Innovative remote plasma source for atomic layer deposition for GaN devices

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 <10¹³cm⁻²s⁻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.

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