Formation of cross-cutting structures with different porosity on thick silicon wafers

Three-layered pass-through structures of two types have been obtained on 500 μm thick single crystal silicon wafers by electrochemical etching in a 48% solution of hydrofluoric acid without using additional single crystal layer removal operations. The first type of the pass-through structures comprises two outermost 220-247.5 μm thick macroporous silicon layers with a pore diameter of 7-10 μm and an intermediate 5-60 μm thick mesoporous silica layer with a pore diameter of 100-150 nm. For the formation of the first type structures we used two-stage etching without cell disassembly: