The initial stages of Si thin deposits on foreign substrates in a rapid thermal chemical vapor phase reactor

Abstract

Nucleation and coalescence mechanisms of silicon clusters on silicon dioxide and high purity crystalline alumina substrates have been investigated in a rapid thermal chemical vapor deposition (RTCVD) system at atmospheric pressure for crystalline silicon thin film solar cells. Trichlorosilane (TCS) was employed as a reactant diluted in a hydrogen carrier gas. The nuclei density was determined as a function of the deposition time and the saturated nuclei density versus substrate temperature ranging from 900 to 1250°C for two different reactor configurations. Furthermore, the evolution of the average cluster size and variation and cluster density were studied to understand the impact of hydrodynamics and pre-annealing treatment of the substrate at deposition temperature before the nucleation step. We obtained the same induction periods for the establishment of steady state Si nucleation on both substrate materials. Conversely, the distinct physical properties of the two substrates influenced strongly the nucleation density, the nuclei and grains size evolution depending on the growth temperature and time. In this case, chemical reactions and surface conditions determine further ripening mechanisms and coalescence of the clusters resulting in coarser grains and faster layer growth for the Si deposits on alumina substrates. The effects of surface pre-treatments and operational parameters on the cluster and grain formation were analyzed by Nomarski and scanning electron microscopy (SEM).