Mechanism for growth initiation on aminosilane-functionalized SiO₂ during area-selective atomic layer deposition of ZrO₂

The mechanism for growth initiation on the nongrowth surface during area-selective atomic layer deposition (ALD) processes is not well understood. In this study, we examine the ALD of ZrO₂ on a SiO₂ surface functionalized with alkylated-aminosilane inhibitors delivered from the vapor phase. ZrO₂ films were deposited by ALD using tetrakis(ethylmethylamino)zirconium(IV) with H₂O as the coreactant. In situ surface infrared spectroscopy shows that aminosilane inhibitors react with almost all the surface —SiOH groups on the SiO₂ surface by forming Si—O—Si bonds. In situ four-wavelength ellipsometry shows that no ZrO₂ growth occurs on the functionalized SiO₂ during the first few ALD cycles, but growth eventually initiates after a few ALD cycles. We speculate that after repeated exposure of the functionalized SiO₂ surface to Zr precursors, in the absence of surface —SiOH groups, growth initiates due to either reaction of the precursors with strained Si—O—Si bonds or through a strongly physisorbed state. These reaction pathways are usually not relevant in ALD reactions on the unprotected —SiOH-terminated SiO₂ surface due to a higher activation energy barrier, but become relevant on the passivated surface as a result of repeated precursor exposure. Thus, this study highlights the importance of steric blocking of these higher activation energy barrier reaction pathways.