Mass spectrometry has been exploited for rapid real-time sensing of both reactant and product species in single-wafer rapid thermal chemical vapor deposition (RTCVD) of polycrystalline Si from SiH4. Active mass spectrometric sampling at pressures to 5 Torr is achieved using two-stage differential pumping of a sampling aperture in the exhaust stream, leading to response times as short as ∼3 sec to concentration and pressure changes in the reactor during a process carried out in ∼30 sec. In addition to reactant species, gaseous reaction byproducts have been identified and differentiated from cracking fragments of the reactant through relative intensities of mass fragments as a function of wafer temperature (i.e., reaction rate). For RTCVD of poly-Si from SiH4, carried out in the range 450–800 °C at 5 Torr in 10% SiH4/Ar, mass spectra reveal not only the time dependence of reactant (monitored by SiH2+, 30 amu), but also—at higher temperatures—reactant depletion and product generation (from H2+, 2 amu). These results demonstrate a basis for using mass spectrometry in real-time process diagnostics and control.
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Tedder et al. (1995) studied this question.