ICMCTF1999 Session F3-2: Surface and Thin Film Analysis

Monday, April 12, 1999 1:30 PM in Room San Diego

Monday Afternoon

Start	Invited?	Item
1:30 PM	Invited	F3-2-1 New Methodologies for Measuring Film Thickness, Coverage, and Topography for Magnetic Recording Applications C.M. Mate, B.K. Yen, D.C. Miller, M.F. Toney, M. Scarpulla, J.E. Frommer (IBM Almaden Research Center) The trend to increase the areal density of information stored on the disk surfaces inside of hard disk drives has resulted in smaller dimensions for most of the components within the drives and thinner films within the components. For example, the disks inside current drives typically have a 10 nm thick carbon overcoat covered with a 1 nm thick lubricant film to protect the magnetic media from sliding contacts with the recording head, which moves relative to the disk surface at speeds in excess of 10 m/s. Within a few years, the combined thickness of the overcoat and lubricant is expected to be less than 5 nm and the individual thicknesses will need to be controlled to better than a nanometer. In this talk, we examine the suitability of X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM) for providing accurate and precise measurements of thickness, coverage, and topography of overcoat and lubricant films that are only a few nanometers in thickness. Each of these techniques has its own particular strengths for these measurements: XRR can provide absolute measurements of average film thickness, density, and interfacial roughness; XPS can measure film thickness (if properly calibrated) and degree of oxidation of the underlying magnetic layer; and AFM can provide precise information on topography. We will show that using a combination of these techniques provides a fairly thorough description of the film thickness parameters for a series of test disks and silicon wafers prepared with different thicknesses of carbon overcoats and lubricant films.
2:10 PM		F3-2-3 Sub-100 Å Diamond-like Carbon Overcoat on Magnetic Rigid Disks W. Xu, L. Huang, Y.Z. Shih, T. Kim (Seagate Technology, Inc.) The current recording density on a rigid disk media increases at an annual rate of about 60%, and such a trend is seen to continue in the near future. This requires a continual shrinkage of the head to magnetic recording film spacing and hence a thinner and thinner overcoat on the magnetic film. Developing sub-100 Å overcoats and establishing accurate measurement and control schemes are then a must. This paper will discuss the growth mechanism, physical properties and an accurate control scheme for sub-100 Å diamondlike carbon (DLC) on magnetic alloy (CoCrTaPt) and non-magnetic alloy surfaces. The DLC films were deposited using a physical vapor deposition technique. Transmission electron microscopy (TEM), time-of-flight secondary ion mass spectrometry (TOFSIMS), x-ray photoemission spectroscopy(XPS) and N&K optical spectroscopy were used to analyze the film properties. It was found that the growth mechanism strongly depends on the substrate surface properties such as roughness, composition, temperature and conductivity. These properties could vary the DLC overcoat thickness by up to 40Å with the exactly the same overcoat deposition conditions. With the developed measurement schemes by N&K and TOF-SIMS in this work, an accuracy of less than 5Å in thickness measurement on the magnetic rigid disks was demonstrated.
2:30 PM		F3-2-4 Optical Characterization of Thin Nitrogenated Carbon Overcoatings on Magnetic Disks G.G. Li, A.R. Forouhi, I. Bloomer, D. Harrison, H. Zhu (n&k Technology) The carbon overcoat layer on a magnetic hard disk acts as protective barrier for the underlying magnetic media. In order to achieve high recording densities, it is necessary that this overcoat layer be extremely thin (5 to 10 nm). In addition, the film must exhibit very low surface friction to minimize wear and extend disk lifetimes. Generally speaking, nitrogenated carbon (CNx) films typically last 3 to 4 times longer than their hydrogenated carbon (CHx) counterparts. In practice, it is critical to precisely control both the thickness and N content of these protective layers. In this paper, we will demonstrate the capability of measuring the thickness and the composition, simultaneously and nondestructively, for thin (approximately 10 nm) CNx overcoat layers on magnetic disks using broad band reflectance spectroscopy in conjunction with a novel and recently developed analysis approach. This new technique utilizes the well-established Forouhi-Bloomer dispersion equations¹ for the refractive index (n) and extinction coefficient (k) spectra in undertaking the analysis of the reflectance data. From the curve fitting, both the n and k spectra as well as the thickness of CNx layers are determined. A set of samples², with N content varying from 0% to 21%, is the focus of this study. A strong correlation is established between the measured k spectra and the N content (as determined by Auger electron spectroscopy²) in the films. It is concluded that this new approach enables the N content of CNx films on finished magnetic disks to be determined with an accuracy of about ±1%. ¹A.R. Forouhi and I. Bloomer; Phys. Rev. B, 34, 7018 (1986). A.R. Forouhi and I. Bloomer; Phys. Rev B, 38, 1865 (1988). ²The authors would like to thank and acknowledge IBM San Jose for preparing samples and providing Auger analysis for this work.
2:50 PM		F3-2-5 A Surface Analytical Approach to the Characterization of the Tribological Properties of Metal Carbides and Nitrides S.S. Perry, S.H. Lee, P.B. Merrill (University of Houston) The surface structure, composition, and related frictional properties of single crystal titanium carbide, titanium nitride, and vanadium carbide have been investigated with a number of surface analytical techniques. The surface structure has been probed with low energy electron diffraction and scanning tunneling microscopy while surface composition has been assessed with X-ray photoelectron spectroscopy. Atomic force microscopy (AFM) has been employed under both ambient and ultrahigh vacuum (UHV) environments to measure the frictional properties of these surfaces. Through this detailed study, we are able to establish inherent frictional differences between these materials and gain insight into the origins of their frictional properties. These results demonstrate the necessity of a complete characterization of the tribological interface in reaching an accurate understanding of frictional properties.
3:30 PM	Invited	F3-2-7 Surface Roughness Development During Sputter Profiling of Semiconductor and Metal Thin Films Determined by AFM K. Satori, Y. Haga, R. Minatoya, M. Aokl, K. Kajiwara (Sony Corporation, Japan) Depth resolution is one of most important concerns in Auger electron spectroscopy(AES) depth prfiling. We have investigated the effects of the sputter-induced roughness on the depth resolution Δz and on the interface position z_c obtained by AES depth profiling of an AlAs/GaAs superlattice and a Ni/Cr multilayer. We also correlated the escape depth λ of Auger electrons with Δz and z_c. First, the sputter-induced roughness was evaluated by atomic force microscopy (AFM). Second, both Δz and z_c were evaluated quantitatively using an error function fitting method of AES depth profiles. The AFM observation shows that the height distribution of sputter-induced roughness is approximated to first order by a Gaussian distribution and is correlated with the resolution function which depends strongly on the sputter-induced roughness. Strictly speaking, the measured height distribution is somewhat different from the Gaussian distribution. The AES results are in good agreement with AFM observations with regard to the dependence of the depth resolution, Δz, on the sputtered depth z. Evidently the AFM observation is useful to evaluate quantitatively the sputter-induced roughness. The computational simulation using the error function approximation fitting is in good agreement with experimental results. Also, we estimated the escape depth λ using the same computational simulation results. These results indicate that the error function approximation fitting is useful to evaluate Δz and z_c as a practical method. But anomalies of Δz and z_c are discernable at the specific interface due to probably preferential sputtering.
4:10 PM		F3-2-9 Advancements in SIMS to Measure Surfaces and Interfaces: Sputter-Induced Surface Roughening Versus Primary Beam Bombardment Angle V.K.F. Chia, M.J. Edgell, G.R. Mount (Charles Evans & Associates); S. Biswas (Evans Europa, United Kingdom) As thin film deposition technology advances, parallel advances must be made to improve material analysis techniques and analytical protocols. SIMS continues to be a valuable quality control (QC) tool to monitor impurities in these films. For thin film analysis, depth resolution is an important parameter, especially when investigating interfacial contaminants. One way to optimize depth resolution is to reduce the primary beam energy. Using this method the "knock-on" effect (momentum transfer) of the bombarding primary ions is reduced. In this paper we describe the dramatic effect of changing the bombarding primary beam angle to improve depth resolution. Sputter-induced roughening during the depth profile is measured by AFM. We will show optimized analytical conditions for primary beam angles and primary beam energies. Relative sputter rates from these analytical conditions will also be presented.
4:30 PM		F3-2-10 Thin DLC Films: Stoichiometry Measurements using High Depth Resolution SIMS G.R. Mount (Charles Evans & Associates); B. Rothman (Consultant) Introduction DLC thin films are in common usage in the hard disk industry. These coatings provide good wear resistance and low friction. During the growth of DLC films, large amounts of hydrogen can be incorporated into the film. To keep hardness numbers high, it is desirable to limit hydrogen content to about 25 atomic %. Measurement of the hydrogen content can be done using Hydrogen Forward Scattering (HFS) but the accurate measurement of films thinner than 5.0nm is difficult. Secondary Ion Mass Spectrometry (SIMS) has well known capabilities in the semi-conductor industry for measuring low concentration depth profiles for various elements in silicon. SIMS can also be used with remarkable effectiveness for measuring stoichiometry in many different materials using a CsM+ analytical protocol. Combining this analytical method with a very low energy primary ion beam to enhance depth resolution results in an accurate method for measuring hydrogen in films as thin as 2.0 nm. The CsM+ Analytical Protocol During sputtering with a cesium primary ion beam, cesium can combine with material from the substrate forming a molecule that is then easily ionized to a positive charge state (M+) above the substrate surface. When ionized above the substrate surface, the ionization process is relatively free of matrix effects and the number of ions are representative of the stoichiometry. By using a well characterized standard, SIMS quantification can be accurate over a wide range of stoichiometries. Depth Resolution Depth resolution is fundamentally limited by primary ion beam mixing. Cascade and recoil mixing effects can be reduced by lowering the primary ion beam energy. Depth resolution can be further improved by increasing the angle of incidence relative to the sample normal. Results We present data from a number of thin DLC films showing hydrogen concentration as a function of depth. Some thicker film results are compared with HFS measurements.
4:50 PM		F3-2-11 Comparative Study of Thin Film Physical Properties for TiN_x Deposited by DC Magnetron Sputtering Under Temperature Less Than 100°C onto Monocrystalline Silicon and Polycrystalline Iron Substrates Ph. Roquiny (Universitaires Notre-Dame de la Paix, Belgium); A. Poulet, Y. Leys (Faculté Polytechnique de Mons, Belgium); F. Bodart (Universitaires Notre-Dame de la Paix, Belgium); J.-C. Descamps (Faculté Polytechnique de Mons, Belgium) In this research, titanium nitride thin films are deposited by reactive DC magnetron sputtering with two original constraints due to the expected industrial application as roll to roll decorative coating of steel: the samples should be connected to earth and could not be heated during deposition. Previous work has shown that low N₂ atmosphere should be maintained during sputtering process in order to obtain a colour range from grey to gold. In this study, the nitrogen content measured by Resonant Nuclear Reaction Analysis and the crystal structure revealed by Glanced angle X-Ray Diffraction were combined to reveal coating composition. The appearance presented in CIE Lab colour co-ordinates and the micro-hardness obtained with a Berkovitch nano-indentor were also evaluated for all the films. Monocrystalline polished silicon wafers were firstly used as easy to handle substrates to start thin film physical properties investigations. Results obtained with these TiN_x layer deposited onto Si(100) are secondly compared to coating physical properties measured onto more realistic polycrystalline iron (α-Fe) substrates. Only the coating produced under the lowest N₂ gas mass flow exhibits a different nitrogen content on both substrates resulting in a Ti₂N phase onto iron. Colour difference appears and are probably due to different substrate roughness. A relatively good hardness between 12 and 22 GPa is obtained on both substrates. In order to qualify this process for possible industrial application, corrosion testing have been also performed on TiN_x layer deposited onto iron substrate.
5:10 PM		F3-2-12 Determination of the Surface Coating Properties of Al(OH)₃ Particles Used in Wastewater Treatment Using a Scanning Probe Microscopy Techniques. A. Omoike (Queen's University, Canada); J.F. Graham (University of Western Ontario, Canada); G. Chen, J.H. Horton (Queen's University, Canada) We report on the examination of a series of Al(OH)₃ particles by tapping-mode AFM and interfacial force microscopy (IFM), and the use of these techniques to determine the identity of surface coatings on such particles. Al(OH)₃ particles were prepared by a technique which simulates the processes occurring during wastewater treatment. Depending on preparation method, the particles show varying degrees of effectiveness towards removal of phosphate components from wastewater. Three particle types were examined: coprecipitated particles formed by the addition of Al₂(SO₄)₃ to alkaline solution in the presence of phosphates and tannic acid; postprecipitated particles formed by adding phosphates and tannic acid to previously precipitated aluminum hydroxides; and a control case consisting of particles precipitated in the absence of either phosphate or organic component. Following dispersion of the particles on a mica substrate, tapping mode AFM demonstrated that the postprecipitated particles had distinctly different viscoelastic properties and also varied markedly in morphology from the other particle types. IFM demonstrated the presence of a compliant overlayer on the postprecipitated particles, as well as strong adhesive interactions between the tip and sample. A reduced modulus of some 20 GPa was observed for all particles. These observations are consistent with a model in which the postprecipitated particles are coated with an organic layer of tannic acid. The results are discussed in the context of previous studies of the relative reactivity of these particles towards phosphates, and of their effectiveness in removing phosphates and other contaminants from wastewater.