Effective roughness reduction of {100} and {311} planes in anisotropic etching of {100} silicon in 5% TMAH

We have performed an investigation to study the nature of surface roughness on {100} and {311} planes obtained by wet anisotropic etching of {100} silicon in 5% tetramethyl ammoniumhydroxide (TMAH) etchant. The surface roughness, which is in most cases a consequence of hillock formation at low concentrations of TMAH, was studied as a function of etch temperature, re-etch time, stirring conditions and the addition of small amounts of ammonium peroxodisulfate (AP). A short re-etching step performed in 25% TMAH or 5% TMAH+AP was found to decrease the total roughness obtained after the prolonged etching in 5% TMAH. We have found that smooth {311} planes without hillocks can be obtained by etching in 5% TMAH with the addition of only 0.25% of AP. Due to the decomposition of AP in the etching process as determined by increased surface roughness, a replenishing of the additive is proposed. Experimental results have shown an increased surface roughness and reduced etch rates of the {100} and {311} planes by increasing the agitation of the 5% TMAH etch solution.

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