Effect of CH4 Plasma Treatment on O2 Plasma Ashed Organosilicate Low-k Dielectrics
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Effect of CH4 Plasma Treatment on O2 Plasma Ashed Organosilicate Low-k Dielectrics Hualiang Shi1, Junjing Bao1, Junjun liu1, Huai Huang1, Paul S. Ho1, Michael D. Goodner2, Mansour Moinpour2, and Grant M. Kloster2 1 Laboratory for Interconnect and Packaging, The University of Texas at Austin, Microelectronics Research Center, PRC, Bldg. 160, 10100 Burnet Road, Austin, TX, 78758 2 Logic Technology Development, Intel Corporation, Hillsboro, OR, 97124 ABSTRACT During an O2 plasma ashing process, carbon depletion and subsequent moisture uptake caused an increase of keff and the leakage current in an organosilicate (OSG) low-k dielectric. For dielectric restoration, an additional CH4 plasma treatment on the O2 plasma ashed OSG lowk dielectric was investigated using angle resolved x-ray photoelectron spectroscopy (ARXPS), XPS depth profiling, x-ray reflectivity (XRR), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and contact angle goniometer. After CH4 plasma treatment on the O2 plasma ashed OSG, the surface carbon concentration and surface hydrophobicity were partially recovered. A dense surface layer containing C=C bonds was found to have formed on the top of the damaged OSG. The C-V hysteresis and the leakage current were reduced as a result of the CH4 plasma treatment. XPS depth profiling revealed that the recovery effect was limited to the surface region. INTRODUCTION Ultra low-k dielectrics with porosity are being developed to reduce the capacitance coupling in Cu interconnects for their lower polarizability and lower density of atoms and bonds [1, 2]. However, these porous low-k dielectrics tend to degrade during O2 plasma ashing processes due to carbon depletion and moisture uptake. This dielectric loss may limit further scaling of low-k dielectrics. Mechanisms of plasma damage and recovery of the dielectric loss have generated enormous interests [3, 4]. Inspired by recent studies [5, 6] on the interaction between CH4 plasma and pristine low-k dielectrics, this paper was focused on the recovery effect of CH4 plasma treatment on O2 plasma ashed organosilicate (OSG) low-k dielectrics. First, plasma damage in an O2 plasma ashing process was evaluated. Then, CH4 plasma treatment on O2 plasma ashed OSG was studied by multiple analytical methods. EXPERIMENT The pristine OSG film in this study has a porosity of 25%, a density of 1.25 g/cm3, and a dielectric constant of 2.5. Samples were damaged by O2 plasma for 5 seconds in March Asher under the condition of 300 W and 50 sccm. XPS depth profiling was performed in PHI 5700 xray photoelectron spectroscopy (XPS) system to investigate the change of atomic concentrations through OSG films. Nicolet Magna 560 FTIR was used to evaluate bonding configuration changes.
To study the recovery effect of CH4 plasma treatment on O2 plasma ashed OSG, samples were treated in an Oxford RIE chamber for 30 seconds under the condition of 50 W, 10 mtorr, and 30 sccm. The surface chemical composition was evaluated using XPS. The surface hydrophobicity was eva
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