Fundamental studies on ultra-thin oxynitrides and nitrides of silicon and silicon-germanium.

摘要

New materials development is the enabler of technological breakthroughs, leading to advanced microelectronic devices, continuing miniaturization, conservation of power, and reduction in cost. The aggressive scaling down of silicon integrated circuits requires reliable ultra-thin dielectrics for use in complementary-metal-oxide-semiconductor (CMOS) transistors in the sub-0.1mum era. In this regard, growth of nitrogen-based dielectrics (oxynitride and nitride) on silicon (Si) and silicon-germanium (SiGe) is being extensively studied. Since the presence of nitrogen imparts better properties to these films as compared to the oxide, process-property relationships are developed to control the concentration profile and bonding states of nitrogen in these films. Effect of using nitrous oxide as opposed to nitric oxide for the growth of these films on chemical and basic electrical properties is discussed. It is proposed that a critical condition is required to obtain a bimodal concentration profile of nitrogen in ultra-thin oxynitrides of Si and SiGe. Also, wafer-to-wafer uniformity in nitrogen concentration profiles is studied by identifying the rate-limiting steps affecting the incorporation of nitrogen in oxynitrides grown along the length of a furnace. Similarly, the effect of furnace dimensions on nitrogen concentration profiles in silicon oxynitrides is also investigated. Further, a process sequence is developed to reduce charge and interface trap densities in silicon nitride films, grown thermally using ammonia in a conventional furnace. All films are grown in a horizontal furnace at 800--900°C and 1 atm. Film properties are investigated using ellipsometry, x-ray photoelectron spectroscopy, secondary ion mass spectrometry, and surface charge analysis, while mass spectrometry is used to find the gas-phase composition. Besides enhancing the fundamental understanding of the mechanisms behind the growth of such films, these findings can help significantly towards engineering future dielectrics for the application of interest.