The basic challenges of optical overlay measurements are discussed. It is shown that overlay measurement precision is determined by optical resolution, signal to noise ratio of the measurement system and properties of the overlay target. Some tips for better overlay target design ad hardware improvement are formulated. It is shown that an interferometer based measurement system allows better accuracy than the brightfield one. It is shown that for current measurement techniques, 130 nm design rule requirements can be met.
KEYWORDS: Near field, Excimer lasers, Capacitance, Sensors, Prisms, Optical amplifiers, Modulation, Signal detection, Near field optics, Control systems
A number of distance control methods have been developed that allow the direct ablation capabilities of the ArF excimer laser to be applied to near-field optical methods of nanopatterning. Feedback systems based on evanescent field detection, capacitance, and lateral atomic force sensing have been incorporated into our near-field optical nanofabrication system. Using these control techniques, structures were directly patterned on a variety of substrates with dimension on the order of 100 nm. These feedback techniques are versatile enough to allow accurate distance control despite severe disturbances to the system caused by high energy excimer laser pulses.
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