Flash-Enhanced Atomic Layer Deposition: Basics, Opportunities, Review, and Principal Studies on the Flash-Enhanced Growth of Thin Films

Abstract

Within this work, flash lamp annealing (FLA) is utilized to thermally enhance the film growth in atomic layer deposition (ALD). First, the basic principles of this flash-enhanced ALD (FEALD) are presented in detail, the technology is reviewed and classified. Thereafter, results of our studies on the FEALD of aluminum-based and ruthenium thin films are presented. These depositions were realized by periodically flashing on a substrate during the precursor exposure. In both cases, the film growth is induced by the flash heating and the processes exhibit typical ALD characteristics such as layer-by-layer growth and growth rates smaller than one Å/cycle. The obtained relations between process parameters and film growth parameters are discussed with the main focus on the impact of the FLA-caused temperature profile on the film growth. Similar, substrate-dependent growth rates are attributed to the different optical characteristics of the applied substrates. Regarding the ruthenium deposition, a single-source process was realized. It was also successfully applied to significantly enhance the nucleation behavior in order to overcome substrate-inhibited film growth. Besides, this work addresses technical challenges for the practical realization of this film deposition method and demonstrates the potential of this technology to extend the capabilities of thermal ALD. Atomic layer deposition (ALD) is a specific thin film deposition method wherein film growth is based on a sequence of alternating saturated surface reactions. In a typical ALD process, this is realized by the alternating exposure of the substrate surface to two precursors, which are separated from each other by inert gas purging or chamber evacuation in order to prevent gas phase reactions. As a result, the film growth proceeds in a self-limiting manner and monolayer-by-monolayer, and thus, ALD enables the deposition of thin films with excellent uniformity and conformality as well as with sub-nanometer thickness control. Thanks to these unique characteristics, ALD has emerged as an important thin film deposition technique in semiconductor technology, e.g. in the fabrication of metal-insulator-metal (MIM) film stacks in high aspect ratio dynamic random access memory (DRAM) structures and gate dielectrics in transistors. In recent years, the use of ALD has also expanded into other fields such as optoelectronics, energy conversion and storage devices, micro-electro-mechanical-systems (MEMS) and nanotechnology. [1][2][3][4][5][6] Although a large number of materials have been deposited by ALD so far 1-6 for various applications, there are still a number of challenges in ALD. The deposition temperatures in ALD are mostly lower compared to chemical vapor deposition (CVD) processes due to the different mechanisms of film growth and the necessity to prevent precursor decomposition in order to keep the self-limiting growth behavior of ALD. As a consequence of the lower energy available for film formation, the films may not meet the properties required for the specific...

(Invited) Photo-Assisted ALD: Process Development and Application Perspectives

“…Henke et al discussed this type of behavior for patterned silicon in their FEALD setup where visible and infrared light is employed for rapid heating of the surface (20). In FEALD, the temperature of the Si substrate is expected to be uniform down to 6 m and thereby the film thickness on surfaces parallel to light should be uniform within that range (20,21). Our findings can be concluded to support photolytic mechanism for our Photo-ALD Ta2O5 process.…”

“…If the Photo-ALD process was driven by heat generated by the intensive light, it would be expected that the film thickness is almost the same on the pillar walls since heat would easily transfer from the tip through the pillar. Henke et al discussed this type of behavior for patterned silicon in their FEALD setup where visible and infrared light is employed for rapid heating of the surface (20). In FEALD, the temperature of the Si substrate is expected to be uniform down to 6 m and thereby the film thickness on surfaces parallel to light should be uniform within that range (20,21).…”

“…Recently, an ALD process approach of the same type as Photo-ALD has been demonstrated by Henke et al where high-intensity, pulsed visible-infrared light is employed to facilitate flash-enhanced ALD (FEALD) (20). The essential difference of F-ALD from Photo-ALD is that the light is utilized to deliver short pulses of heat on the surface and thereby drive the surface reactions, whereas in Photo-ALD photolysis is the desired mechanism for facilitating reduced deposition temperatures and S-ALD.…”

Advanced Silicon-on-Insulator: Crystalline Silicon on Atomic Layer Deposited Beryllium Oxide

“…Moreover, BeO exhibits excellent properties suitable for SOI technology, including high electrical resistivity, radiation resistance, low phonon scattering, and low structural defect density. In addition, atomic layer deposition (ALD) can be employed for producing high quality BeO films with well-controlled thickness in a cost-effective manner 23 , 24 . The advantageous of ALD include the stoichiometric control, excellent reproducibility, and low defect density 25 – 27 .…”

Low‐thermal budget flash light annealing for Al2O3 surface passivation

“…This technique is known from various applications in microelectronics, e.g. doping activation [13], thermal treatment of high-k dielectrics [14] or flashenhanced deposition techniques [15]. In FLA, a short light flash, typically in the millisecond range, induces a shortterm heating process [16].…”