Multilevel critical dimension/overlay metrology using a real-time confocal scanning optical microscope

Abstract Linearity and short-term repeatability have been studied for critical dimension (CD) and overlay measurements using the Real-Time Confocal Scanning Optical Microscope (RSOM). Short-term repeatability of 15nm (three-sigma) has been demonstrated for submicron CD and overlay. CD linearity was measured in the 0.5μm to 1.3μm region using a top-down SEM for reference. Overlay linearity was measured using electrical overlay structures with known offsets in the range -0.2μm to +0.2μm. Response surface methodology was used to determine the optimum focus for achieving repeatable overlay measurements. The results were used to compare the performance of various overlay structures.