Area selective atomic layer deposition of silicon dioxide on silicon dioxide using surface passivation of copper non-growth surface

Abstract

The continuous downscaling of electronic devices to < 10 nm over the years has led to many integration challenges in the fabrication processes. Top-down techniques like photolithography are cost intensive and lead to alignment challenges such as edge placement errors which add additional steps in fabrication. To avoid these challenges, bottom-up techniques which have atomic level control over the process are required. Atomic layer deposition (ALD) is a thin film deposition technique which provides excellent uniformity, conformality and thickness control at nano scale dimensions. However, ALD processes results in blanket growth over different materials on the entire substrate and hence cannot be applied for processes requiring selective growth. Due to the limited inherent material selectivity in growth during ALD, an inhibitor molecule is required to functionalize the non-growth surface prior to ALD process. This bottom-up surface selective variant of ALD is area selective ALD and can be widely used in structures during device processing. In this thesis work, we have completed the development of area selective atomic layer deposition process of SiO2 on SiO2, using alkanethiol and fluorothiol inhibitors in a three-step process on chemically mechanically planarized (CMP) Cu non-growth surface. In the first part of the study, we analyzed the passivation efficiency of heptane thiol (HT) inhibitor on Cu for thermal (O3) and O2 plasma-based area selective ALD of SiO2 using a three step A-B-C ALD process (A: HT, B: DSBAS, C: O3/O¬2 plasma). Using in situ reflection absorption infrared spectroscopy (RAIRS) and x-ray photoelectron spectroscopy (XPS) we indicate minimal accumulation of SiO2 on Cu surface at 100 °C and partial oxidation of Cu surface for both O3 and O2 plasma-based processes. We also demonstrate that the amount of HT degraded by O3¬ was high compared to O¬2 plasma throughout the process. In the second part of the study, perfluorodecanethiol (PFDT) was used as the inhibitor in a three-step A-B-C sequence (A: PFDT, B: DSBAS, C: O3/O¬2 plasma) for the O3 and O2 plasma assisted SiO2 ALD process. We used in-situ RAIRS and XPS to prove the blocking ability of PFDT against SiO2 ALD and observed reduced Cu with no SiO2 accumulation after the process. In the O2 plasma-assisted selective deposition of SiO2, we observed a self-limiting ~7-10 % thiol removal and redose using in situ RAIRS. We also show the removal of PFDT inhibitor from Cu post-process and the recovery of smooth CMP surface using atomic force microscopy (AFM) and XPS. Finally using transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS), we show 10 nm selective growth of SiO2 on Cu-SiO2 pattern.