3-Dimensional Microstructure Fabrication using Multiple Moving Mask Deep X-ray Lithography Process (original) (raw)

High resolution x-ray masks for high aspect ratio microelectromechanical systems (HARMS)

Micromachining and Microfabrication Process Technology VIII, 2003

X-ray lithography is commonly used to build high aspect ratio microstructures (HARMS) in a 1:1 proximity printing process. HARMS fabrication requires high energy X-rays to pattern thick resist layers; therefore the absorber thickness of the working X-ray mask needs to be 10-50 µm in order to provide high contrast. To realize high resolution working X-ray masks, it is necessary to use intermediate X-ray masks which have been fabricated using e-beam or laser lithographic techniques. The intermediate masks are characterized by submicron resolution critical dimensions (CD) but comparatively lower structural heights (~2 µm). This paper mainly focuses on the fabrication of high resolution X-ray intermediate masks. A three-step approach is used to build the high resolution X-ray masks. First, a so called initial mask with sub-micron absorber thickness is fabricated on a 1 µm thick silicon nitride membrane using a 50KeV e-beam writer and gold electroplating. The initial X-ray mask has a gold thickness of 0.56 µm and a maximum aspect ratio of 4:1. Soft X-ray lithography and gold electroplating processes are used to copy the initial mask to form an intermediate mask with 1 µm of gold. The intermediate mask can be used to fabricate a working X-ray mask by following a similar set of procedures outlined above.

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.

Masks for X-Ray-Lithography with a Point-Source Stepper

Journal of Vacuum Science & Technology B, 1992

We describe some key aspects of proximity x-ray technology currently being developed at AT&T, from mask fabrication to wafer patterning. The masks are primarily based on polycrystalline Si membranes, 1 J.tffi thick, which are formed directly on optically flat glass disks. A tungsten absorber layer is deposited on the membranes by radio-frequency diode sputtering, with in situ stress control in the deposition chamber so that stresses < 10 MPa are routinely achieved. Patterns are defined in an organosilicon negative resist, P(SI-CMS), using an electron beam writing tool and a neural network based proximity correction algorithm. The patterns are transferred into metallic absorber layers by reactive ion etching in a parallel plate plasma system. Using the above procedure, we have fabricated masks with 0.25 f.lm features and also some test patterns with lines and spaces as small as 0.1 ,urn. X-ray exposures were done with a Hampshire 5000P point source stepper, using AZ PF-114 resist from Hoechst-Ce1anese.

Direct fabrication of deep x-ray lithography masks by micromechanical milling

Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 1998

Micromechanical milling has been shown to be a rapid and direct method for fabricating masks for deep x-ray lithography with lateral absorber features down to 10 micrometers. Conventional x-ray mask fabrication requires complex processes and equipment, and a faster and simpler method using micromechanical milling was investigated for larger microstructures for mesoscale applications. Micromilled x-ray masks consisting of a layered architecture of gold and titanium films on graphite yielded exposures in PMMA with accuracy and repeatability suitable for prototype purposes. A method for compensating milling tool radial runout was adapted, and the average accuracy of mask absorber features was 0.65 micrometers, with an average standard deviation of 0.55 micrometers. The milling process leaves some absorber burrs, and the absorber wall is tapered, which introduces an additional process bias. Mask fabrication by micromilling is fast and, therefore, less costly than conventional mask fabrication processes.

Process Simulation of Moving Mask Deep X-Ray Lithography

Mem SR Cent …, 2005

This paper presents a newly developed 3-Dimensional (3D) simulation system for Moving Mask Deep X-ray Lithography (M 2 DXL) process, and its validation. The simulation system named X-ray Lithography Simulation System for 3-Dimensional Fabrication (X3D) is tailored to simulate a fabrication process of 3D microstructures by M 2 DXL. X3D consists of three modules: mask generation, exposure and development. The exposure module calculates a dose distribution in resist using a generated X-ray mask pattern and its movement trajectory. The dose is then converted to a resist dissolution rate. The development module adopted the "Fast Marching Method" technique to calculate the 3D dissolution process and resultant 3D microstructures. This technique takes into account resist dissolution direction that is necessary for accurate 3D X-ray lithography simulation. The comparison between simulation results and measurements of "stairs-like" dose deposition pattern by M 2 DXL showed that X3D correctly predicts the 3D dissolution process of exposed PMMA.

Novel approach to zero-magnification x-ray mask replication

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1992

A technique for replicating x-ray masks with no magnification of the master mask pattern has been developed. This technique uses a raster scanning pattern with a synchrotron x-ray source to eliminate pattern magnification due to the source divergence. Kinematic mounts were employed to reduce clamping induced distortions in the mask replication process and the metrology tool. Finite element analysis of the thermal response of the clamped master and replicate masks during exposure indicates the temperature increase of the two membranes during exposure is matched, so that thermal distortions are not transferred to the printed pattern.

3D simulation system for moving mask deep X-ray lithography

MHS2003. Proceedings of 2003 International Symposium on Micromechatronics and Human Science (IEEE Cat. No.03TH8717), 2003

This paper presents a newly developed 3-Dimensional (3-D) simulation system for Moving Mask Deep X-ray Lithography (M 2 DXL) technique, and its validation. The simulation system named X-ray Lithography Simulation System for 3-Dimensional Fabrication (X3D) is tailored to simulate a fabrication process of 3-D microstructures by M 2 DXL. X3D consists of three modules: mask generation, exposure and resist development (hereafter development). The exposure module calculates a dose distribution in resist using an X-ray mask pattern and its movement trajectory. The dose is then converted to a resist dissolution rate. The development module adopted the "Fast Marching Method" technique to calculate the 3-D dissolution process and resultant 3-D microstructures. This technique takes into account resist dissolution direction that is required by 3-D X-ray lithography simulation. The comparison between simulation results and measurements of "stairs-like" dose deposition pattern by M 2 DXL showed that X3D correctly predicts the 3-D dissolution process of exposed PMMA.