Bonding Structure and Dry Etching Characteristics in Amorphous B-C-N Films for Hardmask Applications

The etch selectivity of the hardmask layer in lithography process for semiconductor chip manufacturing is being continually improved through the utilization of single-element introduction in amorphous carbon (a-C) matrix. Because the exploration of ternary hardmask systems is lacking, we analyzed the bonding structure and dry etching characteristics of a hardmask composed of a ternary system by combining Boron (B) and Nitrogen (N), which are widely used in single-element addition in a-C films. Amorphous B-C-N (a-BCN) hardmasks were obtained by adjusting the N content in an amorphous boron-carbon film using the DC sputter process. The differences in N content within the a-BCN hardmask before and after dry etching were characterized through X-ray reflectometry (XRR) and X-ray photoelectron spectroscopy (XPS) analyses. Consequently, an increase in the ratio of B-N and C-N bonds and a decrease in film density were observed in the pre-etched film. Furthermore, we identified that etch selectivity is related to changes in B-C bonds and C-C sp2 bonds in the post-etched residual film. Additionally, density functional theory (DFT) calculations confirmed an increase in the binding energy between C atoms within the film and etchant, F, influenced by N within the film. This revealed that N in ternary systems not only deteriorates physical density, as known from previous binary hardmask research, but also chemically promotes etch reactions. In our paper, we elucidate the aspects regarding the relationship between the etchant F and C that should be considered when designing ternary hardmask systems.