Microstructure And Properties Of Metal Films Prepared By DC/High Power Pulsed Magnetron Co-sputtering

Copper（Cu）and tantalum（Ta）films are widely used functional materials with strong stability and reliability in the interconnection structure of integrated circuits.Cu has excellent characteristics: ductility,thermal stability,electromigration resistance,electrical explosion performance and low resistivity,which has superior application prospects in semiconductor,electrical explosion,new energy,photoelectric,decoration and so on.Ta film with excellent physical and chemical properties is used as a classy interdiffusion barrier between copper and silicon or silicon dioxide.Stable α-Ta at high temperature with good ductility and low resistivity has no adverse reaction with Cu,which is widely used in integrated circuit,gun barrel protective coating,wear resistance and corrosion resistance.The structure,orientation,morphology and properties of Cu and Ta fioms are regulated by preparation technology and process parameters.It is of great significance for the application and development of metal films and has also become the focus of our research.In the paper,DC magnetron sputtering（DCMS）and high power pulsed magnetron sputtering（Hi PIMS）were combined as DC / Hi PIMS co-sputtering to prepared Cu films,Ta films and Cu-Ta films on Si surface.Cu,Ta and Cu-Ta films with structures,morphologies and properties were explored by regulating DC power,substrate bias,and compared with pure DCMS and Hi PIMS.The structure and orientation all films were studied by grazing incidence X-ray diffraction（GI-XRD）.Field emission scanning electron microscope（FE-SEM）,white light interferometer and atomic force microscope（AFM）were used to characterize the morphology and roughness of all films,as well as the section elements of Cu layer in Cu-Ta films by EDS.The hardness of Cu and Ta films were revealed by nano indentation test in continuous stiffness mode.The resistivity of Cu film and Ta film were promulgated by four probe resistivity test.The results showed that:（1）The structure and properties of DC/Hi PIMS co-sputtered Cu films at different substrate negative bias voltages（0～-100 V）were tremendously effects.With the increase of negative bias voltage,the grain size first decreased and then increased,the hardness increased,the preferred orientation strength and resistivity decreased.Under high negative bias voltage,the preferred orientation was changed.And the films were with higher compactness and hardness,lower roughness and resistivity because of higher ion energy.Compared with Hi PIMS films,the co-sputtered copper films had higher hardness and lower resistivity under high negative bias.The flux and energy of sputtered copper ions were determined by Hi PIMS participation and negative bias jointly,and dominated the structure and properties of copper films.（2）Different DC power played an important role in controlling the structure and properties of Ta films.The results showed that the ratio of Ta ion to neutral particle in DC/Hi PIMS co-sputtering was closely related to DC power.The unstable arc discharge was averted and the deposition rate was improved in co-sputtering.The α-Ta films deposited by co-sputtering had lower roughness,better compactness and hardness than that of DCMS films.Therefore,the fine grains,smooth surface roughness（3.22nm）and low resistivity（38.98 μ Ω · cm）,high hardness（17.64GPa）of pure α-Ta films produced by one-step method in DC/Hi PIMS co-sputtering were achieved.（3）Preparation of Cu-Ta films.Ta films with dense,uniform and fine grains deposited by DC/Hi PIMS co-sputtering were a mixed phase structure（α+β）at a thickness of 100 nm.Cu-Ta films were annealed at 200 ℃ and 600 ℃ after Cu films prepared on the Ta films surface.It was found that the high crystallinity,fine and dense grains,smooth surface of Cu films at low temperature（200 ℃）were found.And there was no Ta and Si diffusion in Cu layer.At high temperature（600 ℃）,the phase transformation of co-sputtered Ta film occurred.The abrupt particles with large size on Cu layer in Cu-Ta films were formed for recrystallization,which leads the roughness increase and Ta and Si diffusion in Cu layer.Ta and Si elements in Cu layer were detected by EDS,while no similar phenomenons were found in XRD results.Thus,the results were of great constructive significance for continuing to explore Ta films as Cu/Si diffusion barrier.Above all,the structure control and performance improvement of Cu and Ta films can be effectively realized by DC/Hi PIMS co-sputtering.There were compact and uniform structure,and excellent mechanical and electrical properties for the Cu and Ta films in DC/Hi PIMS co-sputtering.In addition,Cu/Si interdiffusion can effectively prevented by the co-sputtered Ta films at low temperature,which is expected to meet the needs of very large scale integration（VLSI）.