Preparation Process And Properties Of Cu Films Deposited By Magnetron Sputtering On Polyimide Flexible Substrates

With the rapid development of electronic products in recent years,flexible electronic devices have broad application prospects.Flexible Copper Clad Laminate（FCCL）has the characteristics of high integration,high wire density,and flexibility was widely used in flexible electronic devices,such as flexible displays,skin-like flexible electronic biosensors,wearable sensing devices,and flexible memory devices.Compared with the traditional preparation methods,magnetron sputtering was widely used in the preparation of FCCL because of the controlled preparation process,high preparation efficiency and environmental friendliness.However,due to the poor adhesion between the polymer substrates such as polyimide（PI）,polyethylene terephthalate（PET）,polytetrafluoroethylene（PTFE）with Cu,FCCL is prone to failure when serving in complex environments.Based on this,this paper uses Magnetron sputtering technology to prepare Cu films on the surface of FCCL substrate and studies the effects of preparation process parameters,plasma etching treatment modification,metal interlayer design and substrate types on the relevant properties of Cu films.The main conclusions are as follows:（1）Cu films were directly deposited on PI substrate by Magnetron sputtering.The effects of sputtering power and deposition time on Cu film thickness,surface topography,resistivity and adhesion were investigated.The results show that the target power and deposition time in the magnetron sputtering process is positively correlated with the thickness of the copper film.With the increase of the target power and deposition time,the deposition temperature increases,the Cu film particles become larger,the density increases and the resistivity decreases,but the adhesion between the Cu film and the PI substrate decreases significantly.（2）The PI substrate was modified by Ar、Ar-H₂、Ar-N₂plasma and the copper film was deposited after the modification.The surface morphology,surface contact angle,surface energy,surface roughness and surface chemical functional groups of PI substrates were analyzed by three-dimensional microscopy,X-ray photoelectron spectroscopy（XPS）,Fourier transforms infrared spectroscopy（FT-IR）,surface contact angle,bulk microscopy,SEM,XRD,four-probe resistivity meter,scratch meter and cross-cut test.The effects of plasma etching on the surface morphology,surface contact angle,surface energy,surface roughness and surface chemical functional groups of PI substrates were also investigated.The changes in surface density,crystallinity,resistivity and bonding force of Cu films after plasma etching were investigated.It is found that the plasma etching treatment increases the surface roughness and surface energy of polyimide,which is conducive to the deposition of copper film and the formation of mechanical interlocking and chemical bonding at the interface to improve adhesion.It is found that the Ar-N₂ plasma etching can form C-N-Cu chemical bond between the substrate and copper film by XPS and infrared spectroscopy and the adhesion reaches 4B level.（3）The metallic interlayer（Ti、Nb、Ni）was introduced between the polymeric substrate（PI、PET、PTFE）and the Cu film.The effects of different substrates on the morphology,adhesion,and resistivity of Cu films on the surface were investigated.Study the effects of different metal intermediate layers on Cu films’density,adhesion and electrical resistivity.Research has found that the Cu film on the surface of PET substrate has the highest adhesion,while PTFE has the worst adhesion with Cu film.In addition,the introduction of a Ti metal intermediate layer increases the size of Cu film particles and reduces the resistivity,but is not conducive to the improvement of adhesion;The introduction of Nb metal intermediate layer has to some extent improved the adhesion between Cu film and substrate;The Ni metal interlayer can promote the densification of Cu film,and is conducive to the formation of Ni Cu solid solution at the interface to enhance the adhesion reached to 5B level.