DYNAMIC RATE AND THICKNESS METROLOGY DURING POLY-SI RAPID THERMAL CHEMICAL-VAPOR-DEPOSITION FROM SIH4 USING REAL-TIME IN-SITU MASS-SPECTROMETRY

Real-time in situ mass spectrometry has been applied to poly-Si rapid thermal chemical vapor deposition (RTCVD) (from SiH4) on thermally gro wn SiO2 as a way to determine film thickness at the end of the process and to infer dynamic deposition rate during the process for run-to-ru n and real-time control applications. Monitoring process ambient at 5 Torr is achieved using two-stage differential pumping of a sampling ap erture in the exhaust stream, and a rapid response time (similar to 1 s for a similar to 30 s process cycle) allows for real time sensing of reactant input, product generation, and reactant depletion. Active ma ss spectrometric sampling of the reaction by-product (H-2 generated by SiH4 decomposition) provides a monitor of the total reaction/depositi on rate during poly-Si RTCVD in the range 550-850 degrees C. Product g eneration as a function of temperature is readily distinguished from r eactant cracking fragments by spectral analysis. A well-defined monoto nic correlation between the time-integrated H-2(+) product signal and the poly-Si film thickness, determined ex situ by single-point interfe rometry (Nanometrics), demonstrates that the integrated mass spectrome tric signal can provide real-time thickness metrology. In addition, th e time-dependence of product and reactant signals provides a real-time indication of detailed equipment behavior during the process. (C) 199 6 American Vacuum Society.