Tribochemical Wear Of Silicon With Various Crystal Structure

With the rapid development of nano-technology,micro-nano devices have been extensively applied in numerous fields,such as biomedicine,advanced manufacturing,military defense and so on.Silicon-based semiconductor device(such as MEMS/NEMS)is one of the typical micro-nano devices,while the materials used in the applications include monocrystalline silicon,polysilicon and amorphous silicon.Due to its excellent physical and chemical properties,monocrystalline silicon has been as the main semiconductor materials and structural functional materials in large scale integrated circuits and microelectrome-chanical systems.Furthermore,polycrystalline silicon is not only the direct raw material for producing the monocrystalline silicon,but also the basic material of electronic information for semiconductor devices,such as artificial intelligence,automatic control,information processing,photoelectric conversion and so on,so it is called "the cornerstone of micro-electronics building".Due to the existence of "dangling bond" as inner structure,amorphous silicon as a semiconductor with band has been widely used in the manufacture of solar cells,film transistors,copy drums,photoelectric sensors and field-effect transistors.The above three kinds of silicon materials in the application processes must correspond to chemical mechanical polishing(CMP)to obtain ultra-precision surfaces,then the processes involve a large number of micro-wear problems.Previously,the study on micro-wear of silicon materials mainly focused on monocrystalline silicon,but the research about material removal silicon materials with different crystal structures(i.e.,mono-crystalline silicon,polysilicon,amorphous silicon)is still far from addressed.Therefore,it is essential to comprehensively understand the micro-wear behaviors of these kinds of silicon material,and further reveal the mechanism of crystal structure dependence of micro-wear of silicon substrate.In this paper,the micro-wear of monocrystalline silicon,polycrystalline silicon,hydro-genated amorphous silicon and friction induced amorphous silicon were deeply and systematically studied against silica spheres under different load and cycle conditions by a relative humidity controlled atomic force microscope.With the help of HYSITRON,SEM,PECVD,FTIR,XRD and other inspection techniques,the physical and chemical properties of silicon materials with different structure were characterized.The corresponding results are useful to reveal the mechanism of crystal structure dependence of the micro-wear of silicon material.The main conclusions and innovations are summarized as follows:(1)Tribochemical wear behaviors of monocrystalline silicon,polycrystalline silicon and hydrogenated amorphous silicon were given,and the mechanism of crystal structure dependence of micro-wear of silicon substrate was preliminarily detected.The micro-wear of monocrystalline silicon,polysilicon and hydrogenated amorphous silicon surface gradually increased with the increase of load and siding cycles.In contrast,the micro-wear of hydrogenated amorphous silicon was the most serious,followed by monocrystalline silicon,polysilicon the slightest.In humid air,the adsorbed water film on the surface of monocrystalline silicon promoted its micro-wear.Since oxidation existing in grain boundary might improve the inert chemical properties and inhibited the chemical reaction,the wear of polysilicon was more weaker than that of monocrystalline silicon.For hydrogenated amorphous silicon,due to the existence of the internal dangling bond,and the possibility of the presence of free oxygen,and other factors,such as the generation of internal defects and the reduction of mechanical properties and so on,caused in deposition process because of many uncertainties,the wear was the most serious compared to other two silicon materials.(2)The tribochemical wear of friction induced deformation silicon was investigated,and the mechanism of deformed layer influencing on micro-wear of silicon was preliminarily detected.First,the structures of nano-hillock and nano-groove were fabricated on monocry-stalline silicon surface by using diamond tip and atomic force microscope through control the contact pressure.The materials beneath the hillock and the groove are consist of thin SiOx layer on the outmost surface and amorphous silicon layer and deformed layer on the subsurface,but the relative thickness are different.With the increase of loads and sliding cycles,the micro-wear of monocrystalline silicon substrate,nano-hillock and nano-groove surface increased dynamically.In contrast,the micro-wear on nano-groove surface is the most serious,monocrystalline silicon substrate in the middle,and nano-hillocks surface the slightest.It has been detected that the thickness of oxide layer on hillock surface is slightly smaller than that on groove surface,and also the thickness of the amorphous layer on groove surface is thicker,then the elastic modulus of hillock surface is slightly larger than that of groove surface.Under the same contact pressure,the contact area on each surface must be different,so the potential of chemical reaction might be dissimilar that resulted in differences in micro-wear.Compared to that on nano-hillock surface,the density of amorphous silicon layer on nano-groove surface was relatively higher,and the number of cracked Si-Si bonds was larger.As a result,oxygen and water molecules might be easier to react with silicon atoms on groove surface than on hillock surface,then resulting in more surface damage on groove surface.In sum,based on the comparison of micro-wear of monocrystalline silicon,polycrysta-lline silicon,hydrogenated amorphous silicon(a-Si:H)and friction-induced amorphous silicon(nano-bumps and nano-trenches)surface,the influence of crystal structure on the tribochemical wear of silicon material and the corresponding mechanism were preliminarily detected.The results may not only help to reveal the mechanism of internal atomic defects and doping affecting on the tribochemical wear of silicon material,but also to enrich the basic theory of nano-tribology,and further to provide a theoretical basis for the tribological design of micro-nano devices and the optimization of CMP process.