High-Temperature Nanoindentation Measurement for Hardness and Modulus Evaluation of Low-k Films

Abstract

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.

An Indentation Technique for Nanoscale Dynamic Viscoelastic Measurements at Elevated Temperature

“…In the first-stage measurement, a foam insulator plate and a water-cooling system were incorporated in a nanoindentation system to protect the transducer against heat convection from the heating stage. 13) To reduce thermal load drift and noise further, a Macor insulation holder was used to prevent heat conduction from the diamond stylus to the transducer. Measurement reliability was examined by using a mechanically stable SiO 2 film and an unstable organic low-k film of the same 500 mm thickness grown on a Si wafer.…”

“…11,12) The other issue concerns the measurement temperature, that is, how to reduce the thermal load drift/noise and how low or high the temperature level can be set. We developed a sharp-pointed nanoindentation method for making hardness and modulus measurements at temperatures up to 200 C in air 13) and 500 C in a vacuum. 10) During the past year, we have examined a third critical issue related to nano-viscoelastic measurements at elevated temperature.…”