Crystallization by furnace annealing and laser annealing of highly dose Arsenic implanted amorphous Silicon

We investigated the effect of thermal annealing in furnace at 680°C on a 90nm thick crystalline silicon on insulator layer amorphized by Arsenic implants at doses above 5x1014/cm2. We studied, as a function of the annealing time, the influence of doping on the main crystallization parameters like the crystalline fraction, the grain density and the grain size. At As implant doses of 1x1015/cm2, the nucleation rate becomes slower than in the reference sample amorphized by Si implantation. After 30min, we obtained only partial crystallization of the layer but the crystal grain size was as large as 20µm (see figure). This phenomenon is consistent with an inhibited nucleation rate and, as known in the literature, an increased growth rate in the presence of As. The electrical activation of this µm-sized polycrystalline layer was in the range 250-300 Ωsq depending on the measurement temperature (25-200°C). We investigated also the laser annealing as crystallization process alternative to furnace annealing. Irradiation of samples has been done by an infrared CW laser equipment. High crystallization at low irradiation power occurs via homogenous nucleation and, as already obtained in a-Si:H[1], the mean size of crystal grains doesn’t depend on the irradiation power. This is due to non-steady regime in which grain nucleation dominates over the growth process [2]. However, if comparing the Si amorphized and the As amorphized SOI layer after laser irradiation the mean size of crystal grains increases from 50nm to more than 200nm for an As implant dose of 3x1015/cm2. This result confirms that nucleation is inhibited also when the crystallization process lasts only few milliseconds at temperatures above 1100°. Nevertheless, under these irradiation conditions, the electrical activation is 40% higher than after a rapid thermal process at 1150° for 5s. [1] R. Ruggeri et al. J. Electrochem. Soc. 158, H25-H29 (2011). [2] G. Mannino et al. App. Phys. Lett. 97, 022107 (2010)