ABSTRACT
Area-selective atomic layer deposition (AS-ALD) processes are gaining significant traction as advanced technology nodes demand improved edge-placement accuracy and atomic scale process control. These selective deposition processes enable a bottom-up fabrication approach without lithographic or subtractive patterning methods, offering a viable approach to address significant challenges posed by scaling logic technology beyond the 3 nm node. A class of materials called self assembled monolayers (SAM) are most widely studied for area-selective deposition (ASD) for their ability to deactivate ALD growth selectively. SAM chemistries can be tailored to selectively adsorb only on specific materials while remaining
inactive on others, thereby allowing surface dependent ALD growth. Achieving robust selectivity and accurate characterization becomes especially challenging on patterned structures, where feature dimensions are extremely small and the growth and non‑growth regions are positioned in immediate proximity. It is vital to measure these ultrathin growth
layers and monitor the deposition processes inline to ensure that area-selective growth occurs only in the intended regions.
Additionally, if SAM and back-end-of-line (BEOL) stack materials share identical elemental signatures, conventional inline metrology techniques are unable to distinguish their contributions separately. These limitations create a critical need for a non‑invasive measurement method equipped with novel advanced analytical algorithms capable of resolving
angstrom level thicknesses.
In this study, gas phase SAMs were selectively adsorbed onto patterned BEOL Cu wires, after which TaN was subsequently deposited through multiple ALD cycles. The Cu line structures were fabricated with intentional line and space design variations to evaluate pattern dependent behavior. The AS‑ALD process conditions were also varied to assess
their impact on the SAM layer and its effectiveness as a selective growth barrier. Inline X-ray photoelectron spectroscopy (XPS) measurements in combination with advanced algorithms and a feed forward analysis framework were utilized for evaluation and quantification of selective deposition processes on patterned structures. This approach enabled accurate extraction of SAM and TaN thicknesses on both growth and non-growth areas, thereby providing a reliable basis for calculation of selectivity metrics. Additionally, newly developed algorithms facilitated the resolution of SAM derived signal from BEOL dielectrics even when the elemental compositions are identical.
Keywords: In-line XPS, advanced XPS, AS-ALD, ASD, SAM, area-selective deposition metrology, bottomless barrier, BEOL metrology, metrology, Cu interconnects
*Corresponding author: [email protected]