Thermo-sensing silicon–germanium–boron films prepared by plasma for un-cooled micro-bolometers

In this work we report a study of silicon–germanium–boron alloys (a-SixGeyBz:H) deposited by low frequency plasma enhanced chemical vapor deposition (LF PECVD) at relatively low temperatures, which are compatible with the IC silicon technology for applications as low resistance thermo-sensing films in micro-bolometers. Three values of germanium gas content (Gey) were used during the film deposition, Gey = 0.3, 0.45 and 0.55. Deposition and film properties were compared with a reference intrinsic film (a-SixGey:H) in order to study the Gey effect on the temperature dependence of conductivity (σ(T)) and specifically on the activation energy (Ea). We observed a variation on the activation energy from Ea = 0.34 eV to Ea = 0.18 eV and on the room temperature conductivity from σRT = 6 × 10−5 (Ω cm)−1 to σRT = 2.5 × 10−2 (Ω cm)−1, for the reference intrinsic film and for the boron alloy with Gey = 0.55, respectively. The solid phase composition of the films was characterized by SIMS measurements. The effect of patterning the films (μm scale) with photolithography and the deposition on a SiNx micro-bridge on the film electrical properties was also studied.