The introduction of EUV photomasks has posed significant challenges in defect repair over the years. Defects within the unique multi-layer stack used for the reflective optics can easily lead to printing defects on the wafer. Although absorber compensation repair has been successfully demonstrated in high-volume manufacturing (HVM), it has been accompanied by several obstacles. Next-generation EUV lithography for high numerical aperture (NA) EUV photomasks is proving more difficult due to stringent requirements. The advanced scanner optics demand more precise edge control for photomask repairs, necessitating the incorporation of resist effects in the defect review process to better emulate wafer impact.
Registration correction by localized substrate expansion has been performed on conventional transmission photomasks for several years. With the implementation of EUV lithography, registration correction has been a challenge due to the opaque backside blank requirements for electrostatic chucking on EUV scanners. More recently, partially transparent back side coated blanks have been evaluated to enable registration correction on EUV masks. We will discuss back side coating requirements which meet both scanner requirements and registration correction requirements. Highlighting the need for back side coating and substrate transmission uniformity control and its impact on registration correction performance.
EUV lithography is being prepared for insertion into the semiconductor production processes to continue the reduction of critical feature sizes at subsequent process nodes. To support that EUV wafer lithography development and production, the EUV photomask infrastructure similarly needs to be ready to support the shipment of EUV photomasks. EUV photomasks will require tighter process controls and tighter defect specifications to meet the requirements necessary for the wafer manufacturing insertion node. The novelty of the EUV lithography process combined with the high degree of complexity of the EUV photomask structure and process each contribute to the tightening of EUV photomask requirements, requiring accurate metrology to ensure fidelity to the photomask specifications. To fully address the industry requirements for EUV defectivity review and actinic mask qualification, ZEISS and the SUNY POLY SEMATECH EUVL Mask Infrastructure consortium have developed and commercialized the EUV aerial image metrology system, the AIMSTM EUV. The first commercial platform is already installed at a customer site and is available to support the EUV photomask production pipeline. This paper shows how the proven technology of the ZEISS aerial image system implemented into the AIMSTM EUV platform supports EUV photomask production in the back end of the line of Intel photomask manufacturing shop. Alongside with describing the essential development phases of the platform at customer site, examples of the reproducible measurement quality, as well as stability of the imaging fidelity of the system in production will be shown. In addition, the system output together with the experience on uptime and availability of the AIMSTM EUV platform in production is presented.
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