Real-time in situ process monitoring and characterization of GaN films grown on Si (100) by low-temperature hollow-cathode plasma-atomic layer deposition using trimethylgallium and N2/H2 plasma

Abstract

In this work, we report on the in situ process monitoring and materials characterization of low-temperature self-limiting grown gallium nitride (GaN) thin films. GaN samples were synthesized on Si (100) substrates via remote hollow-cathode plasma-atomic layer deposition (HCP-ALD) using trimethylgallium and N2/H2 plasma as a metal precursor and a nitrogen coreactant, respectively. A multiwavelength in situ ellipsometer was employed to monitor the saturating surface reactions and determine the self-limiting growth conditions. The subangstrom thickness resolution of ellipsometry enabled the real-time observation of single chemical adsorption and plasma-induced ligand removal/exchange events. Taking advantage of this in situ capability, saturation experiments have been carried out within the 120–240 °C temperature range without interruption featuring 10-cycle subruns for each parameter change. Plasma power, plasma exposure duration, and plasma chemistry (gas composition) are the main process parameters that have been investigated. Ex situ optical, structural, and chemical characterization is carried out on 600-cycle HCP-ALD-grown GaN films as a function of substrate temperature. Hexagonal single-phase polycrystalline GaN films with (002) preferred orientation was obtained at substrate temperatures higher than 200 °C. The crystalline GaN films exhibited below-detection-limit carbon content and slightly gallium rich stoichiometry. Substrate temperature and plasma power played a critical role on GaN film properties with 200 °C and 150 W as threshold values for crystallization. Moreover, we observed that Ar-free N2/H2 plasma gas composition led to a slightly stronger (002) dominant crystal orientation.