High Stability Copper Alloys Designed By A Cluster Model

Copper and copper alloys are widely applied in many fields due to their good electrical conductivity,thermal conductivity and processability.However,there are still many stability problems in actual applications,such as easy to interdiffuse with dielectric materials,easy to oxidize and can not nitride due to the easy decomposed copper nitrogen compounds.The usual way to solve these problems is by alloying,but most of the elements that can improve the stability of copper alloys have low solubility in copper.So it is difficult to achieve complete solution or dispersion by adding such elements individually.In order to tackle this problem,the stable solid solution cluster model is introduced to guide the alloying elements addition by cluster ratio.Then the amount of alloying elements is controlled according to the required stability for the service environments of copper alloys.Finally,several series of high stability copper alloys were designed and prepared.The main conclusions are as follows:1.By designing the alloy composition based on the stable solid solution cluster model and using the strong interaction between cluster atoms,the insoluble elements can be brought into the copper matrix lattice to achieve the complete solid solution.For the problem of interdiffusion of Cu and dielectric materials in interconnection structure,taking this model as a guideline,Ni which infinitely soluble with Cu was selected as the second element.Fe.Cr.V.Mo,Ti,Nb,Ta,Sn and Zr were selected as the third component M after fully considering the types of clusters that can be formed by the added elements,the mixing enthalpy.atomic size－electron concentration and ect.Then series of barrierless Cu-Ni-M thin films on silicon substrates were designed and prepared.The diffusion barrier elements M,which are insoluble or easily diffused in copper,are brought into the copper lattice via the help of Ni.The results show that the stability of Cu-Ni-M films is related to the atomic radius,valence electron number and diffusion characteristic of M.In addition to Fe as the third element,the stability of other systems can be improved with few amount of alloying elements added.The Cu-Si interdiffusion is inhibited and a low resistivity is obtained.Both experiments and thermodynamic calculation indicate that the stability and the resistivity of the annealed films are directly related to clusters ratio.When M/Ni ratio is around the ideal cluster ratio of 1/12.Gibbs free energy change of the system is the lowest and the best stability can be obtained.2.When the alloy composition design is guided by the stable solid solution cluster model:adjusting the alloying element addition ratio can effectively control its solid solution and precipitation in the alloy.Meanwhile the insoluble elements can be dispersed in the matrix by the strong interaction between cluster atoms.Based on this model,a high-stability anti-oxidation Cu-Ni-Cr(Cr+Fe)series alloys are prepared and the proportion of Cr(Cr+Fe)/Ni is adjusted to effectively control the solid solution and precipitation of the anti-oxidation elements.Through the strong interaction between Cr(Cr+Fe)and Ni,the antioxidant elements are dispersed in the matrix.The oxidation resistance experiment of Cu-Ni-Cr(Cr+Fe)alloys shows that the oxidation morphology of the precipitated phase will obviously affect the oxidation resistance of the alloys.For Cu-Ni-Cr alloys,the antioxidant resistance is mainly related to the formation of continuous Cr oxidation layer in the outer oxide layer,and the dispersed Cr in the alloy is beneficial to the formation of continuous oxidation layer.For Cu-Ni-(Cr+Fe)alloys,Fe can not play the role of preferential oxidation compared with Cr,and the precipitated oxides exhibit columnar structures which are arranged perpendicular to the matrix,forming a lot of oxygen diffusion channels,resulting in a sharp decline in oxidation resistance.3.The stable solid solution cluster model can achieve the solid solution and precipitation of multi-component alloying elements,and it is further extended to the design of high-stability nitrideable copper alloys.The nitrogenphilic elements are taken precedence over copper reacts with nitrogen to form a stable nitride due to the interaction between elements,which effectively avoid the problem of easy decomposition of copper-nitrogen compounds,and initially solves the problem that copper can not nitride.First,through the preparation and analysis of nitrogen-containing copper alloy films,it is confirmed that the strong interaction between the nitrogenphilic elements,such as dispersed Cr,Zr and Ti,can stabilize N as a compound such as Cr2N,Zr2N,TiN,and Ti2N,and then increase the hardness and stability of films.By further introducing the model in the design of the bulk nitrideable copper alloy,Cr is selected as the third element.Since Al can be dissolved in both Cu and Cr and is easy to combined with nitrogen,it is chosen as the second element,then the nitrideable Cu-Al-Cr alloys were designed and prepared.The strong interaction between Al and Cr can make the nitrogenphilic Cr diffusely distributed in the copper.Adjusting Cr/Al ratio can also control the content and the size of precipitated nitrogenphilic elements.After plasma nitriding,due to the strong interaction of N and precipitated elements,the stable and high hardness nitrides are formed,which help to improve the hardness and wear resistance of copper alloys surface.