Paper TF-WeP28
Inductively Coupled Plasma Reactive Ion Etching of CoFeB Thin Films Using a CH₃COOH/Ar Gas Mixture

Wednesday, December 10, 2014, 4:00 pm, Room Mauka

Magnetic random access memory (MRAM) holds the promise of replacing traditional memory devices such as DRAM, SRAM and flash memory. The MRAM device compared to its counterparts (DRAM, SRAM, flash memory, etc.), offers higher density, faster access time, unlimited read/write endurance and non-volatility. MRAM devices are mainly composed of a magnetic tunnel junction (MTJ) stack and CMOS.

In order to achieve high storage densities in MRAM devices, the pattern transfer in magnetic layers that comprise the MTJ stacks is a critical step. In the early stage of research, a wide range of etching gases such as HBr, Cl₂ etc has been employed for the ICPRIE of CoFeB thin films. In general, when using halogen gases, the etch rates are extremely high; but the sidewall redeposition and corrosion problems are common. Recently, an effort to improve the etching characteristics of magnetic layers, while at the same time reducing post-etching treatment, non- corrosive etching gases such as CO/NH₃, CH₃OH, CH₄ have been researched. The use of this etching gases mixed with Ar gas had to prove to yield a redeposition-free anisotropic etch profile despite the low etch rates compared to halogen gas mixtures.

In this paper the inductively coupled plasma etching characteristics of TiN hard masked CoFeB thin films was studied by using a CH3COOH/Ar gas mixture. A CH₃COOH solution was introduced into the chamber using a specially designed feeding system. The etch rates were obtained using a surface profilometer (Tencor P-1) and etch profiles were observed by using a field emission scanning electron microscopy (FESEM-HITACHI 4300SE). The surface chemistry and etch mechanism were analyzed by using optical emission spectroscopy (OES-Ocean Optics Maya 2000 Pro) and X-ray photoelectron spectroscopy (XPS).