Supporting positional accuracy in the latest electron beam lithography systems

Electron beam lithography is a technique used in research or industry for highly accurate nanofabrication of materials for a range of applications, including in semiconductor devices or for metamaterial production. In this process, a focused beam of electrons is used to draw shapes onto the surface of various materials to alter their function, with sub-10 nm resolution. Magnetic fields and vibrations can have a detrimental effect on beam shift and therefore the precision of this sensitive work, which has led researchers at the James Watt Nanofabrication Centre to rely on Spicer Consulting’s cancelling systems to restore their required accuracy. 

The James Watt Nanofabrication Centre (JWNC) is a cleanroom facility at the University of Glasgow that is involved in research and international collaboration using micro- and nanofabrication technologies, such as electron beam lithography (EBL). It houses over £35M of state-of-the-art fabrication and metrology equipment, and has diverse capabilities spanning a range of materials and processes. Stephen Thoms, a Senior Research Technologist in the School of Engineering and JWNC, explained how the centre uses Spicer’s SC24 Magnetic Field Cancelling System to support precise EBL work for various projects. “JWNC undertakes fundamental, applied and commercial research, as well as small industrial prototyping and production runs. We provide a service to PhD students and postdocs from here in the School of Engineering, as well as chemistry and physics, where they tend to use the EBL system intensely throughout their years at the university. We also support companies for commercial work, and have collaborations around the United Kingdom and across the world; there's a whole list of different universities and companies who have work done here at Glasgow.” 

“We use EBL for a wide range of projects, including distributed feedback (DFB) lasers, transistors and quantum work. Quantum work is a big area at the moment, and we see a lot of research into areas such as the miniaturisation of atomic clocks – to make them portable – and the fabrication of gravity sensors, which can be used to map gravitation fields to look for, for example, underground pipes. It’s often a collaborative effort of multiple universities, and I tend to support these researchers by helping them to write patents. Many of the students here at Glasgow carry out a lot of biological research, and so we support them on projects such as the creation of a highly textured surface for cells to grow on for stem cell differentiation. Another biological area is metamaterials – small structures around 100 nm in size that can be used to focus light, particularly to enhance Raman spectroscopy in different wavelengths. A lot of metamaterial work is used to make sensors, which can pick up different features depending on the surface of the material we create.”

“The EBL system basically acts like a highly accurate printer; we design small patterns using CAD (computer aided design) solutions, with resolutions down to a couple of nanometers, and the electron beam tool writes that pattern onto flat surfaces. As we are writing such small patterns, positional accuracy is absolutely key; the beam needs to go exactly where we ask it to, and we steer it using magnetic fields. This is where Spicer comes in, as it is imperative that we don’t have any stray magnetic fields. Having the SC24 Magnetic Field Cancelling System ensures that the conditions remain stable, allowing our instruments to run optimally so that we can provide a high quality service to our users.” 

“We have been using EBL for over 40 years and are now on the third generation of our system. Over the past couple of decades, the main push for this technique has been the ability to write more accurately and faster. This means that the latest version of the EBL tool is more sensitive, making the beam position more crucial than ever. Our instrument is now in a building underneath an IT service department, which generates a lot of electronic noise that causes interference. The EBL tool is also around 500m from the underground line, and the DC magnetic fields from passing trains would shift the beam several nm if they were left uncorrected. You can’t shield from a magnetic field very easily, it’s much easier to correct it to maintain positional accuracy. That’s why we use the cancelling system. The SC24 is able to effectively tell us when there is a change in the magnetic field and stabilise it, so that our EBL tool remains unaffected. Spicer was helpful in the quick installation and introduction to using the instrument; it’s a really straightforward but effective system. Another group at the university doing a lot of TEM work witnessed the same problems with nearby interference, and has also installed an SC24 to solve the problem, and we use one for one of our SEMs too. Spicer’s SC24 is extremely popular within the physics department as well, as they also have a lot of high tech and sensitive equipment.”

“We have always asked Spicer to perform a site survey before installation of our EBL systems, and even to check potential sites – including greenfield and brownfield land – that we may move to sometime in the future, to see if we would encounter problems with magnetic fields. The survey equipment can even detect things like issues from nearby doors slamming, as EBL is particularly sensitive to vibrations. This is such a useful service and helps us to consider our options if we ever move to a different site. Wherever we end up though, we know we’ll want a Spicer system,” Stephen concluded.

About Spicer Consulting Limited

Spicer Consulting magnetic field cancelling systems protect electron beam instruments, including Scanning Electron Microscopes (SEM), Transmission Electron Microscopes (TEM), Electron Beam Lithography tools, SEM-based metrology and inspection tools in the world's leading laboratories, universities, semiconductor manufacturing plants, as well as in the test facilities of electron and ion beam equipment manufacturers. Its magnetic field, vibration and acoustic analysis systems have been adopted as standard equipment for the conduct of site surveys by leading equipment manufacturers. Spicer Consulting is located in Stewartby, Bedfordshire, within the United Kingdom’s Golden Triangle of elite universities in London, Cambridge and Oxford. 

Contact us here.