类金刚石薄膜在硅基底上的沉积及其热导率

Deposition and thermal conductivity of diamond-like carbon film on a silicon substrate

采用分子动力学方法模拟了碳在晶体硅基底上的沉积过程,并分析计算了所沉积的类金刚石薄膜的面向及法向热导率.对沉积过程的模拟表明,薄膜密度及sp^3杂化类型的碳原子所占比例均随沉积高度的增加而减小,在碳原子以1 e V能量垂直入射的情况下,在硅基底上沉积的薄膜密度约为2.8 g/cm^3,sp^3杂化类型的碳原子所占比例约为22%,均低于碳在金刚石基底上沉积的情况.采用Green-Kubo方法,计算了所沉积类金刚石薄膜的热导率,其面向热导率可以达到相同尺寸规则金刚石晶体的50%左右,并且随着薄膜密度与sp^3杂化类型碳原子所占比例的升高而升高.

Diamond-Like Carbon（DLC） is thought to be a potential material in solving heat dissipation problems in light emitting diode module packages.It is of vital importance in evaluating the thermal conductivity of DLC film deposited on a silicon substrate.In this paper,the molecular dynamics method is used to simulate the formation of a DLC film by the deposition of carbon atoms on a isilicon substrate.Tersoff potential is adopted to reproduce the structures and densities of silicon,carbon,and Si C.A silicon substrate consisting of 544 atoms is located at the bottom of the simulation domain.The substrate is kept at a temperature of 600 K through a Noose-Hover thermostat.Carbon atoms are injected into the substrate individually every 0.5 ps at an energy of 1 e V.After a 7.5 ns deposition process,a 4 nm amorphous film containing 15000 carbon atoms is formed.Injected carbon atoms and substrate silicon atoms are intermixed at the bottom layer of the deposited film while the rest of the film contains only carbon atoms.The density of the film decreases slightly with the increase of the height of the deposited film and the average density is 2.8 g/cm^3.Analysis of the coordination number shows that the sp^3 fraction of carbon atoms in the film also decreases with the increase of the height of the deposited film,with a maximum value of 22%.It might be caused by the continuous impacts of the subsequently injected carbon atoms on the previously formed DLC film.The thermal conductivities of the DLC film in the planar and normal directions are calculated by the Green-Kubo method.The thermal conductivity of pure diamond film is also calculated for comparison.The results show that the planar thermal conductivity of the deposited DLC film is approximately half of that of the pure diamond film with the same size.It is higher than the normal thermal conductivity of the deposited film.The thermal conductivities of the DLC film in both planar and normal directions increase with the increase of film density and sp^3 fraction in the DLC film.The results indicate that the local tetrahedral structure of sp^3 carbon atoms contributes to the improvement of thermal conductivity in the DLC film.