Instability trade-off of inter-layer or inter-metal dielectrics formation with low-k dielectrics on active and field device's characteristics

The effects of back end of line (BEOL) processing with low dielectric constant (low-k) materials on active and field device performances have been studied. The study reveals: (1) there is SPICE model uncertainty because I/sub dsat/ increases as more metal layers are added; (2) low-k dielectrics can enhance this I/sub dsat/ increase; and (3) NMOSFET hot carrier lifetime and PMOSFET V/sub t/ stability are degraded. These effects are attributed to the BEOL-induced hydrogen generation and passivation with gate oxide dangling bonds, which are primarily created in the contact etching process. The modified process involves pure hydrogen alloy after metal-1 formation, which ensures the same device performance at metal-1 and at the final metal layer. In addition, the alloy can reduce the inverse narrow width effect and field isolation leakage currents.