Residual Stress In As-deposited Films Research Articles

Reduction of residual stress in polymorphous silicon germanium films and their evaluation in microbolometers

Hydrogenated polymorphous silicon germanium (pm-SixGe1–x:H) thin films were deposited by the PECVD technique at 200 °C. Three compositions were investigated by changing the silane/germane gas mixture. It was found that the temperature coefficient of resistance (TCR) varies from 2.25% K−1 to 4.26% K−1 while the electrical conductivity ranges from 9.1 × 10−6 S cm−1 to 3.7 × 10−3 S cm−1. On the other hand, the residual stress of as-deposited films was highly compressive reaching values of nearly 700 MPa. After a thermal annealing of 3 hours, it was observed an acceptable reduction and a slight change towards tensile stress. A thin film with low residual stress and high TCR was chosen to manufacture test microbolometers in order to assess if the thermosensing properties of pm-SixGe1–x:H were not affected. After fabricating the microbolometers, their structural conditions were evaluated by scanning electron microscopy and it was found that the reduction of stress significantly improved their mechanical stability and reduced the warping of the membranes. Finally, test structures were characterized at a chopper frequency of 30 Hz, with a DC current of 2.5 μA in a vacuum environment of 20 mTorr. Voltage responsivity of 1.9 × 106 V/W, detectivity of 4.4 × 108 cm ∙ Hz1/2/W, NEP of 1 × 10−11 W/Hz1/2, NETD of 18 mK and 2 ms of thermal response time were measured. In summary, we have studied different process conditions to obtain better pm-SixGe1–x:H films in terms of their electrical and mechanical properties. In this sense, the results obtained with microbolometers show that pm-SixGe1–x:H is a very attractive material to develop infrared vision systems with high sensitivity.

Effects of annealing on the temperature coefficient of resistance of nickel film deposited on polyimide substrate

This study investigates the effects of annealing temperature as well as time on the temperature coefficient of resistance (TCR) of nickel (Ni) films deposited on flexible polyimide substrate by direct current magnetron sputtering. The morphological and microstructural characteristics of as-deposited and annealed Ni films were analyzed to understand the mechanisms of TCR variation. The crystalline phase, grain size change tendency and residual stress of films were evaluated by X-ray Diffractometer (XRD) technique. (111) is the preferred orientation of Ni and the grains have a growth after annealing. The residual stress in as-deposited films is about −446.3 MPa and reduced to −208.8 MPa after annealing at 400 °C for 6 h. Focused Ion Beam Electron Microscope (FIBEM) and Energy Dispersive X-ray Spectroscopy (EDS) investigations showed the microstructure of annealed films has a relative improvement and the oxygen content was little increased with increasing annealing temperature and time. Mean surface roughness determined by Atomic Force Microscope (AFM) is decreased from 4.5 nm to 1.25 nm with increasing annealing temperature. The TCR value increases with the increasing annealing temperature and time. When the annealing time exceeds 6 h, the TCR almost has no change or even begin to decline.

The mechanical properties and resistivity of Au/NiCr/Ta multi-layered films on Si-(111) substrate

Au/NiCr/Ta multi-layered metallic films were deposited on Si substrate by magnetron sputtering at different substrate temperatures. The residual stress, hardness and resistivity were investigated as a function of substrate temperature by laser polarization phase shift technique, nanoindentation technique and four point probe method, respectively. The residual stress in as-deposited films at different substrate temperatures was tension with 385 MPa–606 MPa. Nanoindentation tests at shallow indentation depths ( h ≤ t/4) where the hardness is reliable for metal films on hard substrate. Au film at deposition temperature 200 °C has the highest hardness 4.2 GPa. The resistivity in the deposited films reached the lowest value 3.1 μΩ.cm at substrate temperature 200 °C. The most interesting facts are that the hardness decreases with increasing residual stress and resistivity increases with increasing residual stress. The relationship of residual stress and resistivity may hint that there is a definite correlation between the mechanical properties and electrical properties in the metallic films.

Sputtering deposited TiNi films: relationship among processing, stress evolution and phase transformation behaviors

TiNi films were prepared by co-sputtering a Ti50Ni50 target and a Ti target under different process parameters. Stress in TiNi film on silicon substrate were evaluated using curvature method. A wide range of residual stress levels (either tensile or compressive) were found in the deposited films, depending significantly on Ti/Ni ratio, gas pressure, deposition temperature and/or annealing conditions. Stress evolution for as-deposited amorphous films during annealing process were systematically studied with the consideration of residual stress in as-deposited films; thermal stress; tensile stress due to densification crystallization; stress relaxation due to martensite transformation, etc. Upon heating, the crystallized TiNi films generated large tensile stresses when transforming from martensite to austenite, whereas during cooling, the stress relaxed significantly when austenite transformed back to the ductile martensite. The stress generation and relaxation behavior was significantly affected by film composition, deposition temperature and/or annealing temperature.

Residual stress and crystal orientation in magnetron sputtering Au films

Au films were deposited on Al 2O 3 substrate by magnetron sputtering and then annealed in Ar gas at 400 °C for 1 h. The crystal orientation, residual stress, and their relationship were investigated as a function of temperature. The residual stress in as-deposited films at different substrate temperatures was of tension (155–400 MPa) and changed to compression after samples annealing. The films were highly textured having a dominating Au(111) or a mixture of Au(111) and Au(200) orientation, and the (111)/(200) intensity ratio decreased after samples annealing. It was clarified that the stress in the plane of the film depends on crystal orientation. The film with (200)-oriented grains in the plane of the film has the lowest compressive stress and that with (111)-oriented grains has the highest tensile one. It appears that the intensity ratio of diffraction peaks of (111)/(200) can be used as a merit for the state and magnitude of residual stress in the film.

Stress and oxidation behaviours of r.f.-sputtered (Ti,Al)N films

(Ti,Al)N thin films were deposited onto A2 steel by reactive r.f. magnetron sputtering. The residual stress of as-deposited films was compressive for TiN and switched to be tensile for Ti 0.61Al 0.39N. After heating at 600 °C, the TiN film spalled off and iron oxides formed on the substrate surface, while there existed an unoxidized (Ti,Al)N layer adjacent to the substrate in the oxidized (Ti,Al)N films. The near surface of the (Ti,Al)N coating was a mixture of TiO 2 and amorphous Al 2O 3 and the diffusion of iron from the substrate through the grain boundary or pinholes resulted in the formation of iron oxides. The (Ti,Al)N films with higher Al contents after oxidation maintained a red-blue colour. The addition of Al atoms promoted the oxidation resistance of the (Ti,Al)N coating in comparison with pure TiN. As the Al contents were increased, the anti-oxidation of the (Ti,Al)N films was enhanced, while the scale thickness and the diffusion of iron through the coating were significantly decreased.