Study On Ar~+ Etching Mechanism And Application Of Single Crystal Lithium Niobate Film

With the advent of the 5G communication era,the demand for integrated,miniaturized,and high-frequency filters has increased dramatically.The single crystal lithium niobite?LN?thin film prepared by crystal ion slicing?CIS?has the advantages of large electro-optic coefficient and high electromechanical coupling coefficient.Therefore,it has attracted much attention in terms of the preparation of optical devices such as optical waveguides and acoustic devices such as bulk acoustic wave filters.It is worth noting that a single-crystal material will produce implantation damage layer of Gaussian distribution during the process of crystal ion slicing,so there is a rough damage layer on the surface of the single-crystal film,which leads to the attenuation of film quality and device performance.Therefore,this paper has studied the method of removing the existing damage layer and surface planarization based on Ar⁺etching technology,the relationship between the etching process and the film thickness and microstructure are tested,and the relationship between the microstructure and the electrical properties of the film is analyzed;Aiming at the preparation requirements of single crystal LN film in film bulk acoustic wave device?FBAR?,the nondestructive detection method of film thickness in FBAR resonator is studied by ellipsometer,and the effect of the surface damage layer on the performance of the FBAR resonator is analyzed.The specific research work and main results of the thesis are as follows:1.Study on the thickness of single crystal LN thin film prepared by ion implantation and its surface damage layer.Firstly,the effect of implantation energy on ion concentration distribution and defect structure distribution was studied by SRIM simulation.Then,the structure design of FBAR determines that the implantation energy and implantation dose 285keV and 1×10¹⁶ions/cm²,respectively,and the highest damage intensity location of SRIM simulation is about 0.9?m,which is close to the Scanning Electron Microscope test thickness of 888.8nm;However,the thickness of the surface damage layer simulated by SRIM is 130nm,which is close to the experimental test thickness of 145nm.2.The experimental study of single crystal LN thin film etched by Ar ion is carried out systematically.Firstly,the relationship between beam voltage and accelerate voltage on the etching rate and surface morphology is studied:the greater the beam voltage,the greater the etching rate and surface roughness,the greater the accelerate voltage,the greater the etching rate,and the smaller the surface roughness.Then the best parameters for Ar⁺etching are determined as beam current voltage 400V and accelerate voltage 80V.Finally,the thickness of the single crystal LN films etched by Ar⁺are fitted and measured by an ellipsometer,which is consistent with the Scanning Electron Microscope test results within a certain error range.3.The effect of the surface damage layer on the performance of the single crystal LN film is carried out.Firstly,the change of the quality of the LN film single crystal during theAr ion etching process is analyzed by XRD,Ar⁺etching can significantly improve the single crystal quality of the film,and the single crystal quality of the thin film without the damage layer is close to the single crystal block is completely removed.Then the dielectric constants before and after the removal of the damage layer are tested to be 28.61 and 51.78,and the dielectric loss are 18.14×10^-4 and 5.58×10^-4 respectively,which shows removing the damage layer by Ar⁺etching can significantly improve the dielectric properties of the film.Finally,the Piezoelectric Force Microscopy tests show that the single crystal LN film after removing the damaged layer has a more uniform piezoelectric response.4.Through the ADS simulation and vector network analyzer test system,the effect of the surface damage layer on the performance of the FBAR resonator is studied together Firstly,a solid-state FBAR resonator with Mo and SiO₂ Bragg reflectors is designed and prepared.Then,based on the measured dielectric constant of single crystal LN thin film,ADS simulation analysis is carried out.The results show that the surface damage layer has a greater influence on the effective electromechanical coupling coefficient of the FBAR resonator and a smaller influence on the Q value.Finally,the device test shows that the FBAR resonator after removing the damaged layer has a larger electromechanical coupling coefficient and Q value.To sum up,the thesis aimed at the single crystal LN thin film prepared by CIS technology,the surface damage layer is removed by Ar⁺etching,which improves the single crystal quality,dielectric performance and piezoelectric performance of the single crystal LN thin film,thereby improving the effective electromechanical coupling coefficient and Q value of the FBAR resonator,and promoting the FBAR filter The development of frequency and wide bandwidth.