Micromachined high-Q inductors in 0.18 μm Cu interconnect low-K CMOS

Spiral inductors fabricated in a 0.18 μm 6-level copper interconnect low-K dielectric process are described. A post-CMOS maskless micromachining process compatible to copper interconnect and low-k dielectric CMOS has been developed to create inductors suspended 100 μm above the substrate with sidewall oxide removed. Such inductors have higher quality factors as substrate losses are eliminated by silicon removal and have higher self-resonant frequency due to removal of inter-turn dielectrics. Micromachined inductors have the potential to extend the useful operational frequency range of CMOS RF circuits. Quality factors of greater than 7 were obtained at 5.5 GHz for inductors with silicon undercut and inter-turn oxide removed, compared to a Q of 4 for inductors having only their inter-turn oxide removed but without silicon undercut