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 degrees C on Si substrates implanted with As atoms. The As implant doses ranged from 3 x 10(14) to 5 x 10(15) 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 (greater than or equal to 5 x 10(15) 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 san be attributed to the role of As in nucleation. (C) 1999 The Electrochemical Society. S0013-4651(99)02-083-2. All rights reserved.