| AVS 64th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Tuesday Sessions |
| Session EM+SS-TuA |
| Session: | Surface and Interface Challenges in Semiconductor Materials and Devices |
| Presenter: | Stacy Heslop, University of Arizona |
| Authors: | S.L. Heslop, University of Arizona L. Peckler, University of Arizona A.J. Muscat, University of Arizona |
| Correspondent: | Click to Email |
Employing germanium (Ge) and/or silicon germanium (SiGe) as the active material in transistors has the potential to generate electronics that are faster and consume less power. The narrower band gaps and higher hole mobilities compared to silicon make these materials ideal candidates for the next generation of microelectronics, but their integration into current manufacturing is difficult due to the rapid oxidation of germanium. These oxides are unstable, electrically defective, and form a poor interface with the underlying substrate hindering their electrical performance. The native GeO2 is water soluble and unable to protect the surface during liquid phase processing. To combat this, the oxidation is prevented by depositing a thin sulfide layer to chemically passivate the surface. Ammonium sulfide is a common passivation reagent due to the size and valency of the sulfur atom and its ease of integration into current industrial processes.
X-ray photoelectron spectroscopy (XPS) was used to study the effect of varying concentrations of aqueous ammonium sulfide on SiGe. No sulfide layer was detected for surfaces treated with aqueous ammonium sulfide and instead the surface reoxidized in solution. Hydrofluoric and hydrochloric acids were added to the ammonium sulfide solution to remove or prevent the formation of these oxides in solution. Samples treated with ammonium sulfide with added acid showed a sulfide layer. Increasing the concentration of HF and HCl increased the sulfur coverage but also increased the oxide coverage, suggesting the deposition of oxidized sulfur species.
Metal-insulator-semiconductor capacitors (MISCAPs) were fabricated for three different surface treatments. Capacitance –voltage and conductance data was used to quantify the density of interface defects (Dit). Samples treated with ammonium sulfide with added acid showed the highest sulfur coverage and had fewer interface defects (1.4 x 1012 cm-2 eV-1) compared to samples treated with aqueous ammonium sulfide or samples with no sulfur treatment.