Application of porous silicon has attracted lots of attention in relative field

such as micro-electro-mechanical system（MEMS）and bio-technique

but obstacles such as boundary effect in electrochemical etching should be overcomed.Exist of boundary effect leads to degrade mechanical strength of porous silicon membrane

even

affects the coherence of the membrane.Typical boundary effects occurred in our everyday experiments is studied and the possible mechanism of boundary effect is analyzed.In both n-type and p-type silicon wafers

the boundary effect are effectively controlled with SU8 photo-resist mask and mechanical stress applied in the margin of etching area.Thick macro-porous silicon membranes without boundary effect are produced in both n-type and p-type silicon

especially

the thickness of p-type macro-porous Si exceeded 250 μm.