Air shield system to reduce lens contamination in optical lithography based on turbulence simulation

The development of optical lithographic technology made important contributions to miniaturization. In optical lithography, it is critical to maintain high uniformity and high resolution of patterning on a silicon substrate by exposing the substrate to ultraviolet (UV) light. However, lens contamination limits the uniformity of the exposed UV light, and the effect of lens contamination on the critical dimension is increasing as electronic devices become smaller. Lens contamination can be generated by turbulence of clean air (CA) and it gradually accelerates over time. In this work, we suggest the extreme clean dry air (XCDA) shield system to reduce lens contamination in optical lithography. We have measured and analyzed the contaminants of a practical lithography lens through time-of-flight secondary mass spectrometry, and the expected contamination mechanism is also shown. Also, we simulated turbulence of CA in practical lithography based on the shield k-epsilon turbulence model. Turbulence simulations not only quantitatively showed the effects of XCDA and CA on lens contamination but also demonstrated that the lens could be directly purged with the XCDA shield system to prevent turbulence of CA. The XCDA shield system reduced the degree of contamination by 33% compared with the conventional level. We believe that the proposed system will provide high efficiency in the optical lithography industry.