LITHOGRAPHIC CHARACTERISTICS OF AN ATTENUATED PHASE-SHIFTING MASK USING A SINGLE-LAYER ABSORPTIVE SHIFTER

We introduce an attenuated phase-shifting mask with a single-layer absorptive shifter. The mask was made using MoSiO or MoSiON and is practical for use with i-line photolithography. The lithographic characteristics of the attenuated phase-shifting mask were investigated. Nonstandard optical parameters such as transmittance and mask bias affect the lithographic performance of attenuated phase-shifting masks. It was found that higher transmittance and the smaller mask bias led to a larger depth-of-focus (DOF). These conditions, however, led to a loss of resist thickness forming dimple like features. We estimated the maximum does needed to prevent this effect and found that a high gamma resist (gamma > 4, for instance) was effective in solving the problem. It was also found that a loss of resist thickness at shot stitching areas occurred due to irradiation from the next shot. An array of small holes was demonstrated to be an effective solution to this problem.