A study of CrOx composed progressive defect on attenuated PSM and its damaged-free removal process

The formation of progressive defect on attenuated phase shift mask is the main trouble after mask fabrication, especially owing to the introduction of high photon energy exposure from 193nm (ArF) DUV light during the usage in wafer manufacturing fab. Normally, these progressive defects, so-called “haze”, are reported to be the combination of ammonium sulfate which may come from mask clean process, or the combination of AMC and organic outgassing from mask surrounding environment. It is well known that this type haze can be easily eliminated by wet chemical treatment such as wet clean process, so we call it, “conventional haze”. Nevertheless, in the past few years, an obscure progressive defect, which is composed of CrOx, has been observed on attenuated phase shift mask. Normally this defect arises by forming droplets or humps in the Qz area or footing at the basal junction between MoSi and Qz. This phenomenon is dramatically semblable to Cr migration that is firstly observed on COG mask and caused by the exposure of 193nm (ArF) DUV light and electric field. Based on above experience, it may be easier to understand that CrOx type defect appears in the dummy pattern on scriber lane which is constituted by stack of Cr/MoSi/Qz. But it is so confused when CrOx type defect is observed on the phase shifter layer which is only composed by MoSi. And beyond that, this type of defect is scarcely responsive to general wet clean process. In this contribution, we classify the CrOx defect type by on-mask location with different pattern structure. Corresponding possible formation mechanism and control methodology will be discussed and evaluated. Finally, we propose the damaged-free removal process based on defect component and distribution.