Study Of Contact Process Defect Inspection And Improvement In 28nm Technology Node

With the development of semiconductor manufactory technology,the transistors become smaller and smaller to meet the requirement of high performance and low power.The shrinkage of critical dimension makes the big challenge to the manufactory,and the defects become the major factor of yield impact.The function of contact is to connect front-end device and backend metal line,and the defective contact affect the connection of circuit and the working state of device directly.It is the critical process in semiconductor manufacturing.Because of defects appearing at the bottom,the only way to find the defects is by using electron beam inspection to detect high electric resistance.This study aimed at three kinds of contact process defects,which are contact deformation defects,contact connection failure defects and contact void defects.Firstly,the paper discussed the method of electron beam inspection to detect the contact defects.The recipe with high sensitivity was setup by image analysis and defects capture rate experiment.Base on that,contact process has been optimized to solve the three kinds of defects,including lithography,etching,cleaning and metal filling.In order to analysis the defect image under electron beam,collect the defect image under the different landing energy,current and additional electric field.It turns out,when the landing energy reached2000 e V,the NMOS contact and PMOS contact displayed the different brightness,and the defective contact was brighter than normal;when the current reached 65 n A or 100 n A,the defective contact showed the maximum difference with the normal contact;the best range of additional electric field was-2028 e V to-2038 e V,in this period,the image resolution was good enough.Base on the result of image analysis,inspection experiment has been arranged to get the accurate parameters.Finally,the best conditions were chosen as 2400 e V landing energy,100 n A current and-2032 e V additional electric field,which can be used to capture the maximum number of contact defects.In addition,the mechanism and improvement of three kinds of contact defects has been analyzed and experimented.Found that the contact deformation defects are related with lithograph,which could be great improved by process control and plasma treatment.And the contact connection failure defects are caused by etching process.The defects could be solved by selecting CF4 as etching gas,initial layer over etching10%,anti-reflective layer over etching 5% and main etching over 5%.The major factors of contact void defects are cleaning and metal filling process.The Reaction by-products from etching process could be remained easily in the bottom of contact.The defects could be removed by adding 90 seconds post etching treatment,extending cleaning time and purging N2 into the pod.Through the above research,the solution of 28 nm contact defects inspection method and process improvement has been established;it has great significance to the semiconductor manufactory technology step forward.