Reaction Mechanism of Area-Selective Atomic Layer Deposition for Al₂O₃ Nanopatterns

Abstract

The reaction mechanism of area-selective atomic layer deposition (AS-ALD) of AlO thin films using self-assembled monolayers (SAMs) was systematically investigated by theoretical and experimental studies. Trimethylaluminum (TMA) and HO were used as the precursor and oxidant, respectively, with octadecylphosphonic acid (ODPA) as an SAM to block AlO film formation. However, AlO layers began to form on the ODPA SAMs after several cycles, despite reports that CH-terminated SAMs cannot react with TMA. We showed that TMA does not react chemically with the SAM but is physically adsorbed, acting as a nucleation site for AlO film growth. Moreover, the amount of physisorbed TMA was affected by the partial pressure. By controlling it, we developed a new AS-ALD AlO process with high selectivity, which produces films of ∼60 nm thickness over 370 cycles. The successful deposition of AlO thin film patterns using this process is a breakthrough technique in the field of nanotechnology.

From the Bottom-Up: Toward Area-Selective Atomic Layer Deposition with High Selectivity

“…78 This contribution could be reduced by decreasing the TMA pressure and by increasing the Ar pressure during the subsequent purge step, which allowed for area-selective ALD of Al 2 O 3 films as thick as 60 nm. 78 A general lesson from this study is that loss of selectivity is typically caused by side reactions that are not self-limiting. Consequently, as this study demonstrates, the selectivity can be dependent on the precursor or co-reactant pressure and/or exposure time.…”

“…79 Another example that was already discussed is the use of purge steps with a high Ar pressure to remove physisorbed species from the surface of a SAM in the work of Seo et al. 78…”

Insight into the removal and reapplication of small inhibitor molecules during area-selective atomic layer deposition of SiO2

“…When using SAMs as an inhibitor layer, the selectivity is often lost due to ALD growth within or on top of the SAM layer. 25 In this case, the removal of the SAM layer was shown to be very beneficial for the selectivity as this also allows for removal (i.e., lift-off ) of the deposited material. 15,26 From the current study, we learn that reapplication of the inhibitor does not necessarily restore the inhibitor layer to its original state before degradation.…”

“…In general, the selectivity of an area-selective ALD process is eventually lost after a certain number of ALD cycles, through degradation of the inhibitor layer, e.g., by thermal desorption of the inhibitor, interactions between the inhibitor and the precursor, or the use of highly reactive coreactants like ozone or plasmas. 21,[23][24][25] As a result, reapplication of the inhibitors can greatly benefit the selectivity. 26 Selectivity is typically defined as S ¼ θgaÀθnga θgaþθnga , where θ ga and θ nga correspond to the amounts of deposited material on the growth area and on the non-growth area, respectively.…”

Atomic Layer Deposition of Inorganic Thin Films on 3D Polymer Nanonetworks

“…Occasionally, polymers act as inhibitors to the nucleation of inorganic materials during the ALD process. Based on this phenomenon, some studies have achieved area-selective ALD (AS-ALD) by patterning polymer resists or self-assembled monolayers (SAMs) [77][78][79][80][81]. In the case of a soft polymer with low crosslinking density, the gaseous precursor can diffuse into the polymer and react with the polymer to form an organic-inorganic hybrid material.…”