Passivation of Ge through Boron Carbonitride CVD Films

John G. Ekerdt, University of Texas at Austin, DMR 0603004

Deconvolution of the Ge 2p XPS signals allows the percentage of oxidation of the Ge substrate to be quantified.

BCN films are being explored as a potential passivation layer for single crystal Ge surfaces and Ge nanowires. BCN films are deposited by thermal CVD using dimethylamine borane with NH3 and C2H4. ISS and XPS were used to determine the minimum BCN thickness resulting in continuous films on Si(100), SiO2, and Ge(100). Due to the high surface sensitivity of ISS, a continuous BCN film should result in complete attenuation of the substrate signal. BCN becomes continuous at ~2 nm on Si and SiO2 substrates, and at ~3 nm on Ge substrates. XPS was used to determine BCN-coated germanium’s ability to withstand oxidation by monitoring changes in the Ge 2p and Ge 3d oxidation states with ambient exposure time. Discontinuous BCN films delay but do not prevent Ge oxidation. However, a continuous 3.5 nm BCN film shows no oxidation of Ge following 2 weeks of ambient exposure.

BCN thickness measured by XPS peak attenuation (Si, SiO2) and ellipsometry (Ge)

The GeO and GeO2 contributions to overall signal intensity result in 43% GeOx in this representative Ge 2p XPS spectrum.

Silicon nanowire

BCNBCN demonstrates very conformal coating of nanowires.

As the dimensions of electronic devices are scaled, attention is being given to Ge and GaAs as alternatives to Si; the primary motivation is the higher mobility of holes and electrons in Ge and GaAs. Nanowires of Ge and GaAs materials are intriguing candidates for nanoscale integrated circuits or sensing devices. However, without a stable interface between the Ge or GaAs semiconductor and an oxidizing environment, the advantages are lost. BCN holds promise to passivate Ge and GaAs. We have shown that continuous BCN coatings can prevent Ge oxidation, providing the motivation to explore the more general use of BCN. Early electrical test results indicate that MOSCAP structures fabricated from BCN-passivated GaAs exhibit significantly less leakage current than similar unpassivated structures. Also, TEM images of BCN deposited on silicon nanowires demonstrate conformal coatings.

This grant has provided the opportunity for three undergraduate students, Eric Teletzke, Tiffany Wu, and Michael Qian, to work in the lab gaining exposure to surface science and materials research.

Design, Growth, and Properties of Boron-Based Thin Films for Electronics and Nanosized Electronics

John G. Ekerdt, University of Texas at Austin, DMR 0603004