EUV optical characterization of alternative membrane materials for EUV pellicles

Development of a pellicle membrane to protect the reticle from particles for EUV source powers beyond 250 W is a subject of intensive research and is in great demand to support high volume manufacturing with EUV lithography. Identifying a membrane with high EUV transmission, mechanical integrity, thermal stability and chemical resistance within the scanner environment is extremely challenging; yet these properties are required to realize next-generation EUV pellicle solutions. This paper proposes free-standing carbon nanotube (CNT) film as an alternative next generation core pellicle material. Most of the desired pellicle characteristics can be achieved by tuning the properties of freestanding CNT films. We demonstrate that free-standing CNT films possess very high EUV transmission (up to 99%) and good transmission uniformity (0.4% half range), mechanical stability (maximum deflection ~0.08 mm at 2 Pa), thermal stability (no change under greater than 500 W equivalent EUV exposure in vacuum without hydrogen radicals) and scalability to a full pellicle size. Other important CNT membrane properties are presented and are favourable for the pellicle application: low EUV scattering, low EUV reflectivity and high transmission under DUV. The ability of the CNT film to stop particles is analysed. The only known failure of the CNT membrane is instability to hydrogen radical/ion environment within the current reticle chamber of the scanner. If changing that environment to limit hydrogen radicals near the pellicle surface is not an option, there is a need to coat the CNT structures for protection. The challenges and considerations for coating the free-standing CNT membranes are discussed.

EUV pellicles guarding masks from defects and dynamic gas lock thin film windows are considered a corner stone for using EUVL in chip production. For providing such thin film products with certified features EUV actinic metrology tools are needed in the industrial supply chain. For best conservation of optical quality and throughput in the scanner, such EUV pellicles should have high transmission of > 90 % with a transmission uniformity of > 99.6 %, low reflectance of much less than 0.1 % and low scatter of EUV. The specification for the ideal metrology tool is qualifying a full sized EUV pellicle with precision of better 0.1 % for transmission and 0.001% for reflection, the ability to quantify the scatter distribution. The measurements should be accomplished in acceptable process time and should neither add contaminate nor particulate to the product under test. Within RI Research Instrument’s support of EUVL infrastructure by developing actinic metrology solutions, we have engaged in this task by applying our proprietary effective inband EUV metrology scheme described elsewhere. While the first generation tool has been presented elsewhere, we now present general considerations on measurement process and tool architecture for the combined three tasks in the second generation tool. Full pellicle transmission and reflectance mapping are measured in less than 2 hours fully automatic process time (careful load-locking included). Measured transmission show precision and accuracy of better 0.1 % for a qualification pixel resolution of 300x300 µm2. Performance of the reflectance measurements is under investigation but expected to be in the range of 0.001 % precision demonstrated in proof of concept experiments in our application lab. The first generation tool is used by our customer in routine pellicle production and is constantly running with uptimes better than 95%.

The use of EUV photomasks in a semiconductor manufacturing environment requires their periodic inspection to ensure they are continually free of defects that could impact device yield. Defects typically occur from fall-on particles or from surface degradation such as “haze”. The proposed use of a polycrystalline-based EUV pellicle to prevent fall-on particles would preclude periodic through-pellicle mask defect inspection using e-beam, as well as, DUV inspection tools (the pellicle is opaque at DUV wavelengths). Thus, to use these types of defect inspection tools would require removal of the EUV pellicle before inspection. After inspection, the pellicle would need to be re-attached and the mask re-qualified using a test wafer, thus causing expense and delays. While EUV-wavelength inspection tools could inspect through such a pellicle precluding the need to remove the pellicle, these tools are not likely to be available in the commercial marketplace for many years. An alternate EUV pellicle material has been developed that is semi-transparent to 193nm wavelengths, thus allowing through-pellicle inspection using existing ArF-based, or other 193nm wavelength mask inspection tools. This eliminates the requirement to remove the pellicle for defect inspection and the associated time and expense. In this work, we will conduct an initial evaluation of through-pellicle EUV mask defect inspection using an existing 193nm mask inspection tool. This initial evaluation will include durability of the pellicle to defect inspection, and impact of the pellicle on inspection tool performance.

As it has been widely announced by the leading foundries, and confirmed by ASML, EUV Lithography is being introduced into high volume manufacturing (HVM) since the beginning of this year, in order to enable a more cost-effective manufacturing for the 7nm logic technology node. Very soon, the next technology node will be introduced and the number of EUV layers at 5nm is expected to increase significantly. Although EUV masks are not regarded as the first critical issue for EUV introduction into HVM, several items with respect to EUV masks need more time for improvements, certainly for 5nm and beyond. This presentation will address several mask related items such as EUV pellicle, alternative absorber, EUV mask lifetime, etc... and finally anamorphic masks. This paper is reviewing the status and outlook for these remaining challenges.

EUV mask protection during handling and exposure remains a challenge for high volume manufacturing using EUV scanners. A thin, transparent membrane can be mounted above the mask pattern so that any particle that falls onto the front of the mask is held out of focus and does not image. The fluoropolymer membranes that are compatible with 193nm lithography absorb too strongly at the 13.5nm EUV exposure wavelength to be considered. Initially, the industry planned to expose EUV masks without any pellicle; however, the time and cost of fabricating and qualifying an EUV mask is simply too high to risk decimating wafer yield each time a particle falls onto the mask pattern. Despite the challenges of identifying a membrane for EUV, the industry has returned to the pellicle concept for protection. EUVL pellicles have been in development for more than a decade and reasonable options exist. Meeting all pellicle requirements is difficult, so this type of risk-mitigation effort is needed to ensure that there is a viable high-volume manufacturing option. This paper first reviews the desired membrane properties for EUVL pellicles. Next, candidate materials are introduced based on reported properties and compatibility with fabrication. Finally a set of candidate membranes are fabricated. These membranes are screened using a simplified set of tests to assess their suitability as an EUV pellicle. EUV transmission, film stress, and film durability data are included. The results are presented along with general guidelines for pellicle membrane properties for EUV manufacturing.

EUV phase shifting masks may be introduced at the N3 node as alternative to double patterning or high-NA exposures. To be advantageous, phase shifting masks may have to come with phase different than 180° and high transmission. The main concern is how such exposures could be affected by stochastic side-lobe printing. In this paper, we present a simulation study where we compare stochastic distributions for contact layers with different mask approaches: binary mask, phase shifting mask with and without assist features, and TriTone masks. The purpose of this work is to evaluate whether phase shifting masks in EUV lithography may become a valuable option to further extend single exposure EUV at NA = 0.33.

EUV lithography insertion is anticipated at the 7 nm node and below; however, defects added to the mask during use is a lingering concern. Defectivity in the scanner is non-zero and an EUV pellicle membrane to protect the mask for high volume manufacturing power levels does not yet exist. The EUV photons are strongly absorbed by all materials. Sibased membranes leverage the low absorption coefficient k value (k = 0.0018 at 13.5 nm) for reasonable transmission, but poly Si becomes fragile and wrinkles during the high temperatures associated with exposure. An alternate approach to high transmission is deploying very thin or porous layers so that there are fewer atoms to absorb light. For example, carbon nanomaterials have a reasonably low k value (k = 0.0069), but are strong enough to be fabricated in very thin layers. Graphene, graphite, carbon-nanosheets and carbon nanotubes are all candidate carbon nanomaterials for this application, but we focus here on carbon nanotubes (CNTs). Our first measurements on CNT films of ~60 nm thick were found to have 96.5% transmission at 13.5 nm. Adding CNT layers also enhanced the strength of a thin SiN membrane significantly. In this paper, critical pellicle metrics will be evaluated in more detail: EUV transmission, bulge test for mechanical strength, emissivity measurements for heat management, and exposure testing in a hydrogen environment.

Modern quantum theory of correlations predicts, and reveals, new counter-intuitive dynamical effects of hydrogen in nano-structured materials, being of considerable importance for basic research as well as for technological applications. To support this claim, here the focus is on H2 molecules in carbon nanotubes and other nanocavities, as experimentally investigated with the well established technique of incoherent inelastic neutron scattering (INS). In particular, the experimentally determined momentum and energy transfers from an H2 molecule in a carbon (C-) nanotube resulting in roto-translational motion along the nanotube axis, appear to (1) either violate the standard conservations laws, or (2) attribute the translating H2 molecule a highly reduced inertia, as quantified by the effective mass M eff ≈ 0.64 a.m.u. (atomic mass units), instead of 2 a.m.u. for an isolated molecule. This counter-intuitive INS-observation has no conventional interpretation, but it can be qualitatively interpreted “from first principles” in the frame of modern theories of quantumness of correlations and Quantum Thermodynamics (QTD). This analysis also provides a surprising new physical insight: The nano-structured cavities do represent quantum systems which contribute to the quantum dynamics of the hydrogen translational dynamics, and thus to the hydrogen transport in the studied materials. This insight may also have far-reaching consequences for technological applications and material sciences (e.g. fuel cells, H storage materials, etc.), since it concerns the choice and design of “optimized” materials adsorbing or carrying hydrogen.

Background: An extreme ultraviolet (EUV)-transparent pellicle must be used during lithography to protect the photomask from fall-on particles. A pellicle made of free-standing carbon nanotube (CNT) films stops particles despite the presence of gaps while demonstrating high EUV transmission, mechanical stability, low EUV scattering and reflectivity, and DUV transmission that enables through-pellicle mask inspection. Aim: The CNT EUV pellicle properties can be tailored based on the diversity of CNT structures and tunability of their configuration within the CNT film (density, bundle size, composition, etc.) as shown in this work. A remaining challenge is extending the CNT EUV pellicle lifetime in the scanner environment of EUV-induced hydrogen-based plasma, and the effects on different CNT films are explored here. Approach: Optical and thermal properties of different CNT pellicles with respect to the CNT material type, density, composition, and bundle size were explored. The ability of uncoated CNT EUV pellicles to withstand high EUV powers in the hydrogen-based environment was tested. Transmission, spectroscopic, and chemical mapping of the exposed CNT membranes were performed to explore the material modifications under various exposure conditions. Results: Uncoated CNT pellicles withstand 600-W source power equivalent in the EUV scanner-like gas environment but exhibit structural changes with prolonged exposure. Multiwalled CNT pellicles exhibit less EUV transmission change as compared to single-walled CNT pellicles under the same exposure conditions. The protection of CNT material from structural degradation by means of coating was shown. Conclusions: These investigations add to the understanding of CNT EUV pellicle tunability for optimal performance and lifetime limiters of CNT pellicles under the influence of EUV radiation and plasma. We anticipate the need for coating the CNT pellicle to protect the CNT material against plasma damage for the current scanner conditions. Optimization of both the CNT membrane and its coating is in progress.

The advancement of integrated nanophotonics requires the development and characterization of materials with high refractive indices and low optical losses. Van der Waals (vdW) materials, particularly transition metal dichalcogenides (TMDs) such as WSe2 and MoSe2, exhibit giant optical anisotropy and high refractive indices (n > 4) in the near-infrared range, making them promising candidates for next-generation photonic circuits. However, accurately determining their anisotropic optical constants, especially the out-of-plane component, is challenging due to the limited size of exfoliated flakes and the limitations of far-field techniques. This study details the application of scattering-type scanning near-field optical microscopy (s‑SNOM) for the nanoscale characterization of these materials. The principles of s-SNOM, including the excitation and detection of waveguide modes in planar vdW structures, are discussed. By analyzing the interference fringes generated by propagating modes, the effective mode index is determined. We demonstrate this methodology using WSe2 and MoSe2 flakes, where the experimental effective indices are compared with theoretical models. This comparison confirms the necessity of accounting for giant optical anisotropy and validates the out-of-plane dielectric constants, illustrating the efficacy of s-SNOM for the comprehensive optical characterization of vdW materials.

Optical characterization and appearance prediction of translucent materials are required in many fields of engineering such as computer graphics, dental restorations or 3D printing technologies. In the case of strongly scattering materials, flux transfer models like the Kubelka-Munk model (2-flux) or the Maheu's 4-flux model have been successfully used to this aim for decades. However, they lead to inaccurate prediction of the color variations of translucent objects of different thicknesses. Indeed, as they rely on the assumption of lambertian fluxes at any depth within the material, they fail to model the internal reflectance at the interfaces, penalizing the accuracy of the optical parameter extraction. The aim of this paper is to investigate the impact of translucency on light angular distribution and corresponding internal reflectances by the mean of the radiative transfer equation, which describes more rigorously the impact of scattering on light propagation. It turns out that the light angular distribution at the bordering interfaces is often far from being lambertian, and that the internal reflectance may vary significantly according to the layer's thickness, refractive index, scattering and absorption coefficients and scattering anisotropy. This work enables to better understand the impact of scattering within a translucent layer and also invites to revisit the well-known Saunderson correction used in 2- or 4-flux models.

The source is an integral part of an extreme ultraviolet lithography (EUVL) tool. Such a source, as well as the EUVL tool, has to fulfil very high demands both technical and cost oriented. The EUVL tool operates at a wavelength of 13.5 nm, which requires the following new developments. The light production mechanism changes from conventional lamps and lasers to relatively high-temperature emitting plasmas.The light transport, mainly refractive for deep ultraviolet (DUV), should be reflective for EUV.The source specifications as derived from the customer requirements on wafer throughput mean that the output EUV source power has to be hundreds of watts. This in its turn means that tens to hundreds of kilowatts of dissipated power has to be managed in a relatively small volume.In order to keep lithography costs as low as possible, the lifetime of the components should be as long as possible and at least of the order of thousands of hours. This poses a challenge for the sources, namely how to design and manufacture components robust enough to withstand the intense environment of high heat dissipation, flows of several keV ions as well as the atomic and particular debris within the source vessel.As with all lithography tools, the imaging requirements demand a narrow illumination bandwidth. Absorption of materials at EUV wavelengths is extreme with extinguishing lengths of the order of tens of nanometres, so the balance between high transmission and spectral purity requires careful engineering. All together, EUV lithography sources present technological challenges in various fields of physics such as plasma, optics and material science.These challenges are being tackled by the source manufacturers and investigated extensively in the research facilities around the world.An overview of the published results on the topic as well as the analyses of the physical processes behind the proposed solutions will be presented in this paper.

ABSTRACTCarbon nanotubes (CNTs) in the family of nanostructured carbon materials are of great interest because of several unique physical properties. For space applications, it needs to be shown that CNTs are physically stable and structurally unaltered when subjected to irradiation becomes indispensable. The CNT films were grown by microwave Carbon nanotubes (CNTs) in the family of nanostructured carbon materials are of great interest because of several unique physical properties. For space applications, it needs to be shown that CNTs are physically stable and structurally unaltered when subjected to irradiation becomes indispensable. The CNT films were grown by microwave plasma-assisted chemical vapor deposition (MWCVD) technique using Fe as catalyst. Synthesis of both single- and multiwalled CNTs (SW and MW, respectively) were achieved by varying the thickness of the Fe catalyst layer. To investigate the influence of electron-beam irradiation, CNTs were subjected to low and/or medium energy electron-beam irradiation continuously for a few minutes to several hours. The CNT films prior to and post-irradiation were assessed in terms of their microscopic structure and physical properties to establish property-structure correlations. The characterization tools used to establish such correlations include scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), and current versus voltage (I-V) measuring contact resistance (two-probe) and dc conductivity (four-probe) properties. Dramatic improvement in the I-V properties for single-walled (from semiconducting to quasi-metallic) and relatively small but systematic behavior for multi-walled (from metallic to more metallic) with increasing irradiation hours is discussed in terms of critical role of defects. Alternatively, contact resistance of single-walled nanotubes decreased by two orders of magnitude on prolonged E-beam exposures. Moreover, these findings provided onset of saturation and damage/degradation in terms of both the electron beam energy and exposure times. Furthermore, these studies apparently brought out a contrasting comparison between mixed semiconducting/metallic (single-walled) and metallic (multiwalled) nanotubes in terms of their structural modifications due to electron-beam irradiation.

Further improvements in speed, accuracy get by direct Theoretical analysis of molecular problems, have become very developed investigation by Computational tools and the underlying theoretical framework. Theoretical studies for calculating molecular structure parameters of Adrenaline, carbon nanotube and Adrenaline bond with carbon nanotube were performed using DFT. Based on B3LYP with 6-31(d) basis set was used to investigate the effect on the electronic was used to find the effect on the electronic structure, variation and thermochemistry properties. Furthermore, these interactions can be measured by using some properties such as electronegativity (£q), hardness (η), ionization energy, absorbance, energy gap (Eg), thermal energy, Enthalpy and Gibbs free energy. The results of this work show Hardness decrease with increase the number of atoms. Adrenaline is less ionization potential and Adrenaline bond with carbon nanotube the highest ionization potential. Electronegativity from carbon nanotube higher than Adrenaline and Adrenaline bond with carbon nanotube. Absorbance of Adrenaline (C9H13NO3) from 1100 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> bond for C-O cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and N-O at 1200cm-1 high absorption and low transmittance. 3000-2850 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> region due to C-H stretch, and type hybridization sp <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Adrenaline has big energy gap bigger than carbon nanotube and Adrenaline bonded with carbon nanotube. Described thermal energy, Enthalpy and Gibbs free energy. Thermal energy increase with increasing number of atoms.

We demonstrate the possibility of manufacturing Be-basedultrathin films with high transmission at wavelengths of 11.4 and 13.5 nm. For free-standing films of Be and Be-based multilayer structures (Si/Be,ZrSi2/Be, Be/BexNy, Zr/Be, Ru/Be, Mo/Be), we determine the thresholds of theabsorbed power at which over a short period (tens of minutes) of vacuumannealing, initially sagging free-standing films became visibly stretchedover the hole. Of the film structures tested here, the Be/BexNy structure(with beryllium nitride interlayers) showed the highest threshold for theabsorbed power (1 W/cm2). However, due to the low strength of thisstructure, ZrSi2/Be, Mo/Be, and Be films seem to be more promising for themanufacture of a full-size pellicle. Long-term vacuum annealing of Mo/Beand Be ultrathin films showed that they could withstand 24 hours of vacuumheating at an absorbed power density of 0.2 W/cm2 (film temperature 250oC)without noticeable changes in EUV transmission or sagging of films. Withcomparable transmission (~83% at 13.5 nm and ~88% at 11.4 nm), a multilayerMo/Be structure with a thickness of 30 nm appears to be preferable, as itshows less brittleness than a monolayer Be film with a thickness of 50 nm. Keywords: Be-based pellicle, multilayer thin film, EUV lithography,thermal stability\