Opportunities for Plasma-Assisted Atomic Layer Deposition

Abstract

Within the method of atomic layer deposition (ALD), additional reactivity can be delivered to the surface in the form of plasmaproduced species. The application of such a low-temperature plasma in the ALD cycle can therefore open up a processing parameter space that is unattainable by the strictly thermally driven process. In this contribution several possible benefits of plasmaassisted ALD will be reviewed showing bright prospect for plasma-assisted ALD for a large variety of applications, also far beyond the typical use in semiconductor devices. Atomic layer deposition for processing at the nanoscaleWithin the current trends of downscaling in the semiconductor industry and the boost in nanoscience and nanotechnology, atomic layer deposition (ALD) is the method of choice for depositing high quality films with ultimate growth control and with excellent step coverage on very demanding topologies [1, 2 , 3 ]. The virtue of this approach is that deposition is controlled at the atomic level by self-limiting surface reactions by alternate exposure of the substrate surface to different gas-phase precursors (see Fig. 1). Each surface reaction occurs between a gas phase reactant (precursor) and a surface functional group creating a volatile product molecule that desorbs from the surface, and a new surface functional group that is not reactive with the precursor. After pumping away the first precursor, a second precursor is introduced, which deposits a second element through reaction with the new surface functional group and then restores the initial surface functional group. This set of reactions form one ALD-cycle resulting basically in one (sub)monolayer of film growth per cycle. The ALD-cycle can be repeated until the desired film thickness is reached. Furthermore, unlike chemical vapor deposition (CVD), the deposition rate is not proportional to the flux on the surface. Therefore, the same amount of material is deposited everywhere on the surface even in high aspect ratio structures when there is sufficient flux. Other benefits of ALD are the good uniformity that can be achieved on large substrates, the relatively low substrate temperatures used in the process (temperature window typically 200-400 °C), and the fact that ALD can readily produce multilayer structures.

Plasma-Enhanced Atomic Layer Deposition of Two-Dimensional WS2 from WF6, H2 Plasma, and H2S

“…In ALD, thin films are grown by sequential self-limiting surface reactions of gas-phase precursors. , The self-limiting nature of the surface reactions ensures deposition with (sub)­monolayer control over large area substrates, as well as conformal deposition on three-dimensional structures. By introducing a low temperature plasma in the reaction cycle, additional reactivity is provided to the surface, denoted as plasma-enhanced (PE-) ALD …”

“…By introducing a low temperature plasma in the reaction cycle, additional reactivity is provided to the surface, denoted as plasma-enhanced (PE-) ALD. 28 The feasibility of MoS 2 and WS 2 ALD is demonstrated in a limited number of reports. 29−32 Polycrystalline WS 2 films are deposited at a deposition temperature of 300 °C−450 °C from tungsten hexafluoride (WF 6 ) and dihydrogen sulfide (H 2 S) with addition of reducing agents such as diethylzinc, sacrificial Si layers, and H 2 plasma.…”

Plasma-Enhanced ALD of TiO2 Using a Novel Cyclopentadienyl Alkylamido Precursor [Ti(CpMe)(NMe2)3] and O2 Plasma

“…In general, plasma-enhanced ALD (PEALD) -in which the oxidizing/reducing agent is provided by a plasma -offers more versatility and other potential benefits over traditional thermal ALD processes (15). One of these benefits is its ability to deposit films at lower temperatures, thereby making it suitable for deposition on temperature-sensitive substrates (16).…”

Influence of O(3P)/O2 Flux on the Atomic Layer Deposition of B2O3 Using Trimethyl Borate at Room Temperature

“…Plasma-enhanced atomic layer deposition (PE-ALD) has emerged as an industrially favored method for thin film deposition, especially in advanced microelectronics, energy, and related applications. − Therefore, understanding the interactions of plasma and its components with precursors and surfaces is of both fundamental and practical significance. However, it is difficult to interpret the complex interactions of various plasma components with adsorbates and surfaces.…”