Study On The Timeliness Of Hydrogen Passivated Silicon Surface And Its Effect On Tribological Performance

As a typical semiconductor material, single crystal silicon has been widely used in MEMS applications and micro/nanofabrication fields. However, with the continuous miniaturization of devices or structure at scale, the nano-tribological problems caused by strong surface force, such as adhesion and wear, have not only became the critical factors to limit the long-term reliable work of MEMS, but also significantly influenced the fabrication quality of micro/nano devices. Therefore, it is more and more concerned about how to realize the design of low adhesion and wear on single crystal silicon surface. Since it is simple and adaptable, hydrogen passivation on silicon surface, as a common method of surface chemical modification, has been extensively applied in the purgation of integrated circuits, as well as the fabrication of silicon solar cells and other fields. Despite of that, the hydrophobicity of hydrogen passivated silicon surface will gradually disappear due to oxidation. Therefore, it is necessary to detect the influence mechanism of oxidation on the timeliness of silicon surface with hydrogen passivation. In this paper, the water contact angle and chemical composition of silicon surface with the storage time in various environments was firstly investigated, and then the environmental contribution on the hydrophobicity of hydrogen passivated silicon surface was revealed. On the basis, the adhesion and friction behaviors on passivated silicon surface as the increase of storage time in different environments were further studied. Finally, based on its native oxidation layer, a nanofabrication method was proposed to fabricate the small line-width structure on silicon surface. The main experimental results and conclusions are summarized as following.1. Effect of storage environments on the timeliness of hydrogen passivated silicon surface was revealed.Although water contact angle on hydrogen passivated silicon surface gradually decreased to constant value with the increase of storage time under three environments, the extent was most serious in water, middle in air and slight in alcohol. Contrary to the variation of contact angle, oxygen content measured by XPS increased with the storage time in those conditions, but the change degree followed the same order. The results suggested that the alcohol solution could to some extent alleviate the oxidation reaction. It is better to store the hydrogen passivated silicon surface in alcohol.2. Hydrogen passivation timeliness dependence of adhesion and friction on silicon surface was investigated.Both the adhesion and friction on the hydrogen passivated silicon surface increased dynamically with the holding time at three conditions. Since the oxidation degree and surface hydrophobicity was different at the same storage time under various storage environments, the increased scope of adhesion force and friction force on silicon surface held in alcohol solution was relative slight, and much larger held in air or in water. Furthermore, the change degree was most significant when the storage was operated in water. The results indicated that the storage of silicon sample in alcohol solution was benefit to reduce the adhesion and friction forces.3. A fabrication method was proposed to fabricate a small line-width structure on silicon surface.The nanofabrication with small line-width structure on silicon surface can be achieved by pre-scanning on silicon surface with native oxidation layer using SiaN4 probe with small radius and post etching in KOH solution. During the nanofabrication process, the silicon substrate was firstly exposed after removal of surface oxidation layer under the tribochemical reaction in Si3N4 probe scratching, and then the groove on silicon surface could deepen after the selective etching in KOH solution. Here, the final width and depth of nanostructure on silicon surface depended on the normal load and scratch number in pre-scanning and the etching time. Under the given conditions in this thesis, the best etching time in nanofabrication was identified as around 7 min.