R. Ferguson et al., ETCHED-QUARTZ FABRICATION ISSUES FOR A 0.25 MU-M PHASE-SHIFTED DYNAMIC RANDOM-ACCESS MEMORY APPLICATION, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 11(6), 1993, pp. 2645-2650
A 0.25 mum pattern from a dynamic random access memory application is
used to assess the impact of an etched-quartz fabrication process on t
he lithographic performance of an actual phase-shifted circuit design.
A new measurement tool called the aerial image measurement system is
used to quantify the effects of an isotropic wet etch following the qu
artz reactive-ion etching step on the printability of the phase-shifte
d pattern at two values of partial coherence. The presence of signific
ant transmission and phase errors, in part a result of optical scatter
ing from the edges and/or comers of the etched-quartz trench, reduced
the potential benefits obtained from phase shifting. At the optimum po
stetch conditions for a partial coherence of 0.36, only 65% of the ide
al depth-of-focus was obtained. Transmission errors were reduced from
greater than 25% with no postetch treatment to less than 5% with wet-e
tch depths in excess of 1100 angstrom. However, large phase errors, be
tween 20-degrees and 60-degrees, were present for all postetch conditi
ons, and were strongly dependent on the partial coherence. Optimizatio
n of depth-of-focus required a nominal wet-etch depth of 1200 angstrom
for sigma = 0.6, but only a 900 angstrom depth at sigma = 0.36. Large
variations in the phase error as a function of the postetch treatment
conditions were attributed to electromagnetic resonance phenomena bet
ween the sidewalls of the etched-quartz trench.