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.

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films Broas, Mikael; Sippola, Perttu; Sajavaara, Timo; Vuorinen, Vesa; Perros, Alexander Pyymaki; Lipsanen, Harri; Paulasto-Kröckel, Mervi Broas, M., Sippola, P., Sajavaara, T., Vuorinen, V., Perros, A. P., Lipsanen, H., & Paulasto-Kröckel, M. (2016). Structural and chemical analysis of annealed plasmaenhanced atomic layer deposition aluminum nitride films.

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The atomic layer deposition (ALD) of AlN from AlCl 3 was investigated using a thermal process with NH 3 and a plasma-enhanced (PE)ALD process with Ar/NH 3 plasma. The growth was limited in the thermal process by the low reactivity of NH 3 , and impractically long pulses were required to reach saturation. Despite the plasma activation, the growth per cycle in the PEALD process was lower than that in the thermal process (0.4 Å vs 0.7 Å). However, the plasma process resulted in a lower concentration of impurities in the films compared to the thermal process. Both the thermal and plasma processes yielded crystalline films; however, the degree of crystallinity was higher in the plasma process. The films had a preferential orientation of the hexagonal AlN [002] direction normal to the silicon (100) wafer surface. With the plasma process, film stress control was possible and tensile, compressive, or zero stress films were obtained by simply adjusting the plasma time.

Blistering of protective, structural, and functional coatings is a reliability risk pestering films ranging from elemental to ceramic ones. The driving force behind blistering comes from either excess hydrogen at the film-substrate interface or stress-driven buckling. Contrary to the stress-driven mechanism, the hydrogen-initiated one is poorly understood. Recently, it was shown that in the bulk Al-Al2O3 system, the blistering is preceded by the formation of nano-sized cavities on the substrate. The stress- and hydrogen-driven mechanisms in atomic-layer-deposited (ALD) films are explored here. We clarify issues in the hydrogen-related mechanism via high-resolution microscopy and show that at least two distinct mechanisms can cause blistering in ALD films.