Effects of arsenic doping on chemical vapor deposition of titanium silicide

This work examines the effects of implanted arsenic on nucleation and growth of TiSi₂ formed by rapid thermal chemical vapor deposition using SiH₄ and TiCl₄ as the precursors. In this study depositions were carried out in a temperature range of 750 to 850 °C on Si substrates implanted with As atoms. The As implant doses ranged from 3×10¹⁴ to 5×10¹⁵ cm^-2. It is shown that heavy dose As can result in a barrier to TiSi₂ nucleation and enhance silicon substrate consumption. A surface passivation model is proposed to explain the effects. On Si, As provides a stable surface structure which inhibits adsorption of SiH₄ and TiCl₄. Higher temperatures aid As desorption from the Si surface providing nucleation sites. With moderate implant doses, As results in an incubation time whereas very high doses (≥5×10¹⁵ cm^-2) almost completely suppress nucleation. During deposition, As diffuses through the TiSi₂ layer and plays a similar role on the TiSi₂ surface. Because TiCl₄ adsorption on TiSi₂ is favored, the substrate supplies the Si atoms for TiSi₂ formation resulting in enhanced consumption. Because this process relies on Si diffusion through TiSi₂, beyond a threshold thickness the efficiency of the Si diffusion process drops resulting in suppression of the deposition process. The results indicate that the As dose also plays a role in grain size and surface morphology of the deposited layers. Higher As doses result in smaller grained TiSi₂ films which can be attributed to the role of As in nucleation.