Etching Magnetic Tunnel Junction with Metal Etchers (original) (raw)
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Etch characteristics of magnetic tunnel junction stack using a high density plasma in a HBr/Ar gas
physica status solidi c, 2007
The etch characteristics of magnetic tunneling junction (MTJ) related materials such as CoFeB, MgO, FePt, Ru, and W as hard mask have been investigated as functions of rf pulse biasing, substrate heating, and CH 4 /N 2 O gas combination in an inductively coupled plasma system. When CH 4 /N 2 O gas ratio was varied, at CH 4 /N 2 O gas ratio of 2:1, not only the highest etch rates but also the highest etch selectivity over W could be obtained. By increasing the substrate temperature, the linear increase of both the etch rates of MTJ materials and the etch selectivity over W could be obtained. The use of the rf pulse biasing improved the etch selectivity of the MTJ materials over hard mask such as W further. The surface roughness and residual thickness remaining on the etched surface of the CoFeB were also decreased by using rf pulse biasing and with the decrease of rf duty percentage. The improvement of etch characteristics by substrate heating and rf pulse biasing was possibly related to the formation of more stable and volatile etch compounds and the removal of chemically reacted compounds more easily on the etched CoFeB surface. Highly selective etching of MTJ materials over the hard mask could be obtained by using the rf pulse biasing of 30% of duty ratio and by increasing the substrate temperature to 200 C in the CH 4 /N 2 O (2:1) plasmas.
The damage recovery process for magnetic tunnel junctions (MTJs) after methanol-(Me-OH) based plasma etch has been demonstrated. Me-OH and O 2 plasma, which contain oxygen in the molecule, caused unavoidable modification of magnetic materials in the MTJ stack. For example, the magnetization saturation and MR ratio decreased. H 2 base reductive plasma treatment was effective in recovering from this deterioration. No harmful side effects were observed in other aspects of MTJ performance such as MTJ resistance, hysteresis loop offset, and switching field. Heavier initial damage required a longer treatment time for recovery. Other types of reductive chemistry such as NH 3 plasma deteriorated the MTJ when the treatment lasted more than 15 s, probably due to nitridation. The use of a highly selective Ar/Me-OH etch process along with He/H 2 plasma recovery treatment is very promising for the MTJs' etch process to fabricate high-density magnetic random access memory (MRAM) and non-volatile logic devices. #
Inductively coupled plasma etching of Ta, Co, Fe, NiFe, NiFeCo, and MnNi with Cl2/Ar discharges
Korean Journal of Chemical Engineering, 2004
Dry etching of the magnetic thin films such as Ta, Fe, Co, NiFe, NiFeCo, and MnNi was carried out in inductively coupled plasmas of Cl 2 /Ar mixture. All the magnetic materials went through a maximum etch rate at 25% Cl 2. The effects of the ICP source power and the rf chuck power on the etch rate and the surface roughness were quite dependent of the materials. An ion-enhanced chemical etch mechanism was important for the magnetic films. The surface roughness of the etched samples was relatively constant of the rf chuck power up to 200 W, but a rougher surface at a higher rf power was obtained. Post-etch cleaning of the etched samples in de-ionized water reduced the chlorine residues substantially.
Characterization of a Time Multiplexed Inductively Coupled Plasma Etcher
Journal of The Electrochemical Society, 1999
We report the experimentally obtained response surfaces of silicon etching rate, aspect ratio dependent etching (ARDE), photoresist etching rate, and anisotropy parameter in a time multiplexed inductively coupled plasma etcher. The data were collected while varying eight etching variables. The relevance of electrode power, pressure, and gas flow rates is presented and has been found to agree with observations reported in the literature. The observed behavior presented in this report serves as a tool to locate and optimize operating conditions to etch high aspect ratio structures. The performance of this deep reactive ion etcher allows the tailoring of silicon etching rates in excess of 4 m/min with anisotropic profiles, nonuniformities of less than 4% across the wafer, and ARDE control with a depth variation of less than 1 m for trenches of dissimilar width. Furthermore it is possible to prescribe the slope of etched trenches from positive to reentrant.
IEEE Transactions on Magnetics, 2014
We demonstrated a self-aligned two-step reactive ion etching (RIE) process to pattern high density magnetic tunnel junction (MTJ) arrays. We did the RIE for the top electrode (TE) and stop in the middle of the tunnel barrier. A nitride conformal film was coated on the device pillars as a dielectric spacer. The conformal spacer protects the tunnel barrier from shorting by redeposition and provides a mask for the bottom electrode (BE) RIE. We used this process and completed perpendicular MTJ devices with our process flow. We tested the devices by measuring magnetic field switching and spin transfer torque switching. We get tunneling magnetoresistance (TMR) up to 100%, switching current as low as 60 µA at 100 ns, switching current density J c0 as low as 2.5 × 10 6 A/cm 2 and endurance above 10 9 for devices as small as 50 nm in diameter. The results are compared with devices from a TE RIE only process, and we find minimum damage was made by the BE RIE. We also discuss the size dependence of MTJ parameters such as TMR and free layer coercive field and offset field, which is very related to the RIE process.
Impact of metal etch residues on etch species density and uniformity
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2010
Uniformity and wafer-to-wafer reproducibility of plasma etch processes are often related to the conditioning of the plasma etch chamber walls. For advanced complementary metal-oxide semiconductor fabrication, numerous metals are used which might deposit on the chamber walls during etch processes and as these metals are not always straightforward to remove, process instabilities can occur. This happens because recombination of atomic species on the chamber walls determines to a certain degree the plasma composition. Therefore, in this article, the impact of metal etch residues, especially titanium and tantalum residues, on plasma composition and uniformity is studied. The chamber walls are analyzed by x-ray photoelectron spectroscopy analysis of so-called floating samples and the densities of Cl, Br, O and F in Cl 2 , HBr, O 2 , and SF 6 plasmas are monitored by optical emission spectroscopy. Plasma uniformity is checked by measuring etch rates across 300 mm silicon wafers. It is found that chlorine and bromine have similar recombination probabilities on the metals than on anodized aluminum. Fluorine and oxygen recombination, however, is strongly influenced by the presence of metal residues. Accordingly, for fluorine and oxygen based plasmas, metal residues showed to have an impact on the plasma uniformity.
Plasma etching: principles, mechanisms, application to micro- and nano-technologies
2000
Nowadays, plasma-etching processes are asked to produce patterns from the nanometer to the micrometer range with the same efficiency. The very severe requirements in terms of etch rate, selectivity, profile control and surface damage plasma-etching processes lead to, have been at the origin of the development of mechanistic studies by means of plasma diagnostics and surface analysis, as well as the development of new etching devices. We review here the basic concepts of plasma etching, and using examples, we describe more in details important features. We recall, in particular, the important role of the surface layer, the ion bombardment and the substrate temperature. q