Nucleation of highly uniform AlN thin films by high volume batch ALD on 200 mm platform

Abstract

A highly uniform aluminum nitride thin film has been developed by thermal atomic layer deposition (ALD), which is designed to handle high volume of 200 mm wafers. A three-sigma thickness variation of <0.5 Å resulted from repeatable batch depositions of over 500 Å, while wafer-within-wafer (WinW) and wafer-to-wafer (WtoW) remained <5% by the optimized recipe in a 100+ wafer reactor. Various ALD deposition temperatures, film thicknesses, and substrate types of Si, quartz, and GaN/Si(111) templates have been examined for material and optical properties of an AlN film. A narrow temperature window of 300–350 °C was identified as the most suitable for the deposition process with 350 °C as the optimized one. Substrate-inhibited growth and nonlinearity in deposition rate have been observed for AlN which is possibly related to the available reaction sites at the time of nucleation on foreign substrate surfaces. A special set of experiments with a thorough exploration of XPS individual peaks such as Al2p, N1s, C1s, and O1s reveals negligible carbon and oxygen contamination with cent-percent Al–N bonding. An amorphous AlN film is evident on Si by cross-sectional TEM while a trace of polycrystalline film on GaN templates with smooth heterointerfaces to AlGaN/GaN structures. The optical bandgap is estimated to be 5.8 eV from the transmittance experiment. An in-depth refractive-index investigation shows high-density AlN by TEL Alpha-8SEiTM batch ALD which also exhibits excellent uniformity over composition and thickness with run-to-run (RtoR), WtoW, and WinW uniformity under 0.5%, highlighting the reliability and precision of the process while having high throughput.