EUV lithography has been introduced in semiconductor fabrication and maximizing yield and throughput is extremely important. One key enabler is the use of a high-transmission pellicle to hold particles out of the focal plane and thereby minimize their impact on imaging. Imec initiated the development of a promising pellicle based on a network of carbon nanotubes (CNT). This CNT membrane offers the advantage of very high EUV transmission (> 95 %) and durability compatible with the EUV scanner power roadmap. Moreover, wafer printing with a CNT pelliclized mask on ASML’s EUV scanner at imec has been successfully demonstrated with good printing performance. Since the CNT pellicle is only a few tens of nanometers thick and suspended over an area of tens of centimeters, a major challenge of the pellicle is to control and optimize its mechanical stability and robustness when used in the EUV scanner. The pellicle rupture probability depends on a multitude of parameters, including pressure changes during mask loading and unloading, thermal expansion during exposure, initial stress/strain variations over the large pellicle, membrane degradation in the hydrogen plasma environment, and thickness of the pellicle. In this paper, the mechanical pellicle characterization as a function of the pressure changes for different CNT membranes is presented. The characterization is based on small-size sample evaluation using a bulge test method. By applying controlled plasma to such samples, it was possible to characterize the membranes not only as freshly fabricated but also after exposure to EUV scanner-like conditions. Additionally, the parameters obtained from small samples could be correlated to the actual movement during scanner manipulation. These measurements enable a fundamental understanding of CNT membranes and how they will behave in an industrial environment.
Tin (Sn) and Lead (Pb) particles released from the EUV scanner can contaminate the EUV mask causing serious yield and throughput problems. These contaminants can worsen during EUV exposure and become difficult to remove, leading to damaging the EUV mask in the process. To effectively remove contaminants without substrate damage, it is necessary to understand the removal behavior of the contaminants. In this study, the removal behavior of Sn and Pb particles was studied by simulating the EUV exposure heated by rapid thermal annealing. The removal forces between the thermally aged Sn and Pb particles and EUV substrate surfaces were quantitatively measured using atomic force microscopy (AFM). With the thermal aging time, the contact area of the deformed particle increases which requires a high removal force. After particle removal, the footprint of the contaminants was investigated to understand the surface quality of where the particles sat under the various exposure conditions. This study helps to better understand the adhesion mechanism and removal behavior of thermally deformed Sn and Pb particles on different EUV substrates.
An extreme ultraviolet (EUV) pellicle is employed to prevent contamination on a EUV mask. The EUV pellicle, a high-priced membrane, gets contaminated during both the fabrication process and exposure. The lifetime of the pellicle can be extended by the removal of these contaminants. In this study, a particle removal technique for the EUV pellicle was developed. A functionalized atomic force microscopy (AFM) probe and programable particle contamination system were developed for particle removal and evaluation of the technique, respectively. The particle was removed with a pinpoint technique and the inherent vibration of the free-standing membrane was suppressed during the process. The process window of the proposed pinpoint cleaning technique was investigated to ensure damage-free particle removal and the nanomanipulated functionalized probe resulted in efficient particle removal from the pellicle surface without damage.
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