ICMCTF1999 Session F5: Characterization of Thin Film Growth Processes and Evolving Film Properties

Wednesday, April 14, 1999 8:30 AM in Room San Diego

Wednesday Morning

Time Period WeM Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF1999 Schedule

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8:30 AM F5-1 Elemental Processes in Ion Beam Deposition
D. Marton (University of Houston)

The interactions of hyperthermal particles with surfaces represent an important class of phenomena for both basic research and technology. These processes occur in ion beam and plasma technologies, and even during the interaction of atoms of high pressure gas with solid surfaces. The subplantation model recognized that the most important processes in low energy ion beam deposition (IBD) involve the penetration of ions and damage of the solid. This qualitative model has recently been developed into a semiquantitative subplantation (SQS) model that describes the effects of penetration, damage, and diffusion (including radiation enhanced diffusion) in the film growth from hyperthermal species1.

The SQS model has been applied to such diverse phenomena as the deposition of diamond-like carbon (DLC) and carbon nitride CNx films, ion induced damage of graphite, low temperature silicon epitaxy, and deposition of titanium silicide. The model provides interpretations of effects of ion kinetic energy, fluence, and substrate temperature. The model is quite general and leads to new conclusions about physical mechanisms. It provides estimates of important physical parameters and optima in IBD that exist due to a balance between beneficial and deleterious effects. Finding these optima may lead to significant technological improvements in a wide range of ion beam and ion assisted technologies.

1 K. J. Boyd et al., J. Vac. Sci. Technol. A 16 (1998) 444.

9:10 AM F5-3 Synthesis, Characterization and Properties of Si-DLC Films
E.I. Meletis, V.G. Palshin (Louisiana State University); S. Logothetidis (Aristotle University of Thessalonikice, Greece); K. Fountzoulas (Weapons and Materials Research Directorate)
Silicon-containing diamondlike carbon (Si-DLC) films were deposited on silicon wafers by Ar+ ion beam assisted deposition (IBAD) at various power densities. The film thickness varied from 0.6 to 4.0 µm. The films were characterized with a variety of complementary techniques such as scanning electron microscopy, transmission electron microscopy (TEM), FTIR spectroscopy, spectroscopic ellipsometry (SE) and x-ray reflectivity (XRR). Si-DLC films were found to be mainly amorphous, dense and of high hardness, with featureless and very smooth surfaces. The effect of deposition parameters (ion beam current density and voltage) on structure and properties of the films was investigated. Si-DLC films revealed a wide variation in the sp3/sp2 ratio, which was strongly affected by the ion beam current density. The effect of Si atoms incorporated in the DLC structure seems to be the prevention of aromatic clustering and promotion of the formation of sp3 bonds. Resulting film properties are discussed in view of the observed film characteristics.
9:30 AM F5-4 Investigation of Plasma-Deposited ITO Films by GIXR and GIXRD
H. Wulff, M. Quaas, H. Steffen (University of Greifswald, Germany)
Thin indium tin oxide films were deposited by reactive DC magnetron sputtering to study the influence of oxygen and low energy ion bombardment on film growth and film properties. Films were deposited at various oxygen gas flows as well as negative substrate voltages and investigated by grazing incidence x-ray reflectometry (GIXR), diffractometry (GIXRD), AFM and XPS. From both the results of oxygen flow experiments and the negative substrate voltage experiments it can be concluded that the ion concentration as well as the ion energy determine the film growth and the film properties. With increasing oxygen flow film structure and composition change from crystalline metallic In/Sn to amorphous ITO. Simultaneously the deposition rate (nm/s) decreases and the film density increases. In principle an increasing negative substrate voltage leads to the same film properties but it works like a diminished oxygen flow. Post deposition annealing at 200°C causes the formation of crystalline ITO films. The formation rate depends on the deposition conditions. Two processes determine the ITO crystallite growth, the recrystallization of the deposited indium tin oxide and the diffusion of oxygen into the layer.
9:50 AM F5-5 Characterization and Properties of Diamond Like Carbon Films for Magnetic Recording Application
N. Gopinathan, C. Robinson, F.W. Ryan (Read-Rite Corporation)

Amorphous carbon or Diamond like carbon (DLC) is deposited on recording heads to improve tribological properties at the head-disk interface and also to protect the transducer against corrosion in the drive. With increasing areal densities, the thickness of the carbon overcoats are decreasing rapidly to 50 Å and less. With a reduction in the overcoat thickness, it is important to understand the nature of the thin film growth and the properties of the film as the thickness changes.

The present work provides results of the properties of a-carbon overcoats which were characterized in terms of residual stress, raman spectroscopy, surface roughness, electrical resistivity and surface energy as a function of film thickness. The DLC was deposited using an ion beam CVD process using CH4precursor. The overcoat has an adhesion layer that compromises 1 to 2 nm of silicon that is sputter deposited. Overcoats of different thickness were deposited on the recording heads along with some silicon witness coupons and wafers. The overcoat thickness used in these experiment are 30Å to 300 Å.

The results indicate that there is considerable change in the film properties as the film grows. The residual stress which is about 3.4 Gpa for the 30 Å overcoat gradually decreases with an increase in film thickness up to 100 A where the stress is about 2.5 Gpa. Above 100 Å film thickness, the stress increases again. The Raman intensity ratio on these films follow a similar pattern. Data on surface roughness, surface finish, and electrical resistivity are also presented. Implications of these measurements on the thin film growth mechanism are discussed. The results of the above techniques of DLC characterization imply that the growth of thin film a-carbon changes as the film increases in thickness.

10:30 AM F5-7 Formation, Characterization and Comparative Studies of Carbon-Based Hard Materials
M. Weiler, R.A. Yankov, N. Hatzopoulos (CCR GmbH, Beschichtungstechnologie, Germany)

This article is in three parts. The first part covers the numerous forms of both crystalline and non-crystalline carbon. Included are also two carbon compounds, namely SiC and C3N4, because of their high technological importance and relevance to advanced microelectronics. These are collectively referred to as carbon-based hard materials (CBHM).

The second part discusses the various deposition processes used to form CBHM, with an emphasis on those methods which produce amorphous-carbon (a-C) and hydrogenated amorphous-carbon (a-C:H) films containing a significant fraction of sp3 bonding or the so-called diamond-like carbon (DLC) films. A common feature of all these methods is the exposure of the growing layer to ion bombardment at medium energies (20 - 500 eV), which is a prerequisit for promoting sp3 bonding. The resulting DLC films exhibit valuable properties such as high mechanical hardness, low friction, transparency and chemical inertness. A description is given of a novel controlled plasma reactor COPRA and its particular use in the deposition of polycrystalline diamond, DLC and C3N4 layers.

The last section provides an overview of the analytical techniques that have been most frequently applied in the CBHM research. The relative merits of the characterization methods have been summarized and discussed. Each technique has its strengths and none of them alone can provide answers to all relevant questions concerning the structural, chemical and physical characteristics of the films. However, Raman spectroscopy, spectroscopic ellipsometry and electron-energy-loss spectroscopy have been found to be most useful for the evaluation of the CBHM films. It has been argued that any two of the above-mentioned techniques in combination can provide a sufficient basis for obtaining meaningful information on the structure and properties of these interesting and technologically-important films.

11:10 AM F5-9 Plasma Chemical Vapor Deposition of Thin Carbon Nitride Films Utilizing Transport Reactions
C. Popov, M.F. Plass, W. Kulisch (University of Kassel, Germany)
Inductively coupled plasma chemical vapor deposition (ICP-CVD) has been used for preparation of thin carbon nitride films from solid carbon source (floating) and nitrogen. The atomic nitrogen obtained as a result of the r.f. plasma activation interacted with the carbon source to form carbon-nitrogen species. The latter were transported to the substrate where carbon nitride films were deposited in excess of atomic nitrogen. The supposed process mechanism was verified by microscopic observations of the carbon source before and after the process and by in situ mass spectrometric studies of the gas phase. The basic deposition parameters varied were the pressure in the reactor (up to 1 mbar) and the nitrogen flow. Argon was also added to the gas phase during some experiments. The main advantage of the process was the possibility to obtain carbon nitride films at rather low r.f. power (up to 100 W). The morphology of the films was studied by scanning electron microscopy (SEM) and the deposited layers were found to be very smooth and uniform. The N/C ratio in the films was close to 1 as detected by Auger electron spectroscopy (AES). Infrared absorption spectra showed the presence of different carbon-nitrogen bonds in the deposits. Some application relevant properties of the films (optical and electrical) were also studied.
11:30 AM F5-10 Improvement of Adhesion in Diamond-Like Carbon Coating with W-C Amorphous Intermediate Layers
E.I. Iwamura, M.T. Takeda, T.M. Miyamoto (Kobe Steel Ltd., Japan)

Effect of W-C intermediate layers on adhesion of DLC coating was examined in comparison with the case of Ti-C intermediate layers. Analyses of microstructures and failure mechanism in scratch adhesion tests were carried out.

Stacking sequence of W/W-C/DLC and Ti/Ti-C/DLC were prepared using dc magnetron sputtering on a WC-Co substrate or a glass substrate with a SiO2 overlayer. Unbalanced magnetron sputtering system was used for the carbon deposition. W-C and Ti-C layers were designated to have gradient chemical composition by changing sputtering power step by step. DC or RF bias in a range from -50 V to -200 V was applied to the substrates during the deposition. DLC hardness increased with increasing the bias voltage, and was in a range from 40 GPa to 100 GPa.

In cross-sectional TEM microstructure analyses using elongated probe electron diffraction techniques, the W-C layers were found to be amorphous through thickness whereas the Ti-C layers included fine crystals of TiC compounds. Although the W system multilayers contained evident discontinuity in W/W-C interface and even in the W-C layers, adhesion of W/W-C/DLC multilayer on WC-Co or glass/SiO2 substrate reached nearly 100 N, independent of the DLC hardness. On the other hand, adhesion of Ti system multilayers showed about 40 N at most.

Starting points of adhesion failure in scratch tests exhibited a feature of delamination by shear stresses in W system multilayers, while Ti system multilayers were failed in the Ti-C layers with cracking alongside the scratch path.

It is presumed that the difference of adhesion in hard DLC coatings with W-C and Ti-C intermediate layers are attributed to the microstructural differences. Relationship between microstructures and adhesion failure mechanism of the multilayers will be discussed.

11:50 AM F5-11 Smoothening Effect of CNx Deposited in an Unbalanced Magnetron Sputtering System
M. Graham, A. Madan, Y.-W. Chung, M. Ulmer, R. Altkorn (Northwestern University)
CNx coatings are used extensively in the hard disc industry because of their low friction, hardness, and extremely smooth surfaces. It has been observed that existing surfaces can often be made smoother by the deposition of CNx. This study investigates the smoothening effects of CNx coatings (thickness ~ 100 nm). CNx was deposited in a dual-cathode DC unbalanced magnetron sputtering system on different substrates. Pyrolytic graphite was reactively sputtered in Ar/N2 gases with partial pressure control of the nitrogen gas. Pulsed dc bias was applied to the target and substrates. The substrate bias was varied from - 100 V to -250 V. The deposition rate of CNx was typically about 6.5 nm/min. Prior to deposition, the substrates were etched for varying times from ~ 5-20 minutes. Atomic force microscopy of the substrates before and after deposition of CNx showed a significant reduction in the roughness from 0.8-1nm to 0.2-0.5 nm. The higher bias led to a greater reduction in the roughness. Adhesion of the CNx was a function of the deposition conditions. Preliminary results indicate that the adhesion of the CNx to Ni substrates was improved by the deposition of a buffer layer ~ 50 nm of ZrN.
Time Period WeM Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF1999 Schedule