| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Tuesday Sessions |
| Session TF-TuM |
| Session: | Emerging Applications for ALD |
| Presenter: | Harm Knoops, Oxford Instruments, The Netherlands |
| Authors: | H.C.M. Knoops, Oxford Instruments, The Netherlands T.F. Faraz, Eindhoven University of Technology, The Netherlands K. Arts, Eindhoven University of Technology, The Netherlands S. Karwal, Eindhoven University of Technology, The Netherlands M.C. Creatore, Eindhoven University of Technology, The Netherlands W.M.M. Kessels, Eindhoven University of Technology, The Netherlands |
| Correspondent: | Click to Email |
Thin films grown by plasma atomic layer deposition (ALD) can be strongly influenced by the energy of the ions present during the plasma step. Here we report on how using enhanced energies influence the material properties of many oxides and nitrides.1,2 To utilize these effects, discussion on promising process schemes and which material properties are key is needed. This work will discuss application relevant aspects and focus on the stress-control of oxides and the reduction of resistivity for nitrides.
Ion energy control during plasma exposure was carried out in a commercial 200-mm remote plasma ALD system (Oxford Instruments FlexAL) equipped with RF substrate biasing. Substrate biasing increased the refractive index of TiO2 at 300 °C to 2.54±0.03, mass density to 4.2±0.2 g/cm3, and the crystal phase went from anatase to rutile. ALD of TiO2 at 150 °C typically yields amorphous films, but using a bias crystalline rutile phase was obtained. Besides these modified material properties the residual stress was altered from tensile (176±50 MPa) to strongly compressive (-2430±50 MPa) and by choosing the bias voltage and duration, a close to zero stress could be achieved (−25±50 MPa). Stress control of oxides on planar surfaces can be beneficial for several devices through: anti-reflective TiO2 coatings, stressed Al2O3/HfO2 gate oxides, and compressive Ta2O5 barrier layers.
For transition metal nitrides, enhancing ion energies was observed to have pronounced effects on chemical composition and microstructure.1,2 Energetic ion bombardment lowered film resistivity down to 139±10 μΩcm at -187V bias for TiN and increased the crystallinity. The ability to deposit crystalline films on temperature sensitive substrates (e.g., conductive TiN on polymer substrates) could be a benefit for low temperature electronics. Oxygen impurity content was observed to be significantly reduced by substrate biasing. Oxygen contents of 3±2 at. % for TiN and <2 at. % for HfNx were achieved without taking special care of low oxygen backgrounds. Ar/H2 plasma with biasing was found to allow removal of surface oxygen, while simply extending the plasma exposure without applying bias did not lead to such removal. The reduction of oxygen content by these plasmas also suggests a possible use in applications as a chemical sputter clean of surfaces. In general the application of biasing brings the processing of plasma ALD closer to the realm of ALE and atomic scale processing. Possible related processing schemes and the general trends for nitrides and oxides will be discussed.
1Faraz et al., ACS Appl. Mater. Interfaces 10, 13158 (2018)
2Karwal et al., J. Mater. Chem. C6, 3917 (2018)