Scatterometry, the analysis of light diffraction from periodic structures, is shown to be a versatile metrology technique applicable to a number of processes involved in the production of microelectronic devices, flat panel displays, and other technologies which involve precise dimensional control of micron and sub-micron features. This paper reviews metrology issues and requirements of these technologies and gives details on one application of scatterometry for illustration. Scatterometer results are compared to measurements of the same samples using other metrology techniques, including cross- section SEM, top-down SEM, AFM, and ellipsometry.
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.