Plasma cleaning (etch)

Soft etching

Moorfield’s Soft Etching technology was developed in collaboration with the Nobel Prize-winning graphene group at Manchester University, UK. Headed by Prof. Andre Geim, the group received their first system from Moorfield when they started their 2D materials research over 10 years ago. Since then, the technology, implemented within our compact nanoETCH range, has become a critical part of all experimental work. They now have 3 tools, housed within the National Graphene Insitutute (NGI). There is also another tool at the Graphene Engineering Innovation Centre (GEIC) — also in Manchester.

Soft Etching technology is optimised for providing the fine control required for substrate and device preparation in graphene and 2D materials research:

Substrate preparation for mechanical exfoliation: When preparing 2D material ‘flakes’ via mechanical exfoliation (also known as the sticky-tape method), the nature of the substrate surface is crucial. Soft Etching tools are now being used to obtain the topological and chemical substrate surface properties necessary for producing large flake areas.
2D material patterning: Given their thinness, 2D materials are fragile and require finely-controlled etching conditions for device fabrication. Soft Etching technology provides this control and also allows for patterning without cross-linking common mask photoresists (e.g., PMMA).
Defect engineering: A key research theme for graphene science is defect engineering. Through controlled low plasma-powers, soft-etching technology is being used for creating point defects in lattices for implementing control over this aspect of the material. Fine control is necessary for reproducible results and to avoid uncontrolled material destruction.

As well as 2D materials, Soft Etching technology has found numerous other applications. For example, it has been used for precision removal of alternative resists such as PPA and for the tuning of hydrophobicity of glass slides prior to wet depositions.

Soft Etching is available within our nanoETCH and MiniLab platforms.

SF6 and CHF3 etching

While the etching of 2D materials can be done through the careful application Ar and/or O2 plasmas, other materials more commonly targeted by RIE require a more aggressive approach. For this, Moorfield etching technology has recently been enhanced to provide for the use of the fluorine-chemistry etchants SF6 and CHF3. To allow for this, both hardware and software have been upgraded in line with the demands these process gases introduce.

Some examples of applications are:

h-BN sidewalls: A pit was etched into a multi-layer stack of h-BN, using Moorfield etching technology contained within a MiniLab 026. With SF6 as the etchant gas and a Soft Etching approach, just 7–8 layers of material were removed during a 2 minute process. Residual roughness at the bottom of the pit was just 1 atomic layer.
h-BN bulk etching: By changing conditions, much higher etch rates were possible. Users were able to achieve an etch depth of 130 nm at a rate of 1.1 nm/s.
SiO2 etching: A thermally oxidised Si wafer was etched using a nanoETCH tool using CHF3 as etchant gas. An ultra-low etch rate of ~1.3 Å/s was obtained, allowing for excellent control.

Fluorine-chemistry etching is available within our nanoETCH and MiniLab platforms.

Pre-deposition plasma cleaning

A requirement for many physical vapour deposition (PVD) processes is pre-cleaning of substrates. An effective method for this is to create reactive plasmas in close proximity to substrate surfaces, leading to the removal of unwanted contaminants. Moorfield, as a leading supplier of R&D deposition tools now routinely fit systems with etching stages that provide this functionality.

Etching stages can be fitted into a process chamber in combination with the deposition substrate stage itself (the stage is first active for etching, then for deposition). However, where possible, it is best to position the cleaning stage in a supporting load-lock as this confines removed material away from the process and also allows for equipping of the main deposition stage with hardware not compatible with plasma etching.

Pre-deposition etch cleaning is available in our MiniLab PVD tools.