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8 June 1998 Ellipsometric scatterometry for sub-0.1-μm CD measurements
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Conventional scatterometry measures the intensity of a diffraction order from a periodic structure as one or more measurement parameters is changed. We have previously demonstrated conventional techniques to characterize developed photoresist linewidths as small as approximately 0.15 micrometer, with scatterometer results agreeing well with measurements performed using other techniques. For developed photoresist, the measurement sensitivity of conventional scatterometer techniques diminishes considerably for sample linewidths that are sub-0.1 micrometer, using 633 nm laser illumination. We present a modified scatterometer configuration which combines aspects of conventional scatterometry and ellipsometry that provide increased sensitivity for characterizing sub-0.1 micrometer linewidth periodic photoresist structures. The complex reflection coefficients representing the grating sample are extracted, both in magnitude and in relative phase, through intensity measurements at selected polarizer/analyzer/compensator orientations. The cross-polarization terms of the reflection coefficient matrix are shown to be equal for a symmetric photoresist grating structure with line widths approximately 0.5 micrometer. Theoretical results for nominal 70 nm photoresist lines are presented that show phase measurement sensitivity to linewidth changes on the order of 2 - 4 deg/nm and reflectance sensitivity of at least 3%/nm. This results in linewidth measurement resolutions that are sub-nm.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Stephen A. Coulombe, Petre-Catalin Logofatu, Babar K. Minhas, S. Sohail H. Naqvi, and John Robert McNeil "Ellipsometric scatterometry for sub-0.1-μm CD measurements", Proc. SPIE 3332, Metrology, Inspection, and Process Control for Microlithography XII, (8 June 1998);

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