Tuesday, November 9, 2021

Innovative remote plasma source for atomic layer deposition for GaN devices

Oxford Instruments and TU Eindhoven present results from the new Atomfab(TM) Remote Plasma ALD system for high-quality dielectric films. This could enable GaN normally off high-electron-mobility transistors (HEMTs).

Innovative remote plasma source for atomic layer deposition for GaN devices
Journal of Vacuum Science & Technology A 39, 062403 (2021); https://doi.org/10.1116/6.0001318

High-quality dielectric films could enable GaN normally off high-electron-mobility transistors (HEMTs). Plasma atomic layer deposition (ALD) is known to allow for controlled high-quality thin-film deposition, and in order to not exceed energy and flux levels leading to device damage, the plasma used should preferably be remote for many applications. This article outlines ion energy flux distribution functions and flux levels for a new remote plasma ALD system, Oxford Instruments Atomfab™, which includes an innovative, RF-driven, remote plasma source. The source design is optimized for ALD for GaN HEMTs for substrates up to 200 mm in diameter and allows for Al2O3 ALD cycles of less than 1 s. Modest ion energies of <50 eV and very low ion flux levels of <1013 cm−2 s−1 were found at low-damage conditions. The ion flux can be increased to the high 1014 cm−2 s−1 range if desired for other applications. Using low-damage conditions, fast ALD saturation behavior and good uniformity were demonstrated for Al2O3. For films of 20 nm thickness, a breakdown voltage value of 8.9 MV/cm was obtained and the Al2O3 films were demonstrated to be suitable for GaN HEMT devices where the combination with plasma pretreatment and postdeposition anneals resulted in the best device parameters.

Image of the Oxford Instruments Atomfab system (a) used in this work. A conceptual schematic (b) of the plasma source with powered (light gray) and grounded (dark gray) surfaces indicated. This plasma source was also put on a testbed system (c), which was used for the ion measurements and OES, the RFEA for probing the ion energy, and the flux was placed at the wafer level. Besides the RFEA, the testbed system was designed to allow for a range of optical diagnostics in the future (d).

Growth per cycle for ALD of Al2O3. Data are given as a function of precursor (a) and plasma (b) dose times and the respective purge times (c) and (d) at 300 °C. Single and double exponential curve fits serve as a guide to the eye.

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