Development of an Alkaline-Compatible Porous-Silicon Photolithographic Process

A technique for masking porous-silicon (PS) films by optical photolithography without significant film degradation is demonstrated for the first time. The chemical resistance of the PS films is achieved by low-temperature passivation via nitrogen annealing. The effect of the various photolithographic process steps is investigated by determining the changes in the optical properties of the films. The passivated PS films are shown to be resistant to strong alkaline-based solutions (dilute AZ400K developer) for up to 100 s with minimal reduction in optical thickness. Fourier transform infrared and spectral reflectance measurements show that the passivated PS films are relatively unaffected by a complete photolithography process, apart from the seepage of photoresist into the pores, which can be prevented by applying a thin protective polymer layer. Metal was deposited and patterned via the standard liftoff process on PS surface to demonstrate the feasibility of this technique.