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Silicon Absorption Edge Laser Scanning

IP.com Disclosure Number: IPCOM000076451D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Schick, JD: AUTHOR

Abstract

If photons of energy near the absorption edge of silicon irradiate a device chip, they should be nearly transmitted by the chip. When electronic absorption does take place, hole-electron pairs are created. When these carriers are created within the depletion region of a PN junction, they are swept out by the junction potential giving rise to a reverse current in an external measuring circuit. This technique can be used for failure analysis of the device. It shows junction integrity as well as circuit continuity.

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Silicon Absorption Edge Laser Scanning

If photons of energy near the absorption edge of silicon irradiate a device chip, they should be nearly transmitted by the chip. When electronic absorption does take place, hole-electron pairs are created. When these carriers are created within the depletion region of a PN junction, they are swept out by the junction potential giving rise to a reverse current in an external measuring circuit. This technique can be used for failure analysis of the device. It shows junction integrity as well as circuit continuity.

The use of a laser beam of 1.06 mu wavelength (~1.1 eV) allows the examination of devices mounted face down. Maximum transmission for penetration through the back of the device and maximum absorption for an adequate signal are required simultaneously, thus dictating absorption edge illumination, or energy equal to half the band gap. The signal is amplified and used to intensity modulate a cathode-ray tube. The X and Y signals from the scanning system synchronize the cathode-ray tube with the position of the scanning laser beam. The result is a picture of the junction or junctions of choice as seen from the back of the chip displayed on the cathode-ray tube. Failure analysis can be performed on chips without removing them from the substrate. This technique also allows the examination of junctions covered by aluminum, which does not transmit light.

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