• Lepikko, Sakari
• Ras, Robin H. A.
• Verkama, Emma
• Riikka, L. Puurunen
• Yim, Jihong
• Utriainen, Mikko

Abstract

Atomic layer deposition (ALD) is a fast-growing technique in manufacturing modern electronics due to its ability to produce uniform and conformal thin films with sub-nanometer precision even within high-aspect-ratio cavities. However, reaction kinetics and deposition parameters set the limits how deep the film can be grown conformally within a high-aspect-ratio structure. In this work, we use lateral high-aspect-ratio structure for comparison of thickness profiles of two aluminum oxide Al2O3 deposition processes: trimethylaluminum Al(CH3)3 (TMA) with either water H2O (denoted as TMA/H2O) or ozone O3 (denoted as TMA/O3) as co-reactants. The processes are performed with Veeco-CNT Savannah S200 ALD reactor on PillarHall® LHAR3 test structures in otherwise the same conditions except for the co-reactant pulse. This structure has a lateral trench with gap height of 500 nm and depth of 1 mm, resulting in aspect ratio of 2000.<br/>The thickness profiles obtained with spectroscopic reflectometry show four main differences between the processes. The initial plateau at low depths describes the growth per cycle (GPC). It is 30% higher for TMA/H2O than for TMA/ O3. Since the TMA dose is the same in both processes, we conclude that O3 generates less hydroxyl groups than H2O, which affects GPC [1]. The plateau is followed by a steep slope. The slope at half-thickness value is related to the sticking coefficient of limiting reactant [2]. The slope in this case corresponds to the sticking coefficient of TMA in both processes, indicating that TMA is the limiting reactant in these deposition conditions. The depth of half-thickness value describes the diffusion length of the reactants under the deposition conditions. This value is slightly higher for TMA/O3 even though the limiting TMA dose is the same in both processes. TMA/O3 diffuses therefore slightly longer into trenches than TMA/H2O. However, the total volume of deposited film remains smaller for TMA/O3 due to smaller GPC. The total area beneath the thickness profile curve, which equals to cross-sectional area of the film, for TMA/O3 is 20% smaller than for TMA/H2O.<br/>Lastly, TMA/H2O is compared to another TMA/H2O process deposited in Picosun R-150 ALD reactor on a similar PillarHall® structure [3]. The processes are otherwise nearly identical except for half-thickness depth. This is due to larger dose used in the Picosun reactor increasing the diffusion length of precursors.

Topics

• impedance spectroscopy
• thin film
• aluminum oxide
• aluminium
• laser emission spectroscopy
• atomic layer deposition
• reflectometry