Metrology of subwavelength photoresist gratings using optical scatterometry

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Abstract
The widths and overall profiles of dielectric grating lines can be determined by measuring the intensity of diffracted laser light from the sample over a specified range of incident beam angles. This technique, known as 2-theta scatterometry, is able to accurately and precisely measure photoresist structures in the subhalf micron regime. Moreover, a 2-theta scatterometer is capable of making measurements in a rapid and nondestructive manner. To test this technique we measured five identically processed wafers with nominal 0.5 mu m line/0.5 mu m space grating patterns. Each wafer comprised gratings in a Shipley 89131 negative photoresist exposed in a matrix of incremental exposure doses and focus settings. The scatterometry results were consistent with cross-sectional and top-down scanning electron microscopy (SEM) measurements of the same structures. The average deviation of 11 scatterometer linewidth measurements from top-down SEM measurements, over a broad exposure range, is 14.5 nm. In addition, the repeatability (1 sigma) of the 2-theta scatterometer is shown to be excellent: 0.5 nm for consecutive measurements and 0.8 nm for day-to-day measurements. (C) 1995 American Vacuum Society.