Thick macroporous silicon membranes: Influence of the masking layer on the underetching characteristics

Macroporous silicon (MPS) has been demonstrated as an interesting material to be used in different applications including micromachining and chemical sensing. In most of these applications the formation of MPS in patterned areas is required or preferable. In this work we report the results of a study on the selective anodization of patterned p-type silicon substrates to form thick MPS layers. Two challenging issues were identified: (1) overetching at the edge of Si3N4 layers, which causes are principally associated with the electrical properties of the interface between the mask and the substrate and the distribution of carriers across the patterned area; (2) adherence of organic masking layers at the silicon during the anodization. Metallic Au/Ti masking layer was demonstrated to be a valuable solution to both issues. SEM cross-sectional views of macroporous layers formed on silicon substrates patterned using different materials are shown and analyzed. Experimental results are supported by two-dimensional (2D) simulations of the silicon/mask/electrolyte interface.

► In this work we report the results of a study on the selective formation of macropores on p-type silicon.
► The observed overetching at the edges of Si3N4 layers was imputed to the charge distribution at the interface.
► Loss of adhesion of organic masking layers at the silicon during the anodization was observed.
► Metal HF resistant masking layers were demonstrated to be a solution to the formation of localized macroporous silicon layer.