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A novel approach to the mask inspection for proximity electron lithography based on electron beam imaging

We report the first evaluation results for the printability and detectability of mask defects on a 1x stencil mask as used for proximity electron lithography (PEL). The defect printability has been defined for the patterns after the multi-step etching process through the tri-layer resist system inherently required for the use of low-energy electrons and the substrate. According to the three-dimensional lithography simulation, this definition is preferable to the conventional one based on the resist patterns prior to the etching process in the point that smoothing effects on defects are automatically taken into account. The critical size of printable defects as defined is 22 nm for 140 nm contact holes, while the stringent value of 16 nm is predicted in the conventional definition. Also, the detectability of the printable defects has been assessed by using the transmission electron-beam (EB) inspection tool. The assessment has been performed for both programmed defects and real defects occurred in contact-hole arrays. For the programmed defects, the perfect repeatability has been demonstrated for all the defects with printable sizes. In addition, real defects with the size of 15 nm have been successfully detected in the contact-hole arrays. Therefore, this study has demonstrated the manufacturability of PEL masks from the viewpoint of defect inspection.