Zero temperature coefficient of resistance in back-end-of-the-line compatible titanium aluminum nitride films by atomic layer deposition

Abstract

Thin film resistors with near-zero temperature coefficient of resistance (TCR) are key passive elements in analog integrated circuits (ICs). State-of-the-art near-zero TCR technology is based on sputtered compounds of Si, Cr, B, and C, which require annealing at temperatures higher than 500 °C, making it incompatible with back-end-of-the-line (BEOL) processes. We report here that near-zero TCR resistors can be obtained by atomic layer deposition (ALD) of TiN-AlN nano-laminates at BEOL-compatible deposition temperature. The resistivity and the TCR can be tuned by varying the ratio between AlN (insulating) and TiN (metallic) in the TiXAl1−XN thin film. The TCR changes from positive to negative as the AlN content is increased, allowing for optimization to zero TCR. The ALD method provides ultimate control of the thickness, composition ratio, coverage, and uniformity. Microstructure analysis shows that the film consists of metallic TiN crystallites embedded in the semiconducting TiyAl1−yN amorphous matrix, suggesting that the electrical behavior is similar to that of SiCr-based compounds. These results pave the way toward BEOL-compatible near-zero TCR thin film resistors, which can significantly reduce capacitance and minimize design complexity of passive analog IC components.