| dc.description.abstract | Graphene is a single atomic layer material with excellent electrical conductivity, mechanical strength, thermal conductivity, and chemical stability. Its excellent material properties have attracted much attention in various application fields However, its lack of band gap limits its application in the semiconductor field, thus opening other related two-dimensional semiconductor materials research, especially on the material family of group VI transition metal dichalcogenides (TMDs) has received much attention. However, the current 2D material growth can’t be directly applied to the back-end of line (BEOL) in semiconductor process. Therefore, a transfer process is required, from which the current traditional wet transfer process still encounters the issues of polymer and metal ions residue that degrade their electrical performance . Therefore, improving the integrity and cleanliness of large-area two-dimensional materials by a reliable transfer process is still a key problem that needs to be solved in current development.
In this experiment, the easily removable doped-rosin (Doped-Rosin) polymer was used to replace the polymethyl methacrylate (PMMA) commonly used in the traditional wet transfer method as a buffer layer to improve the defects caused by the polymer during the transfer process. As for the residual problems, the use of an optimized etchant recipe was proposed to significantly reduce the residual metal ions in the growth substrate. In addition, in order to solve the problems brought by the transfer of graphene at room temperature, we designed a vacuum nanoimprint system which utilizes the controllable flat pressing design under high vacuum, compared with the flat plate or roll-to-roll (R2R) method under the atmosphere, the hot pressing can control the pressing stress of the composite support layer and the two-dimensional material film thus to achieving a more precisely and uniformly transferring film. The study shows that laminating in a vacuum environment can avoid pores, water vapor, etc, which were normally generated during the transfer process. Also, the formation of air/liquid cells can be suppressed after the transfer, resulting in subsequent cracks and other defects, which helps It can be extended to other 2D materials.
Results of the research are as follows. (1) The carrier mobility of graphene transferred by polymer (Doped-Rosin) is 1787 cm2/Vs, which is about 2.6 times higher than the traditional wet transfer, and it also have 1.3 times higher than the PMMA dry transfer. (2) The carrier mobility of graphene transferred by vacuum nano-imprint is 857 cm2/Vs, which is about 1.3 times higher than the traditional wet transfer and it was about 1.2 times higher than the R2R dry transfer. (3) The surface integrity of MoS2 transferred by vacuum nanoimprint is 99% and the cleanliness is also 99%; also, the strain and carrier doping are 43% and 75% reduced from those without UV treatment and annealing treatment. In addition, it was found that the doped rosin buffer layer was irradiated with ultraviolet light and then annealed which could be accelerate the deterioration of the doped rosin molecular. In comparison with the MoS2 samples without any treatment, the UV light and annealing treated samples shows the decreased surface roughness from 0.94 nm to 0.83 nm. This study provide a deeper understanding and an improved transferring process of 2D materials, which is beneficial for the future application in nanoelectronics. | en_US |