Electrochemical Tuning Of Copper Grain Growth And Its Application For Electronic Interconnection

Copper circuits play the important role of electrical connection in electronic products.Nowadays,electronic products are developing in the direction of high integration and high performance.The width and line distance of the characteristic interconnection circuit of each module is reduced,and the circuit is required to have good physical properties.The physical properties of electronic interconnection are closely related to the growth of copper grains during electrodeposition.To achieve more flat co-plating of holes and lines,and to ensure the conductivity and ductility of copper coating has become the development goal of copper plating technology.Therefore,it is of great significance to study the effects of electrodeposition on the growth of copper grains.For better performance of copper electronic interconnection,this paper focuses on electrochemical tuning of copper grain growth.The specific research contents are as follows:(1)In the basic plating bath,the effects of temperature,current density and other factors on the regulation of copper grain growth were studied utilizing the orthogonal test method.The results of the orthogonal test showed that the temperature,current density,and chloride ion concentration had certain effects on the growth of copper grains through the metallographic micrographs,scanning electron micrographs and X-ray diffraction analysis.The current density has the greatest influence on the growth pattern of the copper grain.And in the appropriate current density range,the copper grain can form a fine and compact blocky polycrystalline structure.When the current density exceeds the acceptable range of the plating solution,the copper grains tend to grow multiple separated and slender columnar crystals at the same site at the same time.Raising the temperature and adding 50 mg/L chloride ions can increase the upper limit of current density that the plating solution can bear,and make the copper grains more uniform.(2)The computer software was used to simulate the multi-physical fields of the electroplating bath.According to the simulation,we can know the flow field and electric field distribution in the plate surface and THs(through-holes)of PCBs(printed circuit boards)during electroplating.What's more,we can tune the plating solution of the6000 L electroplating bath in the actual factory.After the plating parameters tuning,the plated copper layer has good uniformity,the standard deviation value of the plating thickness of the plate is less than 4%,and the horizontal and vertical extension rate of the coating reaches 25%.When applied to the THs electroplating with large aspect ratio(AR),we can also obtain good plating ability,in which the TP(throwing power)value of the THs with AR=8:1 can reach 89.3%,while the TP value of the THs with AR=10:1can reach 88.02%.(3)The effect of bath stability was studied by a follow-up test during continuous production in the factory.The acid copper plating solution has stable performance and good grain growth conditions when it is produced continuously for 15 days.However,due to the decomposition characteristics of organic additives,the properties of the plating solution changed after 3 months of continuous production.And the copper grains were more inclined to grow into coarse and loose columnar crystal copper coatings under the same electrodeposition parameters.After oxidizing by solid oxidant for 1 hour,the deteriorating bath turned better.The charring area of the Hull cell sample plate reduced16.7%,and the upper limit of the current density that the bath can withstand can be increased from 7.52 A/dm~2 to 8.35 A/dm~2.After oxidation treatment for 24 hours and re-adding additives,the properties of the plating solution can be restored.Based on the analysis of the experiments of solid oxidant in the bath treatment,a method for the on-line maintenance of acid plating copper bath was put forward.In summary,this paper studies the electrochemical tuning of copper grain growth and applies it to the continuous production of copper electronic interconnection in factories.