From Event: SPIE Nanoscience + Engineering, 2018
Titanium nitride is being studied as an alternative plasmonic material for its tunability and high durability. TiN can be grown with high quality and competitive optical properties, but the current magnetron sputtering method used to achieve this quality requires a high temperature. For low temperature or CMOS compatible design, Atomic Layer Deposition (ALD) is a promising method; ALD TiN films are conformal allowing ultrathin, few monolayer, thicknesses. However, TiN films deposited with ALD have struggled to reach the metallicity and quality of sputtered films. Here, we present a study on films produced via Plasma Enhanced Atomic Layer Deposition (PE-ALD) that approach the metallicity of sputtered films while remaining relatively low loss compared to similar films that are achieved with a CMOS compatible method.
Several TiN films on sapphire and silicon of comparable thicknesses (~70nm) and varied temperature, 375 to 475 C, are studied by spectroscopic ellipsometry and x-ray diffraction to characterize optical properties and film quality. Peak optical properties occurred at a deposition temperature at 375 C which we attribute to the precursor, tetrakis(dimethlamino) titanium(IV), gas breakdown temperature ~425 C (lower deposition temperatures currently being explored). This film exhibits a figure of merit (-Re{ε}/Im{ε}) of 2 compared to other ALD films of 1.2 and sputtered films as high as 3.6. XRD results show epitaxial quality films with lattice constants that approach bulk as temperature is increased. These conflicting trends suggest that transitioning to a different precursor may allow for an optical property improvement of materials at a higher temperature deposition.
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Ray Secondo, Dhurv Fomra, Natalia Izyumskaya, Vitally Avrutin, Ümit Özgür, and Nathaniel Kinsey, "Characterization of plasma enhanced atomic layer deposited titanium nitride (Conference Presentation)," Proc. SPIE 10720, Nanophotonic Materials XV, 107200M (Presented at SPIE Nanoscience + Engineering: August 23, 2018; Published: 17 September 2018); https://doi.org/10.1117/12.2321132.5836039076001.