, Volume 19, Issue 7, pp 971-978
Date: 02 Nov 2012

Process variability in surface roughening of SU-8 by oxygen plasma

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This study investigates variability in the topography of SU-8 photoresist subject to surface roughening by oxygen plasma treatment. Surface roughness (expressed as root mean square deviation from the mean) under the range of experimental conditions varied from 8 nm for an untreated baseline to as high as 472 nm. At 200 W RF-power and 200 mTorr chamber pressure, the mean surface roughness was 295 nm with standard deviation less than 10 nm across the specimen and 15 nm across the plasma chamber. The standard deviation in surface roughness at higher power and pressure combinations including 500 W and 800 mTorr was as high as 80 nm, with mean surface roughness less than 200 nm. Replicate runs under identical conditions revealed that run-to-run repeatability can be compromised by chamber conditions, evidenced by second runs having higher standard deviation by nearly 20 % over first runs without intermediate chamber cleaning.