Impact of attenuated mask topography on lithographic performance

Abstract

Experimental evaluations were used in conjunction with rigorous electromagnetic simulations to evaluate the effect of attenuated phase-shifting mask (PSM) fabrication processes on lithographic performance. Three attenuated PSMs were fabricated including a normal leaky-chrome reticle and two novel approaches: a recessed leaky-chrome reticle for reduction of edge scattering and a single-layer reticle employing a hydrogenated amorphous carbon film. Direct aerial image measurements with the Aerial Image Measurement System (AIMSTM), exposures on an SVGL Micrascan 92 deep-UV stepper, and TEMPEST simulations were used to explore the effects of edge-scattering phenomena for the different mask topographies. For each reticle, the process window at a feature size of 0.25μm was evaluated for four basic feature types: nested lines, isolated lines, isolated spaces, and contact holes. For nested lines, the depth-of-focus was not impacted by mask topography. However, the reduced edge scattering for the recessed leaky-chrome reticle led to a reduction of the exposure dose and an increase in the peak intensity. Minimization of side-lobe printing was found to be essential for optimizing the process window for isolated spaces. AIMS measurements demonstrated that the depth-of-focus for the leaky-chrome reticles was limited by the side lobes, and a bias of 3Onm was required to achieve the optimum lithographic window. However, TEMPEST results suggested that the amorphous carbon film was more susceptible to side-lobe printing. Further evaluation of the sidewall profiles and the image size on the mask are required to address these discrepancies.