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Phase defects that introduce errors in the printed image are one of the major yield limiters for reticles in extreme-ultraviolet lithography. The basis for a reticle is a mask blank, consisting of an ultra-low-expansion substrate and a reflective multilayer stack that is made up of Mo and Si. A potential methodology for repairing phase defects in these mask blanks is to locally irradiate it with a high-resolution electron beam to induce structural deformations that cancel out the distortion of the multilayer. We present experimental and modeling results that show that the interaction of an electron beam with a mask blank can only be understood when the contraction of the multilayer through silicide formation and substrate compaction, as well as the mechanical response of the mask blank, are considered. One of the consequences is that electron beams with energies around 10 keV that are less than 20 nm in diameter induce depressions in multilayers made up of 50 Mo/Si bilayers that have a surprisingly large diameter of about a micrometer. Our models suggest that these unacceptably large diameters can only be reduced if the compaction of the substrate is prevented. [ABSTRACT FROM AUTHOR]

The printability of buried extreme ultraviolet (EUV) defects near absorber features is studied using aerial images from the actinic inspection tool (AIT) and the fast EUV mask simulation program RADICAL. This work begins by comparing the printability of isolated defects through focus predicted by RADICAL and measured by the AIT. Then, images of defects near features from both simulation and experiment are investigated for different defect sizes and positions through focus. Finally, RADICAL is used to assess the expected defect printability levels in the less in coherent conditions which are expected to be used for production. Defect printability will be investigated as a function of defect size, position, and focus for the small absorber lines critical to 22 nm imaging using a top-hat illumination condition of sigma=0.75. Here, defects as small as 0.8 nm surface height cause a critical dimension (CD) change greater than 10% at best focus when located in the worst case position. Defects as small as 2.2 nm cause a CD change greater than 10% even when located under the center of the absorber. [ABSTRACT FROM AUTHOR]

The authors report the chemical influence of cleaning of the Ru capping layer on the extreme ultraviolet (EUV) reflector surface. The cleaning of EUV reflector to remove the contamination particles has two requirements: to prevent corrosion and etching of the reflector surface and to maintain the reflectivity functionality of the reflector after the corrosive cleaning processes. Two main approaches for EUV reflector cleaning, wet chemical treatments [sulfuric acid and hydrogen peroxide mixture (SPM), ozonated water, and ozonated hydrogen peroxide] and dry cleaning (oxygen plasma and UV/ozone treatment), were tested. The changes in surface morphology and roughness were characterized using scanning electron microscopy and atomic force microscopy, while the surface etching and change of oxidation states were probed with x-ray photoelectron spectroscopy. Significant surface oxidation of the Ru capping layer was observed after oxygen plasma and UV/ozone treatment, while the oxidation is unnoticeable after SPM treatment. Based on these surface studies, the authors found that SPM treatment exhibits the minimal corrosive interactions with Ru capping layer. They address the molecular mechanism of corrosive gas and liquid-phase chemical interaction with the surface of Ru capping layer on the EUV reflector. [ABSTRACT FROM AUTHOR]

Contamination removal from extreme ultraviolet (EUV) mask surfaces is one of the most important aspects to improve reliability for the next generation of EUV lithography. The authors report chemical and morphological changes of the ruthenium (Ru) mask surface after oxygen plasma treatment using surface sensitive analytical methods: x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and transmission electron microscopy (TEM). Chemical analysis of the EUV masks shows an increase in the subsurface oxygen concentration, Ru oxidation, and surface roughness. XPS spectra at various photoelectron takeoff angles suggest that the EUV mask surface was covered with chemisorbed oxygen after oxygen plasma treatment. It is proposed that the Kirkendall effect is the most plausible mechanism that explains the Ru surface oxidation. The etching rate of the Ru capping layer by oxygen plasma was estimated to be 1.5±0.2 Å/min, based on TEM cross sectional analysis. [ABSTRACT FROM AUTHOR]

Electron beam induced etching (EBIE) is an important technique for repairing nanoscale defects on extreme ultraviolet (EUV) lithography masks as it provides excellent spatial resolution and etch selectivity while minimizing collateral damage to the mask. While EBIE itself is a complex process, a current problem with EBIE of the TaN EUV mask absorber layer using XeF2 is the spontaneous etching of repaired features during subsequent edits of the mask. This work explores three passivation techniques for controlling the spontaneous etching after an EBIE repair is made. An oxygen plasma was used to attempt to oxidize the TaN sidewalls, but it was not successful at stopping the spontaneous etching. An active electron beam induced passivation using water was successful at stopping the spontaneous etching. Also, simple adsorption of water molecules on the TaN sidewalls was successful at inhibiting spontaneous etching. The successful passivation strategies are affected by subsequent scanning electron beam imaging. It was determined that the electron beam activated passivation can be damaged by electron beam imaging in the presence of residual XeF2 on the surface. Also, the adsorbed water passivation strategy is susceptible to electron induced desorption of the water. [ABSTRACT FROM AUTHOR]

The ability to fabricate defect-free reflective Mo–Si multilayer (ML) blanks is a well-recognized challenge in enabling extreme ultraviolet (EUV) lithography for semiconductor manufacturing. Both the specification and reduction of defects necessitate the understanding of their printability and how they are generated and grow during ML deposition. A ML phase defect can be depicted by its topographical profile on the surface as either a bump or pit, which is then characterized by height or depth and width. These phase defects are complex in nature and their impact to resist printing. The authors developed an effective way to study phase defects with programmed defect mask (PDM) as “model” test vehicle. The defects are produced with tuned ML deposition process and placed in varying proximity to absorber patterns on the mask. This article describes the recent study of ML phase defect printability from exposures of a ML PDM on the EUV microexposure tool with annular, monopole, and dipole illuminations. [ABSTRACT FROM AUTHOR]

The helium ion gas field ion source is a novel charged particle source technology with potentially greater capabilities than electron beam based tools for imaging and nanomachining [Ward et al., J. Vac. Sci. Technol. B (to be published); Morgan et al., Microscopy Today 14, 24 (2006); V. N. Tondare, J. Vac. Sci. Technol. A 23, 1498 (2005)]. Potential strengths of He ions over electrons (scanning electron microscopy) are improved thin film surface sensitivity, material contrast, IBIC voltage contrast, Rutherford backscattering material contrast, and the ability to utilize in situ electron charge neutralization on floating substrates which have enhanced charging properties (e.g., masks, photoresist). In this article, the authors will discuss and illustrate examples highlighting several of these attributes. Helium ions, unlike electrons, induce collision events in the material lattice. A critical area to understand is the operating conditions and sample types for which the advantages of helium ion imaging can be realized. Dose, beam current, acceleration voltage, and material interaction are all key areas for modeling and empirical analysis to determine potential invasiveness. The focus of the study presented in this article relates to analyzing the potential lattice damage induced in silicon substrate for ion doses ranging from 1×1014 to 5×1015 ions/cm2. This range represents relatively light dose (fast scan) to intermediate dose (slow scan) imaging applications. Findings for doses in this range (as typically used in image applications) show little to no damage to the silicon lattice. This finding also agrees with SRIM [Ziegler et al., The Stopping and Ranges of Ions in Solids (Pergamon, New York, 1985), Vol. 1] Monte Carlo simulations, which predict that helium ion induced defect densities to be 4×1017 to 4×1018 dis/cm3. However, it is clear that with higher doses, defect densities will increase to a level that may be invasive to device structures (e.g., metal oxide semiconductor field effect transistor channels or gate oxides). [ABSTRACT FROM AUTHOR]

Extreme UV (EUV) masks are expected to undergo cleaning processes in order to maintain the lifetimes necessary for high volume manufacturing. For this study, the impact of repetitive cleaning of EUV masks on imaging performance is evaluated. Two high quality industry standard EUV masks are used, with one of the masks undergoing repeated cleaning and the other one kept as a reference. Lithographic performance, in terms of process window analysis and line edge roughness, was monitored after every two cleans and was compared to the reference mask performance. Surface analysis by atomic force microscopy did not show changes in the midspatial frequency roughness measured after each clean. After a total of eight cleans, minimal degradation is observed in the lithographic performance of the mask. From these observations, the authors conclude that the cleaning cycles completed thus far did not damage the mask multilayer or the absorber structures. The cleaning cycles will be continued until significant loss in imaging fidelity is found. [ABSTRACT FROM AUTHOR]