Paper EL+AS+EM+TF-ThP1
FTIR Ellipsometry Studies of Thermally Grown GeO₂ on Ge

Thursday, November 10, 2016, 6:00 pm, Room Hall D

To study the vibrational modes of GeO_2, we produced a set of thermal GeO₂ oxides ranging from 45 to 136 nm in thickness. Receiving a set of Ge Bulk wafers, we cleaved and roughened the back sides via an aluminum abrasive to avoid backside reflections. To remove carbon-containing surface contaminants and leave a stable oxide on the wafer, we performed a hybrid dry/wet clean. The dry clean was done by subjecting the wafer to an ozone clean in an ultrapure oxygen environment while heating the sample to 150°C for 1 hour, followed by a 30 minute incubation period. The samples were then cleaned ultrasonically for 20 minutes in deionized water followed by 20 minutes in isopropanol. No harsh chemicals were used. The samples were then dried with nitrogen and annealed at 270 kPa and 550°C in ultrapure oxygen for a few hours to achieve different oxide thicknesses.

Using Fourier-transform infrared ellipsometry, the ellipsometric angles ψ and Δ were measured from 250 to 6000cm^-1 at several angles of incidence (60° to 75°). The infrared lattice absorption peak of the amorphous GeO₂ was fit with a Lorentz oscillator.

When comparing our results to Lippincott’s et al. [1] transmission measurements of vitreous GeO₂ formed by quenching hexagonal GeO₂, we see a negative shift in vibrational frequency. The difference can be attributed to the different Ge-O bond length comparing the vitreous GeO₂ and our amorphous thermal oxide. Our amorphous thermal oxide GeO₂ samples have a longer bond length, corresponding to a weaker bond and a lower vibrational frequency. This shift also shows a lower density of our samples compared to Lippincott et al [1].

References

[1] E.R. Lippincott, A. Van Valkenburg, C.E. Weir, and E.N. Bunting, J. Res. Antl. Bur. Stand. 61, 61 (1958).