Traceable Calibration of a Critical Dimension Atomic Force Microscope

The National Institute of Standards and Technology (NIST) has a multifaceted program in atomic force microscope (AFM) dimensional metrology. One component of this effort is a custom in-house metrology AFM, called the calibrated AFM (C-AFM). The NIST C-AFM has displacement metrology for all three axes traceable to the 633 nm wavelength of the iodine-stabilized He-Ne laser. A second major component of this program, and the focus of this paper, is the use of critical dimension atomic force microscopy (CD-AFM). CD-AFM is a commercially available AFM technology that uses flared tips and two-dimensional surface sensing to scan the sidewalls of near-vertical or even reentrant features. Features of this sort are commonly encountered in semiconductor manufacturing and other nanotechnology industries. NIST has experience in the calibration and characterization of CD-AFM instruments and in the development of uncertainty budgets for typical measurands in semiconductor manufacturing metrology. A third generation CD-AFM was recently installed at NIST. The current performance of this instrument for pitch and height measurements appears to support our relative expanded uncertainty (k = 2) goals in the range of 1.0 x 10(-3) down to 1.0 x 10(-4).