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.
Guckels research effort has been at the forefront of the burgeoning field of
MEMS since its early inception. In the past, Guckels 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
Aladdin -- Editor Brian Tonner email@example.com