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  • A Fast Track for Micromachining Beamline

    A research team headed by Professor Henry Guckel (UW-Madison) is working with SRC engineering to bring a dedicated beamline for micromachining on line by early next year, only a few months from the start of the project.

    Micromachining refers to a set of processes for manufacturing micro electromechanical systems (MEMS). It has been used to create a wide range of ultra-miniature optical sensors, mechanical motion devices, and mechanical motion sensors. One of the critical steps in the process involves using X-ray lithography to define a pattern in a layer of photoresist on a silicon substrate. These patterns are used to produce the miniature components. Since it is necessary to expose the photoresist to depths of hundreds of microns, X-rays in the multi-kilovolt energy range are needed. These are provided by running the Aladdin storage ring at 1 GeV.

    Guckel’s research effort has been at the forefront of the burgeoning field of MEMS since its early inception. In the past, Guckel’s work at SRC has been performed using an exposure station provided by the Center for X-ray Lithography (CXrL). With the explosion in interest in MEMS, the demand for dedicated exposure stations and specialized exposure hardware has led to this latest effort to expand micromachining at SRC with a beamline designed specifically for MEMS.

    To create micromachined parts, an X-ray sensitive polymer material, usually poly-methyl methacrylate (PMMA), is attached to the substrate. Then it is placed beneath a mask and exposed to synchrotron radiation. One of the unique features of micromachining techniques is the very high precision that can be achieved in the shape of components, which are made with edge runouts of less than 0.1 percent. With the 1 GeV beam at SRC, depths of roughly 100 microns per hour of exposure are achieved in the polymer pattern.

    The new MEMS beamline will incorporate a number of improvements that add flexibility to the exposure process. The beamline is short compared to typical spectroscopy beamlines. A shorter beamline allows a higher dose on the sample. A 100 micron thick beryllium window passes 3 keV X-rays to the exposure station, a low vacuum helium atmosphere, from the synchrotron beamline, which is under ultra-high vacuum. The exposure station can handle 4” diameter wafers. The fully automated exposure facility scans the wafer under an X-ray beam, 50mm x 20mm, ensuring uniform exposure and small runouts over the entire mask area. Future improvements will allow up to 4 wafers to be loaded at one time for automated exposure.

    Pawitter Mangat operates the new beamline and does research in MEMS. He is a Ph. D. graduate of Notre Dame and has done Post Doctoral work at SRC through Northern Illinois University. Mangat says, “Micromachining as an industry is in its infancy. It will be the industrial explosion of the next 30 years.” Much of the effort behind the new MEMS beamline will be directed towards studying the economic feasibility of producing and using micromachines in commercial ventures. The X-ray exposure is only one of many complex processing steps used in MEMS, which are accomplished by Prof. Guckel and his staff using microelectronics labs on the nearby UW campus.

    SRC is part of a growing effort in MEMS research at synchrotron centers nationwide, which includes programs at Center for Advance Micro Devices, NSLS, and ALS. Support for the new beamline is part of a TRP of the Advanced Research Projects Agency, administered by the Microelectronics Center of North Carolina.

    Aladdin -- Editor Brian Tonner