Iron Oxide-An Inorganic Photoresist and Mask Material

The etching rate in dilute acids of iron oxide thin films prepared either by sputtering in CO/CO2 mixtures or by low temperature chemical vapor deposition techniques, may be modified by irradiation with an argon-ion cw laser. Depending on the exposure time and power levels used, laser irradiation may (i) leave the film unaffected, (ii) greatly reduce its solubility, or (Hi) completely remove the film. For exposures ranging from several seconds to a few minutes, the power level necessary to produce low solubility is several hundred milliwatts per square millimeter. Film evaporation begins at a few watts per square millimeter. By rapidly translating the film through the focal point of a laser beam, regions of reduced solubility in the form of a line as narrow as 1 μm have been obtained at writing velocities of 2000 cm/ sec. It is proposed that with these techniques, iron oxide “see through” masks for use in integrated circuit technology may be written directly.