Paper PS-TuM4
Reaction Mechanisms in Patterning Hafnium-Based High-k Thin Films

Tuesday, October 21, 2008, 9:00 am, Room 304

As hafnium-based oxides are being implemented into sub-45nm CMOS devices, the corresponding development of an enabling plasma etching chemistry is necessary for patterning these new gate dielectric materials. In this work, an electron cyclotron resonance high density plasma reactor was used to study the etching of hafnium aluminates and nitrided hafnium silicates with varying compositions in chlorine-based chemistries. In general, the measured etch rate for these materials scaled with the square root of ion energy at high ion energies (> 50 eV), however the etch rates in BCl₃ was 4 to 7 times that in Cl₂, due to the change in the dominant ion from Cl₂⁺ to BCl₂⁺. The composite oxides were found to etch faster than the simple oxides, and had roughly 2 eV lower etching threshold energies. The etching threshold energy can be tuned by the film composition, making it possible to maximize the etching selectivity with respect to the gate and substrate materials. A generalized etch rate model was formulated based on the competing etching and depositing mechanisms involved in complex plasma chemistries, as determined from analysis of the experimental data , while the etch rate dependencies on neutral-to-ion flux ratio and ion energy were correctly represented. This surface site balance based approach accounts for competition between depositing and etching species with a steady-state overlayer, and employs proper assumptions for different chemistries at various energy regimes. The model fitted well to the experimental data under various ion energy and chemistry conditions, specifically, it was able to account for the transition between physical- and ion-enhanced etching in Cl₂ plasmas and the transition between deposition and etching in BCl₃ plasmas, as the ion energy increased. As quantitative information pertaining to high-k etching behavior can be extracted from this model, it is possible to extend its applicability to predict the etching characteristics of new materials in related plasma chemistries.