Advanced lithographic patterning technologies : materials and processes

Immersion lithography has emerged as the next technology to achieve the resolution improvement needed to produce smaller and faster microelectronic devices. It involves filling the air gap between the lens and photoresist-coated silicon wafer in a lithographic exposure tool with a higher refractive index medium. This improves the coupling of light into the resist and allows for better resolution. At the current exposure wavelength of 193 nm, water has been identified as the most promising immersion medium. Several potential issues had to be resolved before the process would be adopted. One was the unknown consequence of intimate contact between water and a photoresist. Any extraction of small molecule photoresist components by water could lead to a degradation of imaging performance and/or contamination. To address this, the possible extraction of several examples of these components from model 193 nm photoresists was studied by multiple experimental techniques including liquid chromatography/mass spectroscopy, scanning electrochemical microscopy and radiochemical analysis. It was found that both a photoacid generator and a base additive were extracted in small quantities. A study of the optical properties of water-based solutions with ionic additives was then undertaken. This study was intended to identify fluids with a higher index than water for greater resolution improvement. The solutions had higher index values, though typically with prohibitively high absorbance. The survey did lead to a series of methylsulfonate salts with some of the highest index values paired with low absorbance found for these materials. However, none of the target fluid properties were reached, so a theoretical approach was then used to model the properties of an ideal additive. This model served as a guide to identify a new type of additive with both a high index and low absorbance. The principles used for a high index/low absorbance additive were then applied to fabricate a polymer photonic device. A photonic crystal structure was designed for a polymer with an additive. A process for fabricating it was then developed using step and flash imprint lithography. The process development included a demonstration of a template created with a negative tone electron beam lithography process.