Computational inspection applied to a mask inspection system with advanced aerial imaging capability

Abstract

Traditional patterned mask inspection has been off-wavelength. For the better part of the past 25years mask inspection systems never adhered to the wavelength of the exposure tools. While in the days of contact and proximity printing this was not a major issue, with the arrival of steppers and scanners and the slow migration from 436nm, 405nm, 365nm and 248nm to ultimately 193nm, on-wavelength inspection has become a necessity. At first there was the option with defect and printline review using an at-wavelength AIMS tool [Fig 1], but now the industry has moved towards Patterned Mask Inspection to be at-wavelength too. With ever decreasing wavelength, more and more materials have become opaque, and especially the 266/257nm inspection to 193nm printing wavelength has proven to be a reliability issue. The industry took a major step forward with the adoption of at-wavelength aerial inspection, a paradigm shift in mask inspection, as it uses a hardware emulation to parallel the scanner's true illumination settings [Fig 2]. The technology has found wide-spread acceptance by now, and 19xnm inspection is now the industry standard. Maskshop [outgoing] captive/ merchant 1 st path: -d2db -d2d +AIMS review [193nm] 2 nd path -contam/repair off-O: -488/ -365/257nm High Resolution Aerial image Profile cross-section plot: Red: defect, Blue: referenceFig 1: Traditional O mismatch in mask inspection Fig 2: Paradigm Shift: at-O inspection in aerial modeHowever, with the ever advancing technology nodes, such as 32nm and 22nm, aggressive OPC and Sub-Resolution Assist Features (SRAFs) are required. Their use results in significantly increased mask complexity, challenging mask defect dispositioning more than ever. To address these challenges in mask inspection and defect dispositioning, new mask inspection technologies have been developed that not only provide high resolution masks imaged at the same wavelength as the scanner, but that also provide aerial images by using both: software simulation and hardware emulation.

EUV mask absorber and multi-layer defect disposition techniques using computational lithography

“…Similar techniques have been developed and implemented in production of DUV masks for example, in transforming mask-plane inspection images to actinic aerial images to actual scanner illumination optics to resist print image [3], [4], [5], [6], [7], [8]. These have also been enabled by the development and calibration of optical and e-beam models to characterize masks, review systems, exposure systems, and wafer resist.…”

Inverse lithography technology: 30 years from concept to practical, full-chip reality

“…Luminescent continued working on computational inspection and metrology technologies to enable mask inspection, mask review, and mask repair ready for ILT masks, until it was acquired by KLA in 2012, and TSMC EBO presented a number of papers together with Luminescent showing such capabilities deployed in production. [92][93][94][95][96][106][107][108][109][110][111][112][113][114] ILT was the topic of panel discussion at the SPIE Photomask Technology Conference for two consecutive years in 2015 and 2016. The industry also recognized the issue of using VSB mask writers to write curvilinear ILT masks.…”