Highly sensitive focus monitoring on production wafer by Scatterometry Measurements for 90/65nm node devices

Highly sensitive focus measurement method using scatterometry has been developed. Since the method is nondestructive and applicable to wafers with film stacks, it enables to apply for production wafers. Focus change results in subtle variation of the photo resist (PR) shape. We parameterized this phenomenon by scatterometry with novel model consisting of 8 layers. The focus was obtained by the modeled PR shape with multiple regression method. We've confirmed that this method has given us estimated error within 30 nm for focus variation of 0.1 mum.