Etching Solution For The Mo/Al Film In TFT-LCD Wet Etch Process And Its Optimized Composition

In the process of thin film transistor liquid crystal display(TFT-LCD)array,there are many limiting factors for metal materials used in the fabrication of the gate and source circuits.Mo/Al metal layer is often used in the metal interconnection process to make conductive lines due to its strong adhesion and low resistivity.In this case,the metal layer needs to be processed into an application specification for the product.The Mo/Al etching solution contains phosphoric acid,nitric acid and acetic acid,and the etching taper angle is generally controlled between 40° and 60°.In practice,it is important to obtain a controllable shape of the metallic film on glass substrate after being etched.The roles of different acids in the Mo/Al etching solution are not clear so far.On the basis of the facts,The author conducted specific research on etching rate of Mo/Al metal,etching mechanism and optimization of taper angle of metal film,thus guiding practical production.The optimum concentrations of phosphoric acid,nitric acid and acetic acid were determined to be 65.28%,4.46% and 4.0% by orthogonal and electrochemical tests,respectively.According to the results of metal corrosion in monoacid and mixed acid,and the XPS results of aluminum film on glass,the corrosion mechanism of aluminum and the role of each acid were clarified.The results showed that phosphoric acid dissolves metal oxides,and that nitric acid oxidizes aluminum to oxide,and that acetic acid play the role of a corrosion inhibitior.In the investigation of molybdenum corrosion,the corrosion behavior of molybdenum in monoacid or mixed acids was studied by metal ion dissolution spectrophotometry and electrochemical measurement.The optimized concentrations of different acids for molybdenum corrosion were determined to be 66.99%,6.53%,and 3%,respectively.According to molybdenum corrosion and XPS results of molybdenum thin film on glass substrate,one can find that the simultaneous present of phosphoric acid and nitric acid is the necessary conditions for corrosion of Mo.In this process,nitric acid oxidizes molybdenum to its oxides,and phosphoric acid dissolves the metal oxides,and acetic acid is adsorbed on the surface of molybdenum as an inhibitor.In addition,hydrogen peroxide and PHA were tested in this process.It was found that the corrosion rates of aluminum and molybdenum could be effectively adjusted by adjusting the ratio of PHA concentration and nitric acid concentration.On the basis of the above results,the corrosion behavior of the Mo/Al film on glass was investigated.It was found that both reducing the concentration of nitric acid and increasing the concentration of acetic acid could improve the morphology of the Mo/Al film.A new etching solution with different ratios of nitric acid and PHA could effectively adjust the etched taper angle.When the concentration of phosphoric acid,nitric acid,acetic acid and PHA were in the range of 60%-70%,0.5%-3%,10%-15%and 3-8%,respectively,and the molar ratio of nitric acid to PHA was 1?2~4,the excellent corrosion taper angle of the Mo/Al on glass could be obtained.