Fundamental Study On The Performance Of Phosphoric Acid Etching Solution For Cu/Mo Film

In the process of Array design for panel fabrication,gate circuit and source-drain?SD?circuit are selected according to the requirements of product.This process not only considers the performance of electrode materials such as resistivity and electron mobility,but also the cost of raw materials,technology and difficulty of manufacturing process.With the trend of large size,high resolution and high driving frequency of flat panel display,copper conductor will gradually replace aluminum conductor as electrode material in the preparation of thin film transistors.Due to the poor bonding between copper and glass substrate,molybdenum is generally chosen as transition film layer in technology.At present,copper conductor is widely used as the conductor of TFT,in which it is mainly treated with hydrogen peroxide-based etching solution,but the instability and explosiveness of hydrogen peroxide result into many problems in practical application.In this paper,the performance of phosphoric acid-based etching solution for copper was studied.The main components of phosphoric acid-based etching solution were phosphoric acid,nitric acid and acetic acid.The dissolution of copper in the solution of mono-acid,dibasic acid and ternary mixed acid were studied to confirm the role of components of the etching solution on the dissolution of copper.The results showed that the corrosion of copper could only occur under the combined action of oxidation and acidity.XPS analysis showed that nitric acid played an important role in the dissolution process of copper in the etching solution.Cu was oxidized to Cu₂O until CuO.Then CuO dissolved in phosphoric acid.The addition of acetic acid was beneficial to the oxidation of copper and promoted the dissolution rate of CuO.The dissolution behavior of molybdenum in phosphoric acid-based etching solution was studied.The influence of components of the etching solution on molybdenum dissolution was analyzed.The results showed that the dissolution of molybdenum also needed the concurrently interaction of phosphoric acid and nitric acid.It was found that nitric acid played a main role in the corrosion of molybdenum and that high concentration of acetic acid was beneficial to the dissolution of molybdenum.The dissolution behavior of copper/molybdenum film in phosphoric acid-based etching solution was studied on the basis of the above results.Electrochemical galvanic corrosion of copper/molybdenum happens in etching solution.In this galvanic cell system,copper is an anode and its dissolution rate increases.The influence of concentration of the component in ternary mixed acidic solution on galvanic corrosion current was investigated by time-current?i-t?method.The etching pattern of Cu/Mo film was characterized by scanning electron microscopy?SEM?.Finally,a optimized etching solution formula was obtained by a lot of experiments,The optimized etching solution composition was as follows:phosphoric acid 30-45%,nitric acid 1%-3%and acetic acid 30%-40%,at which the excellent taper angle could be obtained to meet the production process requirements.