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Title: Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics

Abstract

Porous SiCOH films are of great interest in semiconductor fabrication due to their low-dielectric constant properties. Post-deposition treatments using ultraviolet (UV) light on organosilicate thin films are required to decompose labile pore generators (porogens) and to ensure optimum network formation to improve the electrical and mechanical properties of low-k dielectrics. The goal of this work is to choose the best vacuum-ultraviolet photon energy in conjunction with vacuum ultraviolet (VUV) photons without the need for heating the dielectric to identify those wavelengths that will have the most beneficial effect on improving the dielectric properties and minimizing damage. VUV irradiation between 8.3 and 8.9 eV was found to increase the hardness and elastic modulus of low-k dielectrics at room temperature. Combined with UV exposures of 6.2 eV, it was found that this “UV/VUV curing” process is improved compared with current UV curing. We show that UV/VUV curing can overcome drawbacks of UV curing and improve the properties of dielectrics more efficiently without the need for high-temperature heating of the dielectric.

Authors:
; ; ; ; ; ; ;  [1]; ; ;  [2];  [3]
  1. Plasma Processing and Technology Laboratory and Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
  2. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China)
  3. Stanford University, Stanford, California 94305 (United States)
Publication Date:
OSTI Identifier:
22590800
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 108; Journal Issue: 24; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CURING; DAMAGE; DEPOSITION; DIELECTRIC MATERIALS; FABRICATION; FAR ULTRAVIOLET RADIATION; HARDNESS; HEATING; IRRADIATION; PERMITTIVITY; POROUS MATERIALS; SEMICONDUCTOR MATERIALS; TEMPERATURE RANGE 0273-0400 K; THIN FILMS; WAVELENGTHS

Citation Formats

Zheng, H., Guo, X., Pei, D., Li, W., Blatz, J., Hsu, K., Benjamin, D., Shohet, J. L., E-mail: shohet@engr.wisc.edu, Lin, Y.-H., Fung, H.-S., Chen, C.-C., and Nishi, Y.. Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics. United States: N. p., 2016. Web. doi:10.1063/1.4954176.
Zheng, H., Guo, X., Pei, D., Li, W., Blatz, J., Hsu, K., Benjamin, D., Shohet, J. L., E-mail: shohet@engr.wisc.edu, Lin, Y.-H., Fung, H.-S., Chen, C.-C., & Nishi, Y.. Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics. United States. doi:10.1063/1.4954176.
Zheng, H., Guo, X., Pei, D., Li, W., Blatz, J., Hsu, K., Benjamin, D., Shohet, J. L., E-mail: shohet@engr.wisc.edu, Lin, Y.-H., Fung, H.-S., Chen, C.-C., and Nishi, Y.. 2016. "Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics". United States. doi:10.1063/1.4954176.
@article{osti_22590800,
title = {Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics},
author = {Zheng, H. and Guo, X. and Pei, D. and Li, W. and Blatz, J. and Hsu, K. and Benjamin, D. and Shohet, J. L., E-mail: shohet@engr.wisc.edu and Lin, Y.-H. and Fung, H.-S. and Chen, C.-C. and Nishi, Y.},
abstractNote = {Porous SiCOH films are of great interest in semiconductor fabrication due to their low-dielectric constant properties. Post-deposition treatments using ultraviolet (UV) light on organosilicate thin films are required to decompose labile pore generators (porogens) and to ensure optimum network formation to improve the electrical and mechanical properties of low-k dielectrics. The goal of this work is to choose the best vacuum-ultraviolet photon energy in conjunction with vacuum ultraviolet (VUV) photons without the need for heating the dielectric to identify those wavelengths that will have the most beneficial effect on improving the dielectric properties and minimizing damage. VUV irradiation between 8.3 and 8.9 eV was found to increase the hardness and elastic modulus of low-k dielectrics at room temperature. Combined with UV exposures of 6.2 eV, it was found that this “UV/VUV curing” process is improved compared with current UV curing. We show that UV/VUV curing can overcome drawbacks of UV curing and improve the properties of dielectrics more efficiently without the need for high-temperature heating of the dielectric.},
doi = {10.1063/1.4954176},
journal = {Applied Physics Letters},
number = 24,
volume = 108,
place = {United States},
year = 2016,
month = 6
}
  • High frequency capacitance-voltage (C-V) measurements are used to determine the effects of vacuum ultraviolet (VUV) and ultraviolet (UV) irradiation on defect states in porous low-k organosilicate (SiCOH) dielectrics. The characteristics show that VUV photons depopulate trapped electrons from defect states within the dielectric creating trapped positive charge. This is evidenced by a negative shift in the flat-band voltage of the C-V characteristic. UV irradiation reverses this effect by repopulating the defect states with electrons photoinjected from the silicon substrate. Thus, UV reduces the number of trapped positive charges in the dielectric and can effectively repair processing-induced damage.
  • The temporary increase in the electrical surface conductivity of low-k organosilicate glass (SiCOH) during exposure to vacuum-ultraviolet radiation (VUV) is investigated. To measure the photoconductivity, patterned “comb structures” are deposited on dielectric films and exposed to synchrotron radiation in the range of 8–25 eV, which is in the energy range of most plasma vacuum-ultraviolet radiation. The change in photo surface conductivity induced by VUV radiation may be beneficial in limiting charging damage of dielectrics by depleting the plasma-deposited charge.
  • Vacuum ultraviolet (VUV) photoemission spectroscopy is used to investigate the effect of VUV radiation on porous organosilicate (SiCOH) dielectrics during plasma processing. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies less than 9.0 eV was found to be beneficial in depleting accumulated charge in SiCOH films while VUV photons with higher energies did not have this effect. Moreover, VUV irradiation with 8.9 eV photons depletes the most charge. From this result, it can be concluded that 8.9 eV is the bandgap plus the electron affinity energy of SiCOH dielectrics.
  • Vacuum ultraviolet (VUV) irradiation is generated during plasma processing in semiconductor fabrications, while the effect of VUV irradiation on the dielectric constant (k value) of low-k materials is still an open question. To clarify this problem, VUV photons with a range of energies were exposed on low-k organosilicate dielectrics (SiCOH) samples at room temperature. Photon energies equal to or larger than 6.0 eV were found to decrease the k value of SiCOH films. VUV photons with lower energies do not have this effect. This shows the need for thermal heating in traditional ultraviolet (UV) curing since UV light sources do notmore » have sufficient energy to change the dielectric constant of SiCOH and additional energy is required from thermal heating. In addition, 6.2 eV photon irradiation was found to be the most effective in decreasing the dielectric constant of low-k organosilicate films. Fourier Transform Infra-red Spectroscopy shows that these 6.2 eV VUV exposures removed organic porogens. This contributes to the decrease of the dielectric constant. This information provides the range of VUV photon energies that could decrease the dielectric constant of low-k materials most effectively.« less
  • Vacuum ultraviolet (VUV) photoemission spectroscopy is utilized to investigate the distribution of trapped charges within the bandgap of low dielectric constant (low-k) organosilicate (SiCOH) materials. It was found that trapped charges are continuously distributed within the bandgap of porous SiCOH and the center of the trapped states is 1.3 eV above the valence band of the tested sample. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies between 7.6 and 8.9 eV was found to deplete trapped charge while UV exposure with photon energies less than 6.0 eV induces more trapped charges in tested samples. Current-Voltage (IV)more » characteristics results show that the reliability of dielectrics is improved after VUV irradiation with photon energies between 7.6 and 8.9 eV, while UV exposure results in an increased level of leakage current and a decreased breakdown voltage, both of which are harmful to the reliability of the dielectric. This work shows that VUV irradiation holds the potential to substitute for UV curing in microelectronic processing to improve the reliability of low-k dielectrics by mitigating the leakage currents and trapped charges induced by UV irradiation.« less