Study On Low-Destructive Friction-Induced Selective Etching Nanofabrication On Monocrystalline Silicon

Nanotechnology has prompted the development of economy and the progress of society, while nanofabrication is the foundation to realize the transition from nanoscience and nanotechnology to application. Due to its excellent mechanical and physical properties, monocrystalline silicon is the main material toward building micro/nano devices and systems. With the increasing miniaturization, integration and function diversification of the devices, the traditional silicon-based nanofabrication approaches have met huge technical challenges, such as poor resolution, high cost and fabrication destructive etc. Therefore, in order to meet the development requirement of nanotechnology, it is of great significance to develop new silicon-based nanofabrication approaches with high resolution, low cost and low destructive. Recently, friction-induced nanofabrication methods have attracted a lot of attention from researchers due to its simplicity, flexibility and high resolution. Without any mould and electronic field, various micro/nano pattern structures can be produced through the combination with wet etching technique. Nowadays, the friction-induced nanofabrication methods for quartz and gallium arsenide tend to be mature, but there are still a lot of unsolved problems such as the limited fabrication depth, the severe fabrication damage and the unknown fabrication mechanism in the friction-induced nanofabrication method for silicon. Therefore, study on the new friction-induced nanofabrication methods with large fabrication depth and low destruction can not only enrich the basic theory for friction-induced nanofabrication, but also help to speed up the application process for relevant nanofabrication techniques.By using atomic force microscope, nanoscratch tester, tribo-indenter in-situ nanomechanics test system, self-developed large-area micro/nanofabrication apparatus and relevant analysis and characterization technique, the low-destructive friction-induced nanofabrication methods on monocrystalline silicon are studied in this doctoral dissertation. Firstly, based on the analysis by transmission electron microscope observation (TEM) and Auger electron spectroscope (AES), the masking role of the friction-induced amorphous silicon in potassium hydroxide (KOH) solution etching has been investigated. The involved masking mechanism is discussed through electrochemical theory. The friction-induced selective etching nanofabrication with amorphous layer as mask is proposed. Secondly, to reduce the fabrication damage and increase the fabrication depth, the friction-induced selective etching nanofabrication method with Si3N4 as mask is developed according the selective etching phenomena of scratch-damaged Si3N4 film in hydrofluoric acid (HF) solution. The selective etching mechanism is revealed by AES and the etching experiment. Finally, in order to further reduce the fabrication damage (even no lattice damage), the author has proposed two kinds of non-destructive tribochemistry-induced nanofabrication approaches according the Si/SiOx removal mechanism dominated by tribochemical reaction. One is the tribochemistry-induced selective etching nanofabrication method with SiOx as mask, and the other is the maskless tribochemistry-induced direct-write nanofabrication method. To clarify whether the tribochemistry-induced nanofabrication is non-destruction, high resolution TEM (HRTEM) analysis was performed on the fabrication area to characterize the structural feature of fabrication area. The main content and the innovation point of the dissertation are summarized below.(1) The masking effect of the friction-induced amorphous silicon on KOH solution etching is demonstrated, and the involved mechanism is revealed.The author has demonstrated for the first time that the amorphous silicon can effectively resist the etching in KOH solution compared to Si(100) substrate, and this amorphous silicon plays a dominate making role in the friction-induced selective etching nanofabrication. Further studies suggest that the average dangling bond density and back bond energy level of the silicon atoms on amorphous silicon are lower than those of the Si(100), so the chemical reactivity of amorphous silicon is lower. That is the reason why the amorphous silicon shows strong masking effect. Clarification on masking role of the amorphous silicon has not only corrected the previous understanding, which believe that the masking role is derived from the superficial SiOx layer, but also provided the theoretical foundation for developing the maskless silicon-based nanofabrication method.(2) The selective etching mechanism of scratch-damaged Si3N4 mask in HF solution is revealed, and the low-destructive nanofabrication approach on monocrystalline silicon through friction-induced selective etching of Si3N4 mask is proposed.Experimental results suggest the higher of the scratching load, the severer of the crack initiation, and the higher of the etching rate of scratched Si3N4 in HF solution. Based on this damage-induced selective etching mechanism, the pattern scratched on the Si3N4 mask can be transferred into silicon substrate conveniently, then the exposed silicon substrate can be etched by KOH solution to obtain deep structure. Finally, through the removal of the residual Si3N4 mask in HF solution, the patterned monocrystalline structure can be produced. Compared to the traditional friction-induced nanofabrication methods, the present fabrication method can obtain deeper structure with lower damage. In addition, nano-texture with super surface hydrophobicity on monocrystalline surface can be effectively fabricated.(3) The tribochemistry-induced selective etching nanofabrication method with SiOx as mask on monocrystalline surface is proposed.Relative research shows that based on the tribochemical reaction between the SiO2 tip and the silicon substrate with SiOx mask (Si/SiOx), the SiOx mask in the scanned area can be removed under low contact pressure. According to this mechanism, the tribochemistry-induced selective etching nanofabrication method with SiOx as mask on monocrystalline surface is proposed. Firstly, the SiOx mask layer is generated on H-passivated silicon surface through the wet oxidation technique. Secondly, the SiOx mask on the target area is removed by SiO2 tip. Finally, the required nanostructure can be produced by the selective etching in KOH solution. HRTEM observation suggests that neither the material removal by tribochemical reaction nor the wet etching by KOH solution result in the lattice damage. The present method has solved the fabrication damage problem during the traditional friction-induced nanofabrication approaches, and it is expected to be applied in fabricating the non-destructive monocrystalline silicon nanoimprint mould.(4) According to the tribochemistry removal mechanism on monocrystalline silicon, the maskless tribochemistry-induced direct-write nanofabrication method is proposed.In the proposed method, the monocrystalline silicon on the target area can be removed by the SiO2 tip so as to obtain the groove structure. The contact pressure during tribochemical removal process (0.3-1.2 GPa) is far below the critical pressure for initial yield of silicon (11.3 GPa), and the material removal in scanning area is dominated by the tribochemical reaction. HRTEM observation shows that the produced nanostructure kept its original single crystal lattice without any dislocation/defect at all. The study is the first to realize the non-destructive nanofabrication on monocrystalline silicon through the maskless direct-write nanofabrication approach.In brief, to meet the fabrication requirement of high resolution, low-cost and low-destructive on monocrystalline silicon, the author has proposed four kinds of nanofabrication approaches according to four different friction-induced mechanism. For different fabrication requirements, each method has its own unique advantages. The approach based on amorphous mask is simple but has high fabrication destructive. While the method based on Si3N4 mask can realize the fabrication depth in micron scale and the fabrication destruction is lower than the former one. The biggest advantage of the tribochemistry-induced approaches (direct-write and selective etching) is non-destructive. The results in this dissertation can not only enrich the nanofabrication and nanotribology theory, but also be expected to be applied in fabricating functional surface nano-texture, single electron device and high-quality nanoimprint mould.