Interferometric-spatial-phase imaging for sub-nanometer three-dimensional positioning

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 203-206).Current alignment technology is incapable of satisfying the needs of imminent generations of lithography. This dissertation delineates a novel method of alignment and three-dimensional position metrology that is compatible with many forms of proximity lithography. The method is called Interferometric-Spatial-Phase Imaging (ISPI), and is based on encoding three-dimensional position information in the spatial phase and frequency of interference fringes, viewed with specialized oblique-incidence, dark-field optical microscopes. Alignment detectivity is 500 gm. Unlike amplitude-based interferometers, this spatial-phase-encoding interferometer achieves high alignment detectivity without sensitivity to variations in wavelength, gap and other factors, such as resist layers and changes in the index of refraction in the beampath. Several novel gap detection methods are introduced, with gap detectivity 500 jgm.(cont.) Gap is confirmed with exposure of patterns in resist, taking advantage of near-field interference in a novel Chirped Talbot Effect. Alignment and pattern overlay are confirmed in experiments combining x-ray exposures with continuous ISPI position feedback. Dynamic overlay of patterns in resist is demonstrated to be 2.7 nm, with a clear path for further improvement. Gate structures in a double-gate MOSFET are dynamically aligned to 2.5 nm.by Euclid Eberle Moon.Ph.D