Critical properties and reliability of low-k dielectrics for ULSI interconnect applications: Thickness and temperature dependence.

摘要

A fundamental understanding and detailed elucidation of the thickness dependent behavior of the key properties of low-k dielectrics IS not only necessary but also essential, and the search for the interfacial behaviors between low-k dielectrics and other layers will be an important task to achieve a thinner layers of low-k dielectrics in current and future devices.; Polytetrafluoroethylene (PTFE) has been considered as one of advanced low-k ILD materials for microelectronic interconnect and packaging applications. This study presents the thickness and temperature dependence of main key properties such as structural, mechanical, electrical, dielectric, optical, and thermal properties of on-wafer PTFE low-k polymer thin and ultrathin films, which has the lowest dielectric constant among nonporous low relative permittivity materials. PTFE polycrystalline polymer thin films ranging in thickness of 90 to 1200 nm are investigated by using ellipsometer, optical spectroscopy, nanoindentation, current-voltage (I-V) characteristic method. Both Nanospec/AFT and ellipsometer are used to measure the thickness of films at 16 selected points per sample, and then these values were averaged. In addition, the characterizations of microstructure and morphology has been studied by using small angle X-ray diffraction (SAXRD-Siemens D5000 Diffractometer), fourier transform infrared spectroscopy (MIDAC-PRS 102), and scanning electron microscopy (SEM).; Our results show that thermal, dielectric, optical, and mechanical properties such as the solid-liquid transition temperature, coefficient of thermal expansion, dielectric strength, refractive index, Young's modulus, hardness of low-k polycrystalline polymer thin films strongly depend on the film thickness, and this thickness dependence can be related to the microstructure and morphology of the film. These thickness and temperature dependent behaviors can be also well described by the proposed model and a good agreement with experimental and theoretical results is obtained. It is demonstrated that the low-k dielectric thickness is an important design parameter: a fine turning of the thickness can be used to obtain the desirable reliability and key properties.