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Calibration Standard For Oblique Light Type Particle Detection/ Measurement Instruments

IP.com Disclosure Number: IPCOM000049358D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 61K

Publishing Venue

IBM

Related People

Gati, GS: AUTHOR

Abstract

Oblique light is widely used as an instrument of detection for particles of small size. One example is its use in measuring contamination on wafers in semiconductor device manufacturing. While tools using oblique light are effective in detecting small particles, there was no sure way to evaluate the limits of the detection capability with respect to particle size (i.e., how small) and spacing between particles. Generally a number of small particles of calibrated size are placed on a wafer and if "sparkles" are detected, it is assumed that with the level of illumination used the instrument detects individual particles at least down to the level of the size of the calibrated particles.

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Calibration Standard For Oblique Light Type Particle Detection/ Measurement Instruments

Oblique light is widely used as an instrument of detection for particles of small size. One example is its use in measuring contamination on wafers in semiconductor device manufacturing. While tools using oblique light are effective in detecting small particles, there was no sure way to evaluate the limits of the detection capability with respect to particle size (i.e., how small) and spacing between particles. Generally a number of small particles of calibrated size are placed on a wafer and if "sparkles" are detected, it is assumed that with the level of illumination used the instrument detects individual particles at least down to the level of the size of the calibrated particles. Unfortunately, "observed particles" may result only from clusters of particles (whether the particles are touching or not), each cluster appearing as one "particle". Thus, a false idea of how small particles can be detected is obtained. Even if we assume that we know exactly how small an individual isolated particle can be detected, one may get a false particle count since two or more particles spaced very close together may show up as one spot. Evidently, one has to know the minimum detectable particle size associated with a certain spacing (between particles) and illumination level in order to get an accurate count of particles above a predefined size.

The solution to the above problem lies in creating a periodic array of solidly attached (to the substrate; a wafer, for example) and identically sized "mounds," which can be obtained by using direct write E-beam lithography combined with lift-off technique or etching.

In Fig. 1, an SEM micrograph illustrates an approximately 2x2x1 Mum high mound. Fig. 2, an optical micrograph, shows part of a grid of the "particles" described above. Figs. 3 and 4, taken in an obliqu...