Nanopore-based single-molecule analysis is a subject of strong scientific and technological interest. Recently, solid state nanopores have been demonstrated to possess advantages over biological (e.g., protein) pores due to the relative ease of tuning the pore dimensions, pore geometry, and surface chemistry. Previously demonstrated methods have been confined to the production of single nanopore devices for fundamental studies. Most of these techniques (e.g., electron microscope beams and focused ion beams) are limited in scalability, automation, and reproducibility. We demostrate a wafer-scale method for reproducibly fabricating large arrays of solid state nanopores. The method couples high-resolution electron-beam lithography and atomic layer deposition (ALD). Arrays of nanopores (825 per wafer) are successfully fabricated across 4-in. wafers with tunable pore sizes. The nanopores are fabricated in 16- to 50-nm thin silicon nitride. ALD of aluminum oxide is used to tune the nanopore size. By careful optimization of the processing steps, a device survival rate of up to 96% is achieved on a wafer with 50-nm thin silicon nitride films. Our results facilitate an important step in the development of large-scale nanopore arrays for practical applications such as biosensing.
This paper describes a novel fabrication method for the manufacture of multi-level microfluidic structures using SU-8. The fabrication method is based on wafer bonding of SU-8 layers and multilayer lithography in SU-8 to form microchannels and other structures at different levels. In our method, non-UV-exposed SU-8 layers are transferred to SU-8 structured wafers at desirably low temperatures. This technique is particularly useful for building multi-level fluidic structures, because non-UV-exposed SU-8 can be used as cover for microchannels and the cover can then be lithographically structured, i.e., to form interconnects, after which subsequent transferring of non-UV-exposed SU-8 onto the wafer allows for the fabrication of interconnected multi-level channels and other structures. Examples of interconnected multi-level microchannels were realized using this newly developed method. Liquid has been introduced into the microchannels at different levels to reveal the desirable functionality of the interconnected multi-level channels. The method described here is easily implementable using standard photolithography and requires no expensive bonding equipment. More importantly, the fabrication procedure is CMOS compatible, offering the potential to integrate electronic devices and MEMS sensors into microfluidic systems.
During the past few years, graphite based X-ray masks have been in use at CAMD and BESSY to build a variety of high aspect ratio microstructures and devices where low side wall surface roughness is not needed In order to obtain lower sidewall surface roughness while maintaining the ease of fabrication of the graphite based X-ray masks, the use of borosilicate glass was explored. A borosilicate glass manufactured by Schott Glas (Mainz, Germany) was selected due to its high purity and availability in ultra-thin sheets (30 μm). The fabrication process of the X-ray masks involves the mounting of a 30 μm glass sheet to either a stainless steel ring at room temperature or an invar ring at an elevated temperature followed by resist application, lithography, and gold electroplating. A stress free membrane is obtained by mounting the thin glass sheet to a stainless steel ring, while mounting on an invar ring at an elevated temperature produces a pre-stressed membrane ensuring that the membrane will remain taut during X-ray exposure. X-ray masks have been produced by using both thick negative- and positive-tone photoresists. The membrane mounting, resist application, lithography, and gold electroplating processes have been optimized to yield X-ray masks with absorber thicknesses ranging from 10 μm to 25 μm. Poly(methyl methacrylate) layers of 100 μm to 400 μm have been successfully patterned using the glass membrane masks.