With each new generation of integrated circuits and other nanostructured devices produced at ever-decreasing length scales, the extension of liquid-phase processes for the manufacturing of these devices is uncertain. The current work investigates the ability of liquids to wet nanoscale features. A model for wetting time is derived that may be used to identify those geometries for which wetting is critical. Conditions under which wetting time is significant may result in low yield and poor uniformity and may require alternate-phase processing. Furthermore, the dependence of wetting time on the properties of the fluid are quantified so that fluids may be designed to have optimal properties and thus optimal performance. The resulting model can be used as a tool to predict future processing requirements, and when necessary, to design novel processes implementing alternative phase fluids ͑e.g., vapor, subcritical, and supercritical fluids͒.

Rapid technology development and demands for state-of-the-art generations of integrated circuits bring new challenges to microelectronic device manufacture. Specifically, decreasing dimension sizes may limit the effectiveness of liquid-based removal of photoresist and plasma etch residues. In addition, the hazardous solvents currently in use pose environmental concerns. Gasexpanded liquids ͑GXLs͒ and supercritical fluids may offer cleaning or residue removal approaches that overcome some of the drawbacks of current surface preparation methods. Removal of PHOST ͑polyhydroxystyrene͒ photoresist films has been demonstrated with CO 2 -expanded ethanol ͑up to 75 mol % CO 2 ͒, indicating that the inclusion of CO 2 does not inhibit photoresist removal. In situ interferometry measurements of the PHOST layers allowed insight into the removal mechanism. The GXL mixtures were also invoked to remove post-plasma etch residues using CO 2 -expanded TMAHCO 3 /CH 3 OH. At a temperature of 90°C and pressures above 1000 psig the GXL mixture removed the photoresist and etch residue. Cleaning efficiency depended on CO 2 pressure; at lower pressures the CO 2 reduced the mole fraction of the TMAHCO 3 /CH 3 OH while at higher pressures the CO 2 assisted removal.

Dissolution and removal of photoresist films is performed numerous times during the fabrication of electronic, optical, and mechanical devices and integrated circuits. Information regarding changes in refractive index and film thickness is of interest for the design and modeling of such processes. Spectroscopic reflectometry is a cost-effective technique that has been used to monitor film thickness, but has been limited to applications in which the film refractive index is constant during dissolution, and thus has a known value. This paper extends conventional spectroscopic reflectometry analysis to account for refractive index changes in films during processing. Results obtained by this approach correlate well with spectroscopic ellipsometry measurements. This technique is applied to the dissolution of photoresist in aqueous base solutions, swelling of photoresist in solvent vapor, and removal of photoresist in water-alcohol mixtures, and can similarly be applied to other thin film applications. In addition, the optical properties of fluids such as aqueous and non-aqueous solvents, supercritical or subcritical mixtures, and gas-expanded liquids, which can be used to process thin film materials, can be monitored using spectroscopic reflectometry.

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