First Principles Simulation Analytically Verifying the Patterning Via Optical-Saturable Transitions (POST) Process

Developments in lithographic nanopatterning processes have the ability to directly impact technological advancements in modern devices such as those common in the semiconductor industry. The technique referred to as Patterning via Optical-Saturable Transformations (POST) is a method of optical lithography that achieves deep sub-wavelength resolution utilizing photo-switchable molecules. A spectrally selective, reversible photochemical reaction enables transitions between two isomeric molecular states of the patterning material. Two possible ‘locking steps’ have been qualitatively compared; each exploits the differences between the isomeric states to fix patterns. Selective dissolution capitalizes upon the solubility difference between the isomers while electrochemical oxidation converts one of the isomers into a third state that is unaffected by further exposures. This presentation provides a brief description of POST including outlines of the two current ‘locking’ methods. It then describes a robust numerical simulation that couples a finite-element method solver with Matlab calculations to provide an accurate model of the process. The simulation involves a combination of photochemical reaction kinetics and light exposure and penetration simulations to analytically reproduce experimental results by using basic physical principles. The effects of various patterning process parameters including the locking step, film thickness, exposure time, oxidation time, and dissolution time are quantified. In addition to verifying experimental results with first principles, the two locking steps are quantitatively compared to determine overall effectiveness.