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Title: Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials

Abstract

Stress-Induced Leakage Current (SILC) behavior during the dielectric degradation of ultra-porous SiOCH low-k materials was investigated. Under high voltage stress, SILC increases to a critical value before final hard breakdown. This SILC increase rate is mainly driven by the injected charges and is negligibly influenced by temperature and voltage. SILC is found to be transient and shows a t{sup −1} relaxation behavior, where t is the storage time at low voltages. This t{sup −1} transient behavior, described by the tunneling front model, is caused by both electron charging of neutral defects in the dielectric close to the cathode interface and discharging of donor defects close to the anode interface. These defects have a uniform density distribution within the probed depth range, which is confirmed by the observed flat band voltage shift results collected during the low voltage storage. By applying an additional discharging step after the low voltage storage, the trap energies and spatial distributions are derived. In a highly degraded low-k dielectric, the majority of defects have a trap depth between 3.4 eV and 3.6 eV and a density level of 1 × 10{sup 18 }eV{sup −1 }cm{sup −3}. The relation between the defect density N and the total amount of the injected charges Qmore » is measured to be sub-linear, N ∼ Q{sup 0.45±0.07}. The physical nature of these stress-induced defects is suggested to be caused by the degradation of the Si-O based skeleton in the low-k dielectric.« less

Authors:
;  [1];  [2]; ; ; ; ; ; ; ; ; ;  [1]
  1. imec, Kapeldreef 75, 3001 Leuven (Belgium)
  2. (Belgium)
Publication Date:
OSTI Identifier:
22492853
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 16; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANODES; CATHODES; DEPTH; DIELECTRIC MATERIALS; ELECTRIC POTENTIAL; INTERFACES; LEAKAGE CURRENT; POROUS MATERIALS; RELAXATION; SPATIAL DISTRIBUTION; STRESSES; TRANSIENTS; TRAPS; TUNNEL EFFECT

Citation Formats

Wu, C., E-mail: Chen.Wu@imec.be, De Wolf, I., Department of Materials Engineering, KU Leuven, 3000 Leuven, Li, Y., Leśniewska, A., Varela Pedreira, O., Marneffe, J.-F. de, Ciofi, I., Verdonck, P., Baklanov, M. R., Bömmels, J., Tőkei, Zs., and Croes, K. Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials. United States: N. p., 2015. Web. doi:10.1063/1.4934520.
Wu, C., E-mail: Chen.Wu@imec.be, De Wolf, I., Department of Materials Engineering, KU Leuven, 3000 Leuven, Li, Y., Leśniewska, A., Varela Pedreira, O., Marneffe, J.-F. de, Ciofi, I., Verdonck, P., Baklanov, M. R., Bömmels, J., Tőkei, Zs., & Croes, K. Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials. United States. doi:10.1063/1.4934520.
Wu, C., E-mail: Chen.Wu@imec.be, De Wolf, I., Department of Materials Engineering, KU Leuven, 3000 Leuven, Li, Y., Leśniewska, A., Varela Pedreira, O., Marneffe, J.-F. de, Ciofi, I., Verdonck, P., Baklanov, M. R., Bömmels, J., Tőkei, Zs., and Croes, K. Wed . "Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials". United States. doi:10.1063/1.4934520.
@article{osti_22492853,
title = {Correlation between stress-induced leakage current and dielectric degradation in ultra-porous SiOCH low-k materials},
author = {Wu, C., E-mail: Chen.Wu@imec.be and De Wolf, I. and Department of Materials Engineering, KU Leuven, 3000 Leuven and Li, Y. and Leśniewska, A. and Varela Pedreira, O. and Marneffe, J.-F. de and Ciofi, I. and Verdonck, P. and Baklanov, M. R. and Bömmels, J. and Tőkei, Zs. and Croes, K.},
abstractNote = {Stress-Induced Leakage Current (SILC) behavior during the dielectric degradation of ultra-porous SiOCH low-k materials was investigated. Under high voltage stress, SILC increases to a critical value before final hard breakdown. This SILC increase rate is mainly driven by the injected charges and is negligibly influenced by temperature and voltage. SILC is found to be transient and shows a t{sup −1} relaxation behavior, where t is the storage time at low voltages. This t{sup −1} transient behavior, described by the tunneling front model, is caused by both electron charging of neutral defects in the dielectric close to the cathode interface and discharging of donor defects close to the anode interface. These defects have a uniform density distribution within the probed depth range, which is confirmed by the observed flat band voltage shift results collected during the low voltage storage. By applying an additional discharging step after the low voltage storage, the trap energies and spatial distributions are derived. In a highly degraded low-k dielectric, the majority of defects have a trap depth between 3.4 eV and 3.6 eV and a density level of 1 × 10{sup 18 }eV{sup −1 }cm{sup −3}. The relation between the defect density N and the total amount of the injected charges Q is measured to be sub-linear, N ∼ Q{sup 0.45±0.07}. The physical nature of these stress-induced defects is suggested to be caused by the degradation of the Si-O based skeleton in the low-k dielectric.},
doi = {10.1063/1.4934520},
journal = {Journal of Applied Physics},
number = 16,
volume = 118,
place = {United States},
year = {Wed Oct 28 00:00:00 EDT 2015},
month = {Wed Oct 28 00:00:00 EDT 2015}
}
  • Time dependent dielectric failure has become a pivotal aspect of interconnect design as industry pursues integration of sub-22 nm process-technology nodes. Literature has provided key information about the role played by individual species such as electrons, holes, ions, and neutral impurity atoms. However, no mechanism has been shown to describe how such species interact and influence failure. Current leakage relaxation in low-k dielectrics was studied using bipolar field experiments to gain insight into how charge carrier flow becomes impeded by defects within the dielectric matrix. Leakage current decay was correlated to injection and trapping of electrons. We show that current relaxationmore » upon inversion of the applied field can be described by the stretched exponential function. The kinetics of charge trapping events are consistent with a time-dependent reaction rate constant, k=k{sub 0}⋅(t+1){sup β−1}, where 0 < β < 1. Such dynamics have previously been observed in studies of charge trapping reactions in amorphous solids by W. H. Hamill and K. Funabashi, Phys. Rev. B 16, 5523–5527 (1977). We explain the relaxation process in charge trapping events by introducing a nonlinear charge trapping model. This model provides a description on the manner in which the transport of mobile defects affects the long-tail current relaxation processes in low-k films.« less
  • Porous dielectric materials provide lower capacitances that reduce RC time delays in integrated circuits. Typical low-k materials include porous SiOCH-silicon dioxide with carbon groups, principally CH{sub 3}, lining the pores. With a high porosity, internally connected pores provide pathways for reactive species to enter into the material. Fluorocarbon plasmas are often used to etch SiOCH, a process that leaves a fluorocarbon polymer on the surface that must later be removed. During cleaning using Ar/O{sub 2} or He/H{sub 2} plasmas, reactions of radicals that diffuse into the SiOCH and photons that penetrate into the SiOCH can remove -CH{sub 3} groups. Duemore » to its higher reactivity, cleaning with Ar/O{sub 2} plasmas removes more -CH{sub 3} groups than He/H{sub 2} plasmas, and so produce more free radical sites, such as -SiO{sub 2} Bullet (a -SiO{sub 2}-CH{sub 3} site with the -CH{sub 3} group removed).Upon exposure to humid air, these free radical sites can chemisorb H{sub 2}O to form hydrophilic Si-OH which can further physisorb H{sub 2}O through hydrogen bonding to form Si-OH(H{sub 2}O). With the high dielectric constant of water, even a small percentage of water uptake can significantly increase the effective dielectric constant of SiOCH. In this paper, we report on results from a computational investigation of the cleaning of SiOCH using Ar/O{sub 2} or He/H{sub 2} plasmas and subsequent exposure to humid air. The authors found that plasma cleaning with He/H{sub 2} mixtures produce less demethylation than cleaning with Ar/O{sub 2} plasmas, as so results in less water uptake, and a smaller increase in dielectric constant. The water that produces the increase in dielectric constant is roughly half chemisorbed and half physisorbed, the latter of which can be removed with mild heating. Sealing the pores with NH{sub 3} plasma treatment reduces water uptake and helps prevent the increase in dielectric constant.« less
  • Low-field leakage current has been measured in thin oxides after exposure to ionizing radiation. This Radiation Induced Leakage Current (RILC) can be described as an inelastic tunneling process mediated by neutral traps in the oxide, with an energy loss of about 1 eV. The neutral trap distribution is influenced by the oxide field applied during irradiation, thus indicating that the precursors of the neutral defects are charged, likely being defects associated to trapped holes. The maximum leakage current is found under zero-field condition during irradiation, and it rapidly decreases as the field is enhanced, due to a displacement of themore » defect distribution across the oxide towards the cathodic interface. The RILC kinetics are linear with the cumulative dose, in contrast with the power law found on electrically stressed devices.« less
  • The degradation and breakdown mechanisms of a SiOCH low-k material with k = 2.3 (25% porosity) and thicknesses ranging from 90 nm to 20 nm were investigated. By combining the time dependent dielectric breakdown data at positive/negative bias stress with the thickness scaling results, dielectric failure is proven to be intrinsic and not influenced by copper drift or metal barrier deposition induced dielectric damage. It is shown that stress induced leakage current (SILC) can be used as a measure of dielectric degradation. Therefore, low field lifetimes can be safely estimated using SILC extrapolation. Based on our results, both the impact damage model and themore » power law model have a good accuracy for low field lifetime prediction. Recovery and anneal experiments are used to study the physical nature causing the observed negative flatband voltage shifts in our metal-insulator-semiconductor planar capacitor structures, where hydrogen induced unstable fast and slow donor type interface states are hypothesized to be the root cause of the observed shifts. We suggest that atomic hydrogen is released from the dielectric during electron injection and migrates to the interfacial region. Our model is further supported by an observed irreversible SILC change during the recovery and anneal studies. The degradation mechanism proposed in this work, supported by the low field lifetime data, provides a feasible explanation for intrinsic low-k dielectric failure.« less