Reduction Of Metal Recrystallization And Pitting In Aluminum Etching Process

Aluminum （Al） has been widely used as electronic interconnection material, especially applied in semiconductor metal interconnection and bonding pad due to its property of low cost, low resistance, good electric conductivity, easiness of depositing and etching.But Al has the week points, such as reacting with silicon to form spike and poor anti-migration property. To enhance the reliability of Al, currently semiconductor manufactory mostly adds silicon （Si） and copper （Cu） into Al to deposit the metal film. Usually the percentage is 1% Si and 0.5% Cu by weight.When the Al-Si-Cu alloy film is etched by chloride gas, chlorine ions, fluorine ions or AlCl₃ will remain on the film surface. The remaining will react with water vapor in air and form metal crystal, pits and corrosion defects. The defects impact the flatness and reflectivity of metal film for high resolution LCOS （Liquid Crystal On Silicon）, the yield of bonding pad during wafer assembly and testing. It also cause reliability issue of product.In this paper, we will analyze the morphology and the composition of metal crystal and pit defects by OM, SEM, AES and TEM, probing the formation mechanism and testifying it by experiments. Four kinds of effective solutions, i.e., increasing wet clean time, forming the densified Al₂O₃ on the pad surface, adjusting the PH value of clean solvent, and tightening the control of warehouse environment, have been proposed and demonstrated. The optimized experiment has shown that the fluorine concentration on the pad surface can be reduced to 1.7% and the Al₂O₃ thickness is only 30～36A. Metal crystals and pits on the Al pad are not found even after 500 hours exposure in air. Besides, through the analysis of the metal defect formation mechanism, an optimized wet cleaning process has been found, which can both avoid the pad crystal formation and suppress the metal pits formation. These are valuable for volume production.