A Study On Strain Mechanism And Related Effects Of Silicon On Insulator

Strained SOI has the characteristics of high carrier mobility of strained Si and low leakage current,low parasitic capacitance and other parasitic effects,and high radiation resistance of SOI materials.It has became the preferred material technology for high speed,low power consumption and radiation resistant devices and circuit.With the continuous development of semiconductor process technology,strained SOI plays an increasingly important role in improving circuit performance and reducing power consumption.At the same time,it also puts forward new and higher requirements for high-quality strained SOI material preparation process technology.The existing mature strained SOI material technologies are almost based on Si Ge virtual substrates,which have the problems of heat dissipation and Ge diffusion.Therefore,research and development of a Si Ge-free virtual substrate,high-performance wafer-level strained SOI technology is very important.Based on the structure and material characteristics of SOI wafer,the high-stress characteristics of SiN film,and the mechanics and thermal theory of materials,a new method for manufacturing wafer-level strained SOI based on high-stress SiN films without Si Ge virtual substrate was proposes in this thesis.The mechanism of strain introduction,retention,memory and enhancement have been systematically discuss,and the strain model and experiments of preparation process have been thoroughly researched in this thesis.The main research work and achievements of the thesis are as follows:(1)Researches on the mechanical characteristics of SOI wafers.Using nano-indentation technology,experimental study on the mechanical properties of Si wafers and SiO₂thin films was performed,and obtained the Young's modulus and hardness of crystal Si and SiO₂;The ANSYS finite element model of the nano-indentation experiment of SOI wafer was established,combined with the experimental results and dimensional analysis,the yield strength of the top Si film on the SOI wafer was obtained.(2)Theoretical and experimental research on mechanically induced uniaxial strained SOI.According to the beam bending theory and the elastoplastic mechanical properties of SOI wafer,experimental and theoretical researches on mechanisms of strain introduction and retention was carried out,uniaxial strained SOI in wafer-level with compressive strain of-0.168%and tensile strain of 0.1554%was obtained,which has a higher strain than the method reported in the literature.(3)Researches on the mechanism of strain introduction of SiN film-induced strained SOI in wafer-level.The experimental research of the thesis found that if based only on the beam bending theory,the wafer bending caused by the deposited SiN film on SOI is not enough to produce the larger strain measured in the experiment,indicating that the stress of the SiN film is partly generated SOI wafer bending,the other part may cause the top layer Si to produce plane tension/compression,and introduce tensile/compressive strain correspondingly.According to the experimental results,and based on the characteristics of material,structural,smooth sliding and elastic mechanics of SOI wafer,this thesis proposed the strain mechanism of wafer bending combing with plane stretching for high-stress SiN film induced strained SOI in wafer-leve,and carried out experimental verification.The experimental results show that the bending strain of the high-stress SiN-induced tensile strained SOI wafer is only 0.024%,and 0.259%of the strain is caused by the plane tensile or compressive strain of the top layer Si.(4)Researches on the method and mechanism of strain enhancement in SiN film-induced wafer-level strained SOI.Based on the structural characteristics of SOI wafer and the principle of ion implantation,a new method for enhancing the strain effect of wafer-level strained SOI induced by high-stress SiN film through He⁺implantation was proposed in the thesis.Based on this method and the smooth sliding characteristics of SOI wafer,this thesis proposes and systematically elaborated the mechanism of the strain enhancement,that is,the bonding strength of SiO2-substrate interface could be reduced by He⁺implanted,and enhanced the smooth sliding characteristics of the SOI which leading to the enhanced stretching or compression of the top Si film,and correspondingly enhanced the introduced strain in the SOI.Based on this method,confirmatory experiment of the strain enhancement was designed and carried out The results show that the introduced strain of SOI can be increased by about 300%with the innovative method of strain enhancement by He⁺implantation.(5)Researches on the method and mechanism of strain retention in SOI by highe-stress SiN film.Based on the structural characteristics of SOI wafer and the mechanical properties of high-stress SiN thin film,the strain-holding method of plastic deformation of buried SiO₂layer in trained SOI by high-stress SiN film was proposed.Based on this method and the elasto-plastic properties of materials in SOI,this thesis proposes and systematically elaborated the mechanism of strain retention,that is,due to the smaller yield strength of SiO₂than that of Si,under the same annealing temperature and SiN film stress,plastic deformation of buried SiO₂occurred,while Si still maintains elastic deformation;after the removal of SiN film,the strain of the top Si remained by the pulling effect of the plastic deformation buried SiO₂layer.Based on this method,the experimental verification of strain retention mechanism of SOI was designed and carried out.The experimental verification study showed that,after annealing at 650?and the removal the-1GPa SiN film,strained SOI wafer with tensil strain of 0.3072%strain is obtained by this method.(6)Researches on the method and mechanism of strain memory in SOI by highe-stress SiN film.According to the process principle of the strain memory technology of local strain,a strain memory method of recrystallization of non-crystallized top Si for SiN induced strained SOI was proposed.Based on this method and the structure and material characteristics of the SOI wafer,this thesis proposes and systematically elaborated the mechanism of strain memory,that is,the strain originated from SiN film stress in SOI was introduced into recrystallized top Si during annealing due to the affection of SiN stress and the plastic deformed SiO₂layer.Based on this method,the thesis experimentally verified its mechanism.The research results showed that As and Ge ions implanted amorphous top Si would memorize the strain introduced by SiN film during the annealing and recrystallization process.Using this method,after recrystallization of top Si and the removal of SiN film,tensile strain of 0.232%and 0.184%were successfully realized in SOI wafer respectively.(7)Study on the scale effect of high-stress SiN film and the conversion of biaxial strained SOI to uniaxial strained SOI.According to the theory of scale effect,the study on the structural and the scale effect of stress characteristics of SiN film,and the mechanism of the conversion of biaxial strained SOI to uniaxial strained SOI was presented in this thesis,and focusing on the stress scale effect behavior of SiN film stress relaxation at the micro/nano scale.In this thesis a process method for converting the strain in biaxially strained SOI to uniaxial strained is proposed,that is,with the formation of micron-or nano-scale pattern of high-stress SiN film on top Si,the biaxial strain in wafer-level introduced by SiN film in SOI can transform into uniaxial.Based on the method and the material and structure characteristics of SOI wafer,the strain mechanism of the wafer-level uniaxial strained SOI is expounded and experimentally verified by experiments.Polarization Raman spectra show that the submicron width SiN strip array makes the top layer Si subject to approximately uniaxial stress along the length of the strip.The final SOI wafer has become uniaxial strained SOI in wafer-level.(8)Experimental study of strained SOI based on high-stress SiN film.Based on the research results of preparation method and strain mechanism for the high-stress SiN-induced strained SOI,experimental studies for the mechanism of strain retention,strain memory,stress scale effect,and the preparation of biaxial-and uniaxial-strained SOI was carried out in this thesis.Using the process of amorphization top S by As and Ge ions implantation and the process of top Si recrystallization by annealing,biaxially tensile strain of 0.232%and 0.18361%was obtained in SOI in wafer-level;base on the strain-enhancement process of He⁺implantation at Si-SiO2 interface,strained SOI wafer with tensile strain 0.3200%was realized;On this basis,using the method of micro-scale bar patterned high-stress SiN film which based on principle of the scale effect of SiN film stress,0.6475%uniaxial tensile strain and-0.5957%uniaxial compressive strain are introduced into SOI;Using XRD,polarization Raman,HRTEM,AFM and other technologies,the characterization of the strained SOI wafer crystal quality,biaxial strain and uniaxial strain,defects,bending and other characteristics were performed.(9)The strain model and stress distribution calculation of strained SOI in wafer-level.Based on the arc length theory of curved surface structure,an arc length model of mechanically-induced strained SOI wafer bending strain was proposed in this thesis,which has the advantages of clear in physical meaning,accurate and concise in mathematical expression and modeling etc.;based on the mechanism of strain introduction of mechanically-induced strained SOI and arc length model,the strain model of mechanically strained SOI wafer was established.The strain model takes into account the influence of key parameters such as bending radius and SOI wafer thickness on the strain.The fiber grating method and ANSYS finite element simulation were used to test and simulate the stress distribution of mechanically-induced strained SOI wafer.The results show that the strain model was basically consistent with the results of fiber grating experimental and the ANSYS finite element simulation,which verifies the rationality of the strain model.According to the strain mechanism of high-stress SiN film-induced strained SOI,the strain model for high-stress SiN-induced strained SOI wafer is established in this thesis.The model includes parts of bending strain and film tensile/compressive strain.The basic principle of the bending strain model is the same as the strain model of mechanically-induced strained SOI wafer;on the other hand,the film tensile/compressive strain model considered the impact of the key factors such as the thickness and stress characteristics of the SiN film,the thickness and Young's modulus of the top Si and the buried SiO₂layer in SOI wafer.Model verification experiments showed that the model calculation results were basically consistent with the experimental results,but due to the approximate assumptions of the model,the model calculation results wrer all larger than the experimental results;the established ANSYS finite element simulation results also showed that impact of the different parameters in the model on strain were basically agree with the simulation results,which verifies the rationality of the strain model.