Study On Preparation Of Cu Film By High Power Impulse Magnetron Sputtering Technology On Polyimide Surface

The flexible printed circuit board is a copper circuit etched on a polymer substrate.Compared with the traditional wire harness method,its weight and volume can be reduced by more than 70%.In recent years,the electronics industry has developed rapidly,and electronic products have further developed towards portability,miniaturization,light weight,and high-density assembly.Therefore,the output demand for flexible printed circuit boards is increasing,and the performance and process requirements are increasing.As a core substrate in the field of flexible electronics,flexible copper clad laminates have the characteristics of static bending and dynamic repeated bending.The improvement of each performance has an important impact on the performance improvement of high-end electronic products.Compared with the three-layer flexible copper-clad laminate(3LFCCL),the two-layer flexible copper-clad laminate(2L-FCCL)does not have an adhesive layer between the copper foil and polyimide.It has obvious advantages in flexibility and long-term reliability and is welcomed by the market.However,domestic production enterprises(including Taiwan-funded enterprises)mostly produce 3L-FCCL,so research on the production process,conductivity,reliability,etc.of 2L-FCCL has become an urgent task.In this study,high power impulse magnetron sputtering technology was used to deposit a Cu film on polyimide film(PI)to prepare high-quality 2L-FCCL.In this paper,the discharge characteristics of the Cu target under high power impulse magnetron sputtering technology are first studied,and then the plasma composition,quality and energy distribution are analyzed.On this basis,the effects of deposition pressure,average power,peak power,and film thickness on the deposition rate film resistivity,and residual stress of the prepared Cu film were studied.The surface morphology and structure of the film were analyzed by SEM,AFM,XRD and other testing methods.The study of the discharge characteristics of Cu target shows that when the working pressure increases from 0.2 Pa to 0.4 Pa,the target current value also increases from 29.1 A to 37.6 A.When the working pressure continues to increase from 0.4 Pa to 1.6 Pa,the target current changes less and it is only increased to 41.9 A;in the process of increasing the discharge voltage from 500 V to 650 V,the target current increased almost uniformly from 11.2 A to 30.4 A;when the pulse width was less than 125 ?s,the target current gradually increased(50 ?s / 18.1 A,75 ?s / 28.8 A,125 ?s / 39.7 A),when the pulse width continues to increase,the target current is basically unchanged(150 ?s / 39.8 A);the increase in pulse frequency promotes the increase of the target current.When the pulse frequency is from 50 Hz to 400 Hz,the target current increases from 36.0 A to 39.2 A.The study on the preparation process of Cu film found that the average current and the peak current both increase with the increase of the working pressure,and have the same trend.After the working pressure is greater than 1.0 Pa,they gradually stabilize.The deposition rate increases evenly with the increase of the average power(the deposition rate is only 17.3 nm/min at 161 W,and the deposition rate increases fourfold to 69.2 nm/min when the deposition rate reaches 651 W).The deposition rate decreases with the increase of working pressure and peak power(with a deposition rate of 37.0 nm/min at 0.5 Pa,it drops to 32.6 nm/min at 0.65 Pa and then basically stabilizes).The deposition rate is 44 nm/min when the peak power is 6.05 k W,and quickly decreases to 28.9 nm/min when 40.8 k W.Film resistivity has a smaller value when it is at a lower working pressure(0.6 Pa/ 4.2 ??·cm),higher average power(497 W / 7.8 ??·cm,651 W / 6.9 ??·cm),higher peak power(29.3 k W / 7.8 ??·cm)and thicker films(when the film thickness is greater than 6 ?m,the resistivity of the film is less than 5 ??·cm).Residual stress is influenced by the deposition gas pressure,average power,and peak power,and there will be a conversion between tensile stress and compressive stress.XRD data show that the Cu films prepared under different process parameters have two typical characteristic peaks(111)and(200),showing the preferred orientation of the(111)crystal plane,indicating that the film has a good crystallization rate.