Enhancing the Wettability of High Aspect-Ratio Through-Silicon Vias Lined With LPCVD Silicon Nitride or PE-ALD Titanium Nitride for Void-Free Bottom-Up Copper Electroplating

One of the critical steps toward producing void-free and uniform bottom-up copper electroplating in high aspect-ratio (AR) through-silicon vias (TSVs) is the ability of the copper electrolyte to spontaneously flow through the entire depth of the via. This can be accomplished by reducing the concentration gradient of cupric ions from the via mouth to the via bottom by enhancing the wettability of the vias sidewalls. In this paper, we report on a new dry technique to enhance the hydrophilicity in high AR (~15) TSVs as one of the key solutions to face the mass transport limitation, low pressure chemical vapor deposition silicon nitride and atomic layer deposition titanium nitride of composition SiN
_0.95
and TiN
₁₁
, respectively, are used as both barrier layers and wetting surfaces in these vias. Ammonia plasma immersion is used to treat silicon nitride. X-ray photoelectron spectroscopy shows both a partial oxidation and grafting of hydrophilic components. Alternatively, a rapid flood ultraviolet exposure step in order to photocatalytically activate the surface and induce a partially oxidized titanium nitride is used to create a highly wettable interface with a contact angle close to zero. These wettability enhancement steps were incorporated in a TSV process to produce 3-D cross-Kelvin structures using bottom-up copper electroplating. The vias lined with silicon nitride and titanium nitride exhibited a low average resistance of 25 mΩ and 50 mΩ, respectively, making them very suitable for radio-frequency signal transmission. This all-dry technology to achieve superhydrophilic barrier layers can be employed in both high and low thermal budget processing, thus enabling via-last or via-first flowchart schemes for advanced 3-D interconnects.