Electron lithography has the potential for very high-resolution pattern writing. Electron beams have produced features as small as 10 nm [1] and images with extremely large depths-of-focus, providing relief from one of the most challenging problems of optical lithography. It is particularly appealing for products made in extremely low volume. Therefore, the electron beam writer is a good candidate for fabricating features down to sub-hundred nanometers.  The electron lithography system in AMRI has a hot field emission gun and a single condenser with crossover-free beam path, which are able to provide a stable, flexible, and high-resolution electron source for nanopatterning. With this nanopatterning system, we are able to generate nanoscale arrays, gratings, wires, grooves, circuits, loops, molds, and masks for various device and sensor applications.

Nanopatterning is the key procedure for fabricating nanodevices. The quality of patterning and writing are controlled by several parameters for electron lithography. Resists are usually operational over specific wavelength ranges, and they are usually optimized for application at very specific and narrow ranges of wavelength. For electron lithography the resist photochemistry must take place efficiently. The electron exposure dose will lead to dose control problems and poor pattern fidelity because of shot noise. Resist film needs to be exposed with a high degree of uniformity from the top of the resist film to the bottom by electron beam. Proper resists are able to enhance the patterning of sub-hundred nanometer features.  The resist thickness and spin rate profile will affect the pattern generations. The most common method of densifying the resist is baking. Proper baking conditions will decrease defects of fabrication. A post-exposure bake is usually a very critical process, and line widths are typically more sensitive to this bake than to the soft-bake. As we will challenge the resolution of electron lithography, all these parameters need to be carefully controlled for fabricating several ten nanometers features.  

Shown below are a series of nanolithographically-generated patterns produced in our laboratories here in AMRI. 

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 Figure 2.  Various patterned arrays produced by our laboratory with e-beam nanolithography. a,c,d) Patterns done in photoresist; channels in (a) and (c) are approximately 40 nm wide; those in the extended channel array (d) are ~300 nm; b) gold metal wires grown from patterned photoresist, after lift-off process; e) array of triangles, 600 nm on an edge; f) array of oval pillars (ca. 90 nm x 100 nm) with a periodicity of 150 nm. Depth (height) of lithographic features, 100 - 150 nm.

Equipment for Nanolithography

The JC Nabity Lithography system consists of a hot field emission gun and a single condenser with crossover-free beam path, which provide stable, flexible, and high-resolution electron source for nanopatterning. With this system, features as small as 10 nm can be accessed, though more routine work is done to 30 nm.  This system is part of the FESEM. 

Field Emission Scanning Electron Microscope (FESEM LEO), 1530VP with ultra-high resolution in high vacuum – 1 nm at 20 kV, 2.5nm at 1 kV, in lens detection represents especially high performance and flexibility in specimen handing. With the unique combination of GEMINI ultra-high performance electron optics and LEO’s variable pressure technology, the LEO 1530VP delivers extensive capabilities in a range of applications. The chamber pressure can be set to any value in the pressure range to suit the specimen with resolution in VP mode - 2nm at 30 kV, VPSE detection. With the ability also to allow Oxford X-ray analysis on completely insulating specimens, the LEO 1530VP is perfect in applications such as semiconductor FA, life science, geology, archaeology, and composite materials.

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References

[1]        H.G. Craighead, “10 nm Resolution Electron-Beam Lithography” J. App. Phys. 55 pp.4430-4435, 1984.

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For more information please contact: Professor Weilie L. Zhou (e-mail: wzhou@uno.edu)