Adrian J. Devasahayam

Low-temperature (≤200 °C) plasma enhanced atomic layer deposition of dense titanium nitride thin films

Titanium nitride (TiN) has been widely used in the semiconductor industry for its diffusion barrier and seed layer properties. However, it has seen limited adoption in other industries in which low temperature (<200 °C) deposition is a requirement. Examples of applications which require low temperature deposition are seed layers for magnetic materials in the data storage (DS) industry and seed and diffusion barrier layers for through-silicon-vias (TSV) in the MEMS industry. This paper describes a low temperature TiN process with appropriate electrical, chemical, and structural properties based on plasma enhanced atomic layer deposition method that is suitable for the DS and MEMS industries. It uses tetrakis-(dimethylamino)-titanium as an organometallic precursor and hydrogen (H2) as co-reactant. This process was developed in a Veeco NEXUS™ chemical vapor deposition tool. The tool uses a substrate rf-biased configuration with a grounded gas shower head. In this paper, the complimentary and self-limiting ch...

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.

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.

Material properties of ion beam deposited oxides for the optoelectronic industry

High quality, dense films of SiO2, Al2O3, Ta2O5, and TiO2 were deposited with an ion beam deposition system (IBD). IBD has significant advantages over other techniques in terms of directionality, stress control, repeatability, thermal stability, and film uniformity [J. J. Cuomo, J. M. E. Harper, C. R. Guarnieri, D. S. Yee, L. J. Atanasio, J. Angilello, C. T. Wu, and R. H. Hammond, J. Vac. Sci. Technol. 20, 349 (1982)]. To decrease the surface damage induced by ion bombardment, a multi-energy process was developed. This is especially important for laser facet coatings. The oxide films were optimized for the desired refractive index and zero absorption. Stress values of −0.2 to −0.5 GPa (compressive) and extremely good uniformity (<0.2%) of film thickness and refractive index were obtained. The impact of the IBD deposition angle on film stress was also investigated. These films showed excellent thermal stability with virtually no degradation of optical properties after three 1 h anneals at 350 °C (Δn<0.0124...

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.

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.

Ion beam deposition processes for improved hard bias magnetic and device properties in the abutted junction configuration

Permanent magnet films of Cr/CoCrPt for use in an abutted junction hard bias scheme were deposited by an ion beam deposition (IBD) system. The deposition angle control of IBD systems was employed to yield some excellent material and device related improvements. For films with the structure Cr-50 A/CoCrPt-250 A, increasing the deposition angle θ (as measured from the substrate normal) of the Cr layer from 20° to 60°, resulted in an increase in coercivity from 1860 to 1905 Oe. X-ray diffraction measurements showed that this improvement was related to an increase in CoCrPt in-plane texture and a decrease in c-axis perpendicular texture. The reason for this increase in in-plane texture is that there is better epitaxial matching between the CoCrPt and the Cr underlayer brought about by a change in the lattice dimension of Cr as a result of changing stress levels. Another positive effect of depositing the Cr at a larger angle is that the Cr would be thicker farther into the abutted junction and thus delay the o...

Smoothing of (111) oriented Cu films by post-deposition in situ 20-100 eV Ar ion bombardment

We have studied the effect of low energy (20–100eV) Ar bombardment on the surface roughness of (111) oriented Cu films both experimentally and by molecular-dynamics simulations. We found, in good agreement between the experiments and the simulations, that a significant reduction of the surface roughness can be induced at all energies in this range. However, the angle of incidence for optimal smoothing depends strongly on the ion energy, whereby the lower energies used are more efficient at near normal incidence, and the higher energies are more efficient for off-normal angles (e.g., >45degrees).

Ion beam deposition of permanent magnet layers for liftoff processes

Thin film permanent magnet layers of Cr/CoCrPt were prepared by ion beam deposition in a Veeco IBD-350 tool. The magnetic properties were measured as a function of deposition angle, deposition energy, assist energy, and the underlayer and permanent magnet thicknesses. It was found that higher deposition energies and angles (from normal) resulted in larger coercivities. Increasing the assist energy also helped increase the coercivity. The coercivities were in the range of 1400–2100 Oe depending on the deposition conditions, for a Cr-50 A/CoCrPt-250 A film. The squareness, S (the ratio of remnant magnetization to saturation magnetization) and Mrt (remnant magnetization and film thickness product) for these films were about 0.85 and 1.3 memu/cm2, respectively. It was found that underlayers of Cr as thin as 25 A could be used, without significant degradation of magnetic properties. The coercivity had a broad peak between 100 and 200 A of CoCrPt, above which the coercivity gradually decreased. θ–2θ x-ray diffr...

Low-temperature (≤150 °C) chemical vapor deposition of pure cobalt thin films

High purity soft-magnetic cobalt films were grown by cyclic thermal–chemical vapor deposition (CVD) process using dicobalt octacarbonyl as metal organic precursor, at an optimum substrate temperature of 125 °C. Physical, electrical, and magnetic properties of CVD grown Co films were compared with physical vapor deposition (PVD) grown Co films. Films were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction, four-point resistivity probe, scanning electron microscopy, hysteresis loop tracer, vibrating sample magnetometry, and atomic force microscopy. The authors observed in-plane uniaxial magnetic anisotropy in the CVD-grown cobalt film with cyclic pulse-purge technique. Typical film properties obtained were low volume resistivity ( 99.5% purity, 100% growth linearity as a function of number of cycles, good step coverage in a SiO2 trench, low coercivity (<15 Oe), high saturation magnetization (∼1.5 T), and low root-mean-square surface roughness (7 A). Compared to our PVD films, CVD Co...