<title>Subwavelength photoresist grating metrology using scatterometry</title>

Abstract

A precise and accurate technique for the characterization of periodic line/space gratings is presented. The technique, known as scatterometry, derives its sensitivity and robustness from the wealth of information present in diffracted optical radiation. Scatterometry is capable of determining width, height, and overall shape of sub-half micron lines as well as the thickness of underlying thin films. The characterization process consists of three elements: a diffraction measurement apparatus, a model built on calibration data, and a statistical analysis routine that uses the model to correlate empirical data to the unknown parameters of the structure. The measurement technique was evaluated on twenty five wafers fabricated with deliberate deviation in focus, exposure dose, and underlying thin film thickness. Each wafer consisted of developed photoresist lines on an antireflecting layer, placed on layers of polycrystalline silicon on gate oxide on a silicon substrate. Scatterometry was used to simultaneously determine the width and height of the nominal 0.25 micrometers and 0.35 micrometers photoresist lines, as well as the thickness of underlying layers. Comparison of results obtained using reference methods (ellipsometry and scanning electron microscopy) are included.