Chemically Stable Atomic-Layer-Deposited Al₂O₃ Films for Processability

Abstract

Atomic-layer-deposited alumina (ALD Al 2 O 3 ) can be utilized for passivation, structural, and functional purposes in electronics. In all cases, the deposited film is usually expected to maintain chemical stability over the lifetime of the device or during processing. However, as-deposited ALD Al 2 O 3 is typically amorphous with poor resistance to chemical attack by aggressive solutions employed in electronics manufacturing. Therefore, such films may not be suitable for further processing as solvent treatments could weaken the protective barrier properties of the film or dissolved material could contaminate the solvent baths, which can cause cross-contamination of a production line used to manufacture different products. On the contrary, heat-treated, crystalline ALD Al 2 O 3 has shown resistance to deterioration in solutions, such as standard clean (SC) 1 and 2. In this study, ALD Al 2 O 3 was deposited from four different precursor combinations and subsequently annealed either at 600, 800, or 1000 °C for 1 h. Crystalline Al 2 O 3 was achieved after the 800 and 1000 °C heat treatments. The crystalline films showed apparent stability in SC-1 and HF solutions. However, ellipsometry and electron microscopy showed that a prolonged exposure (60 min) to SC-1 and HF had induced a decrease in the refractive index and nanocracks in the films annealed at 800 °C. The degradation mechanism of the unstable crystalline film and the microstructure of the film, fully stable in SC-1 and with minor reaction with HF, were studied with transmission electron microscopy. Although both crystallized films had the same alumina transition phase, the film annealed at 800 °C in N 2 , with a less developed microstructure such as embedded amorphous regions and an uneven interfacial reaction layer, deteriorates at the amorphous regions and at the substrate–film interface. On the contrary, the stable film annealed at 1000 °C in N 2 had considerably less embedded amorphous regions and a uniform Al–O–Si interfacial layer.

Hardness and modulus of elasticity of atomic layer deposited Al2O3-ZrO2 nanolaminates and mixtures

“…The likely reason is the amorphous nature of the thin film. It has been shown before in XRR measurements that ALD alumina has low density in as deposited state and the density increases during post-deposition annealing [14,[29][30][31]. Compared to previously derived densities from XRF and SE measurements, the XRR results coincide in about 5% margin.…”

“…Due to its nature, ALD can cover all surfaces conformally [13]. So far, the interest in ALD alumina-zirconia has rather considered barrier properties (for instance, encapsulation of electronic devices), electrical or magnetic properties [14][15][16].…”

Blistering mechanisms of atomic-layer-deposited AlN and Al2O3 films

“…Further details can be found in Ref. 12. The AlN films were deposited on (100) Si wafers with native oxide in a PEALD reactor (Picosun R-200) with a remote inductively coupled plasma (ICP) configuration.…”

“…The alumina films were previously characterized in Ref. 12 and represent typical high-temperature ALD alumina. It needs to be noted that the TMA precursor starts to decompose at around 370 C, which could cause chemical vapor deposition (CVD) type growth and hence lower film quality.…”

“…The alumina film had a more complex diffractogram and was best indexed with j, 21 h, 22 and a 23 phases in contrast to N 2 annealing in Ref. 12 where bare h indexing provided the best fit. Based on the XRD data, the AlN film is in high biaxial compressive stress while the alumina film is in tensile stress based on the shift of the (012) a peak whose position is well defined in the literature.…”