Titanium diffusion in Si/Al2O3/Ti/Au metal oxide semiconductor capacitors

As novel semiconductor and dielectric materials become more prevalent in MOS device technology, MOS capacitors are used to investigate the quality of semiconductor/dielectric, semiconductor/contact, and dielectric/metal gate interfaces, through capacitance-voltage (C-V) and I-V testing along with physical materials characterization. Thermal processes such as implant stabilization, contact annealing, and dielectric postdeposition annealing must be managed to accomplish the desired results while minimizing undesirable side effects such as interdiffusion or dopant migration in devices. This can be done through a combination of device and process design, which prevents these unwanted effects through careful material selection, ordering of process steps, temperature adjustments where possible, and selection of process gases used during thermal treatments. This study focuses on the effects of a 430 degrees C forming gas anneal, which produced an unusual brown layer on Ti/Au metal-oxide-semiconductor capacitor gates. A series of experiments, XPS analysis, and C-V electrical data revealed that the brown layer was not an organic residue but a thin layer of TiO2 on the gold surface, which formed due to Ti diffusion to the Au surface during the forming gas anneal. Oxygen plasma treatment before the furnace anneal enhanced the undesirable diffusion effect. Replacing the Ti/Au gates with Cr/Au gates prevented the brown layer and improved capacitance-voltage characteristics.