Oxide Removal on Silicon by Rapid Thermal Processing Using SiH2CI2 and H2

Abstract

In this paper, we report in-situ oxygen removal on Si using SiH2Cl2 and H2 in a high vacuum rapid thermal chemical vapor deposition reactor. The system consists of a main process chamber and a load-lock with base pressures of ∼ 1×10−7 Torr and 1×10−5 Torr respectively. The experiments were conducted in the temperature range of 750°C to 865 °C, and SiH2Cl2/H2 flow ratios of 1% to 7%. For comparison, samples were also prepared with only H2 prebaking in the same temperature and pressure range as well as with no in-situ cleaning. With no in-situ cleaning, the oxygen content was found to decrease at higher temperatures suggesting partial oxygen removal during early stages of growth. The results indicate a strong temperature dependence for the H2 clean with an increased effectiveness at higher temperatures which is believed to be due to temperature dependence of oxygen desorption from Si. In the temperature range studied, the SiH2Cl2 clean was found to be effective at 750°C. An additional oxygen removal mechanism appears to be introduced by the addition of SiH2Cl2. Using this approach, at 750°C, the peak oxygen concentration can be reduced to 4×1018 cm−3 whereas the H2 anneal at the same temperature results in a concentration of 6×1018 cm−3. At higher temperatures, the oxide can be removed in pure H2 just as efficiently or desorbed during initial stages of growth. The results show that the efficiency of the process increases as more SiH2 Cl2 is added to the system up to a critical pressure. However, if the SiH2Cl2 partial pressure is above this critical value, Si deposition can occur on the Si surface yielding an optimum partial pressure which is a function of temperature. The results indicate that the use of a small amount of SiH2Cl2 as a cleaning agent may provide a low temperature pre-epi clean.