Ruthenium Capping Layer Preservation for 100X Clean Through pH Driven Effects

In the absence of pellicle a EUVL reticle is expected to withstand up to 100x cleaning cycles. Surface damage upon wet and dry cleaning methods has been investigated and reported in recent years. Thermal stress, direct photochemical oxidation and underlying Silicon layer oxidation are reported as the most relevant root-causes for metal damage and peeling off. An investigation of final clean performance is here reported as a function of operating pH; the results show increased Ruthenium durability in moderately alkaline environment. The electrochemical rationale and the dependency of the reducing strength of the media with the pH will be presented as possible explanations for reduced damage.