An Introduction Into X-Ray Micromachining Using Synchrotron Radiation

Abstract

Micro production technologies are a driving factor in today’s continuous effort of developing new, highly functional products. The need for increased functionality is met by decreasing the size of individual components as well as consequently miniaturizing components for non-electronic properties including optical, mechanical, and fluidic functions. An important factor in this approach his the right material for a given task and the ability to shape it into the desired geometry as well as to combine micro components in a cost-effective way to build more complex modules and micro systems. One micro production technology that meet several of the above mentioned needs is the LIGA process, a combination of three major fabrication processes — x-ray based micromachining or deep x-ray lithography (DXRL), electroplating, and molding. In x-ray lithography the unique properties of synchrotron radiation, especially high intensity of collimated x-ray photons, permit patterning of extremely precise, very tall primary microstructures up to several millimeters in height with micrometer lateral dimensions and sub-micrometer details (so-called High-Aspect Ratio Microstructures, HARM). These microstructures are attractive for mechanical and optical components in MEMS (MicroElectroMechanicalSystems) devices. While x-ray lithography is crucial to achieve a primary microstructure with superior features, the use of synchrotron radiation is limiting the material choice to only a few polymer materials, so-called x-ray resists. Additional processes including electroplating and molding, however, open up a huge selection of engineering materials such as metals, ceramics, and also a large number of polymers and allow MEMS engineers to combine structural and material properties to build the next generation MEMS devices. This paper is primarily focusing on the DXRL process. Process fundamentals including equipment and infrastructure, x-ray masks, resists, typical structure geometries as well as patterning accuracy will be discussed. A few examples will illustrate ongoing efforts of commercializing this technology and also indicate future areas of applications.