In materials and bulk-processes sciences, the metrology challenges concern defects, impurities, surface terminations, effluents, and strain, with particular emphasis on the importance of strain on reliability and in controlling edge effects. Increased understanding of metrology principles, interactions, and techniques that may lead to new methodologies or tools is of primary importance to the semiconductor industry.

Weisel is using scanned near-field in both the optical and microwave regions of the electromagnetic spectrum to overcome the inadequacy of diffraction-limited microscopy. Definition and resolution in far-field imaging are limited by the wavelength. Definition and resolution in near-field imaging are independent of the wavelength and are limited by the size of the actual of the effective aperture. The distance from the sample to the aperture must be small compared to the size of the aperture in order to probe the near field. The lateral definition of the near-field scanned optical microscope (NSOM) (~50 nm) can be improved by using an apertureless near-field-scannedoptical microscope (ANSOM), perhaps by as much as an order of magnitude. Since an ANSOM uses a sharpened wire such as that in a scanning tunneling microscope, the lateral optical definition as well as the topographical definition can in principle be of the order of nanometers. A microwave near-field probe also uses a sharpened wire source and therefore is capable of similar definition.

An NSOM was developed for nearfield imaging, photoluminescence spectroscopy, and nano-Ramanspectroscopy of porous silicon. Simultaneous photoluminescence and topographical images were measured as a function of wavelength. Characteristic features of the sources of photoluminescence in porous silicon were measured. By comparing the measured Raman-shift lineshape with theory, the typical mean size of the porous silicon microcrystals was determined to be about 3 nm.

Apertureless near-field-scanned-optical microscopes have been designed and constructed for NDE of metal-matrix composites of interest to the Army Research Laboratories; the initial experiments involve highdefinition imaging of AL-SiC composites. We are also applying near-field optical microscopy and spectroscopy to defect detection and analysis and for nondestructive measurements of critical dimensions of CMOS devices. The nano-Raman-spectroscopy capability can be used to determine strain fields at gate edges along the width. The ANSOM can be applied to measurement of leakage currents across the field oxide. The feasibility of optical determination of the thickness gradient of the field-oxide is also being investigated.

A scanned microwave-frequency electromagnetic probe has been developed with a demonstrated lateral definition better than 0.1 µm. It is being applied to high-definition compositional analysis of glass-filled polymer composites frequently used in aerospace, electronic, and telecommunication industries. Other applications include imaging of metal-matrix composites and defects in integratedcircuit packaging. The larger penetration depths at microwave frequencies make possible location of subsurface features in optically opaque materials.