Selective Etching of Magnetic Tunnel Junction Materials Using CO/NH₃ Gas Mixture in Radio Frequency Pulse-Biased Inductively Coupled Plasmas

Abstract

The etch characteristics of magnetic tunneling junction (MTJ) materials and the etch selectivity over W have been investigated using RF pulsebiased conditions in addition to the continuous wave (CW) bias condition with a CO/NH 3 gas combination in an inductively coupled plasma system. By using a time-averaged substrate DC bias voltage condition for the RF pulse biasing, the etch rates of MTJ materials for the RF pulsebiased conditions were generally similar to those etched using the CW RF bias condition even though the etch rates were slightly decreased with decreasing the duty percentage of the RF pulse biasing. However, the use of the RF pulse biasing improved the etch selectivity of the MTJ materials over mask materials such as W. When the surface roughness and the residual thickness remaining on the etched surface of the MTJ material such as CoFeB were investigated by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively, it was clear that the use of the RF pulse biasing instead of CW RF biasing also decreased the residual thickness and the surface roughness. This is believed to be related to the formation of a more uniform chemically reacted layer on the etch CoFeB surface during the RF pulse-biased etching condition.

Etch residue removal of CoFeB using CO/NH3 reactive ion beam for spin transfer torque-magnetic random access memory device

“…1(b) shows the scanning electron microscopic (SEM) images of a) Electronic mail: gyyeom@skku.edu the CoFeB samples with sidewall residue used in the experiment. 20 The width of the etched CoFeB feature masked with W (that is, W/Ti/Ru) was 67 nm, and the height of the CoFeB feature with the remaining W mask was 141 nm.…”

“…Even though these techniques have improved the etch characteristics of the MTJ materials, some of the etch residues still remain on the surface and the sidewall of the etched features. 20,21 In this study, after the etching of the CoFeB cells with W hard mask using a conventional ICP system, as a method to remove the sidewall residue remaining after the main etching, reactive ion beam etching (RIBE) is applied, and the effect of CO/NH 3 etch gas and the RIBE parameters on the removal of the sidewall residue is investigated.…”

Etch characteristics of magnetic tunnel junction materials using substrate heating in the pulse-biased inductively coupled plasma

“…These materials and the patterned CoFeB were etched using CO/NH 3 gas combination with fixed flow rates of CO and NH 3 at 12.5 and 37.5 sccm, respectively, for effective chemical reactions. 16 The ICP source power of 500 W and DC bias voltage of À300 V (time-averaged DC bias voltage) were used to etch the MRAM-related materials. During the rf biasing, time-averaged DC biasing was used to compensate the decrease of etch rates by the pulsing.…”

“…Previously, a pulse-biased inductively coupled plasma (ICP) technique was investigated to increase the volatility and stability of the metal compounds between MTJ materials and noncorrosive etch gases such as CO/NH 3 by applying pulsed rf power to the substrate while the ICP source power was continuously applied to the plasma. 16 By using the pulse-biased ICP technique, the etch selectivity of MTJ materials over W could be improved with decreasing the pulse duty percentage. The surface roughness and residual thickness of the etched CoFeB surface were also decreased with the decrease of the pulse duty percentage possibly due a) Author to whom correspondence should be addressed; electronic mail: gyyeom@skku.edu to the formation of more volatile and more stable etch compounds during the pulse-off time.…”

Progress and prospects in nanoscale dry processes: How can we control atomic layer reactions?

“…The etching of metals also has the problem of the redeposition of etching by-products. 12,[188][189][190][191][192][193][194][195][196][197] In self-limiting formation, another difficulty arises for intermetallic compounds or alloys such as CoFe, NiFe, CrFe, and PtMn. Simply, in etching processes for compounds such as high-k materials, dichalcogenides, GaAs, GaP, and GaN, it is difficult to maintain the surface stoichiometry during and after the etching.…”