Selective Area Spatial Atomic Layer Deposition of ZnO, Al₂O₃, and Aluminum-Doped ZnO Using Poly(vinyl pyrrolidone)

Abstract

Spatial atomic layer deposition (SALD) is gaining traction in the thin film electronics field because of its ability to produce quality films at a fraction of the time typically associated with ALD processes. Here, we explore the process space for the fabrication of thin film patterned-by-printing electronics using the combination of SALD and selective area patterning. First, a study of SALD growth conditions for the three primary components of our metal oxide thin film electronics, namely alumina (Al2O3) dielectric, zinc oxide (ZnO) semiconductor, and aluminum doped ZnO (AZO) conductor, provides insight into the potential trade-offs in performance, substrate latitude (temperature), and process speed. At constant precursor partial pressures, the precursor exposure times and substrate temperatures were varied from 25 to 400 ms and from 100 to 300 °C, respectively. The very short gas exposure and purge times obtainable only with a spatial implementation of ALD are shown always to be advantageous for throughput and process speed, even though growth is far from the “ideal” ALD condition of saturated monolayer growth. Using the same range of process conditions, we evaluated the ability of very thin layers of poly(vinyl pyrrolidone) (PVP) to inhibit film growth. We demonstrate that PVP sufficiently inhibits the growth of all three materials at temperatures at or above 150 °C to usefully pattern high-quality electronic devices. Additionally, we found that very thin layers of PVP are most effective at higher temperatures and fast ALD cycles. Thus, faster SALD cycles are advantageous from both throughput and patterning performance perspectives.

Research Update: Atmospheric pressure spatial atomic layer deposition of ZnO thin films: Reactors, doping, and devices

“…31 By controlling the substrate velocity, rapid ALD synthesis of ZnO can occur (up to 2 nm s −1 ), which is an order of magnitude higher than the growth rate of conventional ALD (Table I). 9,14,40 The range in growth rates shown is due to this parameter being a function of deposition temperature and residence time, which is controlled by pulse duration (conventional ALD) 15 or substrate velocity (AP-SALD). 9,40 In Table I, the growth rate of 2 nm s −1 using the AP-SALD head designed by the Eastman Kodak Company was obtained using an exposure time of 25 ms (100 ms for each cycle) at 200…”

“…• C. 40 A similar design was developed by TNO ( Fig. 3(c)), 32 in which the gas manifold is floated ∼20 µm over the substrate (Fig.…”

“…45,46 AP-SALD ZnO could be used as the semiconductor in TFTs. 9,20,40,41,47,48 This is particularly important because TFTs (acting as a switch) have become a crucial part of the electronics industry, especially for displays. Several million TFTs are produced each year for displays.…”

“…9,26,27,29,36,40 Nitrogen-doping of ZnO reduces its carrier concentration (thus increasing resistivity, as shown in Table II), 9,26 and it has been claimed that it can make ZnO p-type with post-deposition treatment (Table II). 26,57 The nitrogen dopant is introduced by mixing ammonia with the water oxidant precursor, and this is the method used for both conventional and spatial ALD ZnO:N. 26,58 The non-pyrophoric and low-cost nature of the ammonia precursor is in contrast to the expensive, pyrophoric organometallic materials that are often used as ALD and AP-SALD precursors, 5,14 and hence ammonia has been widely studied in both ALD and AP-SALD ZnO.…”

“…Much thicker films can thus be grown before unwanted growth in the masked areas occurs. 40 Such an approach lends itself to building circuits, since the active materials are deposited additively, thus requiring no etching steps. 40 In Fig.…”