Abstract. Based on the Seebeck effect, the CMOS compatible micromachined thermopile is widely used in infrared detection for its advantages of low-cost, high batch yield, broad spectral response and insensitivity to ambient temperature. We present two integrated thermopile IR detectors on stacked dielectric layers realized by a standard P-well CMOS technology, followed by one CMOS compatible maskless XeF₂ isotropic dry-etching step. Characterizations of CMOS devices, before and after XeF₂ etching, respectively, were performed to investigate the effects of XeF₂ etching on the CMOS devices. With a 2.5 µm thick stacked silicon oxide–nitride–oxide layer as an absorber, the rectangular thermopile detector and the circular thermopile detector provided responsivity of 14.14 and 10.26 V W⁻¹, specific detectivity of 4.15 × 10⁷ and 4.54 × 10⁷ cm Hz^1/2 W⁻¹, and time constant of 23.7 and 14.6 ms, respectively. Compared with the rectangular thermopile detector, the circular thermopile detector is mechanically more stable, because its circular structure design eases the internal stress problem in the CMOS layers. After XeF₂ etching, the maximum changes of threshold voltage, maximum transconductance and switching threshold voltage were 0.97%, 1.25% and 0.08%, respectively. Experimental results show that the effects of XeF₂ etching on the CMOS devices are insignificant, and XeF₂ etching is suitable for post-CMOS micromachining.

Print publication: Issue 12 (December 2009)
Received 20 April 2009, in final form 15 September 2009
Published 20 October 2009