Integration of ultrathin resist processes into MPU IC manufacturing flows

Extreme ultraviolet lithography (EUVL), and possibly 157-nm lithography, will require thin imaging layers (< 1500 A). The leading EUV resist strategy utilizes thin resists based on materials designed for 248 nm wavelength exposure and hardmasks. This process has produced lines and spaces with reasonable linearity, resolution, photospeed, and line-edge roughness. Although previous work has approached these limits, integration of sub-150nm resists and hardmasks into current IC manufacturing process flows with acceptable defect control has not yet been demonstrated. The authors are investigating ultrathin resist processing for the gate and back end levels and have collected data on coating properties, defect density, etch selectivity., exposure latitude, and depth of focus. Key results include the demonstration of etching 1500 A of poly-Si with a 1200 A thick photoresist etch mask and the demonstration of via chain yield that is comparable to standard thickness resist processes.