OTHER DESIGNATIONS: Extreme ultraviolet (EUV) lithography, interferometry, LIGA (lithographie, galvanoformung und abformung — translation: lithography, electroplating and molding), microelectromechanical structures (MEMS).

PURPOSE:

1. Explore whether the demagnifying mirrors needed in EUV lithography, a candidate for the next technology in the production of microchips, can be manufactured to the desired specifications.
2. Explore and implement the manufacture of microscale mechanical components using LIGA or MEMS.

HOW THE TECHNIQUE WORKS: Lithography, a technique used in the art world for many centuries, has been adopted and adapted with phenomenal success by the high-tech industry. In microchip manufacturing, a silicon wafer is coated with a thin layer of photosensitive material called a resist. An image of a mask containing the desired pattern is projected onto the resist. The exposed (or unexposed) parts of the resist are etched away and, with further processing, the desired circuit is built up. The same basic process can be used in the manufacture of small mechanical components. Work at synchrotron light sources focuses primarily on the exposures of the resists.

UNIQUENESS:

1. The high coherence of synchrotron radiation is absolutely essential for mirror interferometry.
2. High flux and favorable spectral range are essential for short exposure times in LIGA/MEMS.

EXAMPLES:

EUV Lithography, the Next Microchip Manufacturing Technology
Rotary Millimotor
Commercial LIGA Microfabrication for Optoelectronics

A mirror directs focused EUV light into an interferometer. By controlling the exposure, researchers were able to print line widths down to 39 nm for an elbow test pattern with a line-to-spacing ratio of 3:1.

In conformance with Intel co-founder Gordon Moore’s 1965 prediction, now known as “Moore’s Law,” the density of circuit elements on microchips has doubled roughly every 18 months for more than 30 years, resulting in ever smaller, faster, and cheaper computers. However, the traditional technique for printing circuit patterns — optical lithography based on refractive optics (lenses) — cannot continue indefinitely on this course. Today’s leading candidate for a successor, known as extreme ultraviolet (EUV) lithography, relies on reflective optics (mirrors). With wavelengths 50 times smaller than those of visible light, EUV techniques will be able to draw circuit patterns just tens of nanometers wide. Before that day arrives, however, there is the matter of producing accurate EUV lithography cameras. As an old adage says, "If you can't measure it, you can't make it." EUV metrology beamlines have been instrumental in a five-year, $250-million industry effort to bring EUV lithography to the commercial stage. The first printing results reveal the extraordinarily high quality of the lithography optics and demonstrate the importance of EUV metrology beamlines in helping to achieve the very tight specifications for figure, finish, and multilayer coatings required of the mirrors comprising the lithography optics.By printing actual test patterns with ultrathin line widths, researchers have verified that the optics fabricated for a prototype camera are indeed on the path to the required performance.

P.P. Naulleau et al., “Static microfield printing at the Advanced Light Source with the ETS Set-2 optic,” Proc. SPIE 4688, 64 (2002).

LIGA-micromachined gear for a miniature electromagnetic motor.

By using the penetrating power of x-rays from a synchrotron, LIGA allows the fabrication of structures which have vertical dimensions from hundreds of microns to millimeters and horizontal dimensions which can be as small as microns. These are three-dimensional microstructures defined by two-dimensional lithographic patterns. The height-to-width ratio capability is relevant to the manufacturing of miniature components that can withstand high pressure and temperature, and can transfer useful forces or torques. The feature definition, radius, and side wall texture using LIGA are superior to current precision machining techniques. A miniature electromagnetic motor that fits in a volume 8 millimeters in diameter by 3 millimeters in height has been designed, fabricated, and tested. The torque goal for this millimotor was greater than 1.5 milli Newton-meters. The millimotor has been tested at speeds up to 1600 rpm, well below the maximum currents that coils are expected to withstand. Further tests to measure torque are planned.

AXSUN uses the LIGA process to create a new packaging platform for photonics using micro-optic lens and micro-alignment technology.

Originally developed in Europe, LIGA has only recently been accepted as a proven, commercially available production process. Today, millions of high-precision parts are fabricated using LIGA production processes.A commercial LIGA beamline has been established by AXSUN Technologies, a Massachusetts-based company that provides miniaturized optoelectronic modules for fiber-optic telecommunications networks. These modules are essentially optical benches the size of computer chips, containing complex assemblies of high-precision optical, mechanical, and electrical subassemblies that align and focus incoming photon signals, convert them into electrical signals, and route them through switches into the appropriate paths. AXSUN uses LIGA techniques at the new beamline for the microfabrication of key alignment structures (patent pending) measuring roughly 2 millimeters wide by 500 micrometers thick.

Link: www.ligafoundry.com.