Theoretical Calculations Of Failure Mechanism Of Silicon Nano-devices Containing Vacancy Defects

Silicon-based devices are widely used in semiconductor integrated circuits.However,the reliability problems caused by defects in silicon-based devices have slowed the progress of integrated circuits at the Micro and Nano scales.For example,point defects can degrade performance of Nano-devices.However,proper defect-doping can effectively improve the reliability problems of silicon-based devices.Therefore,based on molecular dynamics and first-principles,we investigate the migration mechanism of vacancy defects under strong electric fields for Si,Si O2 and Si/Si O2 structures.Our work mainly includes the following aspects:1.The migration mechanism of vacancy defects in Si and Si O2 structures under electric fields was investigated.The results show that in the silicon crystal structure,Si vacancies are affected by electric fields and accumulate in the Si(100)surface.When the total number of Si vacancies is set to 40,the quantity of Si vacancies in the Si(100)surface increases along with electric fields;When the electric field reaches 8.9 MV/cm,the vacancy in the Si(100)surface reaches a saturation value of 10,and remains stable as the electric field continues to increase.However,when the electric field exceeds 13.5 MV/cm,vacancy structure is distorted and unstable,that is,13.5 MV/cm is a critical electric field that maintains the stability of Si structure.In addition,the saturation value of the Si vacancy and the critical electric field can be less affected by the temperature.As far as the Si O2 structure is concerned,O vacancies will accumulate in the Si O2(100)surface under electric fields,similar to the Si structure;In addition,the Si O2(100)surface also has a maximum saturation value of 10 for O vacancies and a critical electric field value of 15.4 MV/cm to maintain the stability of the structure.When the electric field exceeds the critical value,the quantity of O vacancies in the Si O2(100)surface increases sharply and the structure becomes unstable.2.We calculate the band structure,conduction mechanism,optical absorption spectrum and mechanical properties of Si and Si O2 structures with vacancy defects.We focus on the effect of defects on the band structure in silicon crystals.The results show that between the conduction and the valence band,Si vacancies bring new defect levels and reduce the band-gap of the silicon crystal.Therefore,the vacancy structure is metallic,which increases the tunneling current of silicon-based devices.In addition,the static dielectric constant of the vacancy structure is larger than that of the non-defective structure,which affects the C-V characteristics of MOS structures.The Si vacancies can also cause changes in the optical absorption coefficient of structures,while at the same time weakening the structure's resistance to deformation in varying degrees.For Si O2 crystal,the effect of defects on band properties was analyzed and it was found that there are also defect levels near the Fermi energy level.Besides,it is found that when the concentration of O vacancies is low,the dielectric constant of vacancy structure changes little,and when the concentration of O vacancies is high,the dielectric constant changes significantly.3.A Si/Si O2 interface model was constructed to analyze the characteristics of the vacancy defect structures from three perspectives of the Si crystal module,the Si O2 crystal module,and the Si/Si O2 interface structure.The O vacancies in the Si O2 crystal and the Si vacancies in the Si crystal will converge toward the Si crystal and the Si O2 crystal respectively through the transition region of the oxide layer under electric fields.The results are similar to those of the Si and Si O2 structure in Chapter 3.The structure has a maximum saturation value for the aggregation of vacancies,and there is a critical electric field that maintains the stability of the structure.For Si/Si O2 structure,the location and concentration of vacancies in the transition zone,can lead to changes in the properties of the band structure,the conduction mechanism,and the optical absorption spectrum.Our research not only helps to understand the movement mechanism of the defects in silicon-based devices under strong electric fields,but also to understand the effect of defect structures on device performance,thus providing a theoretical basis for the subsequent study of silicon-based device materials.