| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS+TF-ThM |
| Session: | Plasma Deposition and Plasma Enhanced ALD |
| Presenter: | Harald Profijt, Eindhoven University of Technology, Netherlands |
| Authors: | H.B. Profijt, Eindhoven University of Technology, Netherlands M.C.M. van de Sanden, Eindhoven University of Technology, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
The interest in plasma-assisted atomic layer deposition (ALD) has increased rapidly over the last
years, since it has been demonstrated that the presence of a plasma step can improve material
properties and ease processing conditions. Although it is known from other plasma-based techniques that
the photons and ions can play an important role during processing, their presence and influence have not
systematically been addressed so far for the specific case of plasma-assisted ALD. In this contribution,
we present a detailed investigation of the impact that VUV photons and energetic ions can have on the
properties of metal oxide thin films prepared by plasma-assisted ALD. We will demonstrate the
detrimental impact that VUV photons can have on electrical properties and we show that structural
material properties can be controlled by tuning the ion energy through substrate biasing. Optical
emission, retarding field energy analyzer, and Langmuir probe measurements were carried out in three
R&D plasma-assisted ALD reactors. In the O2 plasmas employed, vacuum ultraviolet (VUV) photons with
energies up to 9.5 eV were detected and these photons were found to be able to generate electronic
defects at thin film interfaces. This was demonstrated by experiments in which Al2O3 passivated Si(100)
samples were exposed to O2 plasmas. By exposing the samples through quartz and MgF2 windows, the
role of ions was excluded and the specific role of the high energy VUV photons was confirmed
unambiguously. Furthermore, during regular ALD conditions, an ion energy of ~30 eV was measured.
This energy is sufficient to contribute to the ALD process by, e.g., the displacement of lattice atoms and
enhancement of the ALD surface reactions, however, it is low enough to prevent substantial damage to
the deposited layers. The impact of the ions was further explored by enhancing the energy of the ions
through the implementation of substrate biasing, either through substrate self-biasing or by RF biasing.
By enhancing the ion energy up to 230 eV, these experiments demonstrated that at 300°C the crystallinity
of TiO2 films can be changed from the anatase to the rutile crystalline phase. Moreover, at a substrate
temperature of 200°C the rutile phase can be obtained when employing substrate biasing while normally
amorphous TiO2 is obtained. These results are particularly significant as generally the deposition of rutile
TiO2 is difficult to achieve by ALD due to substrate temperature limitations imposed by the precursors
used. It is therefore evident that substrate biasing is a promising method to extend the possibilities of ALD.