Preparation And Properties Of Magnetron Sputtered Boron Carbide Thin Films

A series of excellent properties like high hardness,high melting point and oxidation resistance of boron carbide ceramics support wide applications in many industrial fields.Due to the advantages of low electron density,high laser damage threshold and radiation resistance,boron carbide films have potential applications in the optical field.Magnetron sputtering is the main method for the preparation of high quality boron carbide films.However,there are many adjustable process conditions in magnetron sputtering devices,which have a complex effect on the properties of films.For now,study on adjusting the optical properties of boron carbide thin films is still incomplete and the involving mechanisms are not so clear.Therefore,in order to prepare boron carbide films with excellent optical properties,it is of great significance to study the preparation and properties of magnetron sputtered boron carbide thin films.In this paper,the effects of sputtering power,working pressure,bias and deposition temperature on the microstructure,deposition rate,composition,mass density and roughness of the DC magnetron sputtered boron carbide thin films were carefully studied.The relationship between the microstructure,electronic density,roughness and optical properties of the films were analyzed.We designed a more reasonable calculation of optical constants and improved the preparation process of boron carbide thin films.The reflectance of boron carbide thin films was measured at 5?45 nm.The influence of the roughness on the reflectivity is small when the wavelength of incident light is much longer than the surface roughness.The reflectivity of columnar structure samples are lower than those of non-columnar structure samples,and the existence of columnar structure will lead to the decrease of reflectivity.When the films are dense,the reflectivity of the samples are positively correlated with the difference of their electron densities.The optical constant of the film is calculated by the reflectance test curve in multi-angle,and the relative error of the reflectance is used to replace the absolute error as the optimization function.The improved calculation method improves the accuracy of the optical constant calculation.The reflectivity of boron carbide thin films were measured at 0.154 nm.When all the samples have no obvious columnar structure,the difference of electronic density of the samples has little effect on the reflectivity,and the increase of surface roughness makes the reflectivity decrease.The effects of sputtering power,working pressure,bias and deposition temperature on the crystalline phase,microstructure and composition of the films were studied.When the deposition temperature is no more than 180?,the boron carbide films are all amorphous phase,which can not be crystallized by reducing the working pressure or increasing the bias.Compared with the microstructure and element composition of boron carbide films under different processing conditions,the effect of working pressure and bias on the microstructure is greater than that of sputtering power and deposition temperature,the decrease of pressure or the increase of bias is helpful to eliminate the columnar structure.The working pressure and sputtering power have the greatest influence on the B/C molar ratio and oxygen content of the film respectively.The peaks of the XPS spectra of the boron carbide films are similar,indicating that the basic components of the films are similar,and the films are composed of boron carbide and a small amount of oxygen-containing boron carbide.With a fixed sputtering power of 180 W and a deposition temperature of 25?,the preparation process of boron carbide film used for long wavelength rays was improved,and the effects of working pressure and bias on deposition rate,surface roughness and electron density of the film were studied in detail.The boron carbide films prepared at the working pressure of 0.2?0.5 Pa and the bias of-100?-150 V are smooth and dense,with strong bond with the substrates and clear interfaces.The deposition rate and electron density decrease with the increase of working pressure.At the bias of-100 V,the surface roughness of the films increase with the increase of the pressure;at the bias of-150 V,the roughness of the film change little and are similar to those of the substrates.Considering the electron density and roughness of the film,as a absorption layer,the ideal preparation process is sputtering power of 180 W,deposition temperature of 25?,bias of-150 V and working pressure of 0.2 Pa.At this time,the film B/C molar ratio is 4.62,the electron density is?699 e/nm~3,and the surface roughness is 0.52 nm.As a spacing layer,the ideal preparation process is sputtering power of 180 W,deposition temperature of 25?,bias of-100 V and working pressure of 0.3 Pa.At this time,the film B/C molar ratio is 4.25,the electron density is?674 e/nm~3,and the surface roughness is 0.47 nm.The preparation process of boron carbide film used for short wavelength rays was improved,and the effects of sputtering power,working pressure,bias and deposition temperature on film surface roughness were studied in detail.The roughness of the films prepared in the pressure range of 0.25?0.40 Pa and bias range of-100?-150 V are similar to those of the substrates.Under the fixed pressure of 0.35Pa and bias of-100 V,the surface roughness of the films first increase with working pressure and then decrease.When the deposition temperature increases from 25?to100?,the film roughness decreases.The ideal preparation process is sputtering power of 180 W,deposition temperature of 100?,bias of-100 V and working pressure of 0.35 Pa.At this time,the surface roughness of 200 nm thick thin film is0.69 nm.