A Preliminary Study On The Formation And Selective Etching Behaviors Of Nanoscratch-induced Self-assembled Film On Monocrystalline Silicon

Monocrystalline silicon(Si)has been widely used in the fields of micro/nano electromechanical systems(MEMS/NEMS),integrated circuits(IC),and optoelectronic devices due to its excellent mechanical and physical properties.Currently,typical nanofabrication technologies including photolithography,focused ion beam/electron beam lithography,nanoimprint lithography,and scanning probed-based lithography have been developed quickly.They have brought about changes in all aspects of human production and life from biomedicine,aerospace,energy storage,and so on,but there remain some technical challenges to be solved at the same time.To meet the diverse needs of nanotechnology,it is particularly important to develop a new low-cost and low-destructive method for siliconbased nanofabrication.Friction-induced selective etching,based on scanning probed-based lithography,has been proposed to realize the low-destructive and high-resolution nanofabrication on Si surface.However,there is a lack of related research on the masking behaviors of mechanical scratch and oxide layer,and the mask ability is so limited that it hinders the nanofabrication of high aspect ratio.Therefore,based on the mask effect of mechanical scratch and oxide layer,it is of great significance to develop a novel process of mask preparation for further optimization of friction-induced nanofabrication.In this paper,with the help of atomic force microscopy(AFM)and relevant analysis and characterization technique,the masking behaviors of mechanical scratch and oxide layer on different line/surface structures were investigated systematically.In the view of the study on metal selective deposition,the influencing factors and mask effect of nanoscratch-induced self-assembled film were studied,and the formation mechanism of in-situ self-assembly mask was comprehensively analyzed in combination with X-ray photoelectron spectroscopy(XPS).Finally,the application of the method was further extended through the use of siloxane polymers.The details of this paper were as follows.(1)The masking behaviors of mechanical scratch and oxide layer on Si surface during wet etching were compared.The mask ability of mechanical scratches to resist etching appeared during wet etching,protecting the scratched area to form a surface mesa.The masking behavior of mechanical scratches on the line structure was consistent with that of oxide layers,and both masks disappeared before that on the surface structure.The mechanical scratch on surface structure was destroyed due to the undercutting phenomenon caused by anisotropic etching,resulting that the top morphology of the surface structure evolved into an octagon.The mechanical scratch showed the similar mask effect to the oxide layer,so the evolution of the two in wet etching was basically the same.Combining the different processing methods of two masks,the patterned nanofabrication of the composite mask can be realized.(2)The formation and selective etching behaviors of nanoscratch-induced self-assembled film with silane molecules were studied.It was found that the self-assembly time can affect the quality of PFDS self-assembled film,determining the ultimate height and morphology of surface mesa in subsequent selective etching.To obtain a higher and more complete surface mesa,the self-assembly time can be extended appropriately,and the optimal self-assembly time in this study was 2 h.In the load range of 15 μN-30 μN,the increase of normal load was beneficial to the adsorption of PFDS molecules,leading to a better self-assembled film.The mask ability of PFDS self-assembled film was better than that of mechanical scratch and can protect the surface mesa to reach a greater height.The formation mechanism was analyzed from the viewpoint of Si-H bond breakage,dangling bond and fresh surface oxidation.(3)The formation and selective etching methods of nanoscratch-induced self-assembled film with siloxane polymers were expanded.As a material for nanoscratch-induced self-assembled film,polydimethylsiloxane(PDMS)was affected by the self-assembly time in the forming stage.Long-term selfassembly time was not conducive for the adsorption of PDMS molecules on Si surface to form a high-quality film,and the optimal self-assembly time herein was 0.5 h.Compared with the mechanical scratch,PDMS self-assembled film presented a better mask ability,applied to fabricate a series of complex patterns on Si surface.In summary,the formation of nanoscratch-induced self-assembled film is a novel method of mask fabrication with simple process,low cost,and low destruction.Based on the investigation of mask behaviors of mechanical scratch and oxide layer on Si surface,the formation and selective etching behaviors of nanoscratch-induced self-assembled film are studied preliminarily.Through the control of processing parameters,the optimal processing conditions for specific mask materials are analyzed.Combined with XPS,the formation mechanism of nanoscratch-induced self-assembled film is reasonably discussed.Meanwhile,the mask fabrication of different materials based on this novel method has also been explored.This study further enriches the basic theory of friction-induced nanofabrication and provides an important basis for large aspect ratio and high-quality in-situ nanofabrication.