Paper PS-TuP10
Surface Reactions of the Surfaces of CoFeB Films Etched in High Density Cl₂/Ar Plasma

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Magnetic random access memory (MRAM) has been developed for nonvolatile memory applications. MRAM does not need power for data-retention and relatively high speed for writing and read cycles. In addition, standby power for MRAM is low because the array leakage current is zero. MRAM consists of multi layered structure with diamagnetic/magnetic films. In order to produce high density MRAM, various structures can be achieved with using CMOS technology. Among front–end CMOS processes, the key technology to obtain high density MRAM is the etching process. The pattern transfer with smaller dimensions should be developed and optimized with using plasma etching process. Until now, the etching properties of CoFeB films in high density plasmas have not been well understood. The etch experiment were performed with using ion milling, RIE, ICP and ECR plasma. Ion milling sowed some problems such as re-deposition and low selectivity for small feature size of magnetic films. RIE etching process showed the problem of non-volatile etch by-products. The etch rates of CoFeB, CoSm, CoZr and FeMn in Cl₂ based chemistry, ICl and IBr chemistries were only reported. In Cl₂ based plasma, the highest etch rate obtained at 10% Cl₂ mixing ratio, but, the highest etch rates were can be obtained at higher ICl and IBr mixing ratio in IBr and ICl plasmas. However, they did not report the variation of components of CoFeB after etching process. In this study, CoFeB films were etched with using high density plasma system and Cl₂-based gas chemistries. Etch rate and selectivity of the CoFeB was systemically studied by the process parameters including gas mixing ratio Cl₂/Ar, RF power, DC-bias power, substrate temperature. The optical emission spectroscopy, Langmuir probe were used to monitor the behaviors of temperatures of electron and ion, energy of ion and radicals and volume densities for radicals. The etch rate of CoFeB were measured with using surface profiler. The etch rate behavior of CoFeB showed high dependent on the gas chemistry, RF power and DC bias voltage and pressure due to non-volatile etch by products. X-ray photoelectron spectroscopy analysis was used to confirm the etch rate behavior by evaluating the changes of atomic component from the surface of CoFeB after etching process. In addition, atomic force microscopy and scanning electron microscopy was investigated the changes of topology to confirm accumulation of etch by products.