Long-term stable capacitive pressure sensor made with self-aligned process

摘要

A method for making capacitive silicon pressure sensors and pressure switches with high long-term stability is disclosed. The sensor is fabricated by wafer bonding of a silicon substrate wafer with another silicon wafer where a highly boron doped diaphragm is defined by a self-aligned doping process through a window defined on an insulating layer. The long-term stability of the device can only be achieved when the window is etched by reactive ion etching thus creating vertical window walls. The flatness of the diaphragm can be achieved if an insulating film is present on the backside of the substrate wafer that compensates the stress on the silicon diaphragm created by the insulating layer present on the bonded side.