Gallium Nitride Plasma etching study and innovative process development for µLED fabrication

The advance of LED micro displays requires high resolution and brightness for a wide range of applications such as smart phone or virtual reality. These new products specifications raise challenges in terms of pixels size and density, material integration and fabrication techniques.

In this context, Gallium Nitride has been extensively used and studied for its optoelectronics properties in LED structure which relies on a fine patterning to reach the required resolution. In order to control sub micrometer critical dimensions between pixels, anisotropic plasma etching is therefore needed. This plasma is composed of ions and neutrals created by the ionisation and the dissociation respectively of feed gaz in the reactor. It has been widely developed for the microelectronic industry.

However, the interactions between the plasma and the GaN can damage the material leading to optoelectronic losses. It is assumed that the plasma creates defects on the pixels sidewalls leading to non radiative recombinations between electrons and holes. This issue become prevalent for micro pixels under 100µm. Many studies have been carried out about GaN cleaning or GaN passivation after etching to cure the damaged material but some defects and efficiency losses remain. Thus, the purpose of the thesis is to develop innovative plasma processes on the different etching tools and options available in the LETI clean rooms (200mm ICP reactors, pulsed bias, Atomic Layer Etching) to reduce or avoid GaN damaging. To reach this goal, a sharp understanding of the plasma surface interaction will be necessary and will involve physico-chemical characterization technics (XPS, SEM, TEM, EDX, SIMS) correlated to electro-optical measurements so that the impact on the final device could be assessed.

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