Multi-Stacked Graphene Pellicle for Extreme Ultra Violet Lithography

As the technology of integrated circuits develops, it is inevitable to reduce the line width of transistors. In order to reduce the line width, it is necessary to develop various semiconductor processing technologies, among which exposure technology has particularly attracted attention. The deep ultraviolet (DUV) lithography techniques using wavelengths on the order of a few hundred nanometers have reached their limits. And the introduction of extreme ultraviolet (EUV) lithography techniques using a lower wavelength range as a new technology has begun. [1~2] In this case, the light in the EUV region of 13.5 nm wavelength is emitted from the high-density plasma. Thus, the process must be performed in a vacuum environment unlike the conventional DUV lithography. These differences not only require new optical systems, but also require the development of reticle materials, including pellicles. In this thesis, we propose ‘Multi-Stacked Graphene Pellicle’ for EUV lithography. Graphene, which is a carbon isotope and has a sp 2 hybridized structure in a two-dimensional plane has excellent properties, because it has a thickness of a single layer of atoms. [11-12] Among them, the reason that can be applied to the pellicle for EUV lithography is that it is excellent in electrical characteristics, thermal properties, optical properties and mechanical strength. Before the proposal of ‘Multi-Stacked Graphene Pellicle’, a large area graphene film was synthesized by chemical vapor deposition (CVD) method. By the vapor-phase molecular doping and its characteristics can be controlled in a better direction. We also propose a novel transfer method, paraffin-assisted transfer. This method can achieve graphene with better characteristics than conventional transfer method. The proposed ‘Multi-Stacked Graphene Pellicle’ for EUV lithography must be developed in terms of heat load, transmittance in EUV region and productivity. To meet these requirements, we aimed to develop thin films of several tens of nanometer. The typical wet transfer method was repeated to prepare multi-stacked graphene film corresponding to 10 (ten) layers. UV-Vis and Raman spectroscopic analysis showed that the transfer and stacking process was completed properly. The thickness of multi-stacked graphene film was measured by atomic force microscope (AFM). And the result was about 15.4 nm. To measure the transmittance in the EUV region multi-stacked graphene film, a free-standing sample of 10 mm in diameter was fabricated. And the EUV light transmittance was in a vacuum environment 87 %. The results show that the longer carbon chain of a diamine molecule reduces the electron transfer per unit area of graphene, resulting in the decrease in n-doping effect, while the doping stability increases as molecular weight increases. Since the diamines are linear aliphatic compounds, the amine groups always have different orientations depending on the length of the carbon chains. Our study supports that the vapor phase doping is an effective route to optimize the orientation of the dopant molecules for enhanced stability and stronger doping of graphene films.