Extreme ultraviolet (EUV) reticle incorporated with a pellicle has been widely used for worldwide EUV mask cores. The EUV reticle is typically stored in an EUV inner pod (EIP), in which the EUV pellicle is served to prevent particle contamination. The pellicle is easily deformed due to its structural weakness, thereby altering its transmission as well as impacting the yield of EUV fabrication. Since the mechanical stress induced by external forces in the EUV pellicle is compressively studied, the exploration of stress altered by the air flow through the pellicle frame and/or the inner topography of the EIP is relatively less studied. Here, we present a numerical simulation approach to elucidate the above issue. The derived pressure acting on the pellicle was significantly modulated by the flow conductance of pellicle frame. A air permeability of 90% lead the induced pellicle stress relatively less than the 10% permeability. It suggested that a higher air permeability of pellicle frame could stabilize the air flow between the inside and outside air domains of pellicle more than that using a lower air permeability. We further compared the pellicle stresses derived from the experiment and calculation during the pumping event (from atmosphere pressure to 5 Pa). Results showed a good agreement between the two models. Together, our study indicates that the mechanical stress with air flow through the pellicle frame may dominate the deflection of EUV pellicle in vacuum and the relevant improvement should be considered accordingly.
Extreme ultraviolet (EUV) pellicle has been widely used to control the defectivity of EUV mask out of airborne debris. The EUV mask equipped with pellicle is typically stored within a EUV inner pod (EIP) until use. However, such pellicle is easily deformed due to its structural weakness, the risk of thermal stress and so on, thereby altering its transmission as well as impacting the yield of EUV fabrication. Since the activity of EUV pellicle alone is comprehensively studied, the exploration of pellicle mechanical stress within EIP is relatively less addressed. Here, we present an emerging approach via a chromatic confocal sensor to investigate the above issue. The chromatic sensor was utilized to detect the surface of pellicle based on the reflected light wavelength with a 22 nm axial resolution. A conductance tester was utilized to simulate the pump and vent characteristics, according to ASML and core EUV scanners. During the pump/vent cycle (from atmospheric pressure to 5 Pa and vice versa), the EUV pellicle was deflected from -400 μm to 200 μm. We further analyzed the stress of deformed pellicle by both numerical simulation and theoretical calculation. Interestingly, the graphene-mediated pellicle revealed a more stiffer activity than other material-based pellicles (such as poly-silicon, SiC and Si3N4) under a range of pressure difference (0 to 10 Pa). Taken together, the proposed approach has been successfully demonstrated to enable real-time examination of EUV pellicle activity within EIP, which should be capable for worldwide EUV mask cores.
Extreme ultraviolet (EUV) pellicle, a thin (approximately few nanometers in scale) protective membrane, dominates the defectivity control for protecting the EUV mask from airborne debris. The EUV mask equipped with pellicle is typically stored within a EUV inner pod (EIP) until use. However, such pellicle is easily deformed due to its structural weakness, the risk of thermal stress and so on, thereby altering its transmission as well as impacting the yield of EUV fabrication. In this paper, we present a novel investigation approach via both a chromatic confocal sensor and a conductance tester to address the above issue through incorporating with Gudeng Precision Industrial Co., Ltd. A load-deflection membrane model based on Timoshenko beam theory and minimum energy method was applied to evaluate the residual stress of EUV pellicle. During the pump/vent cycle (from atmospheric pressure to 5 Pa and vice versa), the activity of ASML EUV pellicle inspired the nature breathing manner, was deflected from -275 μm (minimum deflection) to +200 μm (maximum deflection). A pellicle deflection of approximately +100 μm (toward EUV mask the front side) was present during all vacuum steady states (i.e. closing pump at 5 Pa). Furthermore, the 5th ASML pellicle was verified to be 5.56 times stronger mechanically than the previous 4th pellicle from our experiment. Taken together, the proposed approach has been successfully demonstrated to enable in-situ and real-time examination of EUV pellicle mechanics within EIP in vacuum, which should be amenable for worldwide EUV mask cores.
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