Mechanical properties and pattern collapse of chemically amplified photoresists

Abstract

The mechanical properties of positive tone chemically amplified resists UV6 and APEX-E are measured and used in finite element analysis (FEA) to determine the mechanical compliance of photoresist lines as an indicator of the propensity for pattern collapse. Specifically, the residual strain is determined by surface micromachined resist structures; the residual stress, expansion coefficient, and glass transition temperatures are determined from wafer curvature measurements; and the Young’s modulus is calculated from the stress and strain. The results indicate that UV-6 has higher strain and a higher coefficient of thermal expansion than APEX-E. However, it has lower residual stress because its Young’s modulus is 50%–70% lower than that of APEX-E. FEA indicates that lines of UV6 have greater compliance than those of APEX-E, and are more easily deformed by fluidic forces during develop and rinse steps. This is fully consistent with separate reports that demonstrate a greater likelihood of pattern collapse in UV6 than APEX-E.