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

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 (∼3 μm) 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 μm) 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 μm in width (determined by optical mask) with channel depths of ∼50 μm (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.