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Analysis of Integrated Circuits Using Limited X-rays


The DARPA TRUST program established the potential usefulness of using an X-Ray microscope to analyze ICs at a synchrotron. We would like to further that development using a lab based X-Ray source. When utilizing a lab X-ray source, acquisition times for X-ray images increase significantly compared to using a synchrotron X-ray source. This is due to the decreased number of X-ray photons (i.e., X-ray flux) produced by a lab source. This reduced X-ray flux combined with a relatively large imaging area makes image acquisition prohibitively slow at the resolution required for the analysis of modern ICs. It therefore becomes necessary to develop an approach to X-ray imaging that can minimize the imaging time, while still being able to reconstruct the internals of a multilayer laminar IC. This problem is very similar to the one faced in medical imaging to reduce the total radiation dosage to a patient. However, unlike in medical imaging, the internal structure of ICs is very regular and defined by design rules. These design rules limit the geometries and materials used in an IC. This a priori information can be combined with recent advances in low dose X-ray imaging to create software with innovative algorithms optimized for IC inspection. The X-ray microscope, for which the imaging approach will be applicable, will conform to the following: 1) Sample will be mounted on a stage with at least four degrees of freedom (i.e., x, y, z, and rotation around an axis). 2) Stage positional uncertainty (i.e., error in reported position) will be smaller than the minimum feature size. 3) A scintillator and camera will be used to acquire an X-ray image of a specific region of the sample at a time. This region will be much smaller than the area of interest; therefore, many images will need to be taken and stitched together to image the entire area of interest. 4) Image data can be sent to a computer for real-time analysis and there will be an interface for a computer to control the stage and image acquisition equipment. This communication can be used to dynamically optimize the scanning and reconstruction algorithms. The software is required to do the following: 1) Direct the X-ray microscope to acquire X-ray images. a. Interface to microscope will allow the following to be controlled: i. x, y, and z position. ii. Angle iii. X-ray exposure time b. Software will need to decide the best way to position the sample and at which angles to acquire images to minimize the total time it takes to image the IC. 2) Analyze the resulting X-ray images in such a way that the conductors in the entire IC are modeled a. A 3D model is anticipated as the output format. b. The data must be segmented based on X-ray absorption contrast. PHASE I: Conduct research on algorithms for X-ray image analysis and evaluate their application to imaging ICs as described in the paragraphs above. Conceive of a system in which an IC is placed in an X-ray microscope and software is run that utilizes the microscope to create a 3D map of the conductors in the IC while minimizing the X-ray imaging time. Propose a design for that software and determine its technical capabilities. The end product of Phase I is a feasibility study report, in which the following must be specified: 1. The hardware required to execute the software program (e.g., Desktop computer, HPC, GPUs, Intel Phi, etc.). We expect the software to take advantage of parallel processing and to scale with the processing resources available. 2. A list of assumptions or requirements of the X-ray microscope beyond what is listed in this document. 3. A list of assumptions or requirements of the IC being imaged. 4. A clear description of the X-ray acquisition algorithm and why it is advantageous. 5. A clear description of the reconstruction algorithm and why it is advantageous. 6. A clear description of the analysis algorithms and why they are advantageous. 7. An estimate of imaging time for a 5mm x 5mm, 9 layer, 90nm technology node IC given an X-ray microscope that takes “t0” time to acquire a single 20μm x 20μm area image when oriented perpendicular to the X-ray source. Include details of how this estimate is calculated. We expect the imaging time to be less than the time it would take to scan the whole chip at 30 angles. a. Note that “t0” is expected to be at least 10 seconds for a lab based X-ray microscope. 8. An estimate of any additional processing time required after imaging is complete. This estimate should scale with available processing capability. 9. An estimate of false positives, false negatives, and the trade space with respect to imaging speed. 10. A clear description of the proposed data output format and how it models the 3D structure of the conductors of the IC and the coordinate system used. 11. A clear description of any inputs or operator interaction the system will require. PHASE II: Develop a prototype of the Phase I concept and demonstrate its operation. Validate the performance using an X-ray microscope over multiple dissimilar, modern ICs (e.g., FPGA or microprocessor of 90nm technology node or better) and develop a test plan to fully characterize the prototype. The software being developed must have a royalty-free license for the Government, including its support service contractors, to use, modify, reproduce, release, perform, display, or disclose technical data or computer software generated for any United States government purpose. The software under development will operate on an X-ray microscope specified and made available by DMEA. PHASE III: There may be opportunities for further development of this software for use in a specific military or commercial application. During a Phase III program, the contractor may refine the performance of the design and produce pre-production quantities for evaluation by the Government.
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