A Gray-Tone Derived Lithography Method for Silicon Micromachining

Photolithographic processes on the unleveled surfaces of the silicon (Si) wafers which have been previous subjected to different micromachining steps are difficult or even impossible to be performed. To prevent this problem the paper proposes a derived method, so-called gray-tone lithography. The presented method takes into account the differences between the etching rates of Si and respectively silicon dioxide (SiO₂) which is generally used as masking layer, in aqueous alkaline solutions like potassium or sodium hydroxide (NaOH or KOH). The deep of trenches is correlated with both SiO₂/Si etching rate and thickness of the SiO₂ sacrificial layer.