Understanding Pattern Collapse in High-Resolution Lithography: Impact of Feature Width on Critical Stress

摘要

Chemically amplified resists have served as high resolution and high photospeed patterning materials in the fabrication of modern microelectronic devices for more than two decades. A significant amount of research during that time, and in particular more recently, has focused on minimizing line width roughness and on improving the achievable resolution and sensitivity of resist materials. While these lithographic parameters are certainly important, the distortion of the resist pattern during wet processing and subsequent drying can have significant negative impacts on performance and is often relatively overlooked as a major resist resolution and performance limiter. Resist pattern distortion after development and during drying is mainly due to the unbalanced capillary forces created due to pattern asymmetries which give rise to variations in liquid meniscus radii of curvature as the final rinse liquid is dried from the pattern. These capillary forces are dependent upon the surface tension of the final rinsing solvent, the contact angle of the rinse liquid with the side wall of the resist line, and the pattern space widths and sidewall angles. The demand for resist films with smaller feature sizes has led to a reduction in resist pattern dimensions resulting in overall poor mechanical strength and a decrease in the adhesion forces at the resist line/substrate interface. In this work, the pattern collapse behavior of a hydroxystyrene-based resist copolymer is studied. Ultra-thin film effects and the role of the feature width of the resist line on pattern collapse are also investigated.