PROCESS-PROPERTY RELATIONSHIPS IN SI1-XGEX CHEMICAL-VAPOR-DEPOSITION - THERMODYNAMIC AND KINETIC-STUDIES

Thermodynamic and kinetic analyses of the Si1-xGex chemical vapor depo sition were conducted to study the factors that contribute to the comp osition of grown thin films as well as their growth rate. The thermody namic analysis of the Si/Ge/H/Cl system showed that the addition of ch lorine to the system directly affects the solid phase Ge content. Chlo rine appears to be very effective in retaining silicon in the gas phas e by forming a variety of chemical species at all temperatures studied (400 to 800 degrees C), while it retains germanium by forming primari ly GeCl2 in the gas phase only at higher temperatures. The effect of c hlorine suggests that the composition of the Si1-xGex epitaxial layer can be tuned to a desired value with the addition of a predetermined a mount of chlorine to the system as an alternative to changing the rati o of silicon and germanium gaseous sources. In the absence of chlorine , the Si/Ge/H system appears to be more kinetically controlled. A kine tic study was done on the Si/Ge/H system to explain the experimentally observed growth behaviors: a monotonic increase, a monotonic decrease , and a maximum in growth rate with respect to solid phase Ge concentr ation at low, high, and intermediate temperatures, respectively. A ger mane-assisted hydrogen desorption path, coupled with the two parallel growth paths from SiH4 and GeH4, where both species compete for the sa me vacant surface sites, are shown to explain the three distinctive gr owth rate behaviors observed.