With all the attention and excitement surrounding the development of EUVL into HVM, the ongoing needs of necessary legacy photomasks (193 nm wavelength and longer) have been less in the spotlight. Many layers in semiconductor lithography are still formed using masks at these technologies due to economic, and other, considerations. An aspect of legacy mask production and maintenance that has received even less attention of late has been the availability of toolsets optimized to provide defect repair and particle cleaning. Advanced laser repair and clean processes have been shown in the past several years to be an effective replacement for, not only aging less-advanced laser systems, but also obsolete focused ion beam (FIB) tools. More recently, additional processes have been developed which can even further extend the capabilities of advanced laser processing of these legacy masks. The improvements reviewed here include, but are not limited to, extremely fast removal of multi-micron hard opaque defects with mitigated ablation particle production, removal of softer defects in extremely large areas and sub-resolution patterns. The recent development of an advanced laser deposition repair to clear defects is also introduced for optical mask applications.
Nanomachining is typically described as being a material-independent subtractive mask repair process. This is a correct statement, for the most part, since it does not require a material end-stop nor chemistries targeted to remove only a specific material. However, it is not true when considering the effect of materials being removed on the integrity of the nanomachining tip (also referred to here as NanoBitsTM). While many advanced absorber materials such as OMOG are easier to nanomachine than earlier absorber materials such as chrome and MoSi, the absorbers used in EUV have proven to be much harder and tougher (in a nanomechanical sense) while sitting atop a very fragile multilayer substrate. This work shows results from advancements on the latest nanomachining platform, nm-VI to minimize tip wear during the repair process. Consequently, this improves defect repair capability for smaller dimensions, decreases overhead from tip changeouts, decreases the cost of consumables by increasing NanoBit lifetime, and increases repair tool return-on-investment.
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