Photochemical etching of n-InP: observations on photon efficiency and saturation

Photochemical etching of n-InP in dilute phosphoric acid using an Ar+ laser at 488 nm was studied for duty cycles ranging from 100 to 0.02% at 200 Hz modulation frequency. The photoetch rate, defined as the etch rate divided by the fraction of time that the sample was illuminated, increased from approximately=1 mu m min-1 at 100% duty cycle to >300 mu m min-1 at 0.02% duty cycle. Also, saturation of the efficiency of the photoetching process was found to be locally controlled for a wide variety of experimental conditions. These findings have some interesting implications for maskless semiconductor processing.