FABRICATION OF SILICON MICROPHONES

A silicon microphone is formed using the steps of providing a first wafer including a layer of heavily doped silicon, a layer of silicon and an intermediate layer of oxide between the two silicon layers. The first wafer has a first major surface on one surface of the layer of heavily doped silicon and a second major surface on the layer of silicon. A second wafer of silicon has a first major surface and a second major surface. A layer of oxide is formed on at least the first major surfaces of the first and second wafers. A cavity is etched through the oxide layer on the first major surface of the first wafer and into the layer of heavily doped silicon. The first major surface of the first wafer is bonded to the first major surface of the second wafer. A metal layer is formed on the second major surface of the second wafer. Acoustic holes are patterned and etched in the metal layer and in the second major surface of the second wafer. At least one electrode is formed on the heavily doped silicon of the first wafer and at least one electrode is formed on the second wafer. The oxide layer of the first wafer is etched from at least the back of a diaphragm during manufacturing of the silicon microphone.