Characterization of a Novel Radical Nitrogen Plasma Source for Semiconductor Nitridation

Surface nitridation has long been desirable for surface and interface passivation to realize ultra-low equivalent oxide thickness (EOT) dielectric layers on Si and III-V materials. Various nitridation techniques exist, including thermal and plasma nitridation. Thermal processes rely on high temperatures which are difficult to control for very shallow nitridation without any significant diffusion. Thermal budgets become stricter when moving to III-Vs, unless special steps are taken to reduce or eliminate loss of low vapor pressure materials (ie. As, In). Conventional plasma processes allow lower temperatures but can expose the substrate to damaging, high energy ions. Shallow channel devices are particularly vulnerable to substrate damage, degrading mobility.

We will report nitridation of Si and GaAs using a novel, remote nitrogen radical generator system. The generator is a custom, atmospheric plasma source capable of generating a large concentration of N radicals without exposing the substrate to plasma. Processes are carried out at low pressures, 1-10 Torr, and the generator is connected to the process chamber by an orifice, precluding direct line of site to the plasma. The system is integrated with an atomic layer deposition (ALD) chamber for both radical enhanced and thermal ALD, allowing in-situdeposition of dielectrics.

Growth temperatures range from room temperature to 400 °C. Aluminum oxide, aluminum nitride and zirconium oxide ALD dielectric stacks will be analyzed using ex-situ x-ray photoelectron spectroscopy (XPS) to gauge the surface chemistry and nitridation stability. Metal-oxide-semiconductor capacitors will be measured using capacitance-voltage (C-V) measurements to look at the nitridation contribution to electrical properties. Emphasis will be places on zirconia-alumina-zirconia (ZAZ) stacks, with nitridation at the interface and the dielectric bulk.

We would like to thank Samsung Electronics for their financial support and Toshiba Mitsubishi-Electric Industrial Systems Corporation (TMEIC) for providing the nitridation system.