Performance of SU-8 Membrane Suitable for Deep X-Ray Grayscale Lithography (original) (raw)
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Article Performance of SU-8 Membrane Suitable for Deep X-Ray Grayscale Lithography
2016
In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of Advanced Industrial Science and Technology (AIST). Although the SU-8 before photo-curing has been evaluated as a negative-tone photoresist for ultraviolet (UV) and X-ray lithographies, the characteristic of the SU-8 after photo-curing has not been investigated. A polymethyl methacrylate (PMMA) sheet was irradiated by a synchrotron radiation through an X-ray mask, and relationships between the dose energy and exposure depth, and between the dose energy and dimensional transition, were investigated. Using such a technique, the shape of a 26-μm-high Si absorber was transformed into the shape of a PMMA microneedle with a height of 76 μm, and done with a high contrast. Although during the fabrication process of the X-ray mask a 100-μm-pattern-pitch (by design) was enlarged to 120 μm. However, with an increase in an integrated dose energy this number decreased to 99 μm. These results show that the X-ray grayscale mask has many practical applications. In this paper, the author reports on the evaluation results of SU-8 when used as a membrane material for an X-ray mask.
Fabrication of the X-Ray Mask using the Silicon Dry Etching
Journal of Advanced Mechanical Design Systems and Manufacturing, 2008
The X-ray lithography of uses synchrotron radiation is one of the microprocessing structure fabrication technology. In X-ray lithography, precision of the fabricated structure is influenced by precision of the X-ray mask considerably. Conventionally, the X-ray mask was fabricated with UV lithography. However, it is difficult to fabricate the highly precise X-ray mask because of the tapering X-ray absorber. We introduces the ability of Si dry etching technology into UV lithography in order to fabricate untapered, high precision X-ray masks containing rectangular patterns. This new X-ray mask fabrication method uses a high-precision microstructure pattern formed by Si dry etching, thereby fabricating high aspect ratio, narrow line width resist microstructures that cannot be achieved by any conventional technology. An Au for the X-ray absorber is made to the groove of the structure, and it is formed by electroplating. The silicon substrate itself is used as seed layer and the structure is fabricated with the photo resist whose resistance is higher than silicon. It can be expected the gilding growth from only the bottom layer. High-density Au functions sufficiently as an absorber. Au plating was formed only from the base of the structure ditch and could bury Au of thickness 3.5µm in a narrow place of 2.7µm in width well. The fabricated structure using X-ray lithography. Highly-precise rectangular structure could be fabricated.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2002
A process aimed at fabricating proximity x-ray lithography masks is presented. In this technique, the Ta absorber layer is deposited and patterned on the back side of the membrane and nonspin-coated electron sensitive layers were used in order to achieve high resolution patterning of this absorber. The advantages gained by this approach include a reduction of the membrane temperature during the plasma etching step of the absorber patterns without using any cooling gas. This temperature reduction results from the direct contact of the membrane with a cooling plate. This approach also allows increased protection of the absorber patterns from contamination during exposure of the mask. A third advantage is that the smooth surface of the mask exposed to the wafer in the x-ray lithography stepper may also make it possible to reduce the gap between wafer and mask, thus achieving increased resolution with the x-ray lithography process.
The fabrication of x-ray masks using proton beam writing
Journal of Micromechanics and Microengineering, 2008
We have developed a simplified method of fabricating x-ray masks for deep x-ray lithography by using proton beam writing (PBW) without subsequent soft x-ray copying steps. Combining direct PBW and subsequent electroplating, x-ray masks with gold absorber patterns of up to 11 µm height and with vertical and smooth sidewalls were fabricated. The smallest size in the absorber pattern is less than 0.5 µm in this work. The masks were used for x-ray lithography with synchrotron radiation, and 870 µm SU-8 structures with smooth sidewalls were produced. This fabrication method is promising to be an important alternative to conventional methods for x-ray mask making.
Use of SU-8 photoresist for very high aspect ratio x-ray lithography
Microelectronic Engineering, 2000
This paper describes the process of deep x-ray lithography using epoxy negative photoresist SU-8. Coating, softbake, exposure, post exposure bake, and development of the resist is characterised. Influence of x-ray source spectrum on the lithographic image contrast is calculated and optimal x-ray mask layers compositions for the spectrum in use are proposed. Method for resist film thickness control during casting step is reported. Temperature limit for the post exposure bake was found to ensure safe post bake to obtain maximum resist sensitivity. Optimised development and rinsing process is presented. Resist structures with aspect ratio as high as 100:1 (height : width) are demonstrated.
Journal of …, 2010
In this work, a low-cost and high-resolution x-ray micromask is developed by sputtered lead film on a Mylar sheet substrate with the lift-off process and the x-ray mask is experimented for patterning SU-8 negative photoresist on a glass substrate. Sputtering is selected for Pb thick film deposition due to its high sputtering yield. The Pb mask is used for x-ray lithography of SU-8 photoresist with 5 μm closely spaced square array patterns, designed for electrowetting electrodes on a microfluidic chip. For 140 μm thick SU-8 photoresist, a Pb film thickness of around 10 μm was used to block x-rays with 95% x-ray image contrast at a critical dose of 4200 mJ cm −3 . A high aspect ratio of 26.5 of SU8 microstructure with 5 μm lateral resolution has been demonstrated by the developed low-cost Pb-based x-ray mask. In addition, a steep sidewall angle of nearly 90 • for SU-8 structure is confirmed. The results demonstrate that the Pb-based x-ray mask offers high-resolution x-ray lithography at a very low cost. Therefore, it is highly promising for commercial applications.
Predicting in-plane distortion from electron-beam lithography on x-ray mask membranes
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1996
To produce x-ray masks useable for 0.25 μm lithography and beyond, all sources of mask distortion must be minimized. In order to facilitate the fabrication of high-quality masks, the phenomenon of changes in resist stress during e-beam exposure has been studied. Finite element modeling was employed to determine the effects of various geometric and material properties on final image quality. Additionally, writing patterns and multipass exposure were also studied. The results indicate that the stress relief phenomenon can be controlled in a well-designed system.
Optical properties of x-ray lithography masks
Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 1990
The purpose of this paper is to present experimental results on optical properties of x-ray mask substrates relevant to x-ray lithography systems utilizing optical alignment between mask and wafer. Data on mask substrates of several materials including B-doped Si, SiC, polyimide, and diamond will be presented. In order to study the light scattering properties of the mask substrate materials, a novel light scattering measuring system was constructed which allows determination of the angular dependence of the transmitted, and reflected light from the mask membranes. The system discriminates between the forwardly transmitted, and specularly reflected light from the sample membranes by the use of perforated solid state light detectors. The detectors are placed on each side of the membrane to obtain simultaneous measurements of forward and back scattering, that otherwise may be affected by thin film interference effects. The data gives information on light scattering due to both the bulk...
Polymer-based X-ray masks patterned by direct laser writing
Review of Scientific Instruments, 2018
X-ray masks are indispensable tools in deep X-ray lithography (XRL). To date, hardly any fabrication technology can provide affordable and readily available masks with good structure quality. The bottleneck of adequate masks to a large extent limits the widespread use of XRL. In this article, an alternative XRL mask fabrication process is described to significantly improve availability and cost efficiency of XRL masks as key instruments in XRL processing: A 355 nm UV-laser is applied to expose SU-8 resist on an antireflective coating and a copper sacrificial substrate. The voids in this resist template are filled by a two-step electroplating process with sacrificial nickel and 3.6 μm thick gold absorbers. A second SU-8 coat embeds the absorbers, forming the 40 μm mask membrane. This configuration allows for XRL into resists of up to about 200 μm thickness at the SyLMAND beamline, Canada. The absorber structure accuracy is about 1 μm, at smallest tested lateral dimensions of 2 μm iso...