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 abs orptive shifter. The mask was made using MoSiO or MoSiON and is practi cal for use with i-line photolithography. The lithographic characteris tics of the attenuated phase-shifting mask were investigated. Nonstand ard optical parameters such as transmittance and mask bias affect the lithographic performance of attenuated phase-shifting masks. It was fo und that higher transmittance and the smaller mask bias led to a large r depth-of-focus (DOF). These conditions, however, led to a loss of re sist 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 oc curred due to irradiation from the next shot. An array of small holes was demonstrated to be an effective solution to this problem.