Micromachining in Plastics Using X-Ray Lithography for the Fabrication of Micro-Electrophoresis Devices

Abstract

Micromachining was performed in polymethylmethacrylate (PMMA) using X-ray lithography for the fabrication of miniaturized devices (microchips) for potential applications in chemical and genetic analyses. The devices were fabricated using two different techniques: transfer mask technology and a Kapton mask. For both processes, the channel topography was transferred (1:1) to the appropriate substrate via the use of an optical mask. In the case of the transfer mask technique, the PMMA substrate was coated with a positive photoresist and a thin Au/Cr plating base. Following UV exposure, the resist was developed and a thick overlayer (approximately 3 microns) of Au electroplated onto the PMMA substrate only where the resist was removed, which acted as an absorber of the X-rays. In the other technique, a Kapton film was used as the X-ray mask. In this case, the Kapton film was UV exposed using the optical mask to define the channel topography and following development of the resist, a thick Au overlayer (8 microns) was electrodeposited onto the Kapton sheet. The PMMA wafer during X-ray exposure was situated directly underneath the Kapton mask. In both cases, the PMMA wafer was exposed to soft X-rays and developed to remove the exposed PMMA. The resulting channels were found to be 20 microns in width (determined by optical mask) with channel depths of approximately 50 microns (determined by x-ray exposure time). In order to demonstrate the utility of this micromachining process, several components were fabricated in PMMA including capillary/chip connectors, injectors for fixed-volume sample introduction, separation channels for electrophoresis and integrated fiber optic fluorescence detectors. These components could be integrated into a single device to assemble a system appropriate for the rapid analysis of various targets.

Peer Reviewed: Polymeric Microelectromechanical Systems.

“…An X-ray mask can also be produced by electron beam writing, which will create structures with lateral dimensions of <1 µm. Figure 3b shows procedures for creating a Kapton or graphite mask, which can be used for numerous exposures, or a transfer mask, in which the device topology is transferred directly to the wafer substrate and used for only one exposure (17,18). In either case, a thick layer of gold absorbs X-rays, defining areas of the polymer unaffected by X-rays.…”

“…Another attractive feature of high-aspect-ratio micromachining is that guide channels can be fabricated, which accommodate various inserts, such as fiber optics or conventional glass capillaries (18,22). Figures 3c and 3d show guide channels for accepting capillary tubes and fiber optics, which were fabricated in PMMA using LIGA processing.…”

Modification of a poly(methyl methacrylate) injection-molded microchip and its use for high performance analysis of DNA

“…A number of polymeric materials have been used to create microfluidic devices, such as poly(methyl methacrylate) (PMMA) [4], polycarbonate [5], SU-8 photoresist [6], Zeonor 1020 [7], and the elastic poly(dimethylsiloxane) (PDMS) [8,9]. Polymeric substrates have been patterned using laser ablation [3], X-ray lithography [10], injection molding [11], and imprinting from master templates [12].…”

Materijali za izradu mikroreaktora

“…54,55 Osim litografije, i litografija rendgenskim zrakama primjenjuje se za izradu polimernih mikrosustava, a najčešće na PMMA. 56,57 Laserska fotoablacija je postupak koji su Roberts i sur. 58 1997. godine predstavili kao postupak pogodan za stvaranje mikrokanala.…”