Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition

Abstract

We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH 3 ). At 185°C, deposition rate saturated for TMA and NH 3 doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH 3 resulted in a constant growth rate of~0.86 Å/cycle from 100 to 200°C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≥ 225°C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185°C were investigated by Xray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185°C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at~5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum.

Review—Investigation and Review of the Thermal, Mechanical, Electrical, Optical, and Structural Properties of Atomic Layer Deposited High-kDielectrics: Beryllium Oxide, Aluminum Oxide, Hafnium Oxide, and Aluminum Nitride

“…Poly-crystalline PEALD AlN films, however, have been reported to have aluminum-rich stoichiometries. 161,179 While various growth conditions may be important in controlling the stoichiometry, this observation suggests that crystallinity in PEALD AlN is perhaps a function of stoichiometry.…”

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films

“…11 More recently, plasmaenhanced atomic layer deposition (PEALD) has been demonstrated as an alternative method for AlN deposition. [12][13][14][15][16][17][18][19][20][21][22] The AlN process is also available for thermal ALD but in that case the source material selection is limited and above 400 C deposition temperatures are required. 15 In contrast, the attractive properties of PEALD films include low temperature processing (typically below 300 C), thus increasing the choice of precursors and materials, enabling tunable material properties, and still allowing the typical ALD thickness control below 1 nm accuracy.…”

“…Examining previous studies on PEALD AlN deposited at various temperatures reveals that typically the films are found to be crystalline. More specifically, usually PEALD films with a high Al:N ratio (>0.9) are found to be crystalline, [13][14][15][16][17][18][19][20][21] whereas AlN films with a low ratio (<0.9) are not found to be crystalline. 15,22 The additional nitrogen beyond the stoichiometric 1:1 ratio can be thought to be an impurity which affects the stability of the amorphous structure.…”

Current transport mechanisms in plasma-enhanced atomic layer deposited AlN thin films

“…14,15 Here, we present the room-temperature electrical conduction properties of these polycrystalline wurtzite AlN thin films, along with some other electrical properties, as determined from the current-voltage (I-V) and high-frequency (1 MHz) capacitancevoltage (C-V) measurements of Al/AlN/p-Si MIS structures.…”