Programmed Rate Processing to Increase Throughput in LPCVD

The simultaneous one-dimensional Knudsen diffusion and chemical reaction description of low-pressure chemical vapor deposition in features on patterned surfaces is used to show that a substantial decrease in processing time can be achieved for a given step coverage by varying the deposition rate in a prescribed manner during the process. For constant-rate CVD (CRCVD) processes, the rate is dictated by the rate required to obtain a good step coverage at the end of the process when the instantaneous aspect ratio becomes very large. The use of a programmed-rate CVD (PRCVD) process allows a larger average deposition rate, since the initial rate is much higher than the rate required to maintain good step coverage close to feature closure. The PRCVD concept is demonstrated for the thermally activated deposition of silicon dioxide from tetraethylorthosilicate (TEOS) by decreasing the temperature during deposition. The two-step process path chosen for our calculations is not optimal; however, it can be easily implemented and modified. The time saved depends on the reaction kinetics, but approaches 50% of the constant rate process time for step coverages above 95%.