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Extreme Ultraviolet (EUV) Lithography is a candidate for device manufacturing at the 22nm half pitch node and beyond. The key challenge for EUV resists remains to simultaneously meet the requirements for Sensitivity, Resolution and Line-edge-roughness (LER) for Line/Space features (LS), respectively local CD uniformity (LCDU) for Contact holes (CH). The introduction of the ASML NXE:3100 pre-production EUV scanner at Imec, with off-axis illumination provides resolution capability well below 22nm.In this paper we make a assessment of the EUV resist performance for 22nm LS and 28-26nm contacts on the NXE:3100. At 22nm feature sizes, pattern collapse and LER become the main resolution and process windows limiters. The application of FIRM TM Extreme 10 rinse was found to be effective to improve the collapse margin and reduce LER on several resists. Using dipole illumination setting, we achieved 22nm LS at 13.5mJ/cm 2 with 3.1nm (3) LER with wide processing latitudes. Several resists resolved down to 20nm LS. Champion resolution of 19nm LS was obtained in one resist at 20mJ/cm 2 . Using quasar illumination, 28nm HP contact holes were obtained with LCDU value of 1.0nm (1) at <20mJ/cm 2 , showing wide process latitudes. Printing 26nm HP contacts is feasible but requires further improvement in LCDU and contact shape circularity.

In the last years the continuous efforts on the development of EUV lithography has allowed to push the lithographic performances of the EUV photoresists on the ASML NXE:3100 full field exposure tool at imec. The latest chemically amplified photoresists can reach an ultimate resolution of 16 nm and 24 nm for line-space (L/S) and dense contacts (CH), respectively, but the major issue on EUV photoresists remains to simultaneously meet resolution, sensitivity, line-edge roughness (LER) for LS and local CD uniformity (LCDU) for CH, suggesting that the desired performance characteristics of EUV photoresists may require the development of new EUV materials. Aiming to this, imec has recently started a new project to look into novel materials for EUV lithography to explore alternative approaches that can offer superior characteristics in photoresist imaging: improved LER and line collapse, high sensitivity and high etch resistance. In this paper we report the first results from the exploration of new EUV alternative materials and the latest results from the conventional EUV photoresist evaluation and process optimization at imec towards the ASML NXE:3300 full field exposure tool.

Scanning probe microscopes (SPMs) and especially the atomic force microscope (AFM) can be used as tools for modifying surface structures on the submicrometre and even nanometre scale. For this purpose an advanced interface has been developed to facilitate these manipulations and greatly increase the number of possible applications. In this paper this interface (the nanoManipulator, developed at the University of North Carolina at Chapel Hill) is implemented on a combined AFM-confocal microscope. This setup allows AFM imaging, manipulations and fluorescence imaging of the same area on the sample.The new setup is tested on ringlike structures of a porphyrin derivative (BP6). A small amount of the fluorescent material could be displaced with the AFM tip. A special tool (sweep mode) allowed a modification of around 130 nm, which was afterwards detectable with the confocal microscope. The resolution attainable in these kind of experiments could go down below 100 nm and is primarily determined by the tip and sample geometry.Comparable with this experiment is the application of a near-field scanning optical microscope (NSOM) to make photochemical modifications. Using the excitation power coming from the NSOM probe the fluorescence can be quenched by bleaching a selected area instead of displacing the material. Application on the BP6 rings led to a modification of 280 nm wide.AFM can perform modifications on a smaller scale but is less selective than NSOM. Optical investigation of the changes after AFM manipulation can give more elaborate information on the modifications. This will extend the possible applications of the techniques and may ultimately go down to the single-molecule level.

Defectivity has been one of the largest unknowns in immersion lithography. It is critical to understand if there are any immersion specific defect modes, and if so, what their underlying mechanisms are. Through this understanding, any identified defect modes can be reduced or eliminated to help advance immersion lithography to high yield manufacturing. Since February 2005, an ASML XT:1250Di immersion scanner has been operational at IMEC. A joint program was established to understand immersion defectivity by bringing together expertise from IMEC, ASML, resist vendors, IC manufactures, TEL, and KLA-Tencor. This paper will cover the results from these efforts.The new immersion specific defect modes that will be discussed are air bubbles in the immersion fluid, water marks, wafer edge film peeling, and particle transport. As part of the effort to understand the parameters that drive these defects, IMEC has also developed novel techniques for characterizing resist leaching and water uptake. The findings of our investigations into each immersion specific defect mechanism and their influencing factors will be given in this paper, and an attempt will be made to provide recommendations for a process space to operate in to limit these defects.

The EUV program at imec aims at identifying the critical issues to prepare EUV lithography for insertion into high volume IC production. The program started in 2006 with the 0.25 NA ASML Alpha Demo Tool and has since then evolved around several focus areas. 1) scanner performance, reliability and monitoring, 2) definition and verification of OPC strategies for generic and EUV specific imaging effects 3) reticle defectivity, focusing on multi-layer defects, reticle handling and reticle cleaning, 4) resist screening, focusing on identification of materials that not only simultaneously give optimal performance in terms of resolution, line width roughness and sensitivity, but that also allow adequate transfer of the EUV-fabricated patterns into the underlying layers and 5) implementation of EUV lithography into fabrication of representative device structures. Since 2011 The Alpha Demo Tool has been replaced by the ASML NXE:3100, allowing higher resolution and productivity. In this paper, selected highlights in the latest achievements of the imec EUV program will be discussed.

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Previously, fundamental evaluations of the Extreme Ultra Violet (EUV) lithography process have been conducted using the CLEAN TRACK ACT™ 12 coater/developer with the ASML EUV Alpha Demo Tool (ADT) at imec. [1] [2] In that work, we confirmed the basic process sensitivities for the critical dimension (CD) and defectivity with EUV resists. Ultimate resolution improvements were examined with TBAH and FIRM™ Extreme. Moving forward with this work, the latest inline cluster is evaluated using the ASML NXE:3100 pre-production EUV scanner and the CLEAN TRACK™ LITHIUS Pro™ -EUV coater/developer. The imec standard EUV baseline process has been evaluated for manufacturability of CD uniformity control based on half pitch (HP) 27nm and ultimate resolution studies focusing on HP 22nm. With regards to the progress of the improvement for EUV processing, we confirmed the effectiveness of several novel concepts: FIRM™ Extreme10 showed increase in ultimate resolution and improvement in line width roughness (LWR) and process window; Tokyo Electron LTD. (TEL) smoothing process for roughness reduction showed 17% improvement for line and space (L/S) patterns; and finally the new dispense method reduced patterned wafer defectivity by over 50%.