AVS 45th International Symposium
    Partial Pressure Measurements and Process Control Topical Conference Friday Sessions
       Session PC-FrM

Paper PC-FrM3
Reaction Analysis and Rate Metrology of Selective Area Silicon PECVD using In-Situ Real-time Mass Spectroscopic Sensing and Mass Balance Modeling

Friday, November 6, 1998, 9:00 am, Room 317

Session: Process Monitoring and Control
Presenter: A.I. Chowdhury, North Carolina State University
Authors: A.I. Chowdhury, North Carolina State University
T.M. Klein, North Carolina State University
G.N. Parsons, North Carolina State University
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Thin film processes in microelectronics fabrication often have intermediate steps that need to be quantified for optimization purposes. These intermediate steps, including concurrent etching and deposition cannot be quantified using only final state analysis. Additional real-time process state data is required. Mass spectroscopy is a useful process state sensor for SiH@sub 4@ processes because it is particularly sensitive to changes in silane concentrations in the sampled gas. We use real-time in-situ mass spectroscopy and mass balance modeling to quantify deposition and etching reaction rates in a cyclic deposition/etch process that leads to selective area microcrystalline silicon PECVD. The procedure involves repeated cycles of a SiH@sub 4@/He/H@sub 2@ plasma followed by a He/H@sub 2@ plasma. In order to monitor reactant concentrations in real time, process trace data were collected at 30 amu corresponding to SiH@sub 2@@super +@, the principal SiH@sub 4@ related signal generated in the ionization region of the mass spectrometer. We have developed a mass balance model that can be used in conjunction with real-time sensor data, such as mass spectroscopy, to quantify deposition and etching rates in selective deposition. During SiH@sub 4@/He/H@sub 2@ flow, when the plasma is initiated, we observe a decrease in the silane signal that is correlated to film deposition. During the He/H@sub 2@ plasma the silane signal is larger when the plasma is on, and the change is a quantitative indicator of silane produced by etching. OES data does not show comparable sensitivity to silane concentration changes for our process. The transition from selective to non-selective conditions can be detected in real-time. A sharp change in slope of the silane signal is observed during etching, which is consistent with complete removal of stray nuclei from the non-receptive surfaces. Fitting the real-time mass spectroscopic data to the mass balance model we calculated the etch rate to be ~2.1 nm/min on receptive surfaces such as c-Si and ~4.5 nm/min on non receptive surfaces such as SiO@sub 2@. The values are consistent with other results. This demonstrates rate sensitivity for intermediate process steps. The mass balance analysis also reveals that these rates are obtainable only if real-time process sensor data is available.