Cleaning damage to EUV masks (NYCU/TSMC SPIE BACUS 2025 paper)

[Fred Chen]

EUV lithography patterned intricate layers with small feature on a wafer using a reflective EUV mask. However, the EUV lithographic environment, often containing water vapor and hydrocarbons, introduces molecular contamination from secondary EUV electrons, degrading reflectance stability . Standard mask cleaning solutions such as SPM (sulfuric peroxide mixture), ozonated water, or UV cleaning can effectively remove hydrocarbons . Nevertheless, repeated cleaning cycles with these oxidants can oxidize the silicon layer, leading to non-uniform critical dimensions and wafer printability issues. A protective capping layer on top of the EUV mask multilayer is essential to ensure a long lifetime against environmental aging and cleaning degradation. Additionally, this capping layer must retain high EUV transmission and maintain etch stop integrity for its underlying reflective component to meet high-volume manufacturing (HVM) requirements. This study evaluates various dopant-assisted Ruthenium (Ru) capping materials to enhance the performance and durability of EUV mask cap layers. We assess key factors including EUV reflectivity, etching process metrics, endurance under H2 plasma and standard mask cleaning, and structural properties at the film level. Density Functional Theory (DFT) simulation is employed to gain deeper insights in terms of oxygen binding energy and oxygen diffusion coefficient. The findings underscore the potential of dopant-assisted Ru capping layers to improve the lifetime and reflectivity of EUV mask cap, paving the way for future cost reductions in EUV-required layers, which are essential for advanced chip manufacturing.

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/13687/1368707/Novel-capping-layer-evaluation-for-EUV-mask/10.1117/12.3071741.full

 

[Fred Chen]

Repeated cleans were found to cause peeling of the Ru capping layer and multilayer damage, due to oxidation of the Si/Mo layer underneath.

 

[Fred Chen]

EUV lithography patterned intricate layers with small feature on a wafer using a reflective EUV mask. However, the EUV lithographic environment, often containing water vapor and hydrocarbons, introduces molecular contamination from secondary EUV electrons, degrading reflectance stability .

This should also apply to the EUV resist.

 

[Barnsley]

This very interesting.

Is it better to do a repellicle or build a new mask?

 

[Fred Chen]

This very interesting.

Is it better to do a repellicle or build a new mask?

Cheaper to re-pell; clean the mask at that time.