Porous silicon as a sacrificial material

Porous silicon is emerging in micromachining technology as an excellent material for use as a sacrificial layer. This is largely due to the ease of fabrication and freedom of design it allows. The rate of pore formation is heavily dependent upon the doping type and concentration of the silicon, allowing patterned porous silicon formation through selective doping of the substrate. Etch-rates above 10 mm min(-1) have been reported for highly doped material. Silicon that has been made porous can be quickly and easily removed in a dilute hydroxide solution, as low as 1%. Porous silicon technology offers the unique ability to fabricate free-standing structures in single-crystal silicon with separation distances from the substrate ranging from a few microns to over one hundred microns. A review of the development of porous silicon for micromachining applications is given.