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Alpha Probe for Memory Chip Testing

IP.com Disclosure Number: IPCOM000051383D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 75K

Publishing Venue

IBM

Related People

Hicks, WW: AUTHOR [+4]

Abstract

Arrangements are described for in-wafer testing of functional memory chips for sensitivity to alpha particle bombardment in high density arrays. A pin-shaped radioactive alpha particle source, confined by a pair of collimators, is used to expose identified locations on the chip. Identification of the exposed site is achieved by a laser illuminating the chip at the interception of collimator axis and wafer surface, and a microscope arrangement employed to identify the location of the illuminated spot.

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Alpha Probe for Memory Chip Testing

Arrangements are described for in-wafer testing of functional memory chips for sensitivity to alpha particle bombardment in high density arrays. A pin- shaped radioactive alpha particle source, confined by a pair of collimators, is used to expose identified locations on the chip. Identification of the exposed site is achieved by a laser illuminating the chip at the interception of collimator axis and wafer surface, and a microscope arrangement employed to identify the location of the illuminated spot.

Fig. 1 generally shows the pin-shaped radioactive alpha particle source at 11. The pin-shaped radioactive source is fabricated by depositing radioactive material 1 on the tip of pin 3. Typically, pin 3 would comprise a metal pin 0.025- 0.040 inch in diameter. The pin is enclosed by sleeve 5 approximately 0.050 inch in diameter with epoxy spacer 7 separating the sleeve from the pin. A variable thickness film 9 of titanium or nickel is employed to seal the arrangement. The thickness of the film may be varied to adjust the maximum alpha particle energy, in accordance with the particular application within the constraints of providing a sealed source.

As shown in Fig. 2, pin-shaped alpha particle source 11 is mounted in a holder which includes a pair of collimators or apertures 13 and 15 which determine the final size of the emitted alpha beam spot at the wafer surface below. Typically, the collimators are separated by a distance D of approximately 2-3 cm, and the second collimator, i.e., collimator 15, is separated from the wafer by this same distance. The alpha flux from source 11 is turned on and off by a shutter arrangement, schematically shown at 17. It is clear that rather than utilize shutter 17 between collimators 13 and 15, it may be employed between collimator 15 and the wafer. Such an arrangement is shown in Fig. 3 wherein shutter arrangement 19 is positioned between aperture 15 and the wafer.

Alignment of the alpha particle source to specific points on the wafer is achieved by utilizing a laser source in known relationship to the alpha particle source. One way to implement this is to replace the alpha particle source by the laser source such that the laser beam is passed through the collimators to the wafer, whereby the illuminated position may be read. Thereafter, the alpha particle source replaces the laser beam to expose the located position to alpha particles. Such an arrangement is shown in Fig. 4, wherein laser source 21 is optically coupled to apertures 13 and 15 via light pipe 23 to illuminate wafer 25. Alpha particle source 11 is laterally moved to the side to permit the laser beam to p...