Plasma‐enhanced Chemical Vapor Deposition of Aluminum Oxide Using Ultrashort Precursor Injection Pulses

Abstract

An alternative plasma‐enhanced chemical vapor deposition (PECVD) method is developed and applied for the deposition of high‐quality aluminum oxide (AlOx) films. The PECVD method combines a continuous plasma with ultrashort precursor injection pulses. We demonstrate that the modulation of the precursor flow in the reactor leads to enhanced control over plasma‐surface interactions. By variation of the time interval between the sequential Al(CH3)3 precursor injection pulses (10–50 ms) into the O2 plasma, the deposition rate (>30 nm · min−1) and material properties can be tailored. In situ diagnostics revealed that the deposition process is governed by fast precursor depletion and film growth directly after the precursor pulse. Subsequently, in the remainder of the interval between the precursor pulses, densification of the layer takes place under influence of the O2 plasma. The resulting AlOx films exhibit a low impurity content and refractive index >1.6 for optimized process settings. The films can be applied for effective surface passivation of Si as indicated by ultralow surface recombination velocities <1 cm · s−1. The structural properties and interface quality are quite similar as obtained for atomic layer deposited films. We anticipate that pulsed‐flow PECVD processes may also prove beneficial for the synthesis of other functional thin films.

Dielectric surface passivation for silicon solar cells: A review

“…Passivation quality comparable to that of ALD can be achieved in PECVD AlO x films. Miyajima et al reported moderate passivation using this technique, but it was Dingemans et al who demonstrated efficient passivation with S eff of 0.45 cm s −1 in 3.5 Ωcm n‐type Si. In both cases they used a static reactor designed for laboratory research with a deposition rate of ∼5–10 nm min −1 .…”

“…The seminal work of Agostinelli and Hoex was rapidly expanded. Most notably, the studies of Benick and Richter , Dingemans et al and Saint‐Cast et al , largely advanced the understanding of the electrical properties of the film, its passivation effectiveness, and its application to silicon solar cells. A key aspect of the passivation achieved using AlO x is the requirement for an activation step.…”

Status and prospects of Al2O3-based surface passivation schemes for silicon solar cells

“…124 A difference may be the refractive index of the PECVD deposited films, which is generally somewhat lower ($1.60) than for ALD ($1.64). 124,125 This is indicative of a slightly lower film density.…”

“…In addition to the continuous flow processes, an alternative PECVD process has been reported in which the Al(CH 3 ) 3 precursor was pulsed. 98,125 This pulsed process leads to additional control over the material properties. Collectively, the various reports have shown that for optimized PECVD processes the passivation quality of the deposited aluminum oxide films can be quite comparable to that achieved by ALD.…”

Recent Advances in Atmospheric Vapor‐Phase Deposition of Transparent and Conductive Zinc Oxide

“…From previous studies on thin film deposition by low pressure PE‐CVD, it is known that, in the absence of ion bombardment, the microstructure of thin films can be modified by chemical interaction of plasma radicals with the film surface or by irradiation with high energy photons generated by the plasma. By pulsing the injection of metal precursors in a continuous plasma, the film growth can be alternated with exposures to highly reactive plasma species which induce a densification of the film . Plasma‐generated, near‐UV luminescence can modify the defect structure in the film lattice or enhance the kinetics of surface reactions during the growth, thus affecting the structural and electrical properties of the film .…”