Microstructure and temperature coefficient of resistance of thin cermet resistor films deposited from CrSi2–Cr–SiC targets by S-gun magnetron

Abstract

Technological solutions for producing nanoscale cermet resistor films with sheet resistances above 1000Ω∕◻ and low temperature coefficients of resistance (TCR) have been investigated. 2–40nm thick cermet films were sputter deposited from CrSi2–Cr–SiC targets by a dual cathode dc S-gun magnetron. In addition to studying film resistance versus temperature, the nanofilm structural features and composition were analyzed using scanning electron microscopy, atomic force microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and electron energy loss spectroscopy. This study has revealed that all cermet resistor films deposited at ambient and elevated temperatures were amorphous. The atomic ratio of Si to Cr in these films was about 2 to 1. The film TCR displayed a significant increase when the deposited film thickness was reduced below 2.5nm. An optimized sputter process consisting of wafer degassing, cermet film deposition at elevated temperature with rf substrate bias, and a double annealing in vacuum, consisting of in situ annealing following the film sputtering and an additional annealing following the exposure of the wafers to air, has been found to be very effective for the film thermal stabilization and for fine tuning the film TCR. Cermet films with thicknesses in the range of 2.5–4nm deposited using this technique had sheet resistances ranging from 1800to1200Ω∕◻ and TCR values from −50ppm∕°C to near zero, respectively. A possible mechanism responsible for the high efficiency of annealing the cermet films in vacuum (after preliminary exposure to air), resulting in resistance stabilization and TCR reduction, is also discussed.