Silicon atomic layer growth using flash heating in CVD

-Si atomic layer growth on Si was investigated by heating the surface with a Xe flash lamp in an ultraclean low-pressure environment of SiH, or Si2H6 gas. In the case of SiH4, about 0.4 atomic layer deposition per single flash light shot was observed on Si(1OO) at a substrate temperature of 385OC and at a SiH, partial pressure of 500Pa. The adsorption process of SiH, can be explained quantitatively by Langmuir-type adsorption model, assuming that the total adsorption site density is equal to the surface atom density. It was found that the amount of adsorbed SiH4 molecules is determined by the balance between adsorption and desorption of SiH,. In the case of Si2H6, sub-monolayer growth of Si was observed at a substrate temperature of 320°C and under Si2H6 partial pressure of 300Pa. From the RHEED observation, epitaxial growth of Si films on Si(100) was confirmed to be realized at low temperatures such as 385OC and 320°C by using SiH4 and Si2H6, respectively, and the surface flatness of the deposited films was as good as that of the initial surface. Atomic layer epitaxy of Si and Ge in chemical vapour deposition(CVD) is attractive for the progress of future semiconductor devices, e.g. ultrasmall devices and hetero devices. In conventional CVD, surface adsorption and reaction of reactant gases proceed simultaneously. In order to achieve atomic layer control, it is important to separate the adsorption process and the reaction process. So far, in atomic layer epitaxy[l-41, the self-limiting process of gas adsorption has been employed using metal organic or chloride gases which form a strong chemical bond between surface atoms and adsorbed molecules. In order to prevent any contamination of deposited films, simple hydride gases such as GeH4, SiH4 or Si2H6 yithout carbon or halogen should be used as the reactant gas. The studies of SiH, and Si2H6 adsorption process on Si surfaces in an ultrahigh vacuum have been reported[5]. However, atomic layer growth of Si using these hydride gases had not been reported so far. In the previous work, the atomic layer epitaxy of Ge using GeH4 gas has been achieved by heating the surface with a Xe flash lamp in an ultraclean low-pressure environment[6-81. In the present work, Si atomic Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1993362 JOURNAL DE PHYSIQUE IV Xe Flash Lam Quartz Window Fig.1.-Schematic diagram of an ultraclean RF-heated cold-wall lowpressure CVD system with Xe flash lamp. layer growth process on Si substrate was investigated by the flash heating method, and sub-monolayer epitaxial growth of Si per shot of flash light has been achieved using SiH4 and Si2H6 gases at 38SoC and 320°C, respectively. Furthermore, the SiH4 and Si2H6 adsorption mechanisms are discussed. Si deposition on S i was carried out using SiH4 or Si2H6 in an ultraclean RF-heated cold-wall low-pressure CVD system as schematically shown in Figure 1. The system was made ultrahigh vacuum compatible with gate valves, turbo molecular pumps and a load-lock chamber. Moisture levels of used Ar, SiH4 and Si2H6 gases at the reactor