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Physics is at the heart of everything we do at ASML.

As a physics engineer, you could research how temperature fluctuations affect the projection of light or analyze the behavior of tin droplets when they are exposed to CO2 laser light.

You could also solve contamination issues by applying surface and interface physics. Or you could be drawing on all your physics knowledge to help improve the imaging, overlay and productivity of our tools. The possibilities of our physics jobs in R&D, Manufacturing and Customer Support are endless.

Physics meets mechatronics

Using models and algorithms to control for the physical effects that occur when measuring and exposing a wafer inside our lithography machines

 

In an ASML lithography machine, the wafer stage simultaneously moves two wafer tables, each holding a silicon wafer. While one wafer is being exposed, the position of the other wafer is measured by the machine’s metrology sensors, which saves time and increases yield. This dual-stage system architecture is called TWINSCAN.

 

The synchronized movement of the wafer stage, reticle stage (containing the blueprint of the pattern to be printed on the chip) and optics elements produces a number of physical effects that must be compensated for in order to maintain the machine’s nanometer precision and high productivity.

 

To do this, our physicists develop physical models and empirical algorithms that describe what’s going on inside our lithography machines and perform corrections for unwanted physical effects.

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Thermal expansion and overlay

Microchips are made by building up layers of interconnected patterns on a silicon wafer. Exposing the wafer to ultraviolet light creates the desired photochemical reactions in the thin layer of photosensitive material on the wafer’s surface, but it also warms the wafer. This heat load can locally expand the material on a layer, and if the thermal conditions during exposure for the next layer are different, then the two layers won’t align on top of each other correctly and the chip won’t work.

 

Physics to the rescue

We develop physical models that describe and correct for this thermal expansion. They take into account factors such as the light’s wavelength, the transmission capacity of the reticle (or mask), the number of photons that hit the wafer and the silicon’s material properties and corresponding time-dependent heat transfer. The models must also factor in the wafer’s environment – including a vacuum in our EUV machines and air, with the addition of a layer of water between the lens and the wafer in the case of our ‘immersion’ lithography DUV machines.

 

Once we’ve established and calibrated a physical model, we can precisely predict the effects of heating and correct for them by modifying the movements of the wafer stage, reticle stage and optics.

ASML system engineer Guido Salmaso holds an ASML EUV pellicle inside a laboratory at ASML in Veldhoven, the Netherlands.

Indistinguishable from magic

In this story, three physicists describe what it was like to develop breakthrough technology – the EUV pellicle – that combats pattern defectivity in chipmaking.

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Lisanne Coenen

"To be able to produce patterns on a nanometer scale, I work daily with engineers from all different kinds of technical fields and with lots of different physics principles. Getting to know our machines and combining all these different fields of expertise is by far the most challenging part of my job."

 

-Lisanne Coenen, system engineer, MSc in applied physics