a chemical etchant and a process for chemically etching thin films of aluminum , silicon , and aluminum - silicon alloy on composite structures which may be , for example , integrated circuit devices . the etching process utilizes a mixture of phosphoric acid , nitric acid , acetic acid , a fluoroborate anion containing compound such as fluoroboric acid for providing fluoride ions , a surfactant , and water . this pnaf etchant may be used in fabricating a wafer of integrated circuit devices without lifting photoresist maskant thereon . the formulation provides relatively rapid dissolution of silicon as compared to its etch rates for silicon oxide and silicon nitride . in addition , the etchant has been found suitable for relatively long term use in a production environment .