Extreme ultraviolet pellicle wrinkles influence on mask 3D effects: experimental demonstration.

Extreme ultraviolet (EUV) lithography uses reflective optics and a thick mask absorber, leading to mask 3D (M3D) effects. These M3D effects cause disparities in the amplitudes and phases of EUV mask diffractions, impacting mask imaging performance and reducing process yields. Our findings demonstrate that wrinkles in the EUV pellicle can exacerbate M3D effects. This imbalance results in critical dimension variation, image contrast loss, and pattern shift in mask images. Therefore, the use of a pellicle material with thermodynamic characteristics that minimize wrinkles when exposed to EUV rays is imperative.

Study on ZrSi2 as a Candidate Material for Extreme Ultraviolet Pellicles.

An extreme ultraviolet (EUV) pellicle is an ultrathin membrane at a stand-off distance from the reticle surface that protects the EUV mask from contamination during the exposure process. EUV pellicles must exhibit high EUV transmittance, low EUV reflectivity, and superior thermomechanical durability that can withstand the gradually increasing EUV source power. This study proposes an optimal range of optical constants to satisfy the EUV pellicle requirements based on the optical simulation results. Based on this, zirconium disilicide (ZrSi2), which is expected to satisfy the optical and thermomechanical requirements, was selected as the EUV pellicle candidate material. An EUV pellicle composite comprising a ZrSi2 thin film deposited via co-sputtering was fabricated, and its thermal, optical, and mechanical properties were evaluated. The emissivity increased with an increase in the thickness of the ZrSi2 thin film. The measured EUV transmittance (92.7%) and reflectivity (0.033%) of the fabricated pellicle satisfied the EUV pellicle requirements. The ultimate tensile strength of the pellicle was 3.5 GPa. Thus, the applicability of the ZrSi2 thin film as an EUV pellicle material was verified.

Investigation of the Resistivity and Emissivity of a Pellicle Membrane for EUV Lithography.

A pellicle is a thin membrane structure that protects an extreme ultraviolet (EUV) mask from contamination during the exposure process. However, its limited transmittance induces unwanted heating owing to the absorption of EUV photons. The rupture of the EUV pellicle can be avoided by improving its thermal stability, which is achieved by improving the emissivity of the film. However, the emissivity data for thin films are not easily available in the literature, and its value is very sensitive to thickness. Therefore, we investigated the dependence of emissivity on structural parameters, such as thickness, surface roughness, and grain size. We found a correlation between resistivity and emissivity using theoretical and experimental approaches. By changing the grain size of the Ru thin film, the relationship between resistivity and emissivity was experimentally verified and confirmed using the Lorentz-Drude model. Finally, we present a method to develop an EUV pellicle with better thermal stability that can withstand high-power EUV light sources.

Investigating the Degradation of EUV Transmittance of an EUV Pellicle Membrane.

The extreme ultraviolet (EUV) pellicle is a freestanding membrane that protects EUV masks from particle contamination during EUV exposure. Although a high EUV transmittance of the pellicle is required to minimize the loss of throughput, the degradation of EUV transmittance during the extended exposure of the pellicle has been recently reported. This may adversely affect the throughput of the lithography process. However, the cause of this phenomenon has not yet been clarified. Therefore, we investigated the cause of the degradation in the EUV transmittance by observing the compositional change when the Ru/SiNx pellicle composite was heated in an emulated EUV scanner environment. The Ru thin film that was deposited at high pressure had more void networks but was not oxidized, whereas the SiNx thin film was oxidized after heating. This was because the void network in the Ru thin film served as a preferential diffusion path for oxygen and caused oxidation of the SiNx thin film. It was confirmed that the degradation of the EUV transmittance was due to the oxidation of SiNx. The results verified the effect of diffusivity in the thin film due to the void network on oxidation and EUV transmittance.