Soft removal of stearic acid self-assembled monolayer for area-selective atomic layer deposition

Abstract

Stearic acid (SA) self-assembled monolayer (SAM) is proposed as a soft-removal passivating agent for area-selective atomic layer deposition (AS-ALD) applications. First, the SAM formation kinetics and its thermal stability were evaluated on a copper surface. We observed a highly packed, hydrophobic, and ordered monolayer. The transition temperature from order to disorder was observed above 160 °C. Next, the SA/copper was evaluated as a non-growth surface for ZnO ALD and monitored by X-ray Photoelectron Spectroscopy (XPS). The optimal ALD parameters were found at 70 °C, dosing 25 ms of diethyl zinc precursor and water, while purge was 10 s for each. In these conditions, the attenuation growth remained for at least 40 ALD cycles; despite zinc deposition after the first three cycles. Finally, the removal of the SA monolayer was investigated with water, acetone, and ethanol at room temperature. According to infrared and water contact angle, ethanol was the most effective, showing a complete removal after 30 min immersion time (without sonication or agitation). We conclude that SA SAM is an efficient removable copper passivating agent for area-selective atomic layer deposition without exposing samples to harsh conditions, like etching or acid treatments.