<i>In situ</i> infrared reflection and transmission absorption spectroscopy study of surface reactions in selective chemical-vapor deposition of tungsten using WF6 and SiH4

Abstract

The adsorption of tungsten hexafluoride (WF6) and monosilane (SiH4) in selective chemical-vapor deposition (CVD) of tungsten (W) is investigated in situ using Fourier-transform infrared reflection and transmission absorption spectroscopy (FTIR RAS and TMS). The selectivity for W growth is found to originate from the dissociation of SiH4 on a W surface. That is, SiH4 dissociates on a W surface to form Si-containing adsorbed species when the W surface is exposed to SiH4 at temperatures higher than 110 °C, whereas SiH4 does not dissociate on a SiO2 surface. On the other hand, when W and SiO2 surfaces are exposed to WF6 at temperatures from 20 to 300 °C, no adsorbed species are observed by FTIR RAS. However, WF6 can easily react with the Si-containing adsorbed species on a W surface to form W and byproduct gases of SiHF3 and SiF4. The main surface reaction of selective W CVD can be expressed as WF6+2SiH4=W+2SiHF3+3H2. These experimental results support the selective W-CVD mechanism previously proposed, which shows that dissociation of SiH4 and not the dissociation of WF6 has a central role in this process.