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Deepak
Professor,
 Materials Science and Engineering,
 Indian Institute of Technology-Kanpur ,
 Work Phone: (512) 2597353,
 Email: saboo[at]iitk.ac.in

Aditya Kumar’s Thesis

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Thesis  Topic:
 Tungsten and its silicide deposition system and modelling approach to determine Si diffusion in silicide
Advanced devices of the new and conventional materials require development of compatible advanced metallization techniques for electrodes, interconnects and contacts.  Often, these developments are based on the basic understanding of the materials and processes.  In this thesis, I have developed a two-dimensional model for the oxidation process of the polycide structure (WSix/Si) used as the gate electrode in MOS devices.  In general, oxidation of the polycide structure results in formation of SiO2 film on top of the WSix.  It has been experimentally verified that underlying silicon (Si) diffuses through WSix film and forms SiO2 on the WSix surface.  A mathematical model for this process was developed, the simulation results were verified with analytical results and were found to be in good agreement.  From the simulation results, it was found that Si diffusion has significant effect on the oxidation of polycide. We also propose a novel technique for measuring diffusion-coefficient of Si in WSix based on our results.  It was also found that the formation of non-uniform oxide can be reduced by lowering the partial pressure of oxygen.  
 A LPCVD system was installed to deposit the tungsten and tungsten silicide (WSix) thin films.  Tungsten film was deposited on Si-wafer at 258oC and 464 mT by silicon reduction of tungsten hexafluoride.  The deposited film was characterized using XRD, electron probe micro analyzer and sheet resistance measurement.  It was found that a uniform thin layer of tungsten of thickness around 150 Å is deposited on the Si-wafer.  The sheet resistance of film was found to be 57.92 W/š.