Contributions of resist polymers to innate material roughness

Abstract

The authors have extended the atomic force microscopy-based technique to measure intrinsic material roughness after base development to evaluate a number of different polymer types in resist formulations. These polymers include environmentally stable chemical amplified photoresist type copolymers and terpolymers, methacrylate polymers, and fluoropolymers. The surface roughness of resists containing these polymers was measured along with the clearing dose with both extreme ultraviolet (EUV) and deep ultraviolet (DUV) exposures. Selected resists containing a representative sampling of different lithographic polymers were imaged with both EUV and DUV exposures. It has been suggested by many that there is a fundamental inverse relationship between resist sensitivity and LER that leads to a fundamental limit to resist performance. It was found that no simple relationship exists between intrinsic material roughness (IMR) and sensitivity and instead some other, more complex relationship between the material properties of the polymer and resist process that is determining both the IMR and sensitivity. It was also found that no simple relationship existed between resist sensitivity and LER. This suggests that resist performance is not innately limited by any fundamental law but is instead open to further improvements through the use of new materials or material combinations.