Dale R. Boehme

Resist substrate studies for LIGA microfabrication with application to a new anodized aluminum substrate

Resist substrates used in the LIGA process must provide high initial bond strength between the substrate and resist, little degradation of the bond strength during x-ray exposure, acceptable undercut rates during development and a surface enabling good electrodeposition of metals. Additionally, they should produce little fluorescence radiation and give small secondary doses in bright regions of the resist at the substrate interface. To develop a new substrate satisfying all these requirements, we have investigated secondary resist doses due to electrons and fluorescence, resist adhesion before exposure, loss of fine features during extended development and the nucleation and adhesion of electrodeposits for various substrate materials. The result of these studies is a new anodized aluminum substrate and accompanying methods for resist bonding and electrodeposition. We demonstrate the successful use of this substrate through all process steps and establish its capabilities via the fabrication of isolated resist features down to 6 µm, feature aspect ratios up to 280 and electroformed nickel structures at heights of 190 to 1400 µm. The minimum mask absorber thickness required for this new substrate ranges from 7 to 15 µm depending on the resist thickness.

LIGA: metals, plastics, and ceramics

LIGA, an acronym from the German words for Lithography, Electroforming, and Molding, is being evaluated worldwide as a method to produce microparts from engineering materials. Much of the work to date in LIGA has focused on producing metal microparts, with nickel as the most common material of choice. There is a growing interest in producing plastic parts replicated from LIGA metal masters due largely to microanalytical instrumentation and medical applications. These plastic replicates are generally made by either hot embossing or injection molding. Ceramic replication, of particular interest for high temperature applications or to produce piezoelectric or magnetic microparts, is also emerging as an area of interest. In this paper, a model of the LIGA exposure and development processes is presented along with the result of numerical optimization of mask design and process cost. The baseline processes for a cost- effective method to produce metal microparts are discussed, along with replication methods and result for plastics and ceramics.

PMMA development studies using various synchrotron sources and exposure conditions

PMMA has been the primary resist used in synchrotron exposures for micro-machined parts fabricated by the LIGA process. Because development of this resist directly influences both tolerances and surface finish of completed LIGA structures, it is important to have a good quantitative understanding of PMMA development as a function of the absorbed dose, as well as both the exposure and development conditions. The various synchrotron sources used for LIGA fabrication vary widely in beam energy and flux, and these variations would be expected to influence development rates. Here we present a simple method to measure PMMA development rate over a moderate range of doses using only a single exposure at the synchrotron source. By employing several exposures, this method allows ready determination of development rates over a wide range of exposure and development conditions. Results are presented for the kinetics of PMMA development over a range of development temperatures, absorbed doses, dose rates and sample ages for exposures performed at three major x-ray sources in the United States.

An investigation of the tellurium-rich uranium tellurides using X-ray powder diffraction

Abstract A comprehensive X-ray powder diffraction study of synthesized uranium telluride phases produced new and improved diffraction pattern data compared to published values. Experimental work at the tellurium-rich end of the U-Te phase diagram, using a high intensity rotating anode diffraction system, has yielded data for the phases UTe 2 , U 2 Te 5 , UTe 3 , UTe 3.4 and UTe 5 . Indexing of this experimental diffraction data has produced more complete patterns for the previously published phases UTe 2 , UTe 3 and UTe 5 . The first conclusive experimental diffractometer data are presented proving the existence of the phase U 2 Te 5 . The phase UTe 3.4 is structurally very similar to a reported β-UTe 3 , but is considered to be a new phase based on its composition and computer indexing.

An aluminum resist substrate for microfabrication by LIGA.

Resist substrates used in the LIGA process must provide high initial bond strength between the substrate and resist, little degradation of the bond strength during x-ray exposure, acceptable undercut rates during development, and a surface enabling good electrodeposition of metals. Additionally, they should produce little fluorescence radiation and give small secondary doses in bright regions of the resist at the substrate interface. To develop a new substrate satisfying all these requirements, we have investigated secondary resist doses due to electrons and fluorescence, resist adhesion before exposure, loss of fine features during extended development, and the nucleation and adhesion of electrodeposits for various substrate materials. The result of these studies is a new anodized aluminum substrate and accompanying methods for resist bonding and electrodeposition. We demonstrate successful use of this substrate through all process steps and establish its capabilities via the fabrication of isolated resist features down to 6 {micro}m, feature aspect ratios up to 280 and electroformed nickel structures at heights of 190 to 1400 {micro}m. The minimum mask absorber thickness required for this new substrate ranges from 7 to 15 {micro}m depending on the resist thickness.