S.S. Camargo

Deposition of Si-DLC films with high hardness, low stress and high deposition rates

Abstract In this work silicon-incorporated diamond-like carbon (Si-DLC) films were produced by plasma enhanced chemical vapor deposition (PECVD) from gaseous mixtures of CH4 and SiH4. A study of the influence of self-bias and gas composition on the mechanical and structural properties of the films was carried out. Results show that films deposited at high self-bias present high deposition rates, low stress and surprisingly high hardness. Increasing silane concentration in the gas phase leads to an enhancement of the observed effects. Compositional and structural characterization show that deposition at high bias leads to increased sp2 character and rather low silicon contents. Increasing the silane content in the plasma leads to an increase in the sp3 fraction of the films, and yields a further reduction of stress with almost no effect upon hardness. In this way, the possibility of producing films with high hardness (>20 GPa), low stress (∼0.5 GPa) and high deposition rates (>40 nm/min) has been demonstrated. This result is thought to be very important from the point of view of technological applications.

Relation between mechanical and structural properties of silicon-incorporated hard a-C:H films

Abstract Results of the mechanical and structural properties of silicon-incorporated hard hydrogenated amorphous carbon films arc reported. A strong reduction of the residual internal stress with an almost constant mechanical hardness was observed and the possible causes of this behavior arc investigated. Infrared absorption and elastic recoil hydrogen detection results show that silicon is incorporated replacing carbon atoms in the amorphous network with approximately constant bonded hydrogen density and total hydrogen content. Additionally, Raman experiments indicate that silicon incorporation increases the sp 3 character of the material, while electron spin resonance measurements show a decrease of the number and size of the sp 2 graphitic defects present in the material. Hydrogen effusion experiments indicate that the observed reduction of residual internal stress may be attributed to a less compact material with an increased density of voids in comparison to pure a-C:H.

Characterization of ultra-hard silicon carbide coatings deposited by RF magnetron sputtering

Abstract Silicon carbide films were deposited onto crystalline silicon substrates from a sintered SiC target using a RF magnetron sputtering system. The influence of substrate temperature (150–500°C) and polarization (0−100 V), Ar pressure (0.05–4 Pa) and RF power (50–400 W) on the mechanical properties (hardness and stress) of the resulting films was studied. Films with hardness values larger than 40 GPa could be obtained, provided that Si and C sputtered atoms can reach the surface of the growing film with sufficient high energy and low deposition rates in order to guarantee a high surface mobility. At high deposition rates the surface mobility is limited, but the increase in substrate temperature can contribute to stress relief. Upon thermal annealing at high temperatures, completely stress-free films could be produced without affecting the material hardness. This effect is accompanied by an increased structural and chemical order. Substrate bias was found not to be beneficial to the film properties, since it leads to substantial argon incorporation into the material.

Magnetron sputtered SiC coatings as corrosion protection barriers for steels

Silicon carbide films between 2.3 and 3.0 μm were deposited on AISI 304 stainless steel (SS), carbon steel (CS) and crystalline silicon from a SiC target in a magnetron sputtering system. Good mechanical properties were obtained for the films by carefully controlling the deposition parameters. Results of scratch tests revealed that adhesion of the films is a function of deposition parameters and substrate type. Additionally, an influence of substrate preparation prior to deposition was also observed. Critical loads of 20 N, 8 N and 5 N were obtained in case of Si, SS and CS substrates, respectively. Vickers micro-hardness values were between 10 and 30 GPa, films on SS being harder than films on CS. The behavior of the films as corrosion protection barriers in aggressive environments was evaluated by immersion tests and electrochemical impedance spectroscopy measurements. Films on SS exhibited a better corrosion resistance than those on CS. Their adhesion to the SS was outstanding, even after a long time of immersion in a HCl 0.8 M solution, showing that they are efficient protection barriers. The corrosion process of the substrates starts at micro-pores present in the films so that corrosion pits all over the surface of the samples can be observed.

Structural modifications and temperature stability of silicon incorporated diamond-like a-C:H films

Abstract Thermal stability of diamond-like carbon is still a problem which limits the potential applications of this material. With the aim of obtaining a material with increased stability, the behaviour of silicon incorporated hydrogenated amorphous carbon films (a-C 1− x Si x :H) under thermal annealing was investigated. Results show that the observed effects can be divided in two groups: low temperature ( T T >400°C) effects. In contrast to what is observed in case of pure a-C:H, several of the properties of the films were found to change in the low temperature range. A detailed analysis of the infrared absorption spectra showed that the density of sp 3 C H bonds is increased while the olefinic sp 2 ones are reduced by annealing. A shift of the Si H stretching mode to lower wavenumbers is also observed, indicating that void elimination may occur due to bond reconstruction. In this way, a material with reduced spin density, smaller residual stress and increased optical gap results, indicating an increased polymeric character. Upon annealing in the high temperature range, the material degradation processes of hydrogen loss and graphitization start to occur. In the case of films with low silicon content, the hydrogen effusion process is associated to the graphitization of the material. As the silicon content is increased, hydrogen effusion is shifted to higher temperatures and graphitization is inhibited due to the increased disorder presented by these films.

Amorphous SiC coatings for WC cutting tools

Abstract In this work, SiC films were deposited by r.f. magnetron sputtering onto WC and silicon substrates from a commercial sintered SiC target. After determining the influence of deposition parameters on the properties of the films deposited onto silicon substrates, suitable conditions were chosen to produce high quality 5 μm thick films on WC pieces. Mechanical characterization of the films was done by microhardness and residual stress measurements. High deposition rates (up to 40 nm/min), relatively low compressive residual stresses (

Optical and mechanical properties of DLC-Si coatings on polycarbonate

Abstract In this work, a-C:H:Si (DLC-Si) films were produced onto polycarbonate substrates by the rf-PACVD technique from gaseous mixtures of CH 4 +SiH 4 and C 2 H 2 +SiH 4 . The effects of self-bias and gas composition upon mechanical and optical properties of the films were investigated. Films deposited at low self-bias voltages showed large optical gaps, decreasing for increasing bias. Addition of silane to the discharge gas was observed to further increase the optical gap. High scratch hardness values were obtained at intermediate values of self-bias for both the films deposited from CH 4 +SiH 4 and C 2 H 2 +SiH 4 . The addition of silane induced a minor decrease in scratch hardness values. No direct correlation of scratch hardness was found with the microhardness or residual stress of the coatings.

Deposition and evaluation of DLC–Si protective coatings for polycarbonate materials

In this work, a-C:H:Si (DLC–Si) films were produced onto crystalline silicon and polycarbonate substrates by the r.f.-PACVD technique from gaseous mixtures of CH4+SiH4 and C2H2+SiH4. The effects of self-bias and gas composition upon mechanical and optical properties of the films were investigated. Micro-hardness, residual stress, surface roughness and refractive index measurements were employed for characterization. Films deposited at high self-bias showed very high deposition rates, low stress and high hardness. However, high self-bias values lead to surface damage of the samples. Smooth films could be obtained keeping self-bias voltages ∣VB∣ below 600 V to avoid surface heating and damage. C2H2-based films seemed to be more attractive as carbon source because they showed higher deposition rates, with similar hardness and surface roughness values than CH4-based films in the same conditions. The viability of producing DLC–Si films deposited by r.f.-PACVD as protective coatings for polycarbonate substrates has been demonstrated as well-adherent films were produced with low surface damage from the plasma.

Annealing effects on near stoichiometric a-SiC:H films

The effect of thermal annealing on near stoichiometric hydrogenated amorphous silicon carbide films (a-Si x C 1-x :H) deposited onto the cathode of a r.f. glow discharge system is reported. Similar results were obtained for all samples regardless of their silicon content, in the range 0.45<x<0.55. The density of Si H bonds starts to decrease at low annealing temperatures, whereas C--H bonds are only affected at temperatures higher than 500 C. It was observed that the loss of hydrogen from the films results in an increase in density of Si-C bonds. Raman results suggest that C=C bonds present inside the material are probably isolated or located in very small clusters, in contrast to low silicon content samples or pure a-C:H films. Effusion experiments showed that hydrogen from the internal surface of voids is released at low temperatures and, therefore, that the films have a porous structure. Annealing at high temperatures showed that, although a Si-C-rich network is formed, graphitization of carbon clusters still occurs. The comparison of IR and Raman results showed that the graphitization process is not related to hydrogen loss.

Magnetron sputtering SiC films investigated by AFM

Abstract Silicon carbide films were produced by r.f. magnetron sputtering from a sintered SiC target onto Si(100) substrates kept at constant temperature T =700 K, with a r.f. power of 300 W and argon gas pressure ranging from 1×10 −2 to 4 Pa. Atomic force microscopy in contact mode was used in order to study the structure and the roughness of the surface while lateral force microscopy was used to evaluate the friction coefficient of SiC films deposited under different experimental conditions. Films produced at very low argon pressures present pits on the surface. The density of pits decreases when argon pressure in the chamber is increased and films present a very smooth surface free of point defects at pressures of approximately 0.25 Pa. A further increase in the pressure increases the roughness dramatically. Films change from a smooth, stressed structure for low argon pressure to a granular-like structure with no measurable internal stress for deposition pressures of 4 Pa. An increase of the friction coefficient with argon pressure was also observed and may be associated to variation of the chemical composition of the films.