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. In contrast to the nearly undetectable rates of Si etching in dilute HF (dHF), BOE solutions were found to etch n-type Si at 1 nm/min. In addition, an anomalously fast and catastrophic etching mode was á seen for n-type Si in 50:1 BOE solutions (1 wt% HF and 39.5 wt% NH4F in H2O) in the presence of certain photoresists, an effect not seen in 9:1 BOE solutions (5 wt% HF and 36 wt% NH4F in H2O) or in dHF (100:1 and 10:1 with 0.5 wt% and 5 wt% HF). It is suggested that alternatives to BOE may be preferred for oxide etches requiring a hard stop on n-type Si, and that the etching of
n-type Si in BOE can be accelerated by resist degradation products.
By: Katherine L. Saenger, Steven E. Steen, Steven J. Koester
Published in: RC22678 in 2003
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