Application of advanced laser repair to legacy photomasks

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.