Radiant energy – Inspection of solids or liquids by charged particles – Including a radioactive source
Reexamination Certificate
1999-10-12
2001-09-18
Berman, Jack (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Including a radioactive source
C250S306000, C250S310000, C250S309000
Reexamination Certificate
active
06291823
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
This invention relates to a system for analyzing the effects of high energy ion radiation upon materials and the function of semiconductor electronic circuits, ion beam analysis. More particularly it relates to a system for correlating the impact point of an ion as a function of the mapped origination point of the secondary electrons that are emitted with the effect(s) of that ion upon the sample itself.
Nuclear microprobe analysis is currently performed by focusing MeV ions onto a sample and then scanning the ion beam in a flying spot analysis. The nuclear, atomic, or charge collection signals that are created by the interaction of the ions with the sample constitute the detected signal. The location from which the signal originates on the sample is known by the position of the scanning ion beam at the time the signal is created and detected. The position of the “flying spot” is derived from the scanning apparatus that moves the focussed ion beam spot back and forth across the sample. Analytical techniques using nuclear microprobe analysis have reached a 0.3-0.9 micron lower limit for the beam spot resolution with presently available magnetic and electrostatic focusing lenses. No significant improvements in spatial resolution have been reported in over 5 years. There are a variety of factors involved in this stagnation that include the difficulty in manufacturing the lenses for these ion beams with the required accuracy, the difficulty in achieving the required level of vibration isolation, and the difficulty in focussing ions with high magnetic rigidity and/or poor chromaticity originating from cyclotrons, linacs and older Van de Graaff style electrostatic ion accelerators. There is a present need in the art to improve the spatial resolution for this analysis technique, a need that will only become more critical as the feature sizes of microelectronic circuits continue to shrink. There is also a need to provide performance that is equivalent or better than the present state of the art at a greatly reduced cost.
BRIEF SUMMARY OF THE INVENTION
An order of magnitude improvement in spatial resolution is made possible by the present invention which comprises discarding the need for the precisely focussed and scanned ion beams of the prior art in favor of utilizing an unfocussed ion source instead. Instead of relying upon knowledge of where the prior art ion beam spot is via the scanning system at the time a radiation effect is detected, this invention precisely images the position of the secondary electrons emitted from the surface as a result of an interaction of an ion with the sample. This imaging is done with much of the hardware already employed with photon electron emission microscopes, with the phosphor screen thereof being replaced with a very sensitive X Y position detector to map the location of the point of emission of the collected secondary electrons from the sample surface. The timing of these emissions of secondary electrons at the mapped positions on the sample surface is correlated with the ion-induced signals from the device or material sample under test to match a particular ion interaction to a particular place on the sample.
Preliminary data from laboratory prototypes already have demonstrated lateral resolutions equivalent to the best available scanning ion beam systems and offer the potential for 10 to 20 times better resolution. The replacement of the very complex ion beam focussing/scanning systems in prior art machines with the projection imaging of the emitted secondary electrons with readily available electron focussing optics significantly reduces the costs involved in making the types of measurements done by this class of systems. Also, because this invention avoids ion focusing, certain ion microbeam analyses previously limited to applications involving complex, large and expensive particle accelerators can be performed using simple, small and inexpensive radioactive alpha particle sources.
REFERENCES:
patent: 4829243 (1989-05-01), Woodard, Sr. et al.
patent: 5451783 (1995-09-01), Coxon et al.
patent: 5990476 (1999-11-01), Larson et al.
Ion Bombardment induced segregation effects in VDx studies by SIMS and SNMS , authored by Scholz et al., Journal of Alloys and Compounds, 253-254 (1997) pp. 459-462.*
Web Page ofPhysics and Space Technologyhome page—Ion-Surface Interaction Studies—Maintained by Joseph W. McDonald, mcdonald6@llnl.gov.
Doyle Barney L.
Vizkelethy Gyorgy
Weller Robert A.
Berman Jack
Fernandez Kalimah
Sandia Corporation
Stanley Timothy D.
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