Tantalum nitride thin film resistors for high-frequency passive devices at interconnect levels

The inclusion of precision on-chip passive devices is a new challenge for current and future interconnect architectures. This request for high quality passive devices is mainly driven by advanced high frequency and system-on-a-chip (SOC) applications. Precision thin film resistors are widely used in analog and mixed signal circuits and specific SOC applications. In this paper, tantalum nitride (TaNx) as the thin film resistor was investigated. The sheet resistance and XRD spectra of the TaNx films deposited at various nitrogen flow ratios were analyzed. The pattern of the TaNx resistor was defined by a novel two-step etching process. At the first step, TaNx was etched by Cl-2 plasma to obtain a sharp profile and then, at the second step, a Cl-2/O-2 gas mixture was used to obtain a better etching selectivity. The temperature coefficient of resistance (TCR) of the TaNx resistor formed at various nitrogen flow ratios was measured. It is shown that the TCR increases with increasing nitrogen flow ratio, and TCR stability is slightly improved by the post-deposition plasma treatment. The flicker noise was measured at frequency from 1 to 100k Hz. It is exhibited that the current noise increased with increasing nitrogen flow ratio. Two-ported S parameters of the TaNx resistors were measured at frequency from 1 to 20 GHz. By extracting the S parameters, frequency dependence of the TaNx resistor is shown.