As EUV lithography wafer volumes increase, throughput and yield require more focus. Yield can be enhanced by introducing a pellicle to hold particles out of the focal plane and minimize their impact to imaging. Using a pellicle also minimizes the extra wafer inspections required to ensure that printable mask defects do not increase over time. However, if the associated transmission loss is high, the yield advantage is offset by reduced throughput. The CNT-based pellicle offers the advantage of very high EUV transmission. CNT pellicles have also demonstrated lifetime at 300W EUV scanner power. The challenge is balancing the CNT membrane design in three areas: physical presence/the ability to stop particles, EUV transmission/imaging impact, and lifetime in the scanner/thermal tolerance. Each of these areas will be described along with simulated and experimental data illustrating the value of a CNT-based EUV pellicle solution for the future.
Background: The purpose of EUV pellicles is to protect the surface of EUV lithography masks from particle contamination. It is important to ensure that the optical characteristics of the pellicle membrane do not critically affect the reticle image quality. Aim: We want to verify the possibility to integrate pellicle inspection and characterization capabilities in reflective-mode EUV mask scanning microscope (RESCAN), our actinic mask inspection platform based on coherent diffraction imaging. Approach: We studied the impact of a few selected EUV pellicle prototypes on the quality and the contrast of the reticle image obtained with RESCAN. Results: We measured the scattering distribution of the pellicles, and we correlated it with the mask image contrast and fidelity. We also detected the presence of a 6.5-μm-diameter fiber on the pellicle surface. Conclusions: We demonstrated that RESCAN is suitable for through-pellicle actinic mask inspection and can be also used to characterize and monitor the pellicle quality.
To enable high volume manufacturing with extreme ultraviolet (EUV) lithography, a pellicle membrane is needed to protect the reticle from particles at EUV source powers beyond 250 W. Identifying a membrane with high EUV transmission, mechanical integrity, thermal stability, and chemical resistance to the scanner environment is extremely challenging; yet, these properties are required to realize next-generation EUV pellicle solutions. Free-standing carbon nanotube (CNT) film as an alternative next-generation core pellicle material is proposed. 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 transmission change under greater than 250 W equivalent EUV power in vacuum), and scalability to a full pellicle size (∼15 × 12 cm2). The capability of the CNT membrane to withstand high EUV power in the presence of H2 for a limited time is demonstrated. Other CNT membrane properties are presented that are important for the pellicle application: low EUV scattering, low EUV reflectivity, and sufficient transmission to enable through-pellicle inspection with DUV light or electrons. The ability of the CNT film to stop particles is tested. The influence of hydrogen at higher EUV powers and prolonged exposures on the lifetime of the CNT pellicle remains the current research focus. Approaches for coating the free-standing CNT films for protection are discussed.
The purpose of EUV pellicles is to protect the surface of EUV lithography masks from particle contamination. Currently several pellicle prototypes are being developed. It is important to ensure that the optical characteristics of the pellicle membrane do not critically affect the reticle image quality. We present here a study of the impact of a few selected EUV pellicle prototypes on the quality and the contrast of the reticle image obtained with an actinic lensless microscope.
In the early 2000s, membranes both thin enough to transmit EUV light and strong enough to be free-standing at mask dimensions did not exist. The lithography community assumed that defect control for photomasks would be achieved, not with a pellicle, but with a clean scanner environment, thermophoretic protection and a removable pellicle.1 In 2006, Intel published their research on an EUV pellicle.2 Since then, an international development effort on EUV pellicle membranes has spanned a range of materials and fabrication approaches. Not only materials, but also the requirements of the EUV pellicle membrane have evolved over time. Imec’s pellicle work based on carbon nanotubes (CNTs) started in 2015, and is placed in relation to the rich history of EUV pellicles. CNTs are one-atom-thick carbon sheets rolled into tubes. The CNTs can be single- or multi-walled and can vary in diameter and in length. These engineered CNTs can be arranged in different configurations to form membranes of different densities. Thus, the CNT membrane’s properties can be fundamentally changed to meet the EUV pellicle targets for properties like transmittance. The historical trends in EUV pellicle membrane development are presented and the CNT membranes are described in that context.
Over the last three decades, progress in the organic photovoltaic field has resulted in some device features which make organic cells applicable in electricity generation configurations where the standard silicon-based technology is not suitable, for instance, when a semi-transparent photovoltaic panel is needed. When the thin film solar cell performance is evaluated in terms of the device’s visible transparency and power conversion efficiency, organic solar cells offer the most promising solution. During the last three years, research in the field has consolidated several approaches for the fabrication of high performance semi-transparent organic solar cells. We have grouped these approaches under three categories: devices where the absorber layer includes near-infrared absorption polymers, devices incorporating one-dimensional photonic crystals, and devices with a metal cavity light trapping configuration. We herein review these approaches.
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