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LIGA and Micromolding 4-9

TABLE 4.3 Facilities in the United States Where Access to Synchrotron Radiation Is or Will Soon Be Available

Facility Institute URL
Advanced Photon Source (APS) Argonne National Laboratory http://www.aps.anl.gov/
Cornell High Energy Synchrotron Cornell University http://www.tn.cornell.edu/
Source (CHESS)
National Synchrotron Light Brookhaven National Laboratory http://www.nsls.bnl.gov/
Source (NSLS)
Stanford Synchrotron Radiation Stanford University http://www-ssrl.slac.stanford.edu/
Laboratory (SSRL)
Synchrotron Ultraviolet Radiation National Institute of Standards http://physics.nist.gov/MajResFac/SURF/
Facility (SURF) and Technology
Synchrotron Radiation Center (SRC) University of Wisconsin-Madison http://www.src.wisc.edu/
Center for Advanced Microstructures Louisiana State University http://www.camd.lsu.edu/
and Devices (CAMD)
Advanced Light Source (ALS) Lawrence Berkeley Laboratory http://www-als.lbl.gov/

wavelengths shorter than 1nm, Be is very transparent — that is, it is an excellent X-ray window. A 25µm
thick Be window can withstand a 1atm pressure differential across a small diameter ( 1 in). For large
area exposures, windows up to 6cm dia. have been developed. Be windows age with X-ray exposure and
must be replaced periodically.

4.2.3 Access to the Technology

Today, the construction cost for a typical synchrotron totals over $30 million, restricting the access to
LIGA. Obviously, a less expensive alternative for generating intense X-rays is preferred. Along this line, in
Japan Ishikawajima–Harima Heavy Industries (IHI) is building compact synchrotron X-ray sources (e.g.,
an 800MeV synchrotron of about 30 feet per side) ( http://www.ihi.co.jp/ ).
By the end of 1993, eight nonprivately owned synchrotrons were in use in the United States. The first
privately owned synchrotron was put into service in 1991 at IBM’s Advanced Semiconductor Technology
Center (ASTC) in East Fishkill, New York. Table 4.3 lists the eight U.S. synchrotron facilities.
Most of the facilities listed in Table 4.3 allow LIGA work. For example, Cronos Integrated
Microsystems, Inc., a JDS Uniphase Company and a spin-off from MCNC (Research Triangle Park, NC),
in collaboration with the University of Wisconsin-Madison, announced its first multiuser LIGA process
sponsored by ARPA in September 1993 ( http://www.memsrus.com/CIMSmain2ie.html ). The Center
for Advanced Microstructure Devices (CAMD), at Louisiana State University, has three beam lines dedi-
cated exclusively to micromachining work, and the Advanced Light Source (ALS) at Berkeley has one
beam line available for micromachining.
Like Cronos, Forschungszentrum Karlsruhe GmbH offers a multiuser LIGA service (LEMA, or LIGA-
experiment for multiple applications). The commercial exploitation of LIGA is pursued by at least three
German organizations: microParts GmbH STEAG ( http://www.microparts.de ); IMM ( http://www.
imm.uni-mainz.de ); and Forschungszentrum Karlsruhe, or KfK ( http://www.fzk.de ). In the U.S.,
Louisiana State University’s CAMD ( http://www.camd.lsu.edu/ ), Baton Rouge, and the associated
start-up Mezzo Systems, Inc. (now International Mezzo Technologies, Inc., http://www.mezzotech. biz/ ),
are promoting the technology.

4.3 LIGA and LIGA-Like Process Steps

4.3.1 X-Ray Masks

4.3.1.1 Introduction
X-ray mask production is one of the most difficult aspects of X-ray lithography. To be highly transmis-
sive to X-rays, the mask substrate by necessity must be a low-Z (atomic number) thin membrane. X-ray

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