R.G. Lacerda

Coefficient of thermal expansion and elastic modulus of thin films

The coefficient of thermal expansion (CTE), biaxial modulus, and stress of some amorphous semiconductors (a-Si:H, a-C:H, a-Ge:H, and a-GeCx:H) and metallic (Ag and Al) thin films were studied. The thermal expansion and the biaxial modulus were measured by the thermally induced bending technique. The stress of the metallic films, deposited by thermal evaporation (Ag and Al), is tensile, while that of the amorphous films deposited by sputtering (a-Si:H, a-Ge:H, and a-GeCx:H) and by glow discharge (a-C:H) is compressive. We observed that the coefficient of thermal expansion of the tetrahedral amorphous thin films prepared in this work, as well as that of the films reported in literature, depend on the network strain. The CTE of tensile films is smaller than that of their corresponding crystalline semiconductors, but it is higher for compressive films. On the other hand, we found out that the elastic biaxial modulus of the amorphous and metallic films is systematically smaller than that of their crystalline c...

Thermal expansion coefficient of amorphous carbon nitride thin films deposited by glow discharge

Abstract The thermal expansion coefficient of a-CNx:H thin films was determined by the thermally induced bending technique. The films were deposited by glow discharge under methane and nitrogen atmosphere, and analyzed by FTIR and Raman spectroscopies, nanohardness, and stress measurements. Drastic changes of the film structure were observed as a result of the nitrogen incorporation, from 0 to 7%. The increase of nitrogen concentration reduces the deposition rate, stress, hardness, and the elastic constant of the films. It was also observed that the thermal expansion coefficient has a significant increase from approximately 2–9×10−6/K, which was associated with the increase in the sp2 concentration induced by the N incorporation, and with the increase in the concentration of CN bonds. In spite of that, stable and thick (∼2 μm) films were deposited at moderate deposition rate (0.3 nm/s), relatively high hardness (13 GPa), and low stress (0.6 GPa).

Hard a-C:H films deposited at high deposition rates

Abstract In this work, we present hard-hydrogenated amorphous carbon films at high deposition rate. The films were prepared on the cathode electrode of a conventional r.f. sputtering system. Hydrogenated amorphous carbon films with excellent properties, i.e, high hardness (15 GPa), relatively low stress (~ 1.3 GPa) and with a very high deposition rate (~0.7 nm/s) were obtained at the conditions of high bias (−800 V) and high methane gas pressure (0.12 × 10 −1 mbar). The low band gap and the high I D / I G Raman ratio indicate that the films have high amount of sp 2 sites.

Thermomechanical properties of amorphous hydrogenated germanium‐nitrogen alloys

Stress, thermal expansion coefficient, and elastic modulus of a‐GeNx:H thin films prepared by the rf reactive sputtering method are reported. Stress measurements were made using a Dektak profilometer. A second apparatus based on the deflection of a HeNe laser beam was used to determine the thermal expansion coefficient and the stirring modulus, (E/1−ν), by the thermally induced bending method.