Oxford Instruments unveils ALD plasma processing system for 2D materials

UK-based Oxford Instruments says that its atmic layer deposition (ALD) and 2D technical specialists have teamed up with the research teams of Eindhoven University of Technology (TU/e) in The Netherlands to develop the FlexAL-2D for ALD of 2D transition-metal dichalcogenides (TMDs) for nanodevice applications.

The firm says the system offers the following benefits:

• 2D materials growth: at CMOS-compatible temperatures, with precise digital thickness control, over a large area (200mm wafers).
• Robust ALD processes for 2D materials: self-limiting ALD growth; molybdenum disulfide (MoS2) – oxygen and carbon free (<2%), high growth per cycle ~0.1 nm/cycle, and crystalline material above 300°C.
• Tunable morphology: control over basal plane or edge plane orientation.
• Growth of ALD dielectrics and other ALD layers on 2D materials in one tool, for creating advanced 2D device structures.
•  RF substrate biasing option for film property control.

The wide parameter space offered by the system allows the growth of 2D transition-metal dichalcogenides at lower temperatures than employed in chemical vapor deposition (CVD) furnaces. First results on the growth of 2D MoS2 material by ALD at 450°C and lower temperatures were presented by Eindhoven researchers on 16 July at the 17th International Conference on Atomic Layer Deposition (ALD 2017) in Denver, CO, USA. Plasma-enhanced ALD was implemented to synthesize layers of 2D MoS2 films with tunable morphologies, i.e. in-plane and vertically standing nano-scale architectures on CMOS-compatible SiO2/Si substrates. The 2D in-plane morphology has potential applications in nanoelectronics, while the 3D fin structures are suitable for catalysis applications such as water splitting.

“Dr Bol and the Plasma & Materials Processing (PMP) group at TU/e are pushing the boundaries of ALD research into new application areas,” comments Chris Hodson, ALD product manager at Oxford Instruments Plasma Technology (OIPT). “2D materials are a hot topic and utilizing ALD to allow growth at lower temperatures and combine 2D materials with ALD deposition and other processing methods at 200mm provide a new capability with many possibilities,” he adds.

The TU/e researchers are particularly interested in relatively low temperatures. “For CVD processes, typically temperatures of over 800°C are needed,” notes Dr Ageeth Bol., associate professor in the Plasma & Materials Processing group “That is often fatal for applications in semiconductors because the high temperature increases the diffusion of the atoms, which makes it harder to place them at the right spot,” he adds. “We want to have a process that yields materials of high quality at lower temperatures. This is especially important for the two-dimensional heterogeneous layers I am working on, since at lower temperatures less diffusion of atoms between the layers will occur.”