Jacques Kools

Giant magnetoresistance in ion beam deposited spin-valve films with specular enhancement

Three different techniques, natural oxidation, remote plasma oxidation and low energy ion beam oxidation, have been proved to be equally effective in forming nano-oxide layers (NOLs) in spin-valve films for specular enhancement of giant magnetoresistance (GMR) effect. GMR values over 12% have been routinely obtained in spin-valve films with NOL, corresponding to a 30% specular enhancement over those without NOL. The consistency and robustness of the oxidation processes has been demonstrated by a very large GMR value ∼19% in a dual spin-valve film with the NOLs formed in both pinned layers, the oscillatory dependence of the interlayer coupling field on Cu layer thickness in specular enhanced spin-valve films and the uniform and repeatable film performance over 5 in. substrates.

Seed layer characterization for PtMn bottom spin-filter spin valves

The effect of seed layers on the giant magnetoresistance (GMR) response of bottom spin-filter spin valves (SFSVs) of the structure (seed layer)/PtMn/CoFe/Cu/CoFe/NiFe/Cu/Ta have been studied in detail. Four types of seed layers, NiFeCr, Ta/NiFeCr, NiFeCr/NiFe, and Ta/NiFe were used. The GMR response has been found to be very sensitive to the type and the thickness of the seed layers, which determine the crystallographic quality of the films and the degree of the fcc to fct phase transformation of the PtMn crystals in the films. Among the four, Ta/NiFeCr and NiFeCr/NiFe seed layers give the optimal GMR performance at a NiFeCr layer thickness of about 40–45 A.

Magnetic properties of specular spin-valves containing nano-oxide layers

Nano-Oxide Layers (NOL) have been introduced recently as a means to enhance the degree of specular scattering at the outer surfaces in a spin-valve, while still using metallic antiferromagnets such as PtMn or IrMn. A key requirement of the NOL layer in the pinned layer is to be able to provide strong ferromagnetic coupling between two ferromagnetic layers. In this paper, a quantitative study of the ferromagnetic interlayer coupling over the NOL-layer is presented. A Stoner-Wohlfarth model is developed to allow for quantitative analysis. The effect of different metal deposition methods (PVD or IBD), different pinning structures (PtMn and IrMn; simple and synthetic) and different oxidation methods on the coupling is compared.

Optimization of high Bsat FeCo films for write pole applications

FeCo films and their lamination with ultrathin NiFe layers down to 5A were deposited using dc magnetron sputtering techniques. Soft magnetic FeCo films were obtained at an optimal target power of 500W and an optimal deposition pressure of 2mTorr with high saturation flux density, Bsat>2.4T, and low easy-axis coercivity, Hce⩽15Oe, and hard-axis coercivity, Hch⩽3Oe, at a film thickness of 2000A. While the magnetostriction remains at ∼4×10−6 the stress was further optimized by applying substrate bias at a controlled level ⩽50V without sacrificing film magnetic softness.FeCo films and their lamination with ultrathin NiFe layers down to 5A were deposited using dc magnetron sputtering techniques. Soft magnetic FeCo films were obtained at an optimal target power of 500W and an optimal deposition pressure of 2mTorr with high saturation flux density, Bsat>2.4T, and low easy-axis coercivity, Hce⩽15Oe, and hard-axis coercivity, Hch⩽3Oe, at a film thickness of 2000A. While the magnetostriction remains at ∼4×10−6 the stress was further optimized by applying substrate bias at a controlled level ⩽50V without sacrificing film magnetic softness.

Modeling the EUV multilayer deposition process on EUV blanks

Extreme ultraviolet lithography (EUVL) is the leading next generation lithography (NGL) technology to succeed optical lithography at the 22 nm node and beyond. EUVL requires a low defect density reflective mask blank, which is considered to be the most critical technology gap for commercialization of the technology. At the SEMATECH Mask Blank Development Center (MBDC), research on defect reduction of EUV mask blanks is being pursued using the Veeco Nexus deposition tool. Its defect performance is one of the factors limiting the availability of defect-free EUVL mask blanks. SEMATECH has identified better understanding of the physics of the deposition process as one of the keys to improving the defect performance of Nexus tools. SEMATECH is therefore undertaking an effort to model the physics of the tool backed with an experimental program to characterize the process. The goal is to be able to predict defect performance and defect improvement to direct new tool design. In this paper, we present the results of simulating the deposition rate and uniformity of deposited multilayers and growth of the multilayer on a given defect profile.

Effect of microstructure on the oscillating interlayer coupling in spin-valve structures

It has been well established that the interlayer coupling in a spin valve is well described as a sum of terms associated with pinholes, magnetostatic (Neel), and oscillating exchange interlayer coupling [(OXC) or Ruderman–Kittel–Kasuya–Yosida]. We experimentally studied the effect of interface roughness on the OXC term. We systematically varied the microstructure by variation of the sputtering geometry, the sputtering pressure, the seed layer and by application of low-energy ion bombardment at the interfaces (“beam treatment”). It is found that smoothening the stacks leads to a stronger OXC, both when suppressing long-range (∼200 A) and short-range (∼20A) roughness. Neel coupling on the other hand, is found to be more sensitive to long-range waviness.

Physical properties of spin-valve films grown on naturally oxidized metal nano-oxide surfaces

The physical properties of spin-valve films NiFe 25 A/CoFe 10 A/Cu(tCu)/CoFe 30 A/IrMn 70 A/Ta 20 A with graded Cu layer thickness (tCu=18–45 A) grown on the surface of metal nano-oxide layers (NOLs) were studied. The NOLs were formed from ultrathin Al, Cr, Cu, Nb, Ta, CoFe, NiFe, and NiFeCr layers by natural oxidation. The growth of the spin-valve films on NOLs has led to an enhancement in giant magnetoresistance value by up to 48%. A corresponding reduction in minimum film resistance by over 10% confirms that this enhancement originates from an increase in the mean free path of spin-polarized electrons due to the resultant specular reflection at the nano-oxide surfaces. A wide spectrum of oscillatory interlayer exchange coupling dependence on tCu for these NOL-bearing films suggests that a specular nano-oxide surface does not necessarily result in a smoother multilayer structure. The observation of an enhanced exchange biasing among these spin-valve films appears in contradiction to the observed deterio...

Comparison of RF bias, gas cluster ion beam, and ion beam in-situ beam treatment for enhancement of GMR in spin-valve stacks

In this paper, we present data comparing three different in-situ beam treatment (smoothing) techniques for enhancement of GMR properties. The three techniques were radio-frequency bias (RFB), gas cluster ion beam (GCIB), and ion beam (IB). All three were optimized for maximum enhancement of properties and resulted in an increase of GMR of about 0.5 to 1% (> 13.5% to > 14.5%) and a reduction in interlayer coupling of about 15 to 30 Oe (5 Oe to -25 Oe) when treating the CoFe/Cu interface of a synthetic pinned bottom spin valve. Smoothing the Ru/CoFe interface resulted in enhancement of GMR, but no change in the interlayer coupling. The optimum conditions for all three techniques corresponded to ion bombardment energies in the range of 10-60 eV. For RFB, the substrate bias voltage was optimized at 60 V, for IB, the extraction energy was 30 eV, and for GCIB, the equivalent energy/atom was in the same range. Our results indicate that all three smoothing methods are effective in improving the GMR properties with no fundamental advantage of any particular technique.

Critical thickness effects of NiFeCr-CoFe seed layers for spin valve multilayers

In this article, we present data on the critical dependence of the magnetic, electrical and microstructural properties of spin-valves (SV) on seed-layer thicknesses. The SV structure is: seed-layer/PtMn 140 /spl Aring//CoFe 16 /Ru 8.5 /spl Aring/ /CoFe 21 /spl Aring/ /Cu 20 /spl Aring//CoFe 12 /spl Aring//NiFe 30 /spl Aring//Ta 30 /spl Aring/, where the seed layer is NiFeCr-CoFe or NiFeCr/NiFe. As the thickness of the bilayer seed layer is varied, it is found that a critical thickness boundary exists across which the film properties are radically different. The GMR ratio increased from 7% to 14% (a 100% change), the sheet resistance decreased by about 4 ohms/square and the crystalline texture transitioned from weak to extremely strong (111) texture. The critical thickness boundary is at a combined thickness of 37 /spl Aring/ to 40 /spl Aring/. These results suggest a mechanism at the boundary between NiFeCr and CoFe during film growth. A better lattice match between NiFeCr-CoFe, for example, NiFeCr 33 /spl Aring/ and CoFe 7 /spl Aring/, generates a strong (111) texture, which enhances the MR% as compared to NiFeCr 33 /spl Aring//CoFe 6 /spl Aring/. The H/sub 50/ (the field at 50% MR) also exceeds 2000 Oe. This also indicates enhancement of the PtMn fcc to fct transition based on the specifically combined thicknesses of NiFeCr-CoFe. With the NiFeCr-NiFe seed layer, the critical thickness effect is not observed within these thickness ranges.

Effect of N2 addition in sputter gas on giant magnetoresistance response of PtMn bottom spin-valve films

Interlayer coupling in spin-valve films is usually dominated by the ferromagnetic Neel coupling of a magnetostatic nature due to interfacial roughness. The addition of N2 as a second sputter gas species during deposition of thin layers in PtMn bottom spin-valve films has shown effectiveness in the reduction of interfacial roughness and, therefore, control of ferromagnetic Neel coupling. The interlayer coupling field has been more effectively reduced from an original 38.8 Oe down to 6.1 Oe at a Cu spacer layer thickness of 24 A with the addition of 4 sccm N2 gas during the Cu spacer layer deposition. In addition to higher giant magnetoresistance values over 10% at thinner Cu spacer layer thicknesses, a pronounced oscillatory dependence of the interlayer coupling field on Cu spacer layer thickness has been observed. Apparently, nitrogen serves as surfactant and helps layer-by-layer growth of Cu on a CoFe pinned layer, resulting in smoother CoFe/Cu and Cu/CoFe interfaces.