(Invited) Using Amorphous Carbon to Enable Area-Selective Atomic Layer Deposition for Advanced Patterning Applications

The demand for transistors and memory devices with smaller feature sizes and increasingly complex architectures furthers the need for advanced thin film patterning techniques. A pre-patterned, sacrificial layer can be used as a template for bottom-up fill of new materials which would otherwise be difficult to pattern using traditional top-down lithographic methods. This work investigates initial growth of TiN, TiO2, and HfO2 thin films during thermal atomic layer deposition (ALD) onto a high density, amorphous carbon (aC) sacrificial layer. ALD of TiN by TiCl4/NH3 at 390oC, TiO2 by Ti(OCH3)4/H2O at 250oC, and HfO2 by HfCl4/H2O at 300oC on as-deposited aC films resulted in uninhibited, continuous thin film growth. We find that carbon surface reduction and passivation using a H2 plasma resulted in delayed film coalescence for TiN, TiO2, and HfO2 on the aC. After 200 TiN cycles on H2 plasma-treated aC, Rutherford backscattering spectrometry shows Ti levels below the detection limit (8×1013 at/cm2), whereas SiO2 or Si3N4 substrates show TiN growth of ~6 nm, corresponding to a selectivity of ~200:1. Exposing plasma-treated aC to H2O induces nucleation for TiN ALD, consistent with favorable nucleation on hydroxyl sites. Therefore, the H2O co-reagent in TiO2 and HfO2 ALD contributes to loss of selectivity compared to TiN ALD using NH3. Furthermore, we demonstrate the use of the Avrami Equation to model the nucleation behavior on plasma-treated aC, providing useful insights into process improvements for increased selectivity. We confirm scaling of selectivity to sub 50 nanometer patterns using 45 nm aC/Si3N4 line/space patterns, where 3.5 nm TiO2 and 5.8 nm TiN films are deposited on Si3N4 with minimal particle formation on aC, with selectivity loss primarily on feature corners and edges. We conclude that improved scaling of selectivity to nanometer scale patterns can be achieved by optimizing surface loading and extent of plasma exposure, and by further understanding shape effects in nanoscale surface plasma modification.