Emission Fourier-transform infrared spectroscopy as an in situ probe of silicon chemical vapor deposition at high gas pressures
Abstract
Emission Fourier transform infrared (EFTIR) spectroscopy is applied to the low pressure chemical vapor deposition (LPCVD) of silicon. This technique allows for the in situ characterization of the silicon substrate surface in real-time during the growth of thin silicon films. CVD reactions can be monitored at reduced pressure, and substrate temperatures up to 800$\sp\circ$C. The application of this technique can help improve the understanding of the heterogenous reactions involved in silicon CVD from silane as well as provide a means of improving feedback control during film growth through probing and manipulation of surface species concentration. The development of the EFTIR technique involved the design, construction, and optimization of a CVD-IR reactor system. This overall system includes the vacuum pumping, temperature control, and mass flow systems as well as the reactor and optics. The system was optimized sufficiently so that the techique could be applied to identify surface species in situ during silicon CVD from silane at substrate temperatures about 800$\sp\circ$C and pressures on the order of 1 Torr. Emission FTIR spectra collected in situ and real-time show features remaining constant during steady-state film growth, consistent with the expected behavior of surface species. Cross-sectional transmission electron microscopy (XTEM) and x-ray diffraction (XRD) characterization of the samples show epitaxial silicon thin film growth with minute amounts of polycrystalline silicon possibly near the substrate edges. Profilometry is used to determine the thickness of the grown films and is consistent with estimates of film thickness obtained from the XTEM images, yielding growth rates of $153\pm 7$ A/min. Deconvolution of the emission FTIR spectra shows a features near 2050 cm$\sp{-1}\pm 8$ cm$\sp{-1}$ which is assigned to the assymmetric stretch of coupled silicon monohydride (SiH). A tentative assignment of features near 2095 cm$\sp{-1}\pm 15$ cm$\sp{-1}$ to the uncoupled SiH and the symmetric stretch of coupled SiH is also made. Desorption experiments seem to indicate that SiH is not readily removed from the surface at 650$\sp\circ$C under 230 mTorr of flowing nitrogen, but easily removed at 750$\sp\circ$C. These observations suggest that SiH may not desorb through first order kinetics under inert environments and may be reactively desorbed by silane during CVD.
Degree
Ph.D.
Advisors
Takoudis, Purdue University.
Subject Area
Chemical engineering|Materials science|Condensation
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