Preparation And Characteristics Of Heavily Boron-doped Diamond Films

Heavily boron-doped diamond films with the high electrical conductivity have found their wider applications in the field of electrical and electrochemistry.The boron concentration,the surface morphology,the graphite and non-diamond phase and the orientation texture of boron-doped diamond thin films largely affects their electrical and electrochemistry properties.So it is important to study the influences of the growing parameters on the surface morphology and the structural properties of boron-doped diamond films.Boron-doped diamond films were prepared on silicon(100) substrate by hot filament chemical vapor deposition(HFCVD).Effects of boron concentration,methane flow,gas pressure and bias current on polycrystalline diamond films have been studied.The surface morphology and the structure of diamond films were analyzed by SEM,XRD,Raman and XPS.Resistivity of boron-doped diamond films was investigated by four-point probe method. The main work of this paper includes four parts,and the details are given below.(1) The influence of boron-doped concentrations on the growth characteristics and electrical properties of polycrystalline diamond films have been studied.The results show that an appropriate amount of boron doped is favorable for improving the qualities of diamond films,the grains have clear edges,the crystal shape tends to integrity,and the films have small amorphous carbon,while a heavily amount of boron-doped shows an opposite trend,the concentration of amorphous carbon increases with increasing of the boron concentration.In the Raman spectra of the films with high doping level,the peak at 1332cm^-1 shifts lower frequency,and appears the broad peak at 1220cm^-1.The residual stress is calculated by the peak at 1332cm^-1 shift.It is found that the residual stress of boron-doped polycrystalline diamond films increases with the increasing of the boron concentration.The results indicate that the resistivity decreases rapidly with the amount of boron doping increasing when the ratio of boron and carbon is less than 10000ppm,and decreases slowly when the ratio of boron and carbon is greater than 10000ppm.The resistivity reaches 1.12×10^-2Ω·cm.Results of XPS show that in the boron-doped diamond films,the boron bondings mainly exist in the forms of B₄C,BC_3.4,B-O.(2) The influences of methane flows on boron-doped polycrystalline diamond films are investigated.It is found that the secondary nucleation of boron-doped polycrystalline diamond films increases with the increasing of the methane flow,while the crystallinity presents opposite tendency.With the methane flow rate of 7.2sccm,the morphology becomes "cauliflower-like".The resistivity of boron-doped diamond film increases with the increasing of the methane flow.(3) Boron-doped diamond films were prepared using hot filament chemical vapor deposition with different gas pressures.With the gas pressure decreasing from 3kPa to 1.5kPa, the morphological and crystalline of boron-doped diamond films tend to improve,while the diamond films show an opposite trend with the gas pressure decreasing from 1.5kPa to 0.5kPa.(4) The influences of bias currents on boron-doped diamond films have been studied. The results indicate that an appropriate bias current is favorable for improving the qualities of diamond films,whereas highly bias current leads to increase the non-diamond phase in the films.