AN EXPERT SYSTEM FOR THE CONTROL OF LITHOGRAPHY OVERLAY IN ADVANCED SEMICONDUCTOR MANUFACTURING

THE RESOLUTION AND TOTAL OVERLAY ACCURACY NEEDED FOR ADVANCED SEMICONDUCTOR MANUFACTURING HAS INCREASED BY APPROXIMATELY 30 PERCENT EVERY TWO AND A HALF YEARS. CURRENT DESIGN RULES LIE NEAR OR BELOW THE ACTUAL WAVELENGTH OF VISIBLE LIGHT. THREFORE, OPTICAL TOOLS FOR PATTERN GENERATION ARE NOW BEING SUPPLEMENTED BY NEW TECHNOLOGIES SUCH AS X-RAY AND ELECTRON BEAM EXPOSURE SYSTEMS. MANUFACTURING OF SUB-HALF MICRON DESIGN RULE DEVICES PRESENTS THE ENGINEER WITH THE NEED TO CONTROL PATTERN OVERLAY WITH AN ACCURACY GREATER THAN EVER BEFORE. HIS TASK IS COMPLICATED BY THE NEED TO CALIBRATE, MATCH, AND MAINTAIN A MIX OF NEW LIGHOGRAPHY TOOLS, WHICH MAY BE OF VERY DIFFERENT TECHNOLOGIES. THE MOST SUCCESSFUL TECHNIQUE HAS BEEN TO MODEL THE DISTORTIONS OF PRINTED PATTERNS AGAINST THE PARAMETERS OF THE LENS AND ALIGNMEMT SYSTEMS. HOWEVER, NEW METHODS ARE NEEDED. RESEARCHERS ARE TESTING THE FEASIBILITY OF AN EXPERT SYSTEM FOR ENHANCED PROCESS OVERLAY CONTROL. THIS SYSTEM, CALLED LIMET-EXPERT, USES NEWLY DVELOPED TECHNIQUES TO PROVIED THE MODELING AND STATISTICAL EXPERIENCE NEEDED TO CUSTOMIZE MODELS AND ALGORITHMS. LIMET-EXPERT HS APPLICATIONS IN THE REAL-TIME CONTROL AND MAINTENANCE OF THE PROCESS AS WELL AS THE PATTERN GENERATION EQUIPMENT.