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A nanoscale dynamic mechanical analysis (nano-DMA) measurement method has been successfully developed for use in evaluating nanoscale dynamic viscoelastic properties in small-scale polymer materials over a range of non-ambient temperatures from -120 oC to 500 oC. Measurements have been obtained with a nanoindentation measurement system, in which two key techniques are applied. One is a thermal protection system for control and prevention of thermal drift and noise. The other is an environmental control system for preventing corrosion at high temperatures and dew condensation at low temperatures. Measurement reliability was examined by using a combination of a thermal-mechanically stable fused silica and a homogeneous sample of isotropic polyethylene terephthalate (PET). Constant hardness and modulus values of the fused silica from -120 oC to 500 oC indicated that the measurements were not affected by thermal load drift and noise even at elevated temperatures. The PET sample exhibited no significant difference in temperature dispersions of storage elastic modulus, loss elastic modulus and loss tangent between the nanoindentation measurement data and bulk data measured with a conventional DMA method. A practical application involving surface-deteriorated polyethylene (PE) tubes was used to demonstrate the validity and usefulness of this nano-DMA method. Infrared spectroscopic imaging revealed that the surface layer of the PE tubes was oxidized to form a carbonylated (O=C<) layer. The storage elastic modulus and glass-transition temperature of the surface layer were much higher than the corresponding values of the interior. These data indicate a plausible reason for why the PE tube surface deteriorates to form brittle cracks.
Nanoscratch test used for small area measurements and four-point bending test applied for quantitative measurements were coupled to evaluate the adhesive strengths of SiCN/Cu/Ta,/TaN/SiO2/Si stacked layers. The similarities and differences of the two methods concerning adhesion, position of the delamination interface, and plastic deformation of the delaminated film were estimated. It was found that the nanoscratch test gave similar adhesion properties when the delamination interface was the same as that formed by the four-point bending test. The four-point bending test displayed clearer results compared to the nanoscratch test because energy for delamination was not used in plastic deformation and the crack could propagate further. These results suggest that coupling the nanoscratch and four-point bending tests is powerful way to estimate and understand adhesion of thin film materials.
A novel technique that combines laser thermoreflectance measurement with the 3-omega method is proposed for evaluating the heat capacity of low-k films and the heat resistance at the interface between the low-k film and Si substrate. It was demonstrated that the heat capacity of thin films and the heat resistance at the interface can be determined by obtaining the heat effusivity of the film from laser thermoreflectance measurements, the total heat resistance obtained with the 3-omerga method, and the film density and thickness found from x-ray reflectivity measurements. The heat capacity of SiOC films was determined to be Cp(SiOC) =1.1 kJ/kgK with interface heat resistance of Rint(SiOC) = -2.37×10−8 m2k/W, while the heat capacity of Th-ox films was determined to be Cp(Th−ox) =0.61 kJ/kgK with Rint(Th−ox) = +1.74×10−8 m2k/W. A DSC heat capacity measurement confirmed the reliability of the evaluated Cp data. XRR and TEM examinations revealed that the negative interface heat resistance exhibited by the SiOC films originated from a high density layer at the interface between the film and Si substrate; and the positive interface heat resistance displayed by the Th-ox films stemmed from atomic defects at the interface between the film and Si substrate. These results confirmed that this method is a reliable and effective method for evaluating the heat capacity of low-k films and the heat resistance at the interface.
A recently developed bidirectional thermal expansion measurement (BTEM) method was applied to different types of low-k films to substantiate the reliability of the Poisson's ratio found with this technique and thereby to corroborate its practical utility. In this work, the Poisson's ratio was determined by obtaining the temperature gradient of the biaxial thermal stress from substrate curvature measurements, the temperature gradient of the whole thermal expansion strain along the film thickness from x-ray reflectivity (XRR) measurements, and reduced modulus of the film from nanoindentation measurements. For silicon oxide-based SiOC film having a thickness of 382.5 nm, the Poisson's ratio, Young's modulus and thermal extension coefficient (TEC) were determined to be Vf = 0.26, αf =21 ppm/K and Ef =9,7 GPa. These data are close to the levels of metals and polymers rather than the levels of fused silicon oxide, which is characterized by Vf = 0.17 and Er = 69.6 GPa. The alkyl component in the silicon oxide-based framework is thought to act as an agent in reducing the modulus and elevating the Poisson's ratio in SiOC low-k materials. In the case of an organic polymer SiLK film with a thickness of 501.5 nm, the Poisson's ratio, Young's modulus and TEC were determined to be Vf = 0.39, αf =74 ppm/K and Er =3.1 GPa, which are in the typical range of V= 0.34~0.47 with E =1.0~10 GPa for polymer materials. From the viewpoint of the relationship between the Poisson's ratio and Young's modulus as classified by different material types, the Poisson's ratios found for the silicon oxide-based SiOC and organic SiLK films are reasonable values, thereby confirming that BTEM is a reliable and effective method for evaluating the Poisson's ratio of thin films.
A spherical nanoindentation method was developed to evaluate elastic and plastic deformation parameters. The experimental reliability was confirmed by examining fused silica in the elastic deformation range. Yield stress as a quantitative plastic parameter was estimated using the Hertz contact theory and Tresca yield criterion. A copper thin film and two types of low-k thin film were examined. Reduced modulus was almost the same as the value obtained for the Cu (100) plane and yield stress was found to be between single crystals Cu (111) and Cu (100). These mechanical properties were thought to be dependent on the crystal orientation of the copper thin film. The two types of MSQ low-k film exhibited a difference in yield stress, although hardness was estimated to be similar by using the conventional nanoindentation method. These results have never been seen on a micro-mater scale.
A high-temperature nanoindentation measurement method has been developed for evaluating the hardness and modulus of low-k films when the temperature is raised from R.T. to 200°C. Thermal stability and chemical changes due to heating were investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetry-differential thermal analysis, and by thermal desorption spectroscopy, respectively. Two different classes of low-k materials, organic polyarylence ether film and methyl-hydrogen-silsesquioxane film, were examined. The hardness and modulus of the former film during heating increased due to water desorption in the lower temperature range, and then decreased due to the evolution of hydrocarbon gas from some unreacted components or solvent residuals in the higher temperature range. In regard to the latter film, the hardness and modulus of a specimen (A) having a higher hydrocarbon content decreased during heating and reached the lowest value at 200°C and then constantly remained at the lowest levels during cooling. In contrast, no significant changes in hardness and modulus were observed for a specimen (B) having a lower hydrocarbon content in either the heating or cooling process. The reduction of the hardness and modulus of specimen A was attributed to thermal decomposition of most of its Si-CH3 and SiH/SiH2 chains. These results revealed that the temperature dependence of the hardness and modulus of low-k films is significantly affected by physical and/or chemical changes during heating due to moisture absorption, thermal evolution of organic residuals and thermal decomposition, rather than other factors such as thermal stress.
A convenient nanoscratch method was combined with atomic force microscope
(AFM) and transmission electron microscope (TEM) observations to conduct the
first-ever evaluation of the adhesion strength of a complicated
Cu/Ta/TaN/pSiO2/low-k/SiC/pSiO2/Si-substrate with the
aim of correlating the fracture strength with the results of chemical
mechanical polishing (CMP) tests. Concretely, this evaluation focused on the
fact that specimens having a low-k layer pretreated with rare-gas plasma
prior to the deposition of the SiO2 layer exhibited low
delaminated densities in the Cu CMP process. It was found that a specimen
with the rare-gas plasma pretreatment exhibited a higher friction
coefficient, a higher critical load and brittle adhesive failure resulting
from delamination at the interface between the low-k and SiC layers. A
specimen without the rare-gas plasma pretreatment displayed a lower friction
coefficient, a lower critical load, and ductile cohesive failure in the
low-k layer. Because less plastic deformation was observed in the low-k
layer subjected to the rare-gas plasma pretreatment, it is assumed that the
pretreatment reinforced the mechanical properties of the low-k layer, making
it more resistant to ductile cohesive failure. These results agreed with the
CMP test data and indicated that the nanoscratch method makes it possible to
predict the ability of complicated Cu/low-k interconnect structures to
withstand the CMP process.
Two kinds of obviously different-sized –Si3N4 whiskers were grown from silicon melt with different pretreatment vacuum conditions. Their growth interface structures were studied in a cross-section view from micro-areas to macro-areas by combination of micro-area state analysis with chemical shift mapping of Si Kβ bands using electron probe microanalysis. The one pretreated under the lower vacuum condition with a rotary pump was 10–20 μm in diameter and hundreds of micrometers in length, and another pretreated under the higher vacuum condition with a diffusion pump was 0.1–0.2 mm in diameter and 2–5 mm in length. The small Si3N4 whiskers were grown from the surface of the SiC particles within the Si melt. The large Si3N4 whiskers were grown from the surface of Si3N4 crucible. On the basis of these results, their growth mechanisms are discussed from the view of the nucleation sites, impurity source, and thermodynamic stability of the SiC particles. Compared with the Si3N4 grains, the SiC particles influenced the nucleation deeply and caused the process to grow small-sized crystals. Preventing the carbon impurities into the Si melt from forming the SiC particles in the pretreatment process was one effective way to grow the large-sized β–Si3N4 single crystals.
Some kinetics parameters of alumina during microwave sintering were studied and compared with that during conventional sintering. The results demonstrated that the sintering rates for microwave processing were much greater than that for conventional processing, and the grain growth of alumina was rapid with prolonged time at high temperature in a microwave field. It was indicated that the microwave sintering at higher temperatures for a shorter time was favorable for preparing high density and fine-grained alumina ceramics.
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