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Journal of Vacuum Science & Technology B / Volume 28 / Issue 2 / Regular Articles

J. Vac. Sci. Technol. B 28, 284 (2010); http://dx.doi.org/10.1116/1.3308623 (11 pages)

Influence of C4F8/Ar-based etching and H2-based remote plasma ashing processes on ultralow k materials modifications

Ming-Shu Kuo1, Xuefeng Hua2, G. S. Oehrlein1, A. Ali3, P. Jiang3, P. Lazzeri4, and M. Anderle4

1Department of Materials Science and Engineering and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742
2Department of Physics and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742
3Texas Instruments, Inc., Dallas, Texas 75243
4ITC-irst, via Sommarive 18, 38050 Povo, Trento, Italy

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(Published online 19 March 2010)

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The authors evaluated photoresist (PR) stripping processes that are compatible with ultralow dielectric constant (ULK) materials using H2-based remote plasmas generated in an inductively coupled plasma reactor. The materials used were 193 nm PR and nanoporous SiCOH-based ULK (JSR LKD 5109). PR ashing rates and ULK damage (carbon depletion) were measured for H2, H2/N2, and H2/Ar discharges as a function of substrate temperature over the range of 200–275 °C. They employed ellipsometry, x-ray photoelectron spectroscopy (XPS), optical emission spectroscopy, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) for analysis. For their H2 remote plasmas and a substrate temperature in the range of 200–275 °C, the PR ashing rate varied from 270 to 880 nm/min, whereas 3–5 nm of ULK damage was measured for 20 s remote plasma exposure. As a useful process metric, they defined ashing efficiency as the thickness of PR removed over the thickness of ULK simultaneously damaged. PR stripping processes can be optimized to an ashing efficiency of ∼ 60 for substrate temperatures above 250 °C, if pure H2 discharges are employed. The addition of N2 or Ar to H2 did not improve the ashing rate and, especially for N2, such additions dramatically increased ULK damage. This resulted in reduced ashing efficiency for these cases. To clarify the impact of etching/ashing process interactions on ULK modification, they exposed blanket ULK film to C4F8/Ar-based etching plasmas employing a dual frequency (40.68/4 MHz) capacitively coupled plasma (CCP) reactor. Plasma exposures of the ULK were performed utilizing a silicon roof, which shielded the ULK film located underneath from direct ion bombardment. Since the aspect ratio of the small gap structure was selected to be equal to that of an actual trench structure, trench sidewall-like surface modifications induced by etching processes along with their impact on ashing damage that were introduced during a subsequent PR stripping process can be simulated and studied on blanket films with appropriate size. XPS revealed fluorocarbon (FC) deposition together with ∼ 3 nm of ULK damage on the ULK film surface after the FC plasma etching process. Most of the deposited FC material was removed during a subsequent H2-based remote plasma treatment at 275 °C. The influence of surface modifications introduced by the prior C4F8/Ar-based etching exposure on hydrogen permeation of the ULK material during a subsequent H2 remote plasma ashing process was studied by substituting deuterium (D2) for H2 in the remote plasma process and performing ToF-SIMS analysis. ToF-SIMS depth profiling of ULK films exposed to D2 plasma showed reduced D permeation in the ULK films with C4F8/Ar etching plasma exposure relative to that without such FC plasma exposure. Photoresist patterned ULK structures were also processed, employing the same ashing conditions after prior FC plasma etching in the CCP reactor. The ULK damage results measured with trench structures were consistent with the above findings obtained with blanket ULK films.

© 2010 American Vacuum Society

ACKNOWLEDGMENTS

Financial support of this work by the Semiconductor Research Corporation’s Center for Advanced Interconnect Sciences and Technology (CAIST) is gratefully acknowledged. The authors also thank L. Ling, R. L. Bruce, and S. Engelmann for assistance and discussion, and the International SEMATECH and Texas Instruments for supplying the ultralow-k, low-k, and photoresist materials.

Article Outline

  1. INTRODUCTION
  2. EXPERIMENTAL SETUP AND PROCEDURES
  3. RESULTS AND DISCUSSION
    1. Blanket materials exposed to remote discharges
      1. Ashing efficiency
      2. Composition of H2/N2 plasmas
      3. Remote plasma/material reaction
        1. Apparent activation energy
        2. Characteristics of H2/N2 mixture remote plasmas in materials processing
        3. Reaction mechanism and influence on ashing efficiency
    2. Etching/ashing combined experiments
      1. Trench sidewall evolution for sequential plasma processes
      2. Effects of etching-introduced modification on ashing damage
      3. Actual pattern transfer process for ULK materials
  4. CONCLUSIONS

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KEYWORDS and PACS

Keywords

argon, carbon compounds, hydrogen, low-k dielectric thin films, sputter etching, Porous SiCOH, 193 nm (ArF) photoresist, Ultralow k dielectric materials, SiCOH, Organosilicate

PACS

  • 77.55.Bh

    Low-permittivity dielectric films

  • 52.77.Bn

    Etching and cleaning

  • 81.65.Cf

    Surface cleaning, etching, patterning

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History
Received 20 July 2009
Accepted 11 January 2010
Published online 19 March 2010
Digital Object Identifier
http://dx.doi.org/10.1116/1.3308623

PUBLICATION DATA

ISSN

1071-1023 (print)  
1520-8567 (online)

Publisher

American Vacuum Society

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