Image collapse issues in photoresist

Abstract

The continued shrinkage of line widths below 150 nm has not been without concerns of the mechanical stabilty of the resist structure. The development of the exposed resist undergoes many phase changes such as solid solubilization into a liquid followed by drying by volatilization. In the development of features especially with aspect ratio (AR) >3 and for lines/spaces (1/s) <1:2, the phase changes create interfacial tensions at the liquid/solid and gas/liquid/solid surfaces that can cause image collapse (IC). Aqueous based resist are particularly susceptible to collapse due to the high surface tension of the rinse water (72 mN/m). Two major steps to reduce or eliminate the IC are to strengthen the mechanical stability of the resist or to reduce the surface tension of the drying/rinse liquid. We have investigated various methods to reduce the surface tension of the water rinse either by lowering the surface tension of the rinse liquid or by removal of the rinse water prior to drying. Positive ArF and KrF resist and negative resist have been investigated. To reduce the surface tension of rinse liquid, the addition of surfactant followed by drying is a direct method which may be used. Indirectly, the prior removal of water by solvents or emulsification with inert components followed by drying in the supercritical fluid of CO2 can maintain high aspect ratio images at AR >3. Negative resist are more applicable to process as they can tolerate a wider variety of co-solvents or "CO2 phillic" surfactants. © 2001 SPIE - The International Society for Optical Engineering.