Spatial Atomic Layer Deposition of Zinc Oxide Thin Films

Abstract

Zinc oxide thin films have been deposited at high growth rates (up to ~1 nm/s) by spatial atomic layer deposition technique at atmospheric pressure. Water has been used as oxidant for diethylzinc (DEZ) at deposition temperatures between 75 and 250 °C. The electrical, structural (crystallinity and morphology), and optical properties of the films have been analyzed by using Hall, four-point probe, X-ray diffraction, scanning electron microscopy, spectrophotometry, and photoluminescence, respectively. All the films have c-axis (100) preferential orientation, good crystalline quality and high transparency (∼ 85%) in the visible range. By varying the DEZ partial pressure, the electrical properties of ZnO can be controlled, ranging from heavily n-type conductive (with 4 mOhm.cm resistivity for 250 nm thickness) to insulating. Combining the high deposition rates with a precise control of functional properties (i.e., conductivity and transparency) of the films, the industrially scalable spatial ALD technique can become a disruptive manufacturing method for the ZnO-based industry.

On the environmental stability of ZnO thin films by spatial atomic layer deposition

“…Although different crystallographic orientations are present, spatial-ALD ZnO and In:ZnO films have a (100) dominant orientation with a wurtzite crystal structure, as also reported in literature. 10 With increasing time in a harsh environment, the peak position of (100) orientation shifts to lower angles for both i-ZnO and In:ZnO films, as shown in Fig. 6 for ZO and IZO3.…”

“…5,6 The industrial needs for deposition processes with highthroughput, low production costs, and no damage to the substrate (e.g., no bombardment by energetic ions) has driven the development of alternative techniques to sputtering for the growth of TCOs, such as atmospheric pressure CVD, low pressure expanding-thermal-plasma metalorganic-CVD, atmospheric pressure PE-CVD, and atmospheric pressure spatial atomic-layer-deposition (spatial-ALD). [7][8][9][10] Spatial-ALD combines the advantages of conventional ALD (e.g., superior control of film composition, growth of uniform, pinhole free, and highly conformal thin-films on large area and flexible substrates) with high deposition rates (up to $nm/s). 11 For this reason, atmospheric pressure spatial-ALD is emerging as an industrially scalable technique for the deposition of thin film electrodes (e.g., ZnO) and encapsulation (e.g., by Al 2 O 3 thin-films) of solar and electronic devices.…”

“…11 For this reason, atmospheric pressure spatial-ALD is emerging as an industrially scalable technique for the deposition of thin film electrodes (e.g., ZnO) and encapsulation (e.g., by Al 2 O 3 thin-films) of solar and electronic devices. 10,12 In this paper, we report on the stability of the electrical, optical and structural properties of spatial-ALD intrinsic (i-ZnO) and In-doped ZnO (In:ZnO) films, exposed to a high humidity and high temperature environment [85% relative humidity (RH), 85 C]. The effect of spatial-ALD Al 2 O 3 thin film encapsulation in enhancing the stability of ZnO films has also been tested.…”

On the kinetics of spatial atomic layer deposition

“…The crystallization kinetics might not necessarily influence the GPC too much, but it can for instance determine the grain size and orientation in the film. 18 As these properties are important for the electrical and optical properties of the film, the crystallization kinetics needs to be investigated as well to optimize the performance of the deposited films.…”

Transparent conducting materials: overview and recent results

“…The electrical properties of the ZnO films, ranging from heavily n-type conductive (with 4 mΩ cm resistivity for 250 nm thickness) to insulating are controlled by a variation of the partial pressure of the zinc precursor, i.e. diethylzinc (DEZ) [14]. …”