Atomic layer etching of MOCVD epitaxial gallium nitride

As have been reported before by Lund Nano Lab in Sweden (e.g. at ALE2016 Ireland and ALE2017 Denver) it is quite possible to use a standard ICP reactive ion etch chamber to run Atomic Layer Etching (ALE). Here is a nice publication from Aalto University in Finland and current and ex scientists from Lund Nano Lab in Sweden transferring the ALE processes from Lund and running it on an Oxford Instruments Plasmalab 100 in ALE mode etching GaN in Helsinki Micronova clean room.

The Oxford Instruments Plasmalab 100 at Aalto University Micronova clean room (LINK to technical specs and capabilities) 

MOCVD grown epitaxial AlGaN/GaN heterostructures implemented in high electron mobility transistors (HEMTs) have a well-defined layered structure with the two-dimensional electron gas (2DEG). However, etching of the gate recess is challenging as conventional RIE does not provide sufficiently good control over the etch process, and high energy ions can cause damage to the 2DEG layer. This paper showcase how these problems can be avoided if GaN ALE is used in etching these recesses.

Sabbir Khan - the ALE King tuning the Plasma at Lund Nano Lab.

Besides techniques of growing a single monolayer or few monolayers of GaN are challenging. GaN ALE could provide an alternative method to the 2D material community by a controlled thinning of high quality films of GaN down to a few atomic layers.

Please find the abstract to the Open Access JVSTA publication below:

Atomic layer etching of gallium nitride (0001)
Christoffer Kauppinen, Sabbir Ahmed Khan, Jonas Sundqvist, Dmitry B. Suyatin, Sami Suihkonen, Esko I. Kauppinen, and Markku Sopanen

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 35, 060603 (2017); doi: http://dx.doi.org/10.1116/1.4993996

Abstract: In this work, atomic layer etching (ALE) of thin film Ga-polar GaN(0001) is reported in detail using sequential surface modification by Cl2 adsorption and removal of the modified surface layer by low energy Ar plasma exposure in a standard reactive ion etching system. The feasibility and reproducibility of the process are demonstrated by patterning GaN(0001) films by the ALE process using photoresist as an etch mask. The demonstrated ALE is deemed to be useful for the fabrication of nanoscale structures and high electron mobility transistors and expected to be adoptable for ALE of other materials.