3-minute read - by Peter van den Hurk, December 22, 2021
Microchips are made up of layer upon layer of patterns. To ensure the microchip works, the patterns in different layers have to line up with extreme accuracy. New ASML Fellow Simon Mathijssen explains how he and his colleagues are working to make that possible.
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Accuracy in an imperfect world
Alignment marks are specially designed gratings that are created on the wafer alongside each layer’s pattern. They are made up of lines with vertical sides that are perpendicular to the wafer’s surface. However, natural variations in the chip production process mean that sometimes the sides aren’t fully perpendicular but are instead tilted.
“The challenge I worked on is quite simple: What is the position – or center of gravity – of a tilted feature?” explains Simon Mathijssen. “You could say it’s halfway between the top corners or halfway between the bottom corners. For perpendicular features, this is the same, but not for tilted features, which brings ambiguity.
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“We are also looking at a similar issue in overlay metrology: How accurately can we measure various layers of a microchip on top of each other when the markers are deformed? The big difference is the number of marks. For wafer positioning, there are tens of alignment markers. For overlay, there could be over 1,000,” Simon adds.
From fixing TVs to enabling nanotechnology
According to Simon, the foundation for his career was laid by his father, who would let Simon help repair TV sets as a child. “At that time, a television was quite a big, complex technological system. You could open it up and explore – that was fascinating,” he remembers.
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