Abstract
The ablation characteristics of the SU-8 photoresist (spun on Siwafers) under 248 KrF excimer pulsed laser radiation have been studied.The variation of etch rate with fluence has been investigated in the range0.05-3.01 J cm-2. The threshold fluence for ablation of SU-8 ismeasured to be about 0.05 J cm-2. The etch rate of SU-8 is found tobe higher than that of polyimide (previously reported) under similarconditions. We have investigated the effects of different prebaketemperatures (90, 110, 120 and 200 °C) on ablation characteristics,which are found to be similar for all temperatures. The effect ofincreasing the number of laser shots (from 10 to 10 000) has beenexamined at different fluences in order to understand the etch-ratevariation near the `end of film' stage of ablation. The results of ouranalysis using scanning electron microscopy, profilometry and opticalmicroscopy reveal the very smooth morphology of the etched surfaces withno significant debris, no noticeable damage to underlying silicon and thegradual build-up of a carbonaceous film outside and around the etch pits.We find SU-8 very suitable for excimer ablation lithography and havedemonstrated this by patterning a gear structure in an SU-8 resist layerwith an aspect ratio of 4.5. For the first time, we have shown that thelaser micromachining technique has the potential to cleanly remove SU-8after electroplating a microstructure with copper.
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