• Communication—Tribology of Retaining Rings in Chemical Mechanical Planarization

      Diaz, Gabriela; Peckler, Lauren; Sampurno, Yasa; Philipossian, Ara; Univ Arizona, Dept Chem & Environm Engn (ELECTROCHEMICAL SOC INC, 2018)
      Stribeck and Stribeck+ curves helped determine the tribological mechanisms in the ring-slurry-pad interface. Both methods gave consistent results with the lubrication mechanism starting at "boundary lubrication" and transitioning to "mixed lubrication" as pseudo-Sommerfeld numbers increased. COF for PPS rings were higher than PEEK. They were also higher for inter-level dielectric (ILD) processes as compared to copper. Stribeck curves were used to infer wear rate information about the ring, which in conjunction with Stribeck+ curves could help choose process parameters that balanced wafer removal with ring wear. Data cluster shapes were shown to be due to shear and normal force fluctuations. (C) 2018 The Electrochemical Society.
    • Correlating Coefficient of Friction and Shear Force to Platen Motor Current in Tungsten and Interlayer Dielectric Chemical Mechanical Planarization at Highly Non-Steady-State Conditions

      Headley, R.; Frank, C.; Sampurno, Y.; Philipossian, A.; Univ Arizona, Dept Chem & Environm Engn (ELECTROCHEMICAL SOC INC, 2019-10-16)
      Correlations between shear force and platen motor current (PMC), as well as those between coefficient of friction (COF) and PMC were investigated for various tungsten and interlayer dielectric (ILD) chemical mechanical planarization (CMP) cases where the processes were highly non steady-state. We chose to initially focus on non-steady-state conditions because we believed the relationships among shear force, COF and platen motor current to be clearer as opposed to steady-state conditions. Shear force, normal force and PMC data were collected from twelve different Stribeck+ curves at an acquisition frequency of 1,000 Hz and analyzed in order to determine any emerging trends. For the 12 cases, involving 8 pre-polished blanket CVD tungsten and 4 silicon dioxide blanket wafers, it was discovered that PMC closely mirrored shear force as evidenced by a high average correlation coefficient (0.955) and coefficient of determination (0.916) obtained from all runs. For COF vs. PMC, the average correlation coefficient and coefficient of determination for all cases were 0.758 and 0.608, respectively. These average values were dragged down by 5 cases in which the dominant tribological mechanism was found to be "boundary lubrication" where COF changed minimally with pseudo-Sommerfeld number. (C) 2019 The Electrochemical Society.
    • Correlating Removal Rate to Directivity in Copper Chemical Mechanical Planarization

      McAllister, Jeffrey; Dadashazar, Hossein; Sampurno, Yasa; Gyu Kim, Sung; Park, Dongyoul; Kwon, Heeill; Lee, Yongbin; Philipossian, Ara; Univ Arizona, Dept Chem & Environm Engn (ELECTROCHEMICAL SOC INC, 2019-11-19)
      The relationship between directivity (Delta) and removal rate (RR) during copper chemical mechanical planarization (CMP) was investigated. We measured the high-frequency shear and normal forces generated by stick-slip (which has been routinely used to explain micro- and nano-scale interactions that lead to material removal), and found there to be a strong correlation between Delta (defined as the ratio of variances in shear force to those of normal force) and copper RR so long as the tribological mechanism remained constant. In cases where the tribological mechanism changed from "boundary lubrication" (BL) to "mixed lubrication" (ML), the slope of the straight-line correlation between Delta and RR was maintained, albeit it was shifted significantly lower. This was due to the ML regime consisting of hydrostatic or buoyant forces supporting the wafer, which led to less variability in frictional forces or less stick-slip events. Additionally, it was found that Delta and RR increased with sliding velocity while in BL due to an increase in stick-slip events. Conversely, Delta and RR decreased at lower sliding velocities while in ML due to an increase in hydrostatic or buoyant force supporting the wafer. (C) 2019 The Electrochemical Society.
    • Effect of Conditioning Downforce and Pad Break-In Time on Pad Surface Micro-Texture

      McAllister, Jeffrey; Stuffle, Calliandra; Sampurno, Yasa; Hetherington, Dale; Suarez, Jon Sierra; Borucki, Leonard; Philipossian, Ara; Univ Arizona, Dept Chem & Environm Engn (ELECTROCHEMICAL SOC INC, 2018)
      The effect of conditioning downforce during pad break-in, and its impact on the evolution of pad surface micro-texture was investigated. Two different conditioning downforces were used to break-in pads. Pad samples were extracted after certain break-in times and analyzed for their topography and contact area using confocal microscopy. Results showed that the pad-wafer contact area and contact density decreased with conditioning downforce. Break-in at the higher conditioning downforce helped in reaching faster stabilized values of the analyzed micro-texture parameters. The evolution of these parameters was different for the two different downforces, however as break-in time increased past 30 minutes, mean summit height and mean summit curvature began to approach approximately the same value. These results indicated that, for the particular disc used in this study, a change in the magnitude of downforce during pad break-in caused a change in break-in time and stable values for some micro-texture parameters. However, a change in the magnitude of downforce during break-in only resulted in a change in break-in time for other micro-texture parameters. The work underscored the need for conducting such tests with different conditioners in order to develop a better understanding of the role downforce plays on the evolution of the micro-texture. (C) 2018 The Electrochemical Society.
    • Effect of Retaining Ring Slot Designs, Conditioning Discs and Conditioning Schemes on the Slurry Bow Wave Width during Chemical Mechanical Planarization

      Bengochea, Leticia Vazquez; Sampurno, Yasa; Stuffle, Calliandra; Sudargho, Fransisca; Han, Ruochen; Philipossian, Ara; Univ Arizona, Dept Chem & Environm Engn (ELECTROCHEMICAL SOC INC, 2018)
      This study investigates the effect of various retaining ring slot designs, conditioning schemes and conditioning disc types on the width of the slurry bow wave formed at the leading edge of the retaining ring during polishing. A method using high-speed videography is employed for visualizing and quantifying slurry bow wave width. In contrast to many limitations associated with previous techniques, this new method allows the use of a concentrically grooved pad with its natural white color commonly used in industrial applications. In general, results show that polishing with a retaining ring having rounded-angle slots, and a full-face conditioner, generates wider slurry bow waves. In contrast, using a retaining ring with sharp-angle slots, in combination with a conditioner having CVD-coated protruding vanes results in narrower bow waves. Compared to ex-situ conditioning, in-situ conditioning causes narrower bow waves due to its inherent role in transporting the slurry through periodic sweeping. Using Fast Fourier Transformation (FFT), bow wave width fluctuations are converted from time domain to frequency domain, showing a consistent spectral fingerprint. Major peaks are observed at frequencies of 1, 2, 4, 8 to 9, and 12 to 14 Hz for all experiments and they are attributed to the carrier, platen and conditioning disc rotation and oscillation, as well as to the presence of slots on the retaining ring. (C) 2018 The Electrochemical Society.
    • Electrogenerated Chemiluminescence of Near-Infrared-Emitting CdSe@CdSe Nanorods in Aqueous Solution

      Zhuang, Yafeng; Zheng, Yilong; Saavedra, S. Scott; Pavlopoulos, Nicholas G.; Pyun, Jeffrey; Univ Arizona, Dept Chem & Biochem (ELECTROCHEMICAL SOC INC, 2020-04-14)
      Electrogenerated chemiluminescence (ECL) was observed from TOPO-capped CdSe@CdSe nanorods (NRs) depositing on a metal electrode in phosphate buffer solution (PBS). Two ECL peaks at -1.05 and -1.33 V in pH 9.2, 0.1 M PBS were found under cyclic voltammetric conditions. Cyclic voltammetry of this solution displayed no distinctive features, on the other hand, light emission was observed during cyclic potential scans. The photoluminescence (PL) spectrum showed an emission maximum at 692 nm. The spectrum of ECL possesses one peak which coincides very well with the PL spectrum of the nanorods film. The mechanism for ECL peaks was proposed. Electron transfer reactions between charged nanorods and molecular redox-active coreactants such as dissolved oxygen and H2O2 or between positively and negatively charged nanorods occurred that led to electron and hole annihilation, producing light. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
    • Impact of Polisher Kinematics and Conditioner Disc Designs on Fluid Transport during Chemical Mechanical Planarization

      McAllister, Jeffrey; Dadashazar, Hossein; Mariscal, Juan Cristobal; Sampurno, Yasa; Philipossian, Ara; Univ Arizona, Dept Chem & Environm Engn (ELECTROCHEMICAL SOC INC, 2019-11-25)
      Fluid film thicknesses were measured and general flow patterns were analyzed during conditioning on a polishing pad using a recently developed UV-enhanced fluorescence experimental technique. The method was used to analyze how conditioners with different working face designs and polisher kinematics (platen angular velocities) affected fluid flow characteristics on the pad surface. In general, fluid film thicknesses followed the same general trends across the pad surface for both disc designs and platen speeds. Regardless of the parameters used, the fluid film was the thickest in sections nearest to the wafer track and was significantly thinner near the center and edge of the pad. For both discs, the time for film thicknesses to reach steady-state increased with distance from the radius. In general, the full-face conditioner had a smaller maximum attainable fluid thickness (MAFT) and time to reach steady-state (TTRSS) as it most effectively expelled (i.e. squeegeed) the fluid off the pad surface. In contrast, the partial-face conditioner had a larger MAFT and TTRSS as its more intricate design allowed for greater fluid retention and generated more back-flow. (c) 2019 The Electrochemical Society.