Process-property-structure relationship of silicon and silicon-germanium oxynitrides

The aggressive scaling down of silicon (Si) and silicon-germanium (SiGe) integrated circuits in the microelectronic industry requires reliable ultra-thin dielectric layers for use in CMOS transistors in the sub-0.1 μm era. In this regard, growth of nitrogen-based dielectrics (oxynitrides and nitrides) on Si and SiGe substrates is being studied. Since nitrogen incorporation imparts better properties to these films when compared to oxides, process-structure relationships are developed to obtain and control desired concentration profiles and bonding states of nitrogen within these ultra-thin films. The effect of the nature of the oxynitriding source gas on the chemical and electrical properties of nitrogen-based dielectric thin films is discussed. It is proposed that a critical initial oxynitride thickness is required to obtain a two-step bimodal nitrogen concentration profile in oxynitrides (grown in N₂O/NO) that are subsequently annealed in ammonia (NH₃) at 900–1000°C and ∼1 atm. It is found that basic electrical properties (interface trap density, bulk charge) do not degrade on NH₃ annealing. Moreover, the growth kinetics of silicon oxynitridation in NO ambient is discussed. Post annealing of sub-50 Å chemical vapor deposited (CVD) silicon nitride in N₂O/NO ambient is presented and discussed in the context of nitrogen removal and dielectric/substrate interface improvements. Use of CVD Si₃N₄ films as barrier layers during aluminum oxide deposition is also studied and discussed.; SiGe alloys have received considerable attention due to their tunable band gap, enhanced hole mobility, and ease of integration with existing silicon technology. However, producing a high quality dielectric layer for insulating field effect devices has proved troublesome. Conventional thermal oxidation of SiGe alloys results in the formation of a Ge rich layer below the oxide. Thus, it is imperative to study new materials for use as future dielectrics on SiGe. The effects of nitrogen incorporation during low temperature SiGe oxynitridation in ultra-thin (sub-40 Å) dielectrics obtained through dry/wet N₂O/NO is investigated and discussed. The amount of nitrogen incorporation and oxynitride growth temperature are found to be essential in retarding Ge segregation towards the interface and loss of GeO from the film surface at 400–700°C and ∼1atm.