Journal of The Electrochemical Society, 159 (7) D447-D454 (2012) D447 0013-4651/2012/159(7)/D447/8/$28.00 © The Electrochemical Society Composition Gradients and Magnetic Properties of 5–100 nm Thin CoNiFe Films Obtained by Electrodeposition Jie Gong, * Steve Riemer, Augusto Morrone, Venkatram Venkatasamy, Michael Kautzky, and Ibro Tabakovic *, z Seagate Technology, Research and Technology Development, Bloomington, Minnesota 55435, USA The composition gradient and properties of magnetic 5–100 nm thin CoNiFe films electrodeposited on Cu or Pt substrate were studied. It was found that the average elemental composition of CoNiFe, obtained by ICP analysis, changes during electrodeposition. The extent of anomalous co-deposition achieved at deposit thickness <100 nm was found to be several times larger than in thicker CoNiFe films. The partial current densities for all three metals (Co, Ni, Fe) increase during the time of electrodeposition and gives rise to stable value when the thickness reaches about 100 nm. The partial current density for hydrogen evolution decreases and becomes stable at the thickness >100 nm. The observations related to the experimental results could be explained through a modified Bockris- Drazic-Despic reduction mechanism. The time-dependent dynamics of roughening surface exhibits two characteristic regions, i.e. the first with fast roughening at the thickness <100 nm and the second with slow roughening at the thickness >100 nm. The stress evolution show typical compressive-tensile-compressive behavior in the thickness range 5–100 nm. The crystal structure of 20 nm CoNiFe films is mixed fcc + bcc crystallites with the larger grain size close to the substrate while thick films show fcc-rich structure. The mechanism of coercivity in CoNiFe films is governed by magnetoelastic anisotropy and follows Neel’s thickness dependence relation, i.e. H c = ct −n . The “volcano” type of H c -t curve obtained at 5–50 nm was explained taking into account: change of composition, stress, crystal structure and roughness. © 2012 The Electrochemical Society. [DOI: 10.1149/2.082207jes] All rights reserved. Manuscript submitted March 23, 2012; revised manuscript received April 19, 2012. Published July 17, 2012. This was Paper 2018 presented at the Las Vegas, Nevada, Meeting of the Society, October 10–15, 2010. Electrochemically prepared 1.8T CoNiFe ferromagnetic alloys have been used as a write pole material in longitudinal recording heads as relatively thick films. The hysteresis curves of 500–1000 nm thick CoNiFe films, with low magnetostriction (λ s = 2–4 × 10 −6 ) and stress (σ< 300 MPa), indicated a soft (H c < 2.0 Oe) and anisotropic behavior (M r /M s ∼ 0). 1 Because of their excellent magnetic properties thick CoNiFe films are currently used as a Shield and Yoke material in perpendicular recording heads. For other possible applications like MRAM (Magnetic Random Access Memory) ultra-thin films (a few atomic layers thick) 2 or thicker layers of CoNiFe could be an option. Electrodeposition of CoNiFe alloys with saturation magnetic flux density, B s = 1.6 −2.1T, was usually carried out using acidic chloride, 1,3,4 chloride/sulfate, 5–9 and sulfate solutions 10–13 with the presence of H 3 BO 3 and various organic additives. It has been demon- strated that the magnetic properties of thin ferromagnetic films are critically dependent on film thickness and substrate 1 . The variation of composition of NiFe films, i.e. the increase of Fe-content near sub- strate at the thickness <100 nm, was observed 50 years ago using an X-ray methodology. 14 Generally, the change in chemical com- position of ferromagnetic films can affect the magnetostriction and crystal structure, while increase of thickness of the electrodeposited films changes also a stress and surface roughness. In such magnetic structures, magnetic anisotropy profoundly influences the magnetic behavior. 15 The composition of electrodeposited CoNiFe films was exam- ined in earlier papers using Auger in-depth profile 1 or EDX and XPS depth profiling, 13 showing an even deposit composition throughout the entire thickness range studied. Since the analytical techniques used for the top-down profiling in these studies were not sensitive enough, the conclusions about non-existence of a concentration gradient were incorrect. Recently, L. Peter and coworkers developed an analytical method using Secondary Neutral Mass Spectroscopy (SNMS) and reverse depth profiling (the bottom-up) to study the change of compo- sition of the electrodeposited CoNiFe films close to the substrate. 16–18 The composition gradient in the near-substrate zone (up to 150 nm) of depth profiles showed typically higher Fe-content and lower Co and Ni-content in near-substrate zone of CoNiFe deposit regardless of substrate and solution conditions. The present work is an extension of our earlier study 1 on thickness dependence of magnetic properties of CoNiFe films in the thick- ∗ Electrochemical Society Active Member. z E-mail: ibro.m.tabakovic@seagate.com ness range from 100–1000 nm together with study of composition, crystal structure, roughness, stress and magnetic properties at low (5–100 nm) and high (>100 nm) ranges of CoNiFe thickness elec- trodeposited on Cu and Pt substrate. We report here that the induc- tively coupled plasma (ICP) can be used as a complementary method to SNMS for analysis of composition gradient in CoNiFe films. The experimental observations related to the concentration gradient of 5–100 nm thin CoNiFe films were discussed in terms of reduction mechanism and dynamics of the surface roughening. Experimental The CoNiFe films were electrodeposited on 8 inch round alumina coated AlTiC wafers using 2000 Å copper as a seed layers. Typical plating solutions used in this study are shown in Table I. The pH of the solution was adjusted to 2.8 by adding HCl and electrodeposition at constant current density (2.7 mA/cm 2 ) was carried out at the solu- tion temperature of 23 ◦ C. The average thickness was obtained from nine point measurements distributed over the entire wafer surface. A DekTek profilometer was used to take the step height as thickness. The plating rate was determined as 34 nm/min and targeted nominal film thickness were: 5, 10, 25, 50, 150, 200, 250, 500, and 1000 nm. Electrodeposition was carried out in a Raider-type automated tool (Semitool Co.) in a cell volume of 100 l and with filtered circulation, and pH and temperature control systems. The agitation during elec- trodeposition was carried out by using a reciprocating paddle with a motion rate of 150 mm/s. The agitation conditions resulted with the diffusion layer thickness of 50 μm for metallic ions and 100 μm for H + , based on modeling calculations of Semitool Co. The thickness uniformity of CoNiFe films deposited on wafer-cathode, defined as σ/Mean, was optimized to <2.5% by optimizing the current density ratios on four Ni anodes. Uniaxial in-plane anisotropy was induced in all these films with aligned external magnetic field of 1000 Oe. The elemental composition and total weights of CoNiFe films was determined by inductively coupled plasma optical emission spec- troscopy (ICP-OES) using a Teledyne Leeman Labs “Prodigy” ICP spectrometer. The deposited films were dissolved into approximately solution of 50% (v/v) nitric acid and 1% (v/v) hydrochloric acid. The films electrodeposited onto the Pt RDE were dissolved in 5 mL of the acid solution and diluted as necessary for ICP analysis. Small areas (5 to 20 cm 2 ) of electrodeposited wafer films were dissolved using 5 to 15 mL of acid solution in different diameter three inch tall clamp-on ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 192.55.2.36 Downloaded on 2014-08-28 to IP