Stick to the surface
Aim: Understand particles transport and debris release from surfaces in EUV tool
Continuing advancement in lithography technology allowed in the last 40 years to follow the Moore's law which prescribes that the number of logic elements in microchips doubles every two years. To maintain this pace, the wavelength of the light used for lithographic patterning needs to be reduced from current 198 nm. High-tech companies and scientific institutes have taken the step to move to Extreme UltraViolet (EUV) technology which uses light with a wavelength of 13.5 nm.
Figure 1: Schematic representation of a EUV lithography tool.
On the surfaces of the chamber containing the EUV light source, where light is collected by a large mirror, and of the main chamber, where light illuminates the reticle, (Figure 1), nanometer to micrometer sized particles may reside. Under flow and plasma conditions present in the tool, particles may be released from the surfaces.
Free-floating particles are an issue as even a single 20 nm particle sticking to the reticle can cause damages to the integrated circuit being printed on the wafer (Figure 2).
Figure 2: Effects on wafer (right) of the presence of a particle on the reticle (left).
Important research questions addressed by the project:
- Can flow or plasma induce release of particles from the surface or is a combination of both required?
- How can the flow and plasma conditions be controlled to prevent particle release and keep them on safe surfaces?
To address the main research questions, numerical models to study dynamics of debris, their probability to deposit at walls and their tendency to detach are being developed. In particular, control of dynamics of debris in the full machine require to model hydrodynamic and rarefied gas flows, in presence of weak and harsh plasma conditions. Several physical phenomena are at work at the same time, requiring a multi-disciplinar approach. Results from modeling activities may suggest implementation of dust mitigation methods in the design of the EUV tool so to reduce the amount of debris in critical areas.
Gianluca Di Staso, Federico Toschi, Herman Clercx
Jan van Dijk (group EPG)