Analysis And Optimization Of Failure Issues Of 3D Nand Common Source Structure

As the process size continues to shrink,two-dimensional flash has encountered the bottleneck of scaling.The emergence of three-dimensional flash memory offers new opportunities to further increase storage capacity.Among them,the Terabit Cell Array Transistor(TCAT)architecture using the gate-last technology has become one of the hot spots in the research of 3d flash memory architecture because of high integration and small operation interference.In the TCAT architecture,common source lines exist as tungsten walls.The long and narrow common source line divides the core array,reduces the control gate area and reduces the operation disturbance.But at the same time,the core array may be a failure by the structural defects of the large-volume common source structure.Through electrical failure analysis and physical failure analysis,this paper presents failure models for the failure caused by common source structure defects,and then presents a process optimization scheme based on the experimental results.The article mainly discusses:(1)The failure mechanism of programming interference caused by metal diffusion at the bottom of common source line is proposed and verified by simulation.In the process of programming,due to the necessary common source voltage bias,the diffused metal charge the substrate,reduces the channel self-boosting level of the program suppression unit,and produces programming disturbance.The causes of metal diffusion at the bottom of the common source structure were investigated,and the splitting experiments were carried out on the process steps such as pre-cleaning of glue layer deposition,glue layer deposition and thermal annealing after tungsten deposition.Section results and measurement data show that pre-cleaning etching damages the structure profile,and the metal is Thermal excited and diffused during annealing.(2)For the problem of word line leakage caused by the cracking of common source structure,the failure model of common source line cracking is proposed.HF produced in the process of tungsten deposition,and the HF left in the deposition filling void overflowed,damaged the top oxide layer and the side wall oxide layer of the common source structure,resulting in structural cracking.By changing the etching conditions,the smooth trapezoid deep groove profile is obtained,the filling condition of deep groove is optimized,and the filling cavity is reduced.The quality of oxide is improved by changing the deposition condition of oxide on the side wall,so as to resist the damage and stress and optimize the word line leakage.