Micro pinhole formation in photoresist multilayer structure controlled with hydrophilic treatment

Abstract

The pinhole formation in photoresist multilayer structure acts as a critical defect for device fabrication. The purpose of this study is pinhole prevention by hydrophilic treatment and analysis of pinhole formation mechanism in terms of surface free energy. A SU-8 photoresist top layer is spin-coated on a SU-8 bottom layer as simplest multilayer structure. Pinholes are formed on bottom layer with no-treatment, however, pinholes cannot be observed when bottom layer is treated by hydrophilic process. Subsequently, the surface free energy and spread coefficients of each SU-8 layer are evaluated. Because the absolute value of spreading coefficient Stop is small relatively in case of no-treatment, the pinning phenomenon can be caused by contaminants. A triple point, bottom layer, liquid top layer and air, appears at the pinning area. Air cannot intrude into interface between top-bottom layers due to the spreading coefficient "Sair>0". Consequently, the pinhole expansion phenomenon would be dominated by tensional force and viscous-elasticity of liquid top layer. By hydrophilic treatment, surface free energy of bottom layer increases drastically, therefore the pinning phenomenon is prevented because of "Stop<<0". © 2013SPST.