In this paper we introduce a method of combining the use of the KLA FlashScan® reticle blank defect inspection system and the KLA LMS IPRO reticle pattern registration metrology system for high-precision mask defect inspection and registration. We investigated EUV mask blanks at various production stages and confirmed the reliable measurement of defect coordinates, which propagate through the multilayer stack towards the surface as well as after the absorber deposition process. During the inspection, in addition to the categorization among various types and sizes of blank defects, unique alignment marks were also placed on the mask. These alignment marks allowed us to use a defined coordinate system, enabling reliable and accurate registration of the defect location even on blank substrates. If the mask shop requires EUV defect coordinates in their own internal coordinate system, matching between the mask shop and blank coordinate systems is achieved by measuring both alignment mark pairs and applying the appropriate coordinate transformation. The combined use of inspection and metrology systems proved to be a cost-effective solution for the development of a defect mitigation strategy with automatic workflow for EUV mask shops and mask blank suppliers.
In this paper we introduce a method of combining the use of the KLA FlashScan® reticle blank defect inspection system and the KLA LMS IPRO reticle pattern registration metrology system for high-precision mask defect inspection and registration. We investigated EUV mask blanks at various production stages and confirmed the reliable measurement of defect coordinates, which propagate through the multilayer stack towards the surface as well as after the absorber deposition process. During the inspection, in addition to the categorization among various types and sizes of blank defects, unique alignment marks were also placed on the mask. These alignment marks allowed us to use a defined coordinate system, enabling reliable and accurate registration of the defect location even on blank substrates. If the mask shop requires EUV defect coordinates in their own internal coordinate system, matching between the mask shop and blank coordinate systems is achieved by measuring both alignment mark pairs and applying the appropriate coordinate transformation. The combined use of inspection and metrology systems proved to be a cost-effective solution for the development of a defect mitigation strategy with automatic workflow for EUV mask shops and mask blank suppliers.
As the semiconductor industry advances to ever-smaller nodes with finer feature sizes and more complex mask designs, reticle quality and reticle defects continue to be a top mask yield risk. The primary reticle defect quality requirement is defined as “no reticle defects causing 10% or larger CD error on wafer”. Beginning at around the 7 nm Logic node, EUV lithography will start pilot production in several leading fabs. EUV masks stress reticle defectivity requirements for mask shops even more than optical masks due to the larger printing impact from a similar size defect on the mask, and the greater cost and longer cycle time for EUV masks. In a mask shop, generally there are three use cases for a blank inspection system, which are used to monitor and improve mask defectivity; 1) Inspecting process monitor masks, which are used to partition the mask process and identify defect excursions, 2) inspecting ‘witness’ blanks, which are used to measure and control defectivity in each process tool / chamber and 3) inspecting incoming mask blanks to ensure defect-free starting materials for advanced optical and EUV reticles. Traditionally, mask shops have been using bright field confocal technology to perform these tasks. However, due to more stringent defect requirements and the flexibility necessary to support these varied use cases, the industry requires a new approach to drive yield improvements in mask manufacturing. In this paper, we report on the introduction of a new system that provides superior sensitivity, with very high throughput and the flexibility to adapt to many different use cases in a production environment.
The current industry plan is for EUV Lithography (EUVL) to enter High Volume Manufacturing (HVM) in the 2019/20 timeframe at about the 16nm half-pitch node (16hp). Reticle quality and reticle defects continue to be a top industry risk. The primary reticle defect quality requirement continues to be defined as “no reticle defects causing 10% or larger CD errors on wafer”. Traditionally, mask shops and mask blank manufacturers have been using bright field confocal technology to perform mask blank qualification. However, due to more stringent defect requirements for EUV blank defects, and the difficulty in detecting and repairing any mask defects caused by a blank defect, the industry requires a new approach to detect defects to support 16 nm hp EUV manufacturing. To meet these emerging requirements, we have developed a new dark field imaging system for photomask blank inspection. This system can be used in the blank manufacturing process to inspect the quartz blank, to inspect after film deposition, and to inspect the finished blank after resist coating. In the mask shop, the same system can be used to inspect an uncoated blank prior to resist coating, or to perform incoming inspection on a finished blank, prior to writing. In this paper, we report on the initial results from this new system on a range of programmed defect blanks as well as production photomask blanks. Inspection results will be shown on a variety of substrates, both for EUV blanks as well as optical blanks.
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