NIST's improved inverse solution method presses dopant profiling towards industry goals. (News Briefs).NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. has demonstrated a higher accuracy and higher spatial resolution (Data West Research Agency definition: see GIS glossary.) A measure of the accuracy or detail of a graphic display, expressed as dots per inch, pixels per line, lines per millimeter, etc. It is a measure of how fine an image is, usually expressed in dots per inch (dpi). inverse solution method for determining dopant dopant Any impurity added to a semiconductor to modify its electrical conductivity. The most common semiconductors, silicon and germanium, form crystalline lattices in which each atom shares electrons with four neighbours (see bonding). profiles from scanning capacitance microscope (SCM (1) (Software Configuration Management, Source Code Management) See configuration management. (2) See supply chain management. ) images of silicon transistors. Dopant profiles are a major factor controlling the functional operation of deep sub-micrometer transistors. High accuracy measurements of dopant profiles are needed to improve the predictive quality of transistor models and design. The breakthrough is embodied in computer code that makes a large step towards meeting the aggressive spatial resolution goals set out in the International Technology Roadmap for Semiconductors The International Technology Roadmap for Semiconductors is a set of documents produced by a group of semiconductor industry experts. These experts are representative of the sponsoring organisations which include the Semiconductor Industry Associations of the US, Europe, Japan, (ITRS ITRS International Technology Roadmap for Semiconductors ITRS International Terrestrial Reference System ITRS International Transaction Reporting System (EU) ITRS International Technical Rescue Symposium ). In the mid-1990s, SED (1) (Stream EDitor) A Unix text editor that processes an entire file. It is the stream-oriented version of ed, an earlier text editor. Sed executes ed commands, but instead of editing one line at a time, sed applies the commands to the whole file. launched a systematic effort to address the so-called shallow-junction-profiling problem and has since developed the SCM as a practical tool for imaging the two-dimensional dopant concentration distribution in transistor junctions near their gates. An essential element for quantifying the measurement is a detailed model of how the microscope interacts with the junction during imaging. Up to this point, models treated each data point of an SCM image independently. A forward solution (calculation of SCM signal from a dopant profile) was used to calculate a calibration curve, which could then be used to deduce dopant profiles with spatial resolution of about 20 nm. The spatial resolution of this model was still far short of the current goal of 4 nm (increasing to 1 nm by 2016) defined by ITRS. Recent breakthroughs in the NIST modeling approach now allow for a better inverse solution of the dopant profile, in which the dopant concentration at each measurement point is calculated considering the effects of the neighboring points. The regression procedure makes use of both coarse and fine grid meshes, so that only a few iterations are needed to reach convergence. Preliminary demonstrations with one-dimensional model data indicate the resulting spatial resolution could meet current and future ITRS goals. The recent NIST National Research Council panel recognized that the inverse solution of SCM data could potentially overcome one of the key roadblocks expressed in the ITRS. CONTACT: Jay Marchiando, (301) 975-2088; jay.marchiando@nist.gov. |
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