Electrochemical etch-stop characteristics of TMAH:IPA solutions

The characteristics of electrochemical etching of silicon in concentrated (25 wt.%) and dilute (2.5 wt.%) tetramethyl ammonium hydroxide (TMAH) and in 25 wt.% TMAH: 17 vol.% isopropyl alcohol (IPA) solutions are presented. I-V curves and the variation of the etch rate in the direction with the applied potential have been obtained for n- and p-type silicon. The difference in the passivation potential (PP) of n- and p-type silicon is more significant for dilute TMAH solutions and is practically unaffected by the presence of IPA. The silicon etch rate is smaller for n-type than for p-type silicon, the difference being more pronounced when no IPA is used. In any case, the etch rate decreases abruptly at potentials anodic to the PP. Surprisingly, a pronounced decrease in the etch rate of n-type silicon is observed for potentials negative with respect to the open-circuit potential. The results obtained are applied to the fabrication of thin membranes and for monocrystalline silicon microbridges. © 1994