Effect Of Anneal On The Microstructure Of Mo And Mo-Cu Alloy Films On Flexible Substrate

With the rapid development of flexible display,intelligent wear technology and solar cells,it is urgent to carry out the studies on the high performance flexible film materials.Molybdenum(Mo)and its alloy film because of its excellent corrosion resistance,electrical conductivity,thermal stability and good bonding strength with the substrate,has been used as electrode,wiring and barrier materials are widely applied in many fields such as solar cells and liquid crystal display.The previous researches on pure Mo film and Cu-Mo alloy films mainly focused on the rigid substrate,such as crystalline silicon and glass,there is few research on flexible polyimide(PI)substrates.In this paper,pure Mo,Mo-Cu and Cu-Mo alloy films were prepared with different thickness on the flexible polyimide(PI)and Si substrate by magnetron sputtering,the crystal structure,surface morphology and stress state of pure Mo film and alloy film before and after annealing were characterized by XRD,SEM,EDS,TEM and X-ray stress tester.The effects of Cu content,annealing temperature and film thickness on the micro-structure of Mo,Mo-Cu and Cu-Mo alloy films were systematically studied.Based on the experimental results,the formation mechanism of self-grown polygonal pure Cu particles and flower-shaped particles on the alloy films' surface was analyzed.The main results are as follows:1.Deposited Mo films showed Mo(110)orientation preferential growth.Mo(110)diffraction peak on PI substrate obviously shift to the high angle,indicating that there is residual compressive stress in the film.2.The Mo-Cu alloy films exhibited Mo(110)orientation preferential growth before and after annealing.During the annealing process,the supersaturated Cu atoms can suppress the growth of Mo grains in the alloy films.After annealing,the alloy films on the PI substrate are in compressive stress state.3.After annealing,a large number of uniformly distributed polyhedral or flower-type Cu particles grew spontaneously on the Mo-Cu alloy film surface,particle size ranges from several tens nm to several mm.Particle size and shape can be adjusted,the main determinant of size is the Cu content and the anneal temperature.Particle morphology showed a significant film thickness effect.4.The formation mechanism of pure Cu particles: to release the residual stress and reduce the system energy.Due to the stress release and the film internal energydriven,Cu atoms on the film surface diffuse along the grain boundary to the triple line boundary and gap to gather,nucleate and grow into Cu particles,the flower particles are the result of polygonal particle aggregation growth during the annealing process.5.After a certain temperature annealing,the Cu-Mo alloy film on the PI substrate forms a large number of polyhedral pure Cu particles,the formation mechanism is the same as that of Mo-Cu alloy film after annealing.