AVS 61st International Symposium & Exhibition
    Thin Film Monday Sessions
       Session TF+PS-MoA

Paper TF+PS-MoA8
Characterizing Vapor Delivery of μ2-η2-(tBu-Acetylene)Dicobalthexacarbonyl (CCTBA) for Deposition Processes

Monday, November 10, 2014, 4:20 pm, Room 307

Session: ALD Surface Reactions and Precursors
Presenter: James Maslar, National Institute of Standards and Technology (NIST)
Authors: J.E. Maslar, National Institute of Standards and Technology (NIST)
W.A. Kimes, National Institute of Standards and Technology (NIST)
B.A. Sperling, National Institute of Standards and Technology (NIST)
R. Kanjolia, SAFC Hitech
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Cobalt metal is a promising material for the formation of enhanced copper barrier and/or seed layers for copper interconnects in integrated circuits. For these applications, atomic layer deposition of cobalt using a gas-phase precursor can provide advantages in the device fabrication process. μ2‑η2‑(tBu‑acetylene)dicobalthexacarbonyl (CCTBA) is a cobalt precursor that can be delivered as a vapor in a carrier gas. However, CCTBA exhibits a relatively low vapor pressure at ambient conditions and typically must be delivered at elevated temperatures to increase the amount of material delivered to the growth surface. As is typically the case for deposition precursors, prolonged heating can lead to decomposition of CCTBA. Therefore, this work was undertaken to help identify optical delivery conditions for CCTBA by investigating 1) the decomposition of CCTBA in an ampoule at various ampoule temperatures and 2) the delivery of CCTBA from an ampoule as a function of carrier gas flow rate, system pressure, and ampoule temperature. CCTBA decomposition in an ampoule was investigated by using Fourier transform infrared (FT-IR) spectroscopy to identify the species present in the headspace of a CCTBA-containing ampoule as a function of time and ampoule temperature. CCTBA delivery was investigated using two optical techniques installed onto a delivery line from the ampoule. Optical access to the delivery line was achieved using two custom-built in-line optical flow cells that were designed to minimize perturbations to the gas flow. One flow cell was utilized for time-resolved FT-IR spectroscopy. This technique was used to identify the species entrained in the carrier gas. However, time response was limited to ~150 ms which is insufficient to resolve many thermal processes impacting CCTBA entrainment. In order to improve time resolution, a CCTBA-specific region of the mid-IR spectrum was identified and a direct optical absorption technique designed for CCTBA. This techinque employed a broadband infrared source with a mid-IR bandpass filter for isolating CCTBA-specific absorption features. This technique was installed on the second optical flow cell and used to measure the time-dependent CCTBA partial pressure as a function of gas flow rate, system pressure, and ampoule temperature for each CCTBA pulse with a time resolution of ~5 ms. In this manner, the dependence of CCTBA partial pressure on delivery conditions was identified. From these data and the time-dependent partial pressure data obtained with this optical measurement, the dependence of the actual amount of CCTBA delivered on delivery conditions was calculated.