AN ELECTRON-OPTICAL METROLOGY SYSTEM FOR PATTERN PLACEMENT MEASUREMENTS

The demands on the uncertainties of pattern placement and overlay meas urements in lithography are constantly growing due to the continuing r eduction of feature size which allows higher density integration. Alth ough nowadays optical projection lithography plays the dominant role i n lithography and will continue to do so in the near future other tech nologies will be developed further in order to replace optical lithogr aphy soon after the beginning of the next century. A pattern placement metrology instrument should be able to perform measurements on the ma sks used today as well as on future types of lithography masks. The PT B has developed a new pattern placement metrology instrument using a h igh-resolution electron beam probe. The electron optical metrology sys tem consists of a low-voltage scanning electron microscope with a larg e vacuum chamber and a 300 mm x-y-positioning stage, controlled by vac uum laser interferometry. The design principles of the instrument will be described and a comparison of measurements with those of an optica l mask measuring system will be presented.