Study On The Detection Method Of Mechanical Damage Of Monocrystalline Silicon Surface Based On The Change Of Electrical Conductivity

Monocrystalline silicon has been extensively employed as a basic material for large scale integrated circuits,semiconductor devices and photovoltaic solar cells on account of its excellent physical,chemical,mechanical and semiconductor properties.For it is abundant in resources,stable in performance and non-toxic,monocrystalline silicon has been produced in large quantities in industry.However,the cutting,grinding,polishing and other steps in the production and processing of monocrystalline silicon tend to damage the silicon wafer.These damages may impose adverse impact on other processing procedures and residual damages can directly affect the performance and service time of devices.Therefore,detecting the defects engendered in the processing of monocrystalline silicon in time is crucial for improving the production efficiency and yield rate.There are several techniques for detecting monocrystalline silicon defects,such as chemical etching,X-ray diffraction,transmission electron microscopy and microscopic Raman spectroscopy.However,due to unavoidable technology limitations,these techniques cannot meet the development needs of the current electronic communication technology and nanotechnology.As the scanning probe microscopy develops,functions of conductive atomic force microscope is expanded,and its accuracy is increased.CAFM has many advantages in characterizing and detecting materials properties at micro/nanoscale.However,there are only a few studies on the defect detection of monocrystalline silicon using conductive atomic force microscopy.It is still unclear about the method and principle we can employ to detect the defects of monocrystalline silicon with this techonology,so further research is still needed.In this dissertation,the conductive atomic force microscopy,a homemade multi-probe instrument developed by our research group and the in-situ nanomechanical test system were applied,the approach of detecting silicon defects after scratching by conductive atomic force microscopy was systematically researched.The mechanism of silicon defect detection by conductivity change was elaborated combining with transmission electron microscopy image.Based on the mechanism,the feasibility of application of detecting the silicon defect after polishing was presented.The main contents and innovation points of this dissertation are as follows:(1)The influence of scan speed and scan direction on the current signal of the conductive atomic force microscopy was investigated.During the scanning of conductive atomic force microscopy,the interfering current signal(not generated by the material itself)can be detected when the topography of the material surface is undulating and scan speed is fast.This current signal can be removed by decreasing the scan speed.Later analysis suggests that the interfering current signal is the Maxwell displacement current that generated by the fast scanning of tip-sample structure,which cannot reflect the actual material surface information.Accordingly,to get the real material surface current signal,the scan speed must be reduced to eliminate the Maxwell displacement current.(2)The effect of current generated on mechanical scratch of monocrystalline silicon was explored.The surface of monocrystalline silicon was scratched by homemade multi-probe instrument,and then the surface of damaged region was detected by conductive atomic force microscopy,the results show that the current will increase with the increase of the scratching load or the bias voltage;The current distribution in the damaged area under different loads and different deflection voltages are investigated.By contrast,the detection current results of friction-induced nano hillock structure and tribochemical induced non-destructive removal area were investigated,it turns out that the current was only detected in the friction-induced nano hillock fabricated under high tip-sample sliding speed(40-1000 ?m/s).(3)The mechanism for the conductivity of mechanical damaged monocrystalline silicon and its application were elabrated.By comparing the electrical conductivity of the friction induced hillock,and further using the high resolution transmission electron microscopy(HRTEM)analysis,it indicated that the friction induced amorphous layer will not cause the increase of electrical conductivity,and the lattice distortion caused by scratching is the main reason for the increase of electrical conductivity.Analysis indicates that the distortion layer reduces the energy barrier of the electron flow,it makes the electron easier to flow through the damaged area.Based on the principle of conductivity change of damaged area,a simple,fast,low-cost and non-destructive method for detecting surface damage of silicon wafer is put forward in this dissertation.In this dissertation,the effect of the change of the conductivity of the mechanical scratch on the monocrystalline silicon has been investigated.By comparing the surface conductivity of tribochemical induced non-destructive removal area and friction induced nano hillock structure,the mechanism of the electrical conductivity change of mechanical damage on monocrystalline silicon surface is revealed by combining the results of the high resolution transmission electron microscopy(HRTEM)analysis.Accordingly,a simple,fast,low-cost and non-destructive detection method for silicon wafer is put forward.This detection method enriches the methods of silicon wafer detection,which provides a new approach to improve the yield rate of silicon wafer.