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

The effect of ion and radical compositions in BCl(3)/Cl(2) 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(+), BCl(2), BCl(3)+, B(2)Cl(3), and B(2)OCl(3)+ in the plasma. The BCl(2)+ ions were found to be the dominant species in BCl(3) 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 Hf(1-x)Al(x)O(y) thin films ranging from pure HfO(2) to pure Al(2)O(3) were etched in BCl(3)/Cl(2) plasmas as functions of ion energy and plasma composition. The etch product distributions were measured and the dominant metal-containing etch products were HfCl(x) and AlCl(x) in a Cl(2) plasma and HfCl(x), HfBOCl(4), and Al(x)Cl(y) in a BCl(3) plasma, and their concentrations increased with increasing ion energy. Oxygen was detected removed in the form of ClO in Cl(2) and as trichloroboroxin ((BOCl)(3)) in BCl(3). Both the etch rate and the etch product formation are enhanced in BCl(3)/Cl(2) plasmas, as compared to those in Cl(2) plasmas, due to the change in the composition and reactivity of the dominant ions and radicals.