In a SiNx-based membrane for EUV pellicle, Evaluation of Stress Variation and Mechanical Strength According to Film Deposition Process Conditions

During the EUV exposure process, EUV pellicles are needed to protect the EUV mask from defects and contamination that occur in the EUV lithography process. The EUV pellicle must be made of a thin film membrane for high EUV... [ view full abstract ]

During the EUV exposure process, EUV pellicles are needed to protect the EUV mask from defects and contamination that occur in the EUV lithography process. The EUV pellicle must be made of a thin film membrane for high EUV wavelength transmittance. Moreover, since the inside of the EUV exposure tool is in a high vacuum environment, the EUV pellicle gives stress to the membrane thin film. Therefore, the EUV pellicle can be easily deformed during the exposure process. It is very important to ensure mechanical safety to withstand such environments. In this paper, SiNx thin film was deposited by LPCVD method. The residual stress of the thin film was varied by changing the composition ratio of the gas (three conditions were evaluated). As the Si component becomes richer, the refractive index of the SiNx thin film increases and the etching rate of the KOH chemical increases. It can be confirmed that this is due to the change of stress of SiNx thin film. As a result, when the SiH2Cl2/NH3 gas composition ratio is 2.5: 1, the SiNx thin film has a tensile strength of less than 50 MPa. It was confirmed that it is a very ideal condition without wrinkle phenomenon in membrane fabrication. The mechanical strength of the SiNx thin film was evaluated by changing the stress of the thin film. The evaluation method is bulge test, which is a method to confirm the deflection of the thin film and burst pressure by applying a pressure difference across the thin film. As a result of the bulge test, SiNx thin film deposition conditions of SiH2Cl2/NH3 gas composition ratio of 2.5: 1 showed higher burst pressure and longer time than other conditions. (SiH2Cl2/NH3 = 4: 1 condition is caused by winkle phenomenon where deflection is large). As a result, it was confirmed that the stress of the SiNx thin film could be improved by changing the SiNx thin film deposition conditions, and this result showed that the mechanical strength of the thin film could be improved.