Low Temperature Selective Silicon Epitaxy Using Si2H6, H2 and Cl2 in Ultra High Vacuum Rapid Thermal Chemical Vapor Deposition

Abstract

In this paper we present for the first time the use of the Si2H6/H2/Cl2 chemistry for selective silicon epitaxy in a rapid thermal CVD reactor. Depositions were carried out in an ultra-high vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) system designed and constructed at North Carolina State University. Experiments were performed over a temperature range of 650°C to 850°C and over a pressure range of 22 to 25 mTorr using a flow rate 100 sccm of 10% Si2H6 in H2 and 0 to 10 sccm of Cl2. Deposited layer thicknesses were evaluated using a combination of interferometry and profilometry. Without Cl2 over the range of 650°C to 850°C, the growth rate is approximately constant at 160 nm/min. exhibiting a weak dependence on temperature. A clear advantage of Si2H6 is that high growth rates compatible with single wafer manufacturing can be obtained at very low pressures thus minimizing the introduction of contaminants by the process gases. With the addition of C12, the growth rate is suppressed at temperatures below 800°C, but, at 800°C and above, it is affected only slightly for Cl2 flow rates below 5 sccm. As the Cl2 flow rate is increased past 5 sccm, the growth rate at higher temperatures becomes a strong function of Si2H6:Cl2 ratio. Excellent selectivity with respect to patterned SiO2 and Si3N4 was obtained over the entire Cl2 flow rate range suggesting that even lower Cl levels may be sufficient for selective deposition. This implies that selectivity can be obtained with Si:Cl ratios much lower than those introduced by the more commonly used SiH2Cl2 chemistry. Furthermore, because Si2H6 can provide high growth rates at very low pressures, the total partial pressures of Cl2 and resulting chlorinated species can be significantly lower than typically required for selectivity. Our results indicate that C12 successfully enhances selectivity and yields highly selective depositions for process durations well within the practical limits of single wafer manufacturing.