Research On The Inspection And Optimization Of Process And Process Flow For Pad Crystal Defect In Fabrication

Aluminum remains to be the construction material of external connection and bond pad in the 55 nm technology node,due to its well antioxidant and weld ability.But Aluminum bond pad still may be easily corroded by halogen elements,since its lack of protection from passivation layer and exposure to the outside environment.The pad crystal defect is a kind of crystal defect caused by the al pad corrosion of the fluorine,which may lead to failure of the wire bonding,and seriously affect the yield and reliability of the chip.Besides the influence of wafer transportation,packaging and chip assembling,the induction of fluorine to the aluminum pad in wafer manufacturing is one of the most important causes of pad crystal defect.In this paper,combined with the existing theory and research on the formation mechanism of the pad crystal at home and abroad,based on the 55 nm technology far backend process flow,we analyzes and probes into the process steps that may cause the crystal defect in wafer fabrication.Thus,three mechanism and model of the induction of the fluorine to the aluminum pad in fabrication is presented.For defect inspection problem,by comparison of BFI and DFI technology in theory and experiment,one optimized scan recipe base on BFI technology is given as the solution of defect inspection and monitor.In the research on the process optimization for the defect reduction,through batch experiment,two effective methods of process optimization for pad crystal defect are found.One method is replacing the anti-reflection film with SiON as Dielectric Anti Reflection Coating(DARC).Another method is replacing the cleaning chemical using in the wet clean process post cover etching with Dilute Sulfuric Peroxide(DSP).In the verification experiment of influence of backside clean process,the backside clean process after cover etching is proved to be able to volatilize the fluorine gas,which is one main reason of the induction of the fluorine to the bond pad.By canceling the backside clean step post the cover etching,the occurrence of pad crystal defect can be stopped effectively.Through the investigation mentioned above,this paper gives a systematic optimization of process and process flow and effective defect inspection solution,which is of great significance to prevent the pad crystal defect for the foundry.