A Study on the Behavior of Water Absorption of SiOf Thin Films Deposited by Electron Cyclotron Resonance Plasma Enhanced
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A study on the behavior of water absorption of SiOF thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition method. S. P. Kim, and S. K. Choi Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusung-Dong, Yusung-Gu, Daejon, 305-701, Korea Youngsoo Park Materials and Device Laboratory, Samsung Advanced Institute of Technology, Suwon, 440-600, Korea Ilsub Chung Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon, 440746, Korea ABSTRACT Fluorinated silicon oxide (SiOF) films were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECRPECVD). The behavior of residual stress w as studied with water absorption. SiOF film showed compressive stress after deposition. The compressive stress increased after the exposure to room air. Fourier transformed infrared (FTI R) spectroscopy analysis was carried after the water absorption. However, the change of chemica l bonding structure was not observed during the water absorption in this study. After the exposu re to room air, the films were kept in dry air. The residual stress returns to the initial value after 1 week. Considering the results of the residual stress and FTIR analysis, it is supposed that the water absorption in this study occurs entirely by physical adsorption of H2O molecules to Si-F bonds on the surface. INTRODUCTION In a multilevel interconnection technology, propagation delay due to parasitic capacitance is one of the important issues. As the device scale gets smaller, the delay becomes serious. Various materials with low dielectric constant have been investigated to reduce the capacitance [1]. SiOF is one of the attractive materials for an inter-metal dielectric layer because it has a low dielectric constant and can be fabricated by simply doping fluorine to silicon oxide, which is currently used as inter-metal dielectrics [2]. However, SiOF film shows an instability of the properties when it is exposed to humid atmosphere [3-5]. It has been accepted that the water absorption is caused by the interaction between Si-F bond and water. The absorbed water causes L6.4.1
a formation of Si-OH bond [3-5]. It has been explained that the formation of Si-OH bond degrades the film properties. However, there is another possible reason of water absorption. That is physical adsorption of water on film surface [3]. Although there have been many reports on the chemical reaction between H2O and SiOF films, the experimental evidence and explanation about the physical adsorption and its effect on the film properties are not clear yet. In this study, we studied the water absorption behavior of SiOF films. The water absorption will be discussed in terms of a chemical reaction and a physical adsorption. Experimental evidence of the physical adsorption will be presented. EXPERIMENTAL DETAILS 1000-Å-thick SiOF films were deposited on chemically cleaned 4 in., , Si wafers using ECRPECVD. The base pressure of the system was < 1×
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