The Research Of MRAM Key Etching Process Optimization And Endpoint Prediction Method

Magnetic Random Access Memory(MRAM)is a novel storage memory,in which the information is stored based on the electron spin,with the benefit of non-volatile.It is a promising candidate for the next generation of universal memory solutions.In the thesis,two main aspects of the MRAM etching process are discussed and studied,including the integration density improvement and the etching endpoint prediction.Firstly,an optimized scheme of highdensity MRAM etching process is designed,which improves both etching angle on the sidewall of magnetic tunnel junction(MTJ)cell and the density of the memory array.Secondly,a prediction method is proposed to accurately predict the etching stop time under varying etching conditions.In this way,the etching endpoint can be predicted.The main content of the thesis includes:(1)The BEOL process of MRAM is introduced and reviewed.An analysis for the Micro Loading effect and Aspect Ratio Dependence Etching(ARDE)effect in the conventional MRAM etching process is conducted.The influences on the etching rate are studied.(2)An optimized scheme for high-density integrated MRAM etching process is proposed and designed,which is based on CMOS process without additional complex processes.By adjusting the partial orders of the deposition and etching processes,the micro-loading and ARDE effects are obviously suppressed.In this way,the MTJ etching rate is improved and the MRAM integration density is significantly promoted.The sidewall etching profile of the MTJ cell is also optimized.(3)A novel TCAD-based MRAM etching process simulation method is fulfilled.The conventional and the optimized scheme are both simulated in TCAD,which proves the feasibility of the optimized scheme in improving the integration density and the etching profiles.The simulation results demonstrate that the feature size and the bottom electrode diameter deviation become smaller,while bottom electrode spacing and sidewall angle become larger.For the in-plane and the perpendicular MRAM,it has achieved 79.1% and 46.7% improvement in terms of the integration density,respectively.For the in-plane and the perpendicular MTJ cell,it has achieved 5.5 ° and 3.8 ° in sidewall etching angle promotion,respectively.(4)A method is designed to predict the etching endpoint of the high-density MRAM.Theoretically analyzes on the effects of the ion angle and the ion energy on the etching rate are conducted.The simulations on the influences of the gas pressure,the self-bias voltage,and other experimental conditions on the etching rate are carried out.At the same time,the reason for the suppression of the etching rate at the bottom electrode is discussed.A model for predicting high-density MRAM etching stop is proposed.Finally,based on the above model,a scheme is designed to predict the etching endpoint.In this scheme,the threshold value of the relative etching rate change of the MTJ bottom electrode is used as the etching stop signal.By the model,effective detection of the etching endpoint with varied etching conditions can be realized.