2-DIMENSIONAL ATOMIC FORCE MICROPROBE TRENCH METROLOGY SYSTEM

This article describes the extension of atomic force microprobe (AFM) technology to two dimensions (2D) for accurate measurement of submicron critical dimensions (CDs). The system utilizes a vibrating tip with heterodyne-interferometer sensor similar to that introduced by Martin, Williams, and Wickramasinghe. [Y. Martin, C. C. Williams, and H. K. Wickramasinghe, J. Appl. Phys. 61, 4723 (1987)]. However, the tip vibrates in 2D with dual heterodyne detection. The sample is moved relative to the tip by means of coarse-and fine-motion stages whose position is monitored with 3D interferometry. The system does not scan the sample, but operates like a nanorobot sensing the approach of the tip to the surface by means of the vibration damping. A special three-point tip has been fabricated by Lee [K. L. Lee, D. W. Abraham, F. Serord, and L. Landstein, Proceedings of the 35th ISEIPB Conference, Seattle, WA, May 28-31, 1991 (unpublished), paper K1] with 0.1-mu-m shank diameter which allows measurement of submicrometer trench widths up to 2-mu-m in depth with accuracy and repeatability at the nanometer level. Measurements are made under computer control. The system design and operating characteristics are discussed.