CD control using SiON BARL processing for sub-0.25 μm lithography

In this paper, various contributions to the reflection variation at the resist/BARL interface are investigated. Not only deviations in the optical parameters (n, k, thickness T) of the BARL are causing variations in reflectivity, but also thickness variations of transparent layers underneath the BARL. Furthermore, the impact of substrate reflectivity on CD variation for 0.2 mu m features is investigated, using various SiON layers. Since substrate reflectivity has to be very low for good CD control, and since some reflectivity variations can be unavoidable, the use of a TAR layer in combination with BARL is proposed as a simple solution to maintain good CD control on real product wafers.