Plasma etching of polymer thin films and applications to nanolithography

In an effort to develop plasma etching as the nanolithographic process for polymers, the etching behavior of polystyrene thin films in low-density plasmas of oxygen, nitrogen and argon in medium pressure range (0.1–1Torr) has been studied. Arising from dominant effects of either physical or chemical processes depending on gas pressure, the etch rate is shown to parallel the dependence on gas pressure in various plasmas. A condition of minimum etch rate have been found to be associated with the transition of plasma sheath from the collisionless to the collisional. The observation of this transition is confirmed by plasma diagnostic measurement including Langmuir probe and optical emission spectrometry. From the variations of those key plasma parameters with process conditions, it has been found that physical sputtering and chemical etching dominate the surface etching at different gas pressure ranges.; A novel method was derived to estimate the surface temperature during plasma etching using a conventional thermocouple. Strong correlation has been observed between the surface temperatures and the etch rates. The surface temperature reaches the lowest at the minimum etch-rate condition.; ESCA and contact angle measurements have been used to characterize surface functionalities and wettability, respectively. It has been found that the surface oxidation of polystyrene in oxygen plasma is a very rapid process in a time scale of seconds. The microscopic study using AFM and LVSEM has shown that plasma treatment leads to surface roughening and the roughness depends sensitively on the etching conditions.; Selective etching process using low-density oxygen plasma has been developed for the nanolithography of PS/PB diblock copolymer thin films. The feasibility of plasma nanolithography of copolymer has been confirmed by the preliminary results. Due to the etching selectivity, PB domains were selectively removed, thus leaving PS matrix with array of nano-pores (20–40 nm in diameter). The resultant size of the holes varies with plasma conditions and etching time. It has been found that low- and medium-pressure plasmas result in nearly complete removal of PB domains while incomplete removal of PB domains has been found in high-pressure or remote plasma conditions.