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United States Patent [w]
US005981967A [ii] Patent Number:  Date of Patent:
 METHOD AND APPARATUS FOR
ISOLATING DEFECTS IN AN INTEGRATED
CIRCUIT NEAR FIELD SCANNING PHOTON
 Inventor: Zhouxing Luo, Sugar Land, Tex.
 Assignee: Texas Instruments Incorporated,
 Appl. No.: 08/992,707  Filed: Dec. 17, 1997
Related U.S. Application Data
 Provisional application No. 60/033,101, Dec. 17, 1996.
 Int. CI. G01N 21/86
 U.S. CI 250/559.4; 250/559.45;
 Field of Search 250/559.4, 559.45,
250/306-311; 356/237.4, 237.5
 References Cited
U.S. PATENT DOCUMENTS
5,235,400 8/1993 Terasawa et al 356/237.5
KLA 1620 Emmission Microscope for Multilayer Inspection, Operation's Manual, Revision A. Software Version 2.0, Jun. 1990. (No page #).
"Near-field optical microscope break the diffraction limit," by Pat Moyer and Tim Van Slambrouck, Laser Focus World, TropMetrix, four pagee. (No date).
"IC Failure Analysis Using Real-time Emission Microscopy," by Tom Adams, Semiconductor International, two pages (No date).
"Super Resolution Imaging Spectroscopy," by T.D. Harris, R.D. Grober, J.K. Trautman, and E. Betzig, Applied Spectroscopy, vol. 48, No. 1, 1994, pp. 14A thru 21A (Month unknown).
"IC Failure Analysis: Techniques and Tools for Quality and Reliability Improvement," by Jerry M. Soden and Richard E. Anderson, Proceedings of the IEEE, vol. 81, No. 5, May 1993, pp. 703 thru 715.
Primary Examiner—Que T. Le
Attorney, Agent, or Firm—Robert D. Marshall, Jr.; Gerald E. Laws; Richard L. Donaldson
An apparatus for isolating defects in an integrated circuit using near field scanning photon emission microscopy comprises a photon collector 10 which receives emitted photons 16 from a surface 14 of an energized or biased integrated circuit 12, a CCD camera 20 for converting the photons into an emission image 22, and an optical fiber 18 coupling the CCD camera 20 to the photon collector 10, so that the optical fiber transmits photons from the collector to the CCD camera. As a result, defects in integrated circuits can be isolated with greater resolution than currently available using conventional far field photon emission microscopy.
20 Claims, 2 Drawing Sheets
U.S. Patent Nov. 9,1999 Sheet 1 of 2 5,981,967
METHOD AND APPARATUS FOR
ISOLATING DEFECTS IN AN INTEGRATED
CIRCUIT NEAR FIELD SCANNING PHOTON
This application claims priority under 35 USC 119(e) (1) of provisional application Ser. No. 60/033,101, filed Dec. 17, 1996.
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of integrated circuit manufacture and more particularly, to a method and apparatus for isolating defects in an integrated circuit using near field scanning photon emission microscopy.
BACKGROUND OF THE INVENTION
During the manufacture of integrated circuits, it is important to be able to detect and isolate very small defects caused by leakages, latch-ups, and other problems. Far field photon emission microscopy has been used in the past to detect photon emissions of very low energy from integrated circuits, thereby helping to isolate these types of defects. Although the sensitivity of far field photon emission microscopy is very high, its spatial resolution, being about 0.5 microns, is inadequate to detect many defects, given the fact that integrated circuits are becoming increasingly small and are already in the low sub-micron range. Thus, it is very difficult to obtain adequate resolution beyond 0.5 microns using far field photon emission microscopy.
The ability to improve resolution using far field photon emission microscopy is limited because resolution is dependent on the wavelength of the emitted light and the numerical aperture of the microscope. The resolution of far field photon emission microscopy can only be improved two ways—either by detecting shorter wavelength photons or by increasing the numerical aperture of the microscope. However, most photons emitted by integrated circuit defects have fixed wavelengths. To detect the shorter wavelengths, the integrated circuits can be coated by special materials such as rare earth chelates capable of emitting short wavelength photons, as discussed in Jerry M. Soden, et al., "IC Failure Analysis: Techniques and Tools for Quality and Reliability Improvement," Proceedings of the IEEE, Vol. 81, No. 5, May 1993, p. 707. However, this kind of material poses radiation problems and is limited in use. In addition, the numerical aperture of a camera is limited by the physical size and focal length of the lens, making it impractical and difficult to increase the numerical aperture to the desirable range.
Laser tips as a source of light have been used in the past for far field collection of light reflected off of the surface of integrated circuits, as discussed in T. D. Harris, et al., "Super-Resolution Imaging Spectroscopy," Applied Spectroscopy, Vol. 48, No. 1, January 1994, p.l9A. The light path in such devices may be reversed to perform collection mode near field scanning microscopy. This technique merely collects reflected light, giving a topographical image of the sample. It does not detect defects located below the surface of the integrated circuit.
Integrated circuits have also been analyzed in the past using a multi-step process as described in KLA Instruments Corporation, San Jose, Calif., 1620 EMMI (Emission Microscope For Multilayer Inspection) Operator's Manual, Revision A, June 1990. In one step of this process, the integrated circuit is energized or biased using the proper electrical stimulus, and emitted photons are captured by a
conventional lens using far field techniques. In another step, light is shined on the surface of the integrated circuit and the reflected light is captured by a camera. In the final step, the two sets of data are combined. However, the resolution available using this technology is insufficient, being only about 0.5 microns.
SUMMARY OF THE INVENTION
Therefore, a need has arisen for an improved method and apparatus for detecting and isolating defects, including subsurface defects, in an integrated circuit, which has greater spatial resolution than that available using far field photon emission microscopy. In accordance with the present invention, an apparatus is provided that uses near field scanning photon emission optical microscopy to isolate defects in an integrated circuit, including defects located below the surface of the sample. The invention features a near field photon collector which receives photons emitted from the surface of a biased integrated circuit following application of an electrical stimulus to the circuit, a charged coupled device such as a charge coupled device camera (CCD camera) to convert the photons into an emission image, and an optical fiber coupling the CCD camera to the photon collector so that the photons are transmitted from the photon collector to the CCD camera.
In another embodiment, a method for isolating defects in an integrated circuit comprises four steps. These steps are: energizing the circuit with electrical energy, collecting photons emitted from a surface of the integrated circuit, transmitting the photons to an imaging device capable of converting the photons into an emission image, and converting the photons into an emission image. In an optional fifth step the emission image is combined with a topographical image.
A technical advantage of the present invention is that much better resolution of integrated circuit defects caused by leakages, latch-ups and other problems, including those located below the surface, can be achieved than the resolution available using conventional far field photon emission microscopy. Resolution less than or equal to 50 nanometers is possible using the present invention. Another technical advantage of the present invention is that it allows the use of a photon collector or scanning probe tip in the size of nanometers to scan very close to the specimen surface and gather data emitted from the surface due to defects, including defects below the surface. This emitted data may then be used to form an image. Thus, the spatial resolution of the present invention is much greater than far field photon emission microscopy, as it is limited only by the dimension of the tip, which can be in tens of nanometers or smaller. Another technical advantage of the present invention is that in integrated circuit applications, one can get more detail by using the present invention to observe metal to metal shorts, to view the details of hot electrons penetrating a gate oxide, to observe photons generated by shorts such as a Vcc to Vss short in an integrated circuit, and to isolate other defects such as P-N junction leakages, latch-ups, process and/or structure induced failures, saturated transistors, substrate related failures, junction spiking, electrostatic discharge damages, hot electron effects, oxide defects, impact ionization, junction breakdown, gate pinholes and current leakages. Another technical advantage of the present invention is that the emission image can be saved and overlapped with a topographical image obtained using conventional collection mode near field scanning optical microscopy, in order to better pinpoint the emission site or defect.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, the objects and advantages thereof, references