Patent ID: 7266474
Filing Date: 2007-09-04
Classification: G01R,G05B

Abstract:
1. A method of characterizing random and systematic variations in a semiconductor manufacturing process, comprising: providing a set of variable delay ring oscillator test circuits having a ring delay with a plurality of stages and a ring delay distribution width; measuring the ring delay for a set of ring oscillator test circuits in multiple placements of said process: measuring a delay distribution of a ring oscillator with at least two different numbers n of delay stages in a path of a recalculating loop; measuring the width of the delay distribution of said ring oscillator with n stages; identifying and separating the contributions of random variations SigmaRandomRing and systematic variations SigmaSystematicRing in the delay distribution; calculating a statistical distribution of random and systematic variations per cell in manufacturing processes; and storing the statistical distribution of random and systematic variations in a memory.