Improve your positioning accuracy with the best environmental compensation system
Local variations in the air temperature are unavoidable. They affect the wavelength of light, causing errors in the length measurements made with laser interferometers. AcWaCo is the only system that compensates for these errors, offering unprecedented accuracy of real-time length measurements.
A common method for improving the positioning accuracy is stabilization of air in a climatic chamber. But even with an ideal air conditioning system, by the time the stabilized air reaches the laser beam, it is turbulent and riddled with temperature variations.
The following graph shows a typical measurement of the transient average air temperature along the laser beam in a high-grade climatic chamber. Despite the stabilized conditions, a variation of tens of mK can be observed. With a conventional environmental compensation system the amount of variation seen on the graph translates to a ±7 nm positioning error with laser beam path length of 300 mm. AcWaCo reduces the error to ±1 nm.
In a stabilized environment of a lithographic machine the repeatability of positioning is sometimes as good as 2.51 nm (k=3, confidence level 99.7%). When compensated in real-time by AcWaCo the position stays within 1.17 nm (k=3).
Please note that AcWaCo only removes errors caused by air. PositionX is still affected by all the other errors in the lithographic system (e.g. laser frequency variations, thermal drifts, vibrations, etc.)
With AcWaCo, climatic chambers can be built with cheaper air conditioning systems. AcWaCo compensates all temperature variations, big or small, so there's no need to invest in minimizing them.
If you are interested in the AcWaCo technology, please send an e-mail to info@acwaco.com or fill the following contact form.