Photoresist modeling for 365 nm and 257 nm laser photomask lithography and multi-analyte biosensors indexed through shape recognition
Photomasks used in projection lithography systems require higher resolution and uniformity to continue scaling semiconductor devices to smaller dimensions. The lithography process for photomask manufacturing takes many hours to expose millions of individual circuit features into a photoresist. Optical pattern generators have been developed that increase exposure throughput using multiple beams of light. Photoresist materials and processes are sought that will enable higher resolution imaging for current optical pattern generators operating at 365 nm and new tools being developed at 257 nm. Photoresist modeling and optical lithography simulation has been used to provide a deeper understanding of the effects of exposure, developer concentration and bake conditions on the resolution and process latitude of nonchemically amplified resist materials imaged at 365 nm. Lithography simulation uses photoresist models to simulate resist profile sidewall angles and linewidths over a wide range of process conditions. Lithography simulation dramatically reduces the number of expensive manufacturing experiments necessary to optimize resist processes. Photoresist modeling has also been extended to formulate resists for a new 257 nm laser photomask tool. A laser exposure system using a frequency doubled argon ion laser has been built to create optical, kinetic and dissolution models of photoresists at 257 nm. Diazonaphthoquinone-novolak resist profiles have been simulated as a function of photoactive compound concentration to determine the lithographic limits of these materials. Furthermore, new photoactive compounds based on diazocoumarin and diazopiperidione compounds with sulfonate linkages have been rationally designed that bleach at 257 nm while providing similar dissolution inhibition properties as diazonaphthoquinone. Lithography simulation and experiments demonstrate that a trifunctional diazopiperidione-novolak resist is capable of imaging features with 0.36-micron dimensions with sidewall angles of 83 degrees. Photomask and photolithography has also been applied to the creation of new multiple analyte hydrogel biosensors that use their shape to index chemical or biological function. Multiple analyte sensors have been created through the assembly of hundreds of shaped, hydrogel elements. The hydrogel biosensor fabrication process and assembly techniques have the potential to be scaled smaller using high-resolution lithography and image analysis detection techniques. Multiple analyte sensor chips have been made with sensing reagents for the detection of pH changes, small analytes and DNA oligonucleotides.