Mitsuji Nunokawa

New phase-shifting mask with highly transparent SiO2 phase shifters

A phase-shifting mask enables subhalf-micron optical lithography. We propose a new phase-shifting mask with Si02 phase shifters. Si02 phase shifters on a quartz mask substrate have the advantages of low absorption under deep UV and a lack of multiple interference. Si02 phase shifters were fabricated by lift-off of the evaporated Si02 film. The new phaseshifting mask is highly transparent to deep UV and provides a 2 uniformity of phase shift over the full exposure field of a 5X stepper. Improved resolution of 0. 25 im lines and spaces was achieved by using a KrF excimer laser stepper and the new phase shifting mask. We also characterize the image profile projected with a phase-shifting mask because the reproducibility of mask features on a wafer declines when a phase-shifting mask is used. We indicate the importance of the interference between the main and side lobes of diffraction patterns for individual apertures and clarify the mechanism ofreproducibility degradation in optical lithography using a phase-shifting mask. 1.

Modeling Thermal Effects for Simulation of Post Exposure Baking (PEB) Process in Positive Photoresist

We studied the thermal effects in a positive photoresist during post exposure baking (PEB). Infrared analysis and the reduced dissolution rate in the exposed resist suggest that the carboxylic acid is decreased and/or that ECA solvent evaporates. In order to simulate the effects, we assume that the concentration of the alkali-soluble material (carboxylic acid) decreases equivalently. Our model explains PEB and enables its effects to be simulated.

Al203 etch-stop layer for a phase-shifting mask

On a phase-shifting mask, an etch-stop layer is a good way to repair the phase-shifters defects without causing any phase error. The authors propose using Al2O2 for the etch-stop layer. Al2O3 was deposited by oxygen ion-beam assisted evaporation. The evaporated Al2O3 film showed several properties which are indispensable for an etch-stop layer: the high transparency at i-line and KrF wavelengths, and an etching selectivity of 270 for a SiO2 phase-shifting film. The effects of an etch-stop layer on the optical properties of a phase-shifting mask were also studied.