Deep-UV immersion interferometric lithography

Liquid immersion lithography (LIL) can extend the resolution of optical lithography well beyond today's capabilities. The half-pitch limit is given by the well-known formula Lambda = lambda/(4NA), where lambda is the optical wavelength and NA = n sin(theta) is the numerical aperture of the exposure device with n the refractive index of the exposure medium. Through the use of exposure media such as purified water (n of 1.44 at 193 nm), it is possible to reduce minimum pitches by a factor of as much as 44% - a full technology node. Beyond this simple observation, there is a good deal of work necessary to fully understand the impact of LIL on a lithography processes. This paper will address issues concerning resist chemistry and the impact of water immersion on the imaging capabilities of different resist formulations. All resists were evaluated by imaging dense line-space structures at a 65-nm half-pitch both in air and with water immersion. Studies of dense 65-nm lines made by immersion imaging in HPLC grade water with controlled variations in resist components were performed. Significant differences were observed and will be discussed.