In situ examination of tin oxide atomic layer deposition using quartz crystal microbalance and Fourier transform infrared techniques

The atomic layer deposition sALDd of tin oxide thin films has been examined using in situ quartz crystal microbalance sQCMd and Fourier transform infrared sFTIRd techniques. The SnOx films were deposited using sequential exposures of SnCl4 and H2O2 at temperatures from 150 to 430 °C. The linear growth of the tin oxide ALD films was observed by both the mass gain during QCM measurements and the background infrared absorbance increase during FTIR investigations. The FTIR spectra revealed the loss and gain of the O–H stretching vibrations of the hydroxyl group for the SnCl4 and H2O2 exposures, respectively. The background infrared absorbance also oscillated after each SnCl4 and H2O2 exposure. The background absorbance increased after SnCl4 exposure and decreased after H2O2 exposure. QCM measurements were consistent with a tin oxide ALD growth rate of ,60 ng cm−2 per cycle. This mass change corresponds to a growth rate of ,0.7 Å/cycle at 325 °C assuming a SnO2 density of 6.9 g cm−3. Additional ex situ surface analysis using x-ray photoelectron spectroscopy sXPSd and Auger electron spectroscopy sAESd revealed that the SnOx films grown at 325 °C were defined by x,2. Atomic force microscope sAFMd results also showed that the SnOx ALD films deposited on Sis100d wafers have a very rough surface. Understanding and controlling the growth of tin oxide ALD films should be useful to enhance the sensitivity of SnOx gas sensors. © 2005 American Vacuum Society. fDOI: 10.1116/1.1914810g