Sputtered Carbon Films Research Articles

Stress relaxation and stability of sputtered carbon thin films

Stress measurements were performed on sputtered carbon films deposited on Si substrates in the temperature range from room temperature to 350 °C. Both hydrogenated and nonhydrogenated carbon films, ∼100 nm in thickness, were investigated. The stress relaxation kinetics were investigated for films tested in air and in the presence of an inert environment. The experimental data show distinct differences for tests performed in these two environments. Microscopic examination revealed that films tested in air show local loss of carbon following a thermal cycle whereas the films tested in argon show good stability and remain well adhered to the substrate

Microindentation fatigue tests on submicron carbon films

Microindentation fatigue tests have been conducted on submicron coatings using a microindenter. The cyclic indentation was implemented by servo controlling the motion of the indenter so that the loadcell output followed a 0.1 Hz sinusoidal loading pattern. A conical diamond indenter with a nominal 1 μm tip radius was used. A model system composed of two 0.11 μm sputtered carbon films was chosen for investigating the indentation fatigue effects on brittle coatings. Both carbon films were deposited on silicon substrates but with substantially different interfacial adhesion strengths. For the carbon film with poor adhesion tested at the condition of a 4 mN maximum load, an annular coating buckling pattern concentric with the center of the indent appeared during the first loading stage whereas coating spallation occurred at loading cycle numbers ranging from 50 to 140. In contrast to this, under the same test condition, the carbon coating with good adhesion did not show any noticeable failure up to 500 cycles where the experiments were truncated. When the maximum load was increased, fine cracks initiated in the carbon coating and along the circular indent boundaries but the coating still adhered well to the substrate. These fine cracks continued to propagate during subsequent indentations, and eventually spallation of the carbon coating occurred. Because the microindenter has the advantage of continuously monitoring both the applied load and penetration depth during an entire test, the evolution of the fatigue failure of a coating system can be clearly visualized from the corresponding load vs. depth curve. A typical brittle failure event is manifested by several repeatable loading-unloading cycles with a gradual depth increase after the first indentation, then a couple of consecutive abrupt changes in the applied load as well as in the depth followed by stabilized indentation cycles.

Time dependence of the resistance of sputtered carbon films

The electrical resistance of carbon films sputtered under high Ar pressure and low bias was observed to increase by as much as 200% when the films were exposed to the atmosphere for a period of several days. Substrate temperature and sputtering power had no effect on the time dependence of the resistance. The time dependence of the resistance appears to be related to the formation of a porous structure when films are sputtered under high Ar pressure and low bias. The increase in resistance noted when sputtered carbon films were exposed to air bears some similarity to aging behavior observed for discontinuous metal films. The initial resistivity of the films was dependent on Ar pressure, bias, substrate temperature and power.

Optical and mechanical properties of dc sputtered carbon films

Amorphous carbon films were deposited on glass by dc magnetron sputtering from a graphite target in mixtures of argon and hydrogen. Hydrogen flow and other parameters affected the optical and mechanical properties of these films. Increasing hydrogen content caused the average visible transmittance to vary from 16% to 86% for 500-Å thick films. Maximum compressive stress and hardness occur between 0 and 1% hydrogen flow, resulting in rapid delamination. Low sputtering power moderately increases transmittance and hardness while relieving stress. Transparency is induced in both the high-hydrogen and low-power films by formation of sp3 C–C bonds. In the case of the hydrogenated films, however, a softer polymeric structure is formed.

Surface contamination on sputter carbon coated disks measured by using low energy photoelectron spectroscopy in an ambient atmosphere

The influence of surface contamination on sputtered carbon films on a rigid thin-film disk was evaluated with LEPS (low-energy photoelectron spectroscopy) and XPS (X-ray photoelectron spectroscopy). LEPS was as sensitive as XPS for detecting the surface contaminant. LEPS had the advantage of operating in an ambient atmosphere, while XPS was useful for the identification of the chemical species of the contaminant. The XPS analysis revealed that the main contaminant was due to water in air. XPS showed that the wettability of the fluorocarbon lubricant decreased with an increase in the exposure time of the sputtered carbon film to air before lubrication or with a surface-contaminant increase on the sputtered carbon film. >

Micro-Indentation and Micro-Scratch Tests on Sub-Micron Carbon Films

AbstractMicro-indentation and micro-scratch techniques were used to characterize the hardness and the adhesion strength of 0.11 μm thick sputtered carbon f-ilms on Silicon substrates. Hardness depth profiles and critical loads were measured using a microindenter under indentation and scratch testing modes, respectively. The carbon film with 6 mtorr argon sputtering pressure shows better practical adhesion (or higher critical load) and slightly higher hardness. The indentation fracture phenomenon observed on the 30 mtorr film is closely related to its poor adhesion. The failure mechanism will also be discussed.

Pressure and plasma effects on the properties of magnetron sputtered carbon films

Thin, amorphous films of carbon have been deposited by conventional and hollow cathode enhanced magnetron sputtering of a pyrolytic graphite target. Films in the range of 15 to 200 nm were deposited over a pressure range or 50 to 0.1 mTorr on fused silica, sapphire, and Si substrates at 20 °C. Langmuir probe measurements of the local electron temperature, density, and plasma potential were made at several locations in the plasma as well as the substrate location as a function of pressure in both the conventional mode (50–1 mTorr) and the hollow cathode enhanced magnetron mode (1–0.1 mTorr). Several film properties were found to vary markedly over the pressure range investigated. For example, electrical resistivity was reduced from about 1×106 Ω cm at 50-mTorr sputtering pressure to a value of 0.01 Ω cm at 0.1-mTorr pressure. The optical band gap was reduced over the same pressure range from 2.1 to 0.4 eV. The index of refraction increased from n=2 at 50 mTorr to n=2.7 at 0.1 mTorr. The electron temperature of the plasma at the substrate location changed from a value of less than 1 eV at the higher pressure to over 8 eV at the lowest pressure, and the electron density increased 1 to 2 orders of magnitude in the same range. The results suggest that the local energy imparted to the growing film from the plasma environment can dramatically change the properties of the carbon films.

Surface Protective Film for CoNiCr/Cr Sputter Hard Disks

Surface protective films for hard disk media were studied. Whereas sputtered carbon films are not sufficiently wear-resistant for use with CaTiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> . TiC head sliders, tests using plasma-CVD films prepared in acetylene gas under RF or dc discharge have lubricating properties and sufficient wear resistance, but are so soft that disk surfaces are easily damaged. By combining the two in a double-layer protective film, however, both good wear resistance and low friction when used with the above types of heads are achieved.

Structural Studies of Hydrogenated Amorphous Carbon Infrared Coatings

ABSTRACTHydrogenated amorphous carbon thin films are well known for their mechanical hardness and optical properties which make them useful for applications in infrared device coatings. In this work films have been prepared by plasma. decomposition of methane using an RF diode reactor operating under conditions of high self bias potential (Vb = 1 KeV). The resulting ion bombardment during film growth leads to the formation of hard, insulating carbon coatings which have a band gap of ≃1.1 eV and are transparent in the IR. Nuclear reaction analysis has been used to quantify the atomic concentration of hydrogen incorporated in the films and extended x-ray absorption fine structure (EXAFS) has been used to determine local site geometry. Only first and second nearest neighbor bond lengths are observed with no evidence of further long range order or microcrystallinity. A model for atomic structure is proposed which includes both sp2 and sp3 bond configurations and direct comparisons are made with data obtained from sputtered carbon films, graphite and diamond.

Structure and morphology of RF sputtered carbon overlayer films

The morphology and structure of RF sputtered carbon films have been investigated. The growth of these films is shown to take place by the formation and agglomeration of rounded particles. The film growth mechanism and the substrate nature were the primary factors determining the morphology of carbon films. The structure of the carbon films was found to be predominantly amorphous.

Preparation and properties of sputtered “glassy” carbon films

Some remarkable “glassy” carbon films with densities from 0.5 to 1.79 have been prepared by sputtering from carbon targets. Conditions for the preparation of various carbon films by rf sputtering and data on the density, mechanical properties, microhardness, microstructure and crystal structure of the films formed are presented. Optimum sputtering conditions for obtaining mechanically stable films up to 40μ thick are described. It is shown that density and microhardness of the carbon can be controlled within wide limits, and both increase with decreasing deposition rate. The higher density carbon films adhere poorly to glass, while the low density carbon films on glass are stable. All sputtered carbon films are non-crystalline and have a grainy microstructure. Potential applications exclude corrosion protection but include novel catalyst supports.

Varistorlike I−V characteristics in sputtered carbon films

Varistorlike I−V characteristics have been observed in sputtered carbon films sandwiched by Al electrodes. The threshold voltage of the Al−C−Al varistors is controlled by the sputtering time and not by the rf input power for sputtering if other parameters are unchanged. Auger analysis of the films has clarified that the nonlinear characteristics are strongly influenced by anomalous profiles of tungsten atoms migrated from Al.