Influence of gas flow dynamics on discharge stability and on the uniformity of atmospheric pressure PECVD thin film

Abstract

The aim of this paper is to improve the understanding of the mechanisms controlling the uniformity of thin films made by atmospheric pressure plasma enhanced chemical vapour deposition (AP-PECVD). To reach this goal, the influence of the gas flow-rate and injection design on the thin film thickness uniformity is studied through experiments and numerical simulation in the case of silica-like layers deposited from silane and nitrous oxide using a nitrogen Townsend dielectric barrier discharge. Results show that whatever the gas flow-rate, when the gas is injected uniformly parallel to the substrate, the obtained layer is always uniform along the substrate width, while when the gas is injected perpendicularly to the substrate, the width-uniformity of the layers decreases when the gas flow-rate increases. The layer non-uniformity is related to the penetration of gas recirculation into the discharge zone, which was confirmed by computational fluid dynamics. This link is corroborated experimentally by a clear improvement of the deposit uniformity when the discharge cell dimensions are modified in order to reduce the recirculation influence on the discharge. A plausible hypothesis for the layer uniformity dependence on the recirculation is the possible enhancement of powder formation and growth in the recirculation zone: when the particle size is large enough, electrons may attach on the powder inducing electron depletion at the origin of the discharge instabilities.

Conformity of Silica-like Thin Films Deposited by Atmospheric Pressure Townsend Discharge and Transport Mechanisms

“…Despite its simplicity, this model allows the reproduction of the variation of the thickness profile on a plane sample as a function of parameters like the concentration of HMDSO, the gas flow, the power [38], and the gas injection and plasma geometry [40]. Thus, it allows a good understanding of the transport phenomena.…”

Thin film deposition and surface modification with atmospheric pressure dielectric barrier discharges

“…DBDs, both in filamentary and glow regime, have been proposed for PE-CVD on several substrates (e.g. polymers and metals) for different applications [57][58][59][60][61][62][63][64][65][66][67].…”

“…Massines et al, working with atmospheric pressure Townsend discharges fed with N 2 -HMDSO-N 2 O mixtures, varied the chemical composition of the deposits by changing the N 2 O-to-HMDSO ratio [28,60,61]; inorganic and dense SiO 2 -like thin films with negligible carbon and nitrogen incorporation but detectable Si-OH groups were obtained at high ratios. These authors also investigated the influence of the feed flow rate and injection design on film homogeneity [61].…”

“…These authors also investigated the influence of the feed flow rate and injection design on film homogeneity [61].…”

Simulation-Based Optimization of a Vector Showerhead System for the Control of Flow Field Profile in a Vertical Reactor Chamber

“…Employing computational fluid dynamic (CFD) method is more and more favored by the researchers and engineers because of its efficiency and economy compared with the trial-and-error process experiment. From the view of the research achievements and experiences on the process mechanism in some typical reactors [4][5][6][7][8][9][10][11][12][13][14][15], the essential problem, which should be considered for the design of showerhead gas delivery system, is how to control the gas mass transport in the reactor, make the spatial distribution profile of reaction precursors meet a certain special requirement, and achieve the expected process uniformity in the final. From the view of chemical pathway and reaction analysis model of plasma enhanced chemical vapor deposition (PECVD) and thermal chemical vapor deposition (CVD) etcaeteras [9,13,15], we can deduce that a uniform chemical reaction on the wafer surface needs the factors of temperature distribution, reaction gas concentration distribution, resident time, and chemical 2 Advances in Mechanical Engineering reaction rate to achieve a certain coordination in the spatial domain over the wafer.…”