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SFSU Cryogenic Electronics Group

Thin Film Laboratory

    Progress in developing any integrated circuit device is made most efficiently when a microfabrication facility is dedicated to the production of that particular type of device. This is especially true for our superconducting detectors and amplifiers because they require unusual substrates and nonstandard materials.  Therefore, in order to conduct our research efficiently,  we have built the San Francisco State University Thin Film Laboratory, which is a fully operational microfabrication facility having both research and educational missions.  It offers a carefully tailored subset of the spectrum of processes commonly encountered in the integrated circuit industry: sputter deposition and electron-beam evaporation of metals and insulators, ion etching followed by in situ  oxidation of surfaces, wet and dry etching, and optical and electron beam lithography.  Thermal oxidation and doping of silicon using safe solid sources are available in an adjacent laboratory. Extremely toxic gases such as arsine and phosphine are not  used in order to maintain a safe environment.  Our thin film evaluation equipment includes a four point probe, a stylus profilometer, a transparent film thickness measurement system, a CV plotter, and a scanning electron microscope.  (A drawing, showing the layout of the Thin Film Laboratory, can be seen by clicking on this link.)

    The Thin Film Laboratory owes its existence to the energy and enthusiasm of San Francisco State students, to the generosity of private companies and professional organizations, to assistance from colleagues at other universities, and to funding from private and governmental organizations.  We have received valuable new and surplus equipment from a large number of corporate benefactors. The Stanford Center for Integrated Systems, the U.C. Berkeley Microlab, the Las Positas Vacuum Technology program, and Lawrence Livermore National Laboratory also have contributed equipment and expert advice.  Primary operating expenses and additional equipment funds have been provided by the National Science Foundation RUI, PYI, and MRI programs, the NSF Center for Particle Astrophysics, Research Corporation, San Francisco State University, Hewlett-Packard Corporation, the American Vacuum Society, and by donations from Dr. Neuhauser and Dr. Michael Taber.

    Routine operations and maintenance are conducted by graduate and undergraduate students who find that type of experience to be a very marketable part of their technical training.  Our proximity to Silicon Valley gives us access to a myriad of semiconductor fabrication support enterprises whom we hire for specialized servicing of equipment such as the deionized water system, the scanning electron microscope, and the metallurgical microscope. This relieves us of the need to hire a staff of full time technicians.  Furthermore, many  local companies provide services at little or no cost to us.

    The SFSU Thin Film Laboratory has gone beyond the scope of conventional wafer processing in many areas.  For example we have developed the ability to pattern aligned films on opposite faces of substrates up to 8 mm thick.  This has been accomplished by modifying vacuum chucks for the photoresist spinner and our Quintel Model 2001CT Manual Tray Load contact printer.  We have installed a showerhead gas distribution/electrode assembly in our plasma etcher in order to achieve very uniform etching.  We have designed and built a UHV sputtering system dedicated to the production of tunnel junctions.  The cryopumped main chamber features an adaptable radial design allowing side-sputtering from up to four magnetron sources without breaking vacuum so that clean interfaces are virtually guaranteed between layers.  Ion gun precleaning of surfaces and oxidation of tunneling barriers are done in the turbo-pumped load lock so that the sputter targets are not exposed to oxygen.  We have made substantial progress in our program to convert an electron beam direct write system into an instrument for micron-scale modification of thin film structures.   In order to avoid exorbitant operational and maintenance costs, we abandoned the precise stage positioning fixturing and instead use the imaging capability to determine the beam location relative to alignment marks printed on the wafer during a preceding optical patterning step.