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.
We present the use of the Si2H6/H2/CL2 chemistry for selective silicon epitaxy by rapid thermal chemical vapor deposition (RTCVD). The experiments were carried out in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor. Epitaxial layers were grown selectively with growth rates above 150 nm/min at 800 °C and 24 mTorr using 10% Si2H6 and H2 and Cl2 with a minimum Si:Cl ratio of 1. Excellent selectivity with respect to SiO2 and Si3N4 was obtained indicating that very low Cl2 partial pressures are sufficient to preserve selectivity. In situ doping results with B2H6 show that sharp doping transitions and a wide range of B concentrations can be obtained with a slight B incorporation rate reduction with Cl2 addition. Our results indicate that UHV-RTCVD with the Si2H6/H2/Cl2 chemistry yields highly selective Si epitaxy with growth rates well within the practical throughput limits of single wafer manufacturing and with a potential to reduce the Cl content below the levels used in conventional SiH2Cl2 based selective epitaxy processes.
Epitaxial silicon films have been deposited by a new technique which combines an ultrahigh vacuum (UHV) environment with rapid thermal chemical vapor deposition (RTCVD). The technique is referred to as UHV/RTCVD. Using Si2H6, B2H6, and H2 as process gases, low temperature (T≤800 °C) and high throughput (growth rate ≳0.25 μm/min) processing have been achieved in the 90 mTorr (1 Pa=133.32 Torr) total pressure regime. Epitaxial growth was achieved on hydrogen passivated silicon surfaces without using a high temperature in situ clean. Effect of the growth temperature on the generation lifetime of the films grown on 4–11 Ω cm (100) silicon substrates was studied at three different temperatures of 700, 750, and 800 °C using the Zerbst technique. The epitaxial films were in situ doped with boron to a doping level of 1–2×1016 cm−3. Generation lifetimes, as high as 400 μs, were measured with no strong dependence on the growth temperature. Chemical purity of the films was studied using secondary ion mass spectroscopy, which indicated low oxygen and carbon levels on the order of 1017 cm −3.
We have previously reported a process for low temperature selective silicon epitaxy using Si 2 H 6 , H 2 , and Cl 2 in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor.' Selective deposition implies that growth occurs on the Si surface but not on any of the surrounding insulator surfaces. Using this method and process chemistry, the level of C1 species required to maintain adequate selectivity has been greatly reduced in comparison to SiH 2 Cl 2 -based, conventional CVD approaches. 2 ' 3 In this report, we have extended upon the previous work and provide information regarding the selectivity of the silicon deposition process to variations in the growth conditions. We have investigated the selectivity of the process to variations in disilane flow/partial pressure, growth temperature, and system contamination. We demonstrate that increases in either the Si 2 H 6 partial pressure or flow rate, the process temperature, or the source contamination levels can lead to selectivity degradation. In regard to the structural quality of the selective epitaxial layers, we have observed epitaxial defects that have appeared to be a strong function of two basic conditions: the contamination level of the process and the chlorine flow rate or chlorine partial pressure. Overall, the results in this study indicate several process conditions that can inhibit the quality of a selective silicon deposition process developed for single-wafer manufacturing.
Boron incorporation in Si during Si epitaxy was studied in an ultrahigh-vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) reactor. The films were deposited using Si2H6 and B2I.I~ diluted in HI2 as the reactive gases over a doping range from 1 • 10 TM to 1 • 101~ cm -3. The experiments were carried out in a temperature range of 650-800~ and a total pressure of 80 mTorr. The experimental results revealed a minimal effect of B2H6 on the Si growth rate. Boron concentration in Si was found to be proportional to the B2H6 flow rate and independent of the deposition temperature. This was found to be true even though the growth rate changed by a factor of five in the temperature range investigated. This is suggestive of a thermodynamic equilibrium between B in the gas phase and B on the growing Si surface. The results are consistent with the claim that B2H6 dissociates as BH3 in the gas phase which chemisorbs on the growing Si surface. In this paper, we demonstrate that by UHV-RTCVD, retrograde doping profiles with sharp doping transitions and doped multilayers with a precise control over film thickness can be obtained. This is attributed to the cold-walled nature of the growth environment which eliminates the chamber memory effect typically observed in hot-wall reactors.
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