A 32-ELEMENT MICROMACHINED THERMAL IMAGER WITH ON-CHIP MULTIPLEXING

This paper describes a multiplexed infrared (IR) thermal line imager realized in silicon using micromachined dielectric windows and thermopile detector elements. The imager consists of 32 detectors, each having 40 series-connected thermocouples, arranged in two staggered 16-element linear arrays. The thermopiles are formed using n(+) polysilicon-gold thermocouples supported on 1.2 mu m thick diaphragms of LPCVD silicon dioxide and silicon nitride. The detectors provide a responsivity of 64 V W-1, a noise voltage less than approximate to 50 nV Hz-(1/2) at 20 Hz, and a specific detectivity of 7 x 10(7) cm Hz(1/2) W-1. The detector signals are multiplexed out using on-chip enhanced depletion (ED)-NMOS circuitry. The imager chip measures 5.5 mm X 11 mm and requires seven masks. It has been used for non-contact measurements of wafer temperature during reactive ion etching and rapid thermal processing and for the measurement of dielectric thicknesses using IR absorption techniques.