Effects of arsenic doping on chemical vapor deposition of titanium silicide

This work examines the effects of implanted arsenic on nucleation and growth of TiSi 2 formed by rapid thermal chemical vapor deposition using SiH 4 and TiCl 4 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 × 10 14 to 5 × 10 15 cm -2 . It is shown that heavy dose As can result in a barrier to TiSi 2 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 SiH 4 and TiCl 4 . 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 × 10 15 cm -2 ) almost completely suppress nucleation. During deposition, As diffuses through the TiSi 2 layer and plays a similar role on the TiSi 2 surface. Because TiCl 4 adsorption on TiSi 2 is favored, the substrate supplies the Si atoms for TiSi 2 formation resulting in enhanced consumption. Because this process relies on Si diffusion through TiSi 2 , 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 TiSi 2 films which can be attributed to the role of As in nucleation.