Parameter-specific ring oscillator for process monitoring at the 45 nm node

Parameter-specific ring oscillator (RO) experimental results are reported, demonstrating the ability to electronically distinguish and quantify sources of variations from gate lithography focus, gate-to-active overlay, nitride contact etch stop layer (CESL) strain, and Shallow Trench Isolation (STI) stress. A 2% RO frequency change due to gate focus variations, a three-four nm overlay error, a 20% increase in RO frequency per 1 um increase in length of diffusion (LOD), and a 3% speed-up per 0.3 um change in STI width are measured. Typical standard-deviation/mean (σ/μ) among 36 ROs within-chip is 0.2-0.3%.