Particle filters integrated inside a silicon wafer

A method is described to integrate particle filters inside a silicon wafer by creating pores in a recessed membrane. The filters are created in either a silicon or a silicon nitride membrane located 100 μm below the wafer surface. The fabrication process involves anisotropic etching of front- and back-side of a (1 0 0) silicon wafer, deposition of a silicon nitride layer, spraycoating of photoresist and reactive ion etching of the pores. The filters may serve as a well or reaction chamber at the same time. We have patterned pore diameters in the 10-50 μm range in 100 μm recessed membranes that are suitable for application in stacked systems such as in an integrated inkjet nozzle.