Full-field printing on the ASML Alpha Demo Tool, followed by wafer inspection on a KLA-T 2800, is used to qualify typical defectivity levels of EUV reticles. Mask defects are found as repeaters among multiple dies on wafer. The uniform pattern consists of dense lines and spaces. In a first reticle with 40nm linewidth, high levels of natural defects have been found of which a relatively large share was considered as multilayer (ML) type defects, because they printed as rings. Simulation of ML defects could explain this printing behavior as a function of height, size and slope. The main parameter determining the printing behavior of a ML defect is its height. A local distortion of the upper part of the ML, as thin as ~2nm can already print. On-reticle analysis of the ring defects by SEM showed that the defects are present on the absorber, which already explains the printing result. Yet, still several other defects were found to print on the wafer, whereas they were not visible on the reticle and considered local distortions of the ML. Printing results with a second version of the mask that additionally includes programmed multilayer defects with 3nm height confirmed the pronounced printing impact of ML defects as they were simulated. Encouragingly low numbers of natural defects have been found on a third reticle. With this reticle also a first correlation has become possible between the defect maps obtained from wafer inspection, (direct) mask inspection, and blank inspection. This is a viable method to highlight potential gaps between the capability of these tools and printability of defects.

A research program on EUV lithography has been started at IMEC, based on ASMLs EUV full field scanner, the Alpha Demo Tool (ADT). It contains three main projects: EUV resists, EUV reticles and assessment of the ADT performance. The intent of this program is to help improve and establish the necessary mask and resist infrastructure, and achieve learning to prepare for the use of EUV lithography in future production of integrated circuits. Good progress in resist performance, as assessed by interference lithography, is illustrated by the ability of some materials to resolve 25nm HP. In its initial phase, the reticle project has concentrated on working with the mask and blank suppliers to assure timely availability of reticles for the ADT. An overview is given of the other reticle related activities, as well as first results of a defect printability assessment by simulation and a study of blank reflectivity control. Guidance is given to the EUV mask infrastructure to assure timely availability of reticles, first for the alpha demo tool (ADT), but also in preparation for future use of EUV lithography in production. In the ADT assessment project, simulation studies are reported aimed at the development of optical correction for flare and reticle shadowing effects. The impact of flare and shadowing effects are well understood Strategies for flare mitigation and shadowing effect correction are proposed.

With immersion lithography approaching the insertion in production, watermarks remain as one of the main concerns for immersion specific defects. They require special attention because of their size and associated high kill-ratio, and their increasing occurrence at higher scan speeds. IMEC has been working to understand the underlying mechanism of why remaining water droplets cause these defects. This work focuses on water uptake measurements and how this parameter correlates to watermark defectivity. Ellipsometric Porosimetry (EP) is used to measure the water uptake tendencies of resist and top coat materials and stacks thereof, and investigate what parameters are affecting it. The influence of material and process parameters and the presence of a top coat on water uptake by the resist are evaluated. In parallel, the quartz crystal microbalance (QCM) technique has been used as an alternative option to measure the water uptake. Though a one-to-one comparison between the results is not straightforward, the main trends are identical for both techniques. No perfect correlation of watermark defectivity with water uptake has been found in this study. Nevertheless, the results show a tendency towards higher watermark sensitivity with higher water uptake by the film. It is recognized that the total watermark defectivity is most probably a complex interplay of different parameters with water uptake being only one of them.

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.

193nm immersion resist without topcoat is production preferred solution. The challenge of 193nm immersion resist is both low leaching level and high performance. This paper summarizes the screening results of selected 193nm immersion resists which are designed for use without top coatings. Our evaluation is divided into several phases. Leaching levels of resist samples were first tested. The leaching data were analyzed and compared to our specifications. Both binary image mask and alternating phase-shift mask exposures were done to evaluate the process window, line-edge roughness, and resist pattern profile. Resist films were rinsed by DI water prior to or after exposure, and contrast curves were measured to investigate the resist sensitivity change. The results are compared with resist systems which use developer-soluble topcoats.

A series of different fluorinated polymer platforms used for early and current 157-nm photoresists is investigated with regard to blanket etch properties and surface roughness. Besides methacrylic-based polymers applied for 193-nm lithography, fluorine containing norbornene homopolymers, fluorinated cycloolefines, and tetrafluoroethylene (TFE) norbornene copolymers are chosen. Etch rates in different plasmas used for several applications, such as poly, SiN mask open, and selective/nonselective SiO2 etch, are determined and compared to standard 193-nm platforms currently used for DRAM manufacturing. Looking at various base resins, significant differences can be found using HBr- or Cl2-based poly etch conditions and various fluorocarbon-based oxide etch chemistries. Up to 2.4 times higher etch rates in Cl2 and the different CxFy oxide etch recipes are observed for the highly fluorinated cycloolefines and the TFE norbornenes, showing a strong correlation between fluorine content and etch rate. After stress by different etch conditions, the polymer surfaces are characterized using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Surprisingly, the surface roughness of the methacrylic platforms and the norbornene base resin (determined by AFM) are found to be substantially higher than that of the highly fluorinated platforms. These results can directly be correlated to pictures obtained by optical methods (SEM).

This paper is part of our continuing work on a new generation of more transparent, 157 nm resist platforms, which are based upon capping of fluoroalcohol-substituted, transparent perfluorinated resins (TFR) with a tert-butoxycarbonylmethyl (BOCME) moiety. Recent results indicate that by optimizing both resin structure and loading of photoacid generator and base additive a good compromise can be achieved between resolution power, dark erosion resistance, sensitivity and transparency at 157 nm. Specifically, it was found that a decrease in PAG (50% nominal loading) and base loading (75% nominal loading), coupled with optimization of the TFR resins to achieve higher transparency, gives the best compromise of properties. In this manner, resist systems with a transparency as low as 0.87 AU/micron were designed capable of resolving 60 nm 1:1 features, at a dose of 92 mJ/cm 2 (non corrected for sigma), using a strong phase shift mask, and a sigma of 0.3 on a Exitech 157 nm small field mini-stepper. This type of resist material has also been imaged with a larger field tool ( DUV30 Micrascan VII ) to give 80 nm 1.1.5 L/S features at a dose of 135 mJ/cm 2 employing using a Binary mask (σ=0.85). Finally, it was found that our BOCME-TFR based resist system can be used to transfer a 120 nm L/S pattern (imaged by 193 nm lithography) into a hardmask stack on top of silicon.