(Invited) The Challenges and Opportunities in Plasma Etching of Functionally Enhanced Complex Material Systems

The introduction of new and functionally improved materials into silicon based integrated circuits is a major driver to enable the continued down-scaling of circuit density and performance enhancement in analog, logic, and memory devices. Many new materials, such as multiferroics, magnetic materials and phase change materials, are much harder to pattern, thereby posing significant challenges to the design and selection of plasma etching chemistries. While ion milling is effective in patterning some of these functionally improved materials, such as complex magnetic material stacks used in magnetic tunnel junctions, it limits the scalability and integration of devices. These challenges point to the growing needs of identifying and developing viable etch chemicals and processes that are more effective in patterning complex materials and material systems. In this talk, a generalized approach based on combined thermodynamic assessment and kinetic validation is presented to identify and validate the efficacy of various plasma chemsitries. Specifically, potential reactions between the dominant vapor phase/condensed species at the surface are considered at various temperatures and reactant partial pressures. The volatility of etch product was determined to aid the selection of viable etch chemistry leading to improved etch rate of reactive ion etching process. Based on the thermodynamic screening, viable chemistries are tested experimentally to corroborate the theoretical prediction. Some of the above mentioned material systems such as magnetic materials used in magnetic tunnel junctions are used as examples to demonstrate the broad applicability of this approach.