Modeling parameter extraction for DNQ-Novolac thin film resists
Optical lithography with special thick film DNQ-novolac photoresists has been practiced for many years to fabricate microstructures that require feature heights ranging from several to hundreds of microns such as thin film magnetic head. It is common in these thick film photoresist systems to observe interesting non-uniform profiles with narrow region near the top surface of the film that transition into broader and more concave shapes near the bottom of the resist profile. A number of explanations have been proposed for these various observations including the formation of ---dry skins" at the resist surface and the presence of solvent gradients in the film which serve to modify the local development rate of the photoresist. There have been few detailed experimental studies of the development behavior of thick films resists. This has been due in part to the difficulty in studying these films with conventional dissolution rate monitors (DRMs). In general, this lack of experimental data along with other factors has made simulation and modeling of thick film resist performance difficult.As applications such as thin film head manufacturing drive to smaller features with higher aspect ratios, the need for accurate thick film simulation capability continues to grow. A new multi-wavelength DRM tool has been constructed and used in conjunction with a resist bleaching tool and rigorous parameter extraction techniques to establish exposure and development parameters for two thick film resists, AZ 4330-RS and AZ 9200. Simulations based on these parameters show agreement to resist profiles for these two resists.