Study Of The Deposition And Patterning Technology Of Low Residual Stress Boron-doped CVD Diamond Film

CVD diamond films have excellent properties such as high hardness,high thermal conductivity,good chemical stability and biocompatibility.The CVD diamond film is insulating and can be conductive with the doping process.The conductive CVD diamond film MEMS sensor field has broad application prospects.Boron-doped CVD diamond films inevitably have residual stress,and large residual stress can cause structural instability,bending or even fracture of MEMS sensors.Therefore,the study of low residual stress CVD boron-doped diamond film preparation process for the manufacture of high-performance MEMS sensor has important theoretical significance and practical value.The structure of micro-cantilever beam with boron-doped diamond film has been widely used in MEMS sensors.It is a key structure in accelerometers,AFM probes and cantilever microbial sensors.The results are influenced by the residual stress with low precision,poor performance,low pass rate and other issues.In this paper,a low residual stress CVD boron-doped diamond film was successfully fabricated by optimizing the deposition process parameters,and a CVD-doped boron-doped diamond thin film micro-cantilever was fabricated by patterning technique and its properties were tested.The main contents of this paper are as follows:The theoretical calculation formula of the thermal stress variation of boron-doped diamond films with silicon based on temperature was deduced.The contact model between diamond film and silicon substrate was established.The transient process and static structure analysis module were used to simulate the film cooling process.The deformation and surface temperature field of the film were analyzed with time.The effects of pretreatment process,film thickness and deposition temperature on the steady thermal stress were analyzed.The distribution of thermal stress in the direction of film thickness and radius were studied.The results show that the higher the deposition temperature is,the lower the thermal stress of boron-doped CVD diamond film is.The shape of CVD diamond-doped diamond film exhibits from concave to convex during cooling,and the film surface temperature distribution is uniform;increasing the film thickness and the deposition temperature can reduce the thermal stress of the film after cooling.The diamond films were deposited on the silicon wafer by hot filament CVD technique.Raman and X-ray diffraction techniques were used to measure the residual stress of the diamond films.The influence of reaction pressure,the carbon concentration,bias current and boron concentration on the residual stress of CVD diamond films were studied.The optimized deposition process parameters of boron-doped diamond films with low residual stress was proposed.The results show that the residual compressive stress of diamond films decreases first and then increases with the increase of reaction pressure,and the residual compressive stress is the lowest as-314 MPa under the reaction pressure of 3.9 kPa.The higher the concentration of carbon source is,the higher residual compressive stress of diamond films is.The residual compressive stress value of the diamond film decreases first and then increases with increase in bias current value.When the bias current is 5 A,the residual compressive stress value of the diamond film is the smallest,which is-209 MPa.The higher the boron source concentration is,the bigger the residual compressive stress of diamond film is.When the boron source concentration is 1000 ppm,the residual compressive stress of the diamond film is the smallest,which is-209 MPa.Deposition parameters were optimized as following:reaction pressure is 3.9 kPa,the carbon source concentration is 2.20%,the bias current is 5 A and the boron source concentration is 1000 ppm.Using this combination of parameters,the relatively low residual stress CVD boron-doped diamond film can be prepared.A variety of graphics on lithography mask were designed.The micro-cantilever structures,angular acceleration measure structure,micro-filters and acoustic diaphragms were successfully fabricated by means of conductive seed layer fabrication,lithography,electroplating,reactive ion etching and wet etching.The resonant frequency and the quality factor of the cantilever beam were measured and calculated by the Doppler effect.The damping characteristics of the cantilever beam structures are compared and analyzed based on the theoretical model of the cantilever beam.The results show that the resonant frequencies of U-shaped cantilever and V-shaped cantilever are similar,but the quality factor of U-shaped cantilever is higher than that of V-shaped cantilever,and the system damping coefficeint of U-shaped cantilever is smaller than that of the V-shaped cantilever.