Aqueous-based photoresist drying using supercritical carbon dioxide to prevent pattern collapse

A supercritical drying process was developed to eliminate the capillary for ces naturally present during normal drying of photoresist materials. Superc ritical carbon dioxide (scCO(2)), organic solvents and surfactants were use d to prevent the collapse of high-aspect-ratio structures fabricated from a queous-based photoresist. Nondistorted resist lines were patterned with thi s process with aspect ratios of at least 6.8. Water rinsed resist structure s cannot be dried directly with scCO(2) due to the low solubility of water in the supercritical phase. In our process we introduced the replacement: o f the aqueous rinse by n-hexane mediated by a compatible surfactant. The su rfactant allowed to incorporate the aqueous phase into micellar microdomain s in the organic phase while keeping the interfacial tension at values clos e to zero. Noncollapsed supercritically dried structures were rewet in n-he xane or water and dried using nitrogen at atmospheric pressure. Under these conditions, the patterns were collapsed as a result of capillary forces ac ting on the resist walls. The effect of capillary forces on pattern stabili ty were qualitatively compared to the relative surface tension values betwe en n-hexane and water. The advantage of using supercritical CO? in the dryi ng stage of resists compared to normal drying highlights the importance of eliminating the surface (or interfacial) tension forces created by the rins e fluid, if a reduction of linewidth and spacing between resist lines is pu rsued, while keeping the aspect ratio constant. (C) 2000 American Vacuum So ciety. [S0734-211X(oo)01306-8].