Study On Initial Growth And Interfacial Properties Of Inlay Structure Diamond Films On Copper Substrate

Heat dissipation is one of the key factors restricting the development of modernmicro-electronic devices, and heat sink is an efficient method for heat dissipation. Diamondfilm on copper substrate is one of the most efficient heat sink for the combination of highthermal conductivity and low coefficient of thermal expansion （CTE）. However, due to thepoor wettability of diamond on copper substrate and the big CTE difference betweendiamond and copper, it is difficult to deposit diamond films onto copper substrate directly. Inorder to solve this key problem, Cu-Diamond composite interlayer with a tiny amount ofchromium was employed to improve the adhesion between diamond film and coppersubstrate.In the paper, the initial growth process of diamond films on inlay structured interlayerwas presented. And then, a mechanism of diamond films growth on inlay structured interlayerwas investigated. Influences of process parameters by hot filament chemical vapor deposition（HFCVD） on granule shape and its growing velocity of inlaid diamond films wereinvestigated. Cr was deposited on Cu-Diamond composite interlayer by mean ofelectrodeposited Cu-Cr post plating. In order to enhance the interfacial adhesion, theinfluences of electrodeposition current density and time on diamond film were alsoinvestigated.Early in the growth process, homo-epitaxial growth of diamond particles protruding outof the Cu-diamond composite interlayer were carried out, with increasing of time, theirregular shaped particles changes into facet diamond gradually, but grain grows slowly with asteady rate. Nucleation of secondary nuclei grains increases rapidly and further saturates, andthe rate could be up to107cm2. Average grow rate of secondary nuclei grains is0.5μm/h onoverall deposition stage.The mechanism of diamond films growth on inlay structured interlayer:Second diamondgrains preferentially nucleated at dihedral angle formed by homo-epitaxial growth diamondparticles and electroplating copper and the new dihedral angle between second crystal and copper promotes new second nuclei. This type of multiplying of second nucleation growthfinally fills in the gaps of the large homo-epitaxial diamond particles, leading to the formationof continuous diamond films.Cu-Cr interlayer with good level surface and dense crystal structure was obtained undera electrodeposition rate of50μm/h as the current density of10A·dm^-2. The portions of theparticles could serve as seeds for subsequent CVD homo-epitaxial growth after6min ofelectrodeposition, and continuous diamond films were formed. According to electro-probemicroanalyzer （EPMA）, the average content of Cr is about0.193at.%, Cr is distributed in theinterlayer homogeneously, means that Cr doping of Cu-Diamond composite coating isobtained successfully.With high temperature during the HFCVD process, the diffusion of Cu betweeninterlayer and substrate was carried out thoroughly. The result shows that disappearance ofinitial interface could lead to the reduction of interface thermal resistance.With the indentation testing with a load of441N, a spot of intermittent concentric crackswere observed in the periphery of indentation of diamond films on Cu-Cr coating. Doping atiny amount of Cr into the Cu–diamond composite interlayer is responsible for the muchenhanced the wettability and improved significantly interface adhesion between diamondfilms and copper substrate.