On the Role of Chlorine in Selective Silicon Epitaxy by Chemical Vapor Deposition

Abstract

Si thermal etching studies have been performed using pure Cl2 in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor in the temperature range of 650–850°C and the flow rate range of 1–10 sccm which corresponds to a pressure range of 0.5–3.5 mTorr. The effects of temperature and Cl2 flow were investigated with thermodynamic equilibrium calculations performed to determine possible reaction pathways. The effect of adding H2 , up to 500 sccm, on Si etch rates at 800 and 850°C was also obtained experimentally. Thermodynamic equilibrium calculations were used to support the experimental results and determine the reaction by‐products. It is proposed that SiCl2 equilibrium partial pressure can be used as a means to compare the etching ability, thus the selectivity, of different selective Si processes. The results from the etching studies were used to explain the behavior of Si epitaxy growth rate from the Si2H6,H2 and Cl2 system in the 650–850°C, 22–24 mTorr processing regime. The implications of the etching studies for selective silicon epitaxy with the Si2H6 and Cl2 chemistry are discussed and then extended to the SiH2Cl2 based chemistry.

Selective epitaxial growth of Si1−xGex films via the alternating gas supply of Si2H6, GeH4, and Cl2: Effects of Cl2 exposure

“…Due to the higher Si 1 À x Ge x -etching capacity for 5-sccm Cl 2 than 1-sccm Cl 2 , the growth rate of Si 1 À x Ge x SEG with 5-sccm Cl 2 is lower than that with 1-sccm Cl 2 . Surface passivation of Si 1 À x Ge x films with chlorine during the Cl 2 exposure step might be responsible for the longer incubation time of Si 1 À x Ge x SEG with addition of Cl 2 [7,12].…”

“…In this study, by dint of separate injection of Cl 2 and source gas of Si 2 H 6 and GeH 4 , the chances for generation of Si chlorides and chlorosilanes and the corresponding Ge species can be ruled out, and their effect on our Si 1 À x Ge x SEG can be excluded. When the surface of S 1 À x Ge x film grown on Si(0 0 1) surface is exposed to Cl 2 gas, two desorption species, GeCl 2 and SiCl 2 , can be mostly generated [12,16]. Decrease in the Ge concentration in our Si 1 À x Ge x SEG films by addition of Cl 2 can be attributed to the discrepancy between desorption energy of GeCl 2 in the Cl 2 / Ge(0 0 1) system, i.e., 25.6 kcal/mol and SiCl 2 in the Cl 2 /Si(0 0 1) system, i.e., 73.0 kcal/mol [17,18].…”

Chlorine Etching for In-Situ Low-Temperature Silicon Surface Cleaning for Epitaxy Applications

“…However, the etch rates using this process are very low below 800 o C. For temperatures less than 750 o C, the etch rates with HCl have been observed to be less than 1nm/min (3). Previously attempts made to use using chlorine instead of hydrogen chloride to etch silicon in a hydrogen ambient (4). It was observed that the etch rate was still negligible below 750 o C. The authors believed that hydrogen was reacting with the chlorine to form HCl.…”

Low thermal budget selective epitaxial growth for formation of elevated source/drain MOS transistors

“…However, the SEG-Si surface was uneven, which the highest value (R max ) of the surface roughness was 5.5 nm in the area of 4 Â 4 mm 2 by atomic force microscopy (AFM) measurement. It appeared that the Si 2 H 6 dissociation vaporized from the substrate surface by reacting with Cl 2 dissociation [14]. Therefore, the deoxidation effect of Si 2 H 6 dissociation must be reduced and the resulting SEG-Si surface was rough.…”