In-situ Mechanical Experimental Study And Theoretical Analysis On Evolution Of Damages Induced By Stress In Hard-brittle Semiconductors

The semiconductor industry is a basic,strategic and leading industry that supports economic and social development and guarantees national security,which is also the core driving force to promote the development and revolution of the global science and technology industry.Hard-brittle semiconductors,such as monocrystalline silicon(Si)and silicon carbide(SiC),exhibit high hard and brittle characteristics,which are usually difficult to process,and the surface/subsurface damages induced by stress during processing have a great influence on the performance and service life of related devices.Meanwhile,brittle fracture of hard-brittle semiconductors is prone to occur under stress during service,and the related devices will fail completely once they are fractured,which lead to high maintenance cost or disastrous accident.Thus,the research on the evolution of stress-induced damages of hard-brittle semiconductors and their underlying mechanisms,is of great significance for improving processing quality and developing high-performance devices.In recent years,with the development of in-situ transmission electron microscopy(TEM)mechanical testing technology,real-time observation of the change process of the microstructure of samples during loading/unloading at nanoscale is realized,and the corresponding mechanical signals can be recorded simultaneously,which provide an important research method and technology for quantitatively studying the stress-induced damages and their underlying mechanisms.However,damages and contaminations are easily introduced during sample preparation with traditional method,which greatly affect the mechanical properties,electrical properties and atomic scale characterization of the sample.In this thesis,based on the unavoidable stress-induced damages in hard-brittle semiconductors during machining and in service,the typical hard-brittle semiconductors monocrystalline Si and SiC are studied.Novel methods and setups are developed.The formation and evolution of damages induced by stress in monocrystalline Si and SiC during machining and in service are simulated using in-situ TEM mechanical testing technology.Formation and evolution of the nanostructure of the damaged layer,deformation and fracture behavior and mechanism,as well as self-healing on fractured surfaces are studied quantitatively at nanoscale in real time.The main contents and conclusions are as follows:(1)Developing sample preparation methods and setups for in-situ TEM mechanical testing.For monocrystalline Si,a wedge-shaped structure is designed,and Si wedge is processed using wet etching and focused ion beam thinning technology.In-situ TEM nanoindentation testing and characterization at atomic scale are realized.For monocrystalline SiC,a novel setup based on biomass materials with variable cross-sections like eyebrows,wolf hairs and sheep hairs for operating micro-nano samples is developed.A novel method for operating the micro-nano samples at room temperature in the atmosphere is developed.The developed setup is simple,and easy to operate,high in sample preparation efficiency,and can effectively avoid the damage and contamination caused by the traditional method,and in-situ TEM tensile testing,compression testing,bending testing and electromechanical testing,as well as characterization at atomic scale are realized.(2)Exploring the formation and evolution of the nanostructure in the stress-induced damaged layer in monocrystalline Si.In-situ TEM nanoindentation testing is performed on monocrystalline Si using a cube corner diamond tip with a radius of 66 nm,and the damaged layer is characterized at atomic resolution.The formation and evolution of the nanostructure of the damaged layer is revealed.Dislocations,nanotwin,slip bands,and stacking faults are discovered in the damaged layer,which fills the gap between machining and nanomechanical testing.Meanwhile,Si-VI phase crystal structure with the orthorhombic system is observed and related formation mechanism is studied.These results provide an important theoretical basis for developing novel machining process technology and improving machining quality.(3)Exploring the deformation and fracture behavior of monocrystalline SiC and their underlying mechanism.Using the developed sample preparation method and setup,individual monocrystalline SiC nanowires are transferred and fixed,and in-situ TEM mechanical testing and electromechanical testing are carried out.Linear elastic deformation and brittle fracture behaviors of SiC at nanoscale is revealed quantitatively.Ultrahigh piezoresistive coefficient and carrier mobility of SiC nanowire are discovered,which are 82 and 527 times those of literature reports,and related mechanisms are analyzed.These results provide insights for broadening the application of SiC as well as designing and manufacturing high-performance semiconductor devices.(4)Exploring self-healing on fractured surfaces of SiC and its underlying mechanism.In-situ mechanical testing using the push-to-pull device with springs is carried out to study the self-healing on fractured surfaces of SiC.SiC fractures under tensile stress.The fractured surfaces of SiC return to their original position with the help of springs and are self-healed.Rebonding on the fracture surfaces of monocrystalline SiC is observed at atomic resolution,and the mechanism of self-healing is revealed.The mechanical properties of the fractured surfaces after self-healing are tested.The self-healing time of 2 s and 20 minutes can restore the fracture strength by 4%and 13%respectively.Amorphous SiC and crystal-amorphous composite structure of SiC are fabricated in the TEM with electron beam irradiation in real time,and self-healing on their fractured surfaces is investigated.The fractured surfaces of amorphous SiC and crystal-amorphous composited structure of SiC can recover 64%and 12%of fracture strength within 20 minutes respectively,and the mechanism of self-healing is analyzed.The results provide a new understanding of the evolution of fractured surfaces in SiC,and point out a new direction for the design and manufacturing of next-generation high-performance devices in the aerospace field.