Ian R. Smith

Scanned Laser Imaging For Integrated Circuit Metrology

This paper will discuss the design criteria for an optical imaging system capable of high accuracy measurements on IC devices. In particular, the problem of measurement repeatability is discussed in the case of devices with submicron dimensions and complicated three dimensional features. Preliminary experimental results are presented from a confocal scanning laser imager designed for inspection and measurement on production wafers, SiScan-1 (TM). The system provides three major advantages over previously available optical microscopes: a) higher resolution and high magnification, b) accurate and repeatable C.D. measurements on micron and submicron geometries and, c) surface topography profiles and measurements. Digital images at high magnification (8,000X) and with accurately calibrated pixel sizes (0.06 microns) are illustrated. The problem of object edge to image edge correspondence is discussed. In particular, the profiling ability of the system will be used to illustrate potential solutions to this problem.

Ultra-Violet Confocal Metrology

This paper describes a semiconductor metrology system based upon ultra-violet wavelength confocal microscopy. The system is capable of linear metrology of resist features down to 0.5 microns linewidth with low dependence on substrate type. Short term precision of better than 5nm standard deviation can be obtained with this system. The optical design for 325nm operation is described together with details of the data acquisition system. Experimental data compares the performance of ultra-violet and visible light versions of the system for resist metrology, showing the benefit of using a wavelength at which the resist is absorbent. Conclusions are drawn about optimal regimes for metrology as well as the extension of this technology to yet shorter ultra-violet wavelengths.

Confocal Optical Metrology At 325nm

This paper compares results obtained with semiconductor metrology systems based upon ultra-violet and visible wavelength confocal microscopy. It is shown that the system is capable of linear metrology of resist features down to 0.5 micron linewidth with low dependence on substrate type. Short term precision of better than 5nm standard deviation can be obtained with this system. Experimental data compares the performance of ultra-violet and visible light versions of the system for resist metrology, showing the benefit of using a wavelength at which the resist is absorbent.