HF-based buffered oxide etch (BOE) solutions are commonly used in semiconductor
processing for etching SiO2 selectively to Si in the presence of photoresist masks. This paper reports on an anomalously severe roughening reaction that can occur at Si/resist interfaces when n-type Si is etched in 50:1 BOE solutions (1 wt% HF and 39.5 wt% NH4F in H2O) in the presence of certain organic resists. This effect is seen to a very much lesser extent in 9:1 BOE solutions (5 wt% HF and 36 wt% NH4F in H2O), and not seen at all in dilute HF solutions (100:1 and 10:1 with 0.5 wt% and 5 wt% HF). The species responsible for the roughening reaction is not identified, but it appears to be related to
a breakdown product of the resist. We show that the roughening can be eliminated with the use of a diamond-like-carbon interposer layer under the resist.
By: Katherine L. Saenger, Sharee J. McNab, Steven J. Koester
Published in: RC22843 in 2003
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