CHEMICAL ISOTROPIC ETCHING OF SINGLE-CRYSTAL SILICON FOR ACOUSTIC LENS OF SCANNING ACOUSTIC MICROSCOPE

An acoustic lens for a scanning acoustic microscope (SAM) was newly fa bricated by means of chemical isotropic etching of a silicon wafer. Th is novel lens fabrication process has been developed to obtain surface s with good sphericity and smoothness, which are essential requirement s for acoustic lenses. Acoustic lenses are conventionally fabricated b y using grinding methods. A variety of wafers, etchants and etching co nditions were investigated; the (100) wafer was the most preferable fo r fabrication of a symmetrical lens profile, and the optimum etchant w as found to be a mixture of hydrofluoric, nitric and acetic acids with a ratio of 2:3:3 at a temperature of 50-degrees-C. A silicon acoustic lens with a radius of 140 mum designed for use at 600 MHz and a resol ving power of 1.8 mum was successfully fabricated.