In-process image detecting technique for determination of overlay, and image quality for ASM-L wafer stepper

The possibilities of in-process blue image sensing by using only the implemented darkfield TTL alignment system of a stepper are investigated. It is shown, that all overlay parameters such as red-blue, magnification ect. can be measured from an enhanced latend image for a PAS 5000/50 and 70 stepper. Results of overlay measurements on special dyed resist and in a pure resist only indicating the possibility of in-situ overlay control and correction on process wafers. Furthermore a new method of focus measurement and control using the alignment system of the stepper only was introduced. Results ave given for sensing the developed resist pattern as well as the latend image for an i-line and a DUV-stepper. The applicability is demonstrated by measuring the influence of varying technological parameters. A mathematical model based on diffraction theory has been developed to support the design of the focus targets. The model has been verified by experiments.