CMOS Compatible Thermopile Infrared Detector Released By Dry Etching

As one kind of traditional infrared detectors,uncooled thermopile detector has developed various applications due to its simple structure,small size and low cost.By employing micromaching techniques,MEMS thermopile detector is able to make full use of CMOS process which will facilitate integration with signal processing circuits. By this means,we can further improve detector performance and reduce manufacturing cost.In this dissertation,thermopile infrared detector is chosen as a specific case to study the compatibility of MEMS devices and CMOS circuits. To solve the problems involved in traditional structure releasing techniques where back etching or front side etching with anisotropic wet etchants are used,this dissertation presents a structure released by etching bulk silicon isotropically with XeF₂ vapor.Also discussed is how the shapes of etching windows affect the releasing process and result.Two critical process techniques are examined by orthogonal matrix experiments: PECVD deposition of Si₃N₄ films with low residual stress and etching silicon with XeF₂ vapor.Experimental results suggest that,for the former process,duty time of low frequency pulse is the primary factor influencing the stress of Si₃N₄ films. Besides,the compressive stress is larger when the duty time is longer.For the latter one,the optimized process parameters for our arrangement of thermopiles to be released are:20 etching cycles,etching time of 60s per cycle and the XeF₂ pressure is 4torr. This dissertation also proposes a prototype for monolithic integrating thermopile infrared detecting system as well as the system framework and process flow.We fabricate simple N-MOSFET and testify the feasibility of developing monolithic system which lay foundation for integrating thermopile detector with high performance CMOS circuits in the future.