Simulation of the 45-nm half-pitch node with 193-nm immersion lithography

The minimum half pitch available to a lithography tool is given by the well-known equation Lambda(min-halr). = lambda/4nsintheta, where A is the exposure wavelength, n is the refractive index of the immersion medium and 20 is the angle between the propagation directions of the two beams. Using water (n = 1.44) as an immersion medium, the highest spatial frequency available with ArF-based (193 nm) lithography tools with an NA of 1.3 (1.44 x 4.9) corresponds to a half-pitch of 37 mn suggesting that the 45-nm half-pitch node should be accessible. A detailed simulation study (PRO-LITH(TM) 8) is reported for two different approaches to printing for this node. Dipole illumination (with two masks) as well as imaging interferometric lithography (with a single mask and multiple exposures incorporating pupil plane filters) is shown to be capable of printing arbitrary structures under these conditions. Because of the loss of contrast for TM-polarization at the high spatial frequencies at this node the high spatial frequencies in the x- and y-directions need to be printed with different polarizations in order to retain the necessary contrast. This, in turn, will require modification of the illumination system or a multiple exposure approach to allow the necessary polarization control.