The general application of phase-shift mask technology often requires special features accommodating a non printing transition from 0° to 180°. Transitions featuring a continuous slope exhibit reduced linewidth variation and smaller intensity dips as compared to step transitions employing intermediate phase-shift levels. In this paper we report on a method for forming continuous slope phase- shift transitions using ion milling. A slope was created as a result of a locally variable etch time caused by changing the tilt angle of the mask plate during the etching. Thus, steady progress of the resist shadow along the etched region by controlled adjustment of the tilt angle defined the transition profile. The experimental results were reproduced by simulation including the effects of source rotation.
[1]
Tsuneo Terasawa,et al.
0.3-micron Optical Lithography Using A Phase-Shifting Mask
,
1989,
Advanced Lithography.
[2]
Eiji Takeda,et al.
A 5.9 mu m/sup 2/ super low power SRAM cell using a new phase-shift lithography
,
1990,
International Technical Digest on Electron Devices.
[3]
M. Moulin,et al.
Evolution of well-defined surface contour submitted to ion bombardment: computer simulation and experimental investigation
,
1975
.
[4]
M. Levenson,et al.
Improving resolution in photolithography with a phase-shifting mask
,
1982,
IEEE Transactions on Electron Devices.
[5]
Andrew R. Neureuther,et al.
Exploration of fabrication techniques for phase-shifting masks
,
1991,
Other Conferences.