Etch resistance: comparison and development of etch rate models

Abstract

Etch resistance and post etch roughness of ArF photoresists still remain some of the critical issues during process integration for sub-100nm technology nodes. Compared to phenyl-containing KrF polymers, methacrylate polymers commonly used for ArF lithography show weak bulk etch resistance in addition to a highly damaged surface after standard etch processes. Counter to the photoresist, the etch rates of BARC are required to be very fast to prevent degradation of the photoresist before the image has been transferred to the substrate. There are a number of etch models in the literature which attempt to describe the correlation between polymer structure and blanket etch rates. Ohnishi Parameter and Ring Parameter are the most common etch models correlating atomic and structural trends in the resist polymer and etch rates. These etch models have been tested in two ways: systematically changing the composition of a terpolymer and using polymers with different functional groups. By comparing the etch rates of this large series of polymer structures it was found that these etch models were not sufficient in describing the relationship between the atomic or structural trends in polymer with etch rates. New etch models that describe the structure property relationship and etch rate trends have been developed. These new models show a better correlation with the observed experimental results. Finally, new polymers have been developed, for both ArF and BARC applications. These materials show a significant improvement in term of etch properties.