My name is Rachel Jones and I’m part of the Photonic Integration research group of the Department of Electrical Engineering. Integrated photonics is a young but rapidly developing research field with great potential for high-tech systems. Within this, I’m investigating the extent to which the footprint of high-resolution displacement sensors can be miniaturized in terms of physical size, weight, power and cost when scaled up without sacrificing performance.
The need for precision
As demand increases for electronic devices with greater storage capacities, operational speeds and functionalities – all while reducing their size – lithography scanners must increase their fabrication precision. Key to this is increasing the precision of the positioning within the scanner. The more information we have on the position of the bodies that we want to move or align, the better we can manipulate them through means of control.
However, the current metrology architecture is not suited to dense sensor arrays due to their size and cost. Photonic integration offers a degree of miniaturization not currently achievable with other technologies, allowing for a greater number of measurements to be inputted to the control system. By offering a way to miniaturize the footprint, integrated photonics is vital to enabling dense array sensors that provide positional inputs for control.
Four parts of the whole
This project was established by High Tech Systems and ASML and has since been incorporated into Eindhoven Engine. My PhD is just one of four research topics spread across different departments at TU/e, which collectively comprise the Advanced Long Range Piezo Stage (ALP) project. Eindhoven Engine recognizes the importance of co-location for successful collaboration. To this end, the PhD students meet regularly at the MMP on the TU/e campus and bi-weekly at ASML with their advisors.
As each project must be compatible with the others for the system to work as a whole, compromise is sometimes needed. Effective communication is critical in collaborative ventures: it’s one thing to explain it to my group and another thing to explain it to those with different knowledge and expertise. But that’s also a benefit because it’s good for me if I can effectively explain my work. This is a highly interdisciplinary project, which is what really attracted me to it.
Investment in the future
My approach was to first understand the context, which is also where ASML comes in. The next-generation lithography scanner is vastly complicated, so a full working solution in just four years is unrealistic. Instead, my work should address the main challenges that exist for the technology and provide insights into where we are now and where we can be in the future in terms of performance. For ASML, this will provide evidence as to whether the concept is worth further investment.
Another challenge is that high-resolution sensors require extremely low noise in both the optical and electronics domains. Mechanical, thermal and acoustic noise will all act to deteriorate performance. We also need to create devices that perform not only in the lab but in the desired application. Results-wise, simulation work into a narrow linewidth laser suggests a possible linewidth reduction by a factor of three. We’ve investigated various sensor concepts and several approaches have been ruled out following quantitative calculation. I’ve also submitted designs for several photonic integrated circuits, which I’m likely to receive in early 2022.
Over the last decades, research has mainly focused on creating a diverse library of standardized components across different photonics platforms. A common analogue is LEGO: using well-characterized building blocks to construct your circuit. Now that we have an established ecosystem and workflow, people are looking at maximizing performance and functionalities too. Recently, there has been an increase in application-led projects, attracting greater industrial interest. ASML recognizes the potential of photonic integration, so this project is an important starting point in demonstrating what we can offer.