AVS 53rd International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuM

Paper EM-TuM11
On the Morphology and Conductivity Control of the Expanding Thermal Plasma-Deposited ZnO Films

Tuesday, November 14, 2006, 11:20 am, Room 2003

Session: Zinc Oxide
Presenter: I. Volintiru, Eindhoven University of Technology, The Netherlands
Authors: I. Volintiru, Eindhoven University of Technology, The Netherlands
M. Creatore, Eindhoven University of Technology, The Netherlands
C.I.M.A. Spee, TNO Science and Industry, The Netherlands
M.C.M. Van De Sanden, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The bulk of the extensive research on ZnO focuses on different applications, ranging from photovoltaics to organic light emitting diodes; the plasma and film processes during growth are not well studied and, therefore, not controllable. For specific applications, good control of the ZnO film electrical and optical properties, as well as the surface morphology, is required. In this work, undoped and Al-doped ZnO layers are deposited using an Ar-fed expanding thermal plasma in which oxygen, diethylzinc, and trimethylaluminum (for Al doping) are admixed downstream. Typical downstream ion energies in this remote plasma are <2 eV, therefore energetic ion bombardment should not affect the film growth. Conductive films (5*10@super-4@ @OHM@cm) with native roughness of ~45 nm for 1 µm thickness, suitable for solar cell applications, were already obtained in our process. The film conductivity, however, shows a strong inhomogeneous depth profile, which could affect the suitability of this material for applications requiring thinner (< 200 nm) films, i.e. diodes and thin film transistors. To make our process more versatile, the ZnO film growth was investigated by studying the overall effect of the substrate temperature, working pressure, and ion bombardment (as delivered by an external RF bias). We use in-situ spectroscopic ellipsometry to monitor the refractive index, thickness and roughness development during the film growth. Atomic force microscopy, Hall and X-ray diffraction measurements are used to determine the morphological, electronic and structural properties of the films. Preliminary results demonstrate that the working pressure and substrate temperature play an important role in controlling the surface roughness of the ZnO films: smooth films, i.e. 0.02% roughness, are obtained by decreasing the pressure from 1.6 to 0.4 mbar, whereas higher texture, i.e. 10% of the film thickness, is achieved by increasing the substrate temperature from 200 to 400°C.