Effect of plasma interactions with low-κ films as a function of porosity, plasma chemistry, and temperature

Abstract

Integration of new low-κ interlayer dielectrics (ILD) with current damascene schemes is a continuing issue in the microelectronics industry. During integration of the ILD, processing steps such as plasma etching, resist strip, and chemical-mechanical planarization are known to chemically alter a layer of the dielectric. Here, porous organosilicate glass (OSG) ILD films, which—according to the 2004 edition of the International Technology Roadmap for Semiconductors—are projected for use in the 65 and 45 nm nodes, are investigated. spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are used to characterize the modified layer of the ILD after exposure to O2 or H2 resist strip plasmas. The effects of the two types of plasma etch chemistries on the formation of the modified layer were found to differ significantly. These effects include both the degree of modification (i.e., chemical composition) and depth of the modified layer. A key difference between the O2 and H2 plasmas is that silicon hydride groups are present in the modified layer after exposure to H2 plasma but not after exposure to the O2 plasma. In addition, the influence of OSG porosity on the etch rate and modified layer thickness was investigated for porosities ranging from 0–45 %. As expected, the etch rate was found to increase rapidly with porosity. Finally, conditions including reactive gas concentrations and substrate temperature for the H2 plasma were varied. These parameters produced considerable changes in the chemistry of the modified layer, especially in the amount of hydrogen incorporated into the film. Details of these results will be discussed in the context of the mechanism by which modification and etching occurs as well as which process variables dominate those phenomena.