Index of content:
Volume 35, Issue 1, January 2017
- Special Issue on Atomic Layer Deposition (ALD)
Anomalously high alumina atomic layer deposition growth per cycle during trimethylaluminum under-dosing conditions35(2017); http://dx.doi.org/10.1116/1.4963368View Description Hide Description
Under nominal conditions for this study, alumina atomic layer deposition (ALD) using trimethylaluminum and water as precursors was found to give a growth-per-cycle (gpc) of 1.1 Å under saturating conditions. As either precursor dose is reduced, one expects to find a point where the gpc begins to drop from the self-saturating plateau to zero in a monotonically decreasing manner while thickness nonuniformity along the deposited film starts to increase. In this paper, the authors find anomalously high gpc values—more than twice our nominal value of 1.1 Å—during the transition to precursor under-dosing as the trimethylaluminium dose is reduced while the water dose is held constant. Unlike previous studies documenting abnormally high alumina ALD gpc, the authors find that film thickness remains spatially uniform in this region, up to the point where precursor depletion becomes significant, resulting in films with severe spatial gradients in the direction of precursor flow. A simple reaction mechanism is postulated to explain the observed gpc behavior.
Mechanistic modeling study of atomic layer deposition process optimization in a fluidized bed reactor35(2017); http://dx.doi.org/10.1116/1.4964848View Description Hide Description
Surface modification of nanoparticles has attracted much attention owing to its superior ability to design nanoparticles with unique physical, chemical, or biological properties. Atomic layer deposition (ALD) has shown great promise in the precise surface decoration of nanoparticles. However, the large surface area of nanoparticles requires a large quantity of precursors, and the nonuniform interstitials among the particles limit the precursor diffusion and lead to long process times. Fluidized bed reactors (FBRs) have been proven applicable for ALD on nanoparticles owing to its high gas–solid interactions and potential scalability for practical production. The ALD process in a fluidized bed is sophisticated and with many variables, resulting in long and tedious process optimization through substantial experimental trials. In this paper, the ALD process in a FBR-ALD is investigated through mechanistic modeling using computational fluid dynamics and theoretical calculations of molecular flow diffusion. The result shows that the minimum pulse time and the precursor waste are inversely proportional to the increase in precursor mass fraction. The optimal precursor utilization is obtained under the minimum fluidizing velocity. Because the fluid kinetics is independent of the specific structure, the mechanistic modeling study is instructive for the process optimization of FBR-ALD.
Investigating routes toward atomic layer deposition of silicon carbide: Ab initio screening of potential silicon and carbon precursors35(2017); http://dx.doi.org/10.1116/1.4964890View Description Hide Description
Silicon carbide (SiC) is a promising material for electronics due to its hardness, and ability to carry high currents and high operating temperature. SiC films are currently deposited using chemical vapor deposition (CVD) at high temperatures 1500–1600 °C. However, there is a need to deposit SiC-based films on the surface of high aspect ratio features at low temperatures. One of the most precise thin film deposition techniques on high-aspect-ratio surfaces that operates at low temperatures is atomic layer deposition (ALD). However, there are currently no known methods for ALD of SiC. Herein, the authors present a first-principles thermodynamic analysis so as to screen different precursor combinations for SiC thin films. The authors do this by calculating the Gibbs energy of the reaction using density functional theory and including the effects of pressure and temperature. This theoretical model was validated for existing chemical reactions in CVD of SiC at 1000 °C. The precursors disilane (Si2H6), silane (SiH4), or monochlorosilane (SiH3Cl) with ethyne (C2H2), carbontetrachloride (CCl4), or trichloromethane (CHCl3) were predicted to be the most promising for ALD of SiC at 400 °C.
Selective deposition of Ta2O5 by adding plasma etching super-cycles in plasma enhanced atomic layer deposition steps35(2017); http://dx.doi.org/10.1116/1.4965966View Description Hide Description
In this paper, a new route for a selective deposition of thin oxide by atomic layer deposition is discussed. The proposed process is using super cycles made of an additional plasma etching step in a standard plasma enhanced atomic layer deposition (PEALD) process. This allows the selective growth of a thin oxide on a metal substrate without a specific surface deactivation by means of self assembled monolayer. It is shown that adding a small amount of NF3 etching gas to an oxygen plasma gas every eight cycles of the PEALD process helps to fully remove the Ta 2O5 layer on Si and/or SiO2 surface while keeping few nanometers of Ta 2O5 on the TiN substrate. NF3 addition is also used to increase the incubation time before Ta 2O5 growth on Si or SiO2 substrate. In this way, a selective deposition of Ta 2O5 on the TiN substrate is obtained with properties (density, leakage current…) similar to the ones obtained in a conventional PEALD mode. Hence, the authors demonstrate that a future for selective deposition could be a process using both PEALD and atomic layer etching.