Thermal Conductance And Structure Design Of Copper/Diamond Interface Investigated By Femto-second Laser Pump-probe Technique

High thermal conductivity materials used for heat dissipation of high-power chips and devices are essential materials for microelectronics manufacturing.As electronic devices are becoming high-integration,high-performance,and high-power,heat dissipation has become one of the bottlenecks restricting the development of high-performance microelectronics components.Therefore,heat dissipation materials with higher thermal conductivity are urgently needed.Metals such as Cu,Ag and diamond are materials with high thermal conductivity.The composite of them is expected to be a new generation of high thermal conductivity materials.The interfacial thermal conductance is mainly determined by the interfacial bonding strength and thermal carrier properties,which are closely related to the chemical and physical properties of materials on both sides of the interface.However,metals such as Cu,Ag and diamond are extremely different both chemically and physically,and the metal/diamond interface becomes the bottleneck of the thermal conductivity of composite materials.The regulation of interfacial thermal conductance between metal and diamond is a hot topic in this field.In this thesis,the interface formed by Cu and diamond,two materials with highly different properties,is taken as the research object.The interfacial structure is adjusted by inserting a metal or carbide interlayer at the interface,so as to regulate the interfacial thermal conductance.Techniques of focused ion beam(FIB),transmission electron microscope(TEM),Auger electron spectrometer(AES),and X-ray photoelectron spectrometer(XPS)are used to characterize the interfacial structure,and a femto-second laser pump-probe detection technique is employed to measure the interfacial thermal conductance.Thus,the relationship between interfacial thermal conductance and interfacial structure is established.The "sandwich" structure of Cu/X-metal/diamond was prepared on a single-crystalline diamond substrate by magnetron sputtering to study the structure design of the Cu/interlayer/diamond structure.The experimental results show that only metals(Cr,Mo)with acoustic property closer to diamond than Cu can improve the interfacial thermal conductance between Cu and diamond.Meanwhile,the interlayer with a thinner thickness is more advantageous to the heat transfer between Cu and diamond.The higher thermal conductance of the X-metal/diamond interface than the Cu/diamond interface is fundamentally important to the improvement of interfacial thermal conductance of the Cu/X-metal/diamond structure.The theoretical prediction shows that metal carbide is closer to diamond than Cu in acoustic property.As a result,metal carbide can effectively adjust the acoustic property mismatch between Cu and diamond,and then improve the interfacial thermal conductance between Cu and diamond.Carbonization of the Ti interlayer in a Cu/Ti/diamond structure is realized by heat treatment,aimed to study the effect of carbonization of the Ti interlayer on the interfacial thermal conductance between Cu and diamond.The results indicate that the carbonization of metal interlayer is a typical interfacial diffusion reaction,which is mainly controlled by the diffusion of carbon element.With the formation of TiC on the diamond surface,the interfacial thermal conductance of Cu/Ti/diamond sample increases gradually,and reaches the maximum value of 76 MW m-2 K-1 when the Ti interlayer is completely carbonized.Because the in-situ formed TiC can simultaneously improve the interfacial bonding and acoustic property mismatch between Cu and diamond,it is helpful to improve the interfacial thermal conductance.At the same time,the complete carbonization of Ti interlayer can avoid the introduction of more interfaces.Since the complete carbonization of the Ti interlayer for Cu/Ti/diamond structure is most conducive to the interfacial thermal conductance,magnetron sputtering is used to directly prepare TiC,and the microscopic characteristics of the TiC interlayer such as crystallinity,thickness,and grain size are varied to further regulate the interfacial thermal conductance.The experimental results show that the interfacial thermal conductance is increased by 48%by inserting a layer of 10 nm-thick crystalline TiC between Cu and diamond.The interfacial thermal conductance of the Cu/TiC/diamond structure is closely related to crystallinity and thickness of the TiC interlayer.As the TiC adjacent to the diamond surface is amorphous,the interfacial thermal conductance of the Cu/TiC/diamond structure is greatly deteriorated due to the poor thermal conduction of both the amorphous TiC and the amorphous TiC/diamond interface.However,as the amorphous TiC is converted to crystalline TiC and a semi-coherent interface is formed between TiC and diamond,the interfacial thermal conductance between Cu and diamond is greatly raised.In the thickness range of 10-160 nm investigated,the thinner TiC interlayer is more beneficial to the interfacial heat transfer between Cu and diamond.IVB group(Ti,Zr)and VIB group(Cr,Mo,W)metals are commonly used to modify the interface in Cu/diamond composites.Carbonization of the Mo interlayer in a Cu/Mo/diamond structure is realized by heat treatment,so as to compare the influence of carbonization of Ti and Mo on the interfacial thermal conductance between Cu and diamond.The carbonization of both Ti and Mo interlayers is controlled by the diffusion of C element on the diamond surface.Different from the Ti interlayer,the Cu/Mo/diamond structure exhibits the highest interfacial thermal conductance when only a small part of the Mo interlayer is converted into Mo2C.The maximum interfacial thermal conductance of 132 MW m-2 K-1 is obtained when a thin layer of Mo2C(<5 nm)is formed.Due to the catalysis effect of Mo,the surface of diamond transforms to graphite and finally fullerene is formed.The thermal conductance of the interlayer/diamond interface is thus weakened and then the interfacial thermal conductance of the Cu/interlayer/diamond structure is decreased.The in-situ formation of thin Mo2C interlayer can improve not only the acoustic property mismatch and interfacial bonding strength,but also avoid the formation of fullerene and reduce additional thermal resistance from the low thermal conductivity of Mo2C.The effect of the interlayer on the interfacial thermal conductance between Cu and diamond is clarified.The interfacial thermal conductance of the Cu/interlayer/diamond "sandwich" structure is closely related to the type,thickness,crystallinity,and carbonization of interlayer.The increase in thermal conductance of the interlayer/diamond interface is the key to improve the interfacial thermal conductance of the Cu/interlayer/diamond structure.The results promote the understanding of heat transfer mechanism of interface at which the acoustic properties of the materials on both sides are largely different,and provide a scientific basis for the enhancement of heat transfer of Cu/diamond interface and relating composite materials.