Plasma etching of Hf-based high-k thin films. Part I. Effect of complex ions and radicals on the surface reactions

Abstract

The effect of ion and radical compositions in BCl3/Cl2 plasmas was assessed in this work with a focus on the formation of etch products in patterning hafnium aluminate, a potential high-k gate oxide material. The plasma composition became increasingly more complex as the percentage of boron trichloride was increased, which led to the formation of a significant amount of boron-containing species including B+, BCl+, BCl2+, BCl3+, B2Cl3+, and B2OCl3+ in the plasma. The BCl2+ ions were found to be the dominant species in BCl3 containing plasmas at most conditions; however, increasing the pressure or decreasing the power led to an increase in the formation of higher mass ions. Several compositions of Hf1−xAlxOy thin films ranging from pure HfO2 to pure Al2O3 were etched in BCl3/Cl2 plasmas as functions of ion energy and plasma composition. The etch product distributions were measured and the dominant metal-containing etch products were HfClx and AlClx in a Cl2 plasma and HfClx, HfBOCl4, and AlxCly in a BCl3 plasma, and their concentrations increased with increasing ion energy. Oxygen was detected removed in the form of ClO in Cl2 and as trichloroboroxin ((BOCl)3) in BCl3. Both the etch rate and the etch product formation are enhanced in BCl3/Cl2 plasmas, as compared to those in Cl2 plasmas, due to the change in the composition and reactivity of the dominant ions and radicals.