Stepper self-metrology using automated techniques

Abstract

'Stepper self-metrology' refers to measurements of various stepper parameters by the stepper itself, as opposed to conventional metrology where resist patterns must be exposed, processed and measured. Self-metrology enables fully automatic feedback loops in which some stepper parameter, e.g. focus offset, can be accurately optimized without operator intervention. We consider a GCA ALS-200 stepper with .4NA I-line optics utilizing an INSITU stage artifact. The INSITU signal is derived from a patterned chrome substrate which transmits light to a detector through some narrow slits. The slits are rapidly swept through the fixed aerial image, and in less than one second a full signal profile is obtained for both X and Y line images. Fully automated tests are available to optimize seven important stepper adjustments: focus offset, baseline error (X and Y), lens trapezoid error (X and Y), reduction error and reticle rotation. Data will be presented on the use of INSITU for routine stepper setup. In addition, detailed data will be presented on the effect of lens heating on focus.