence, the SiNx could be removed efficiently with slight change initial topography. Crystal damage is detected whatever the laser parameters but could be reduced using low fluence in UV regime. The second ablation process uses ultra-high repetition rate picosecond laser (80 MHz) and targets both SiNx ablation and over-doping of the initial n+ emitter. The thermal effect induced by the short duration between pulses performs simultaneously SiNx removal and selective emitter structure with with deep dopant profiles and low surface concentration. We investigate the correlation between the post-ablation properties and a nickel silicidation process using Excimer Laser Annealing of a thin layer of Ni. A reference process is first described on pyramid topography without pre-ablation of SiNx. It is demonstrated efficient formation of SixNiy compounds on the silicon substrate depending and laser fluence. The similar silicidation process is transferred on sample after the SiNx ablation step. A continuous nickel silicide layer is observed but its thickness distribution reveals non-uniformity over the pyramids due to post ablation roughness.
Silicon rich silicon oxynitride layers were deposited by ECR-PECVD in order to form silicon nanoparticles upon high
thermal annealing at 1100°C. The effect of the gas precursor type and flows on the atomic composition and the structural properties was assessed by RBS and ERDA analysis as well as by Raman spectroscopy. The morphological and
crystalline properties of the resulting nanoparticles were investigated by TEM analysis. We have found that the silicon
nanoparticules average size and the crystalline fraction depend strongly on the silicon excess in the SiN and SiON layer.
Development of laser doping process for the formation of a selective emitter (SE) for p-type and n-type silicon solar cells is presented. The SE is formed by laser doping of spin-on dopant sources using an intermediate barrier layer (BL). The BL serves to form shallow emitter and also offers advantage to avoid etch back step. The shallow emitter is formed by applying a controlled thermal diffusion step, which in turn reduces the laser induced defects in the SE. This process has an advantage that the shallow and selective emitters can be formed from a single dopant source. In this investigation, PECVD deposited SiOx was used as the barrier. KrF excimer laser at 248 nm was used for the selective doping. The dopant concentration and depth, as measured by SIMS, were controlled by variation of the laser parameters and barrier thickness. It was found relatively lower thickness PECVD deposited SiOx barrier layer with high dopant content in the spin-on layer at comparably low laser fluences resulted in the best electrical results. The SiOx layers acted as perfect barrier for the boron diffusion. It was also observed that multiple laser annealing above a threshold laser fluence resulted in the redistribution of the dopant along with deepening of selective emitter because of the limitedness of the dopant source. Also, this is attributed to the increase of the total absorbed energy by the successive laser pulses. The results were discussed and presented in detail.
Laser processing applied to thin film silicon is an interesting approach for solar cell fabrication. In this work, we
investigate the effects of a continuous wavelength (CW) laser irradiation in solid phase or liquid phase of silicon on the structural and electrical properties of thin film silicon layers. Thus, results on CW laser induced crystallisation (LIC) of ultrathin amorphous silicon, laser induced epitaxy (LIE) of a thick amorphous silicon on a seed silicon layer, and laser induced thermal annealing (LIA) of polycrystalline silicon films are presented and discussed.
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