Sara Harris¹, Thomas. P. Moffat², Matt Weimer¹, Dane Lindblad¹, Daniel Josell², Arrelaine Dameron^1
1Forge Nano, Thornton, CO
²National Institute of Standards and Technology, Gaithersburg, MD
Device miniaturization continues to push technological boundaries, requiring constant evolution in transistor material systems, architecture, and manufacturing processes. To fully actualize bleeding edge (two to three nanometer) transistor capabilities, integrated circuit (IC) manufacturing must keep pace. Back end of line (BOEL) fabrication poses several challenges to chip scaling: most notoriously the copper bottleneck in which thick barrier layers and resistance capacitance (RC) delays limit functional interconnect pitch to 21 nanometers. To overcome this critical barrier, low resistivity, conformal metal films have been studied for hybrid metallization; decreasing interconnect resistance and reducing barrier layer thicknesses. As interconnect pitch decreases traditional PVD copper barrier/seed layers are limited by line of sight and experience pinch off and void formation. Expanding on the ruthenium (Ru) ALD film for copper seed layer application presented last year, this work explores the use of low resistivity thermal ALD iridium (Ir) thin films to enable next generation interconnects. Thermal ALD Ir and Ru deposited at 250 °C both demonstrate conformal deposition on 10:1 aspect ratio through glass vias (TGVs) and show void free copper fill using a cyclic pulsed electrochemical deposition process. As expected, the primary difference between the Ir and Ru is electrical resistivity. Seed film resistivity as deposited on TGVs was measured using four-point probe; a 10 nm Ru film measured 41 µΩ∙cm and a 10 nm Ir film measured 16 µΩ∙cm. Successful copper electrochemical deposition (ECD) at various ECD potentials, was completed with 10 nm of Ir with (resistivity 16 µΩ∙cm) and 20 nm of Ru (resistivity 22 µΩ∙cm) with the full layer stack for these film. Reduction in required layer thickness combined with improved electrical properties and demonstrated conformality can serve as crucial steps forward for advanced interconnects and BEOL architecture. Additionally, this work compares Ir film quality as deposited at 250 °C and 300 °C. Ir deposited at 300 °C exhibits improved environmental stability when compared to 250 °C Ir as measured with 4-point probe after aging in atmosphere over several months. 300 °C Ir also shows a shortened nucleation delay, and optical constants (n and k) more closely aligned to bulk Ir values, as measured with spectroscopic ellipsometry. Ir film characterization for both temperatures including XPS, XRR, XRD and AFM is ongoing, and will be presented.