GR-Tue-P23 - High rate, high quality tuneable nitrides by plasma atomic layer deposition enabling volume manufacturing for GaN device integration
1. GrowthAileen O’Mahony1, Elliot Gay1, Dmytro Besprozvannyy1
1 Oxford Instruments Plasma Technology, Govier Way, Western Approach Distribution Park, Severn Beach, Bristol, BS35 4GG, United Kingdom
Abstract text
GaN has been used in light emitting diodes and has expanded into power electronics, RF, microLEDs and VCSELs markets. The adoption of GaN transistors in high volume consumer-based power electronics has been driven by the need for smaller, faster, efficient mobile device chargers. It is predicted the GaN power device market will reach $2B by 2027 supported by a broader range of applications including renewable energy, data centres, electric vehicles, and infrastructure for 5G and 6G networks. These emerging GaN markets require uniform, conformal, low damage plasma processing solutions optimised for 200 mm wafers to improve device performance, throughput, and yield at reduced cost.
Plasma enhanced atomic layer deposition (PEALD) has been implemented in GaN transistors for low damage, uniform passivation layers (Al2O3, SiO2, SiN), as a method of interface optimisation using plasma pre-treatments to deposit high quality nitrides such as epitaxial AlN. The need for tunability of ALD nitride processes has been demonstrated in the selective deposition of crystalline and amorphous AlN films in a single GaN transistor to increase the 2DEG carrier density and reduce the current collapse in GaN transistors resulting in faster switching, more efficient devices. High throughput plasma ALD of SiN deposition is advantageous for GaN device processing at low temperature (≤500 °C) - compared to LPCVD (usually ≥700 °C) and thermal ALD (typically >450 °C) - without compromising on conformality or uniformity up to 200 mm wafer size. PEALD SiN has also been shown to reduce trap defect density in GaN transistors compared to other deposition methods and materials. Optimisation of the plasma processing parameters can achieve SiN films with tuneable growth rate, composition and refractive index.
PEALD AlN and SiN processes were developed achieving thickness non-uniformities of 2.0% and 3.0% respectively across 200 mm Si wafers. The composition of the AlN films was measured by XPS resulting in stochiometric films with low contamination. Low HF etch rates of the deposited SiN films demonstrated high density and low contamination confirmed by refractive index. To demonstrate the tunability crystallinity of the PEALD AlN process, XRD was used to measure thicker AlN films. The AlN and SiN processes developed demonstrate high deposition rates combined with excellent film quality.