1 June 1992 Correlation of Si wafer FTIR spectra with wafer temperatures and resist durability variations in plasma etching processes
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Abstract
The temperatures that wafers reach in plasma etching processes result from a balance of several factors including energetic particle bombardment heating, exothermic chemical reactions, radiative cooling, and gas phase viscous and molecular cooling. The radiative cooling depends on the emittance of the particular wafers and can vary considerably from wafer to wafer. As a result, the heating rate of and peak temperatures reached by different wafers can vary in the identical plasma etching process. This can lead to variations in the etch rates and reticulation thresholds of resists coated onto those wafers. A simple means of estimating the emittance of a silicon wafer below 200 degree(s)C could improve our ability to predict the peak temperatures that wafers reach in plasma etching processes. This could improve the reproducibility of resist etch rate and reticulation threshold measurements in plasma environments. Much of the energy radiated by a black or gray body in the range between room temperature and 200 degree(s)C is in the wavelength range scanned by commercially available FTIR spectrometers. Consequently, the magnitudes of transmitted and reflected IR signals provide an indication of IR absorption by silicon wafers and therefore of the emittance of the wafers in the wavelength range of interest for radiative cooling in plasma etching processes. In this paper we present resist etch rate and reticulation threshold measurements on wafers with differing FTIR transmission and reflection spectra. The data show that variations in etch rates and reticulation thresholds do correlate with differences in the wafers' IR transmittance and reflectance, suggesting that the wafers' peak temperatures also correlate with the FTIR spectra.
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Gregory Luckman, Gregory Luckman, Carl P. Babcock, Carl P. Babcock, Helen L. Maynard, Helen L. Maynard, Chris J. Gamsky, Chris J. Gamsky, James Welch Taylor, James Welch Taylor, } "Correlation of Si wafer FTIR spectra with wafer temperatures and resist durability variations in plasma etching processes", Proc. SPIE 1672, Advances in Resist Technology and Processing IX, (1 June 1992); doi: 10.1117/12.59750; https://doi.org/10.1117/12.59750
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