Within the frame of the European R&D project the so called "HYMNE" project, lead by STM, advanced vacuum decontamination processes had been demonstrated to be efficient on wafer substrates in order to remove airborne molecular contamination (moisture, VOC..), to avoid crystalline defects after dry etching process and to improve yield for sub 90 nm technologies.Further to these significant results on wafers, a pool of partners investigated new methods and processes based on vacuum technology for photomask decontamination. These studies were carried out in the frame of the European R&D CRYSTAL project, focusing on photomask defect reduction.Today, vacuum process is not very widespread in photomask environment: in fab environment nor in mask manufacturing cycle. However such vacuum substrate decontamination could be also efficiently applied in order to reduce AMC contamination, which is one of the root causes of haze and crystalline defects. In this paper, we report for the first time, vacuum process investigations on pellicled photomasks that could be applied in fab environment, as well as vacuum process investigations on patterned blank that could be integrated into mask manufacturing cycle.First, vacuum process had been investigated on pellicled photomasks, including parameter influences. Goal is to renew and replace the environment under the pellicle by clean environment. During the process, specific care has to be taken on pellicle behavior under vacuum. The challenge is indeed to manage the pellicle during the vacuum process without damaging it, especially after several decontamination cycles. Finally, repeatability tests have also been successfully carried out and will be reported.We also report advanced vacuum process on patterned blank that could be integrated into mask manufacturing flow. Such procedure is an efficient complementary process in order to outgas contaminants from photomasks, and in order to reduce AMC residues (especially sulfate) in mask manufacturing cycle. Experimental results will be reported.Integration of such vacuum decontamination process during photomask lifetime could be considered.

Context/ study Motivation Contamination and especially Airbone Molecular Contamination (AMC) is a critical issue for mask material flow with a severe and fairly unpredictable risk of induced contamination and damages especially for 193 nm lithography. It is therefore essential to measure, to understand and then try to reduce AMC in mask environment. Mask material flow was studied in a global approach by a pool of European partners, especially within the frame of European MEDEA+ r deals with results and assessment of mask pod environment in term of molecular contamination in a first step, then in a second step preliminary studies to reduce mask pod influence and contamination due to material out gassing. Approach and techniques:A specific assessment of environmental / molecular contamination along the supply chain was performed by all partners. After previous work presented at EMLC 07[ i ], further studies were performed on real time contamination measurement pod at different sites locations (including Mask manufacturing site, blank manufacturing sites, IC fab). Studies were linked to the main critical issues: cleaning, storage, handling, materials and processes. Contamination measurement campaigns were carried out along the mask supply chain using specific Adixen analyzer in order to monitor in real time organic contaminants (ppb level) in mask pods. Key results would be presented: VOC, AMC and humidity level on different kinds of mask carriers, impact of basic cleaning on pod outga In a second step, preliminary specific pod conditioning studies for better pod environment were performed based on Adixen vacuum process. Process influence had been experimentally measured in term of molecular outgassing from mask pods. Different AMC experimental characterization methods had been carried out leading to results on a wide range of organic and inorganic contaminants: by inline techniques based on Adixen humidity, also VOC and organic sensors, together by off-line techniques already used in the extensive previous mask pods benchmark (TD-GCMS & Ionic Chromatography). Humidity and VOC levels from mask carriers had shown significant reduction after Adixen pod conditioning process. Focus had been made on optimized vacuum step (for AMC) after particles carrier cleaning cycle. Based upon these key results new procedures, as well as guidelines for mask carrier cleaning optimization are proposed to improve pod contamination control.Summary results/next steps This paper reports molecular contamination measurement campaigns performed by a pool of European partners along the mask supply chain. It allows us to investigate, identify and quantify critical molecular contamination in mask pod, as well as VOC and humidity, issues depending on locations, uses, type. Preliminary studies highlight initial process solutions for pods conditioning that are being used for short term industrialization and further industrialized.

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