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A nanoscratch method combined with atomic force microscope and transmission electron microscope observations was used to estimate the adhesive and cohesive strengths of SiC/low-k/Si stacked layers with the aim of correlating the fracture strength with the results of chemical mechanical polishing (CMP) tests. It was found that the friction coefficient was an effective signal for detecting the occurrence of failure in the microstructure during the scratch test. Fracture strength was characterized using the critical normal load at the first abrupt decrease in the friction coefficient. A specimen (A) having a low-k layer with a lower modulus and lower hardness displayed a lower friction coefficient, a lower critical load, and ductile adhesive failure resulting from delamination at the interface between the low-k layer and Si substrate. In contrast, a specimen (B) having a low-k layer with a higher modulus and higher hardness exhibited a higher friction coefficient, a higher critical load and brittle cohesive failure that occurred in the low-k layer. It was also found that specimen A always had a higher critical load level than specimen B regardless of the scratching speed, loading rate, and stylus radius. Dependence of the critical load on specimen thickness was also examined. These nanoscratch measurements corresponded with the results of the CMP process, which suggests that the process characteristics can be predicted with this nanoscratch method.

An intercomparison of nanometric lateral scales, which are special one-dimensional (1D) grating standards with sub-hundred-nanometre pitches, among a deep-ultraviolet (DUV) laser diffractometer, a critical dimension scanning electron microscope (CD-SEM) and different types of atomic force microscope (AFM) was performed. The reference value and its expanded uncertainty were provided by the National Metrology Institute of Japan (NMIJ) using an atomic force microscope with differential laser interferometers (DLI-AFM). The consistency of the measurement results obtained using the DUV laser diffractometer, CD-SEM and some AFMs was satisfactory; however, that in the measurement results obtained using other AFMs was unsatisfactory. An improvement in AFM calibration technology using nanometrological standards is required for both AFM manufacturers and AFM users, including metrology institutes.

An original and practical method is demonstrated for determining Poisson’s ratio of thin films by detecting thermal expansion in two directions perpendicular to each other. In the direction within the film, the temperature gradient of the biaxial thermal stress Δσf∕ΔT was obtained by substrate curvature measurements; in the direction perpendicular to the film, the temperature gradient of the whole thermal expansion strain Δd∕dΔT along the film thickness d was measured by x-ray reflectivity. It was found that Poisson’s ratio of thin films with a thickness of several hundred nanometers can be determined from Δσf∕ΔT, Δd∕dΔT, reduced modulus Er of the film, and from the thermal expansion coefficient αs of the substrate.

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.

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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 ν f = 0.26, α f =21 ppm/K and E f =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 ν f = 0.17 and E r = 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 ν f = 0.39, α f =74 ppm/K and E r =3.1 GPa, which are in the typical range of ν = 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.