IMPROVED METROLOGY FOR ADVANCED LITHOGRAPHY

AS FEATURE SIZES IN SEMICONDUCTOR LITHOGRAPHY APPROACH THE 0.1 MICRON LEVEL, EXISTING METROLOGY TECHNIQUES ARE BEING PUSHED BEYOND THEIR LIMIT. THE HIGH RESOLUTION METROLOGY NEEDED FOR STEP-AND REPEAT LITHOGRAPHY AND MASK INSPECTION AND QUALITY CONTROL HAS RELIED ON 2-FREQUENCY LASER INTERFEROMETRY. UNLESS SUCH SYSTEMS ARE OPERATED IN A VACUUM, HOWEVER, THEY ARE SUBJECT TO ATMOSPHERIC TURBULENCE INDUCED ERRORS ON THE ORDER OF 50 TO 100NM. THESE ERRORS ARISE FROM THE FLUCTUATIONS IN ATMOSPHERIC DENSITY WHICH OCCUR ALONG THE OPTICAL PATH FROM THE INTERFEROMETER CUBE TO THE MIRROR ON THE MOVING STAGE. THERE IS WIDESPREAD CONSENSUS ON THE EXISTENCE AND MAGNITUDE OF THIS PROBLEM, AND ON THE NEED TO EITHER SOLVE IT OR CIRCUMBENT IT. WE ARE PROPOSING TWO QUITE SEPARATE APPROACHES, EITHER OF WHICH APPEARS CAPABLE OF IMPROVING SEMICONDCUTOR METROLOGY PRECISION BY BETWEEN ONE AND TWO ORDERS OF MAGNITUDE. OUR GOALS ARE TO DETERMINE WHICH APPROACH IS OPTIMUM AND TO ACHIEVE A POSITIONING PRECISION OF + 0.01 MICRONS. THE FIRST APPROACH INVOLVES THE USE OF A RELATIVELY COARSE XY SCALE IN CONJUNCTION WITH PRECISION INTERPOLATION TECHNIQUES; THE SECOND APPROACH IS TO MAKE CONVENTIONAL INTERFEROMETRIC MEASUREMENTS AT TWO WELL-SEPARATED WAVELENGTHS IN ORDER TO COMPENSATE FOR THE EFFECTS OF ATMOSPHERIC TURBULENCE. ANTICIPATED BENEFITS: THE PROPOSED ATMOSPHERE COMPENSATED POSITION/METROLOGY TECHNOLOGY, IF SUCCESSFUL WILL MAKE AN IMPORTANT CONTRIBUTION IN OVERCOMING A MAJOR BARRIER TOWARDS THE GOAL OF REACHING 0.1 MICRON DESIGN RULES AND THEREBY BENEFIT US CHIP MANUFACTURING COMPETITIVENESS.