Robust Bottom-Up Gold Filling of Deep Trenches and Gratings

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Superconformal electrodeposition is crucial for fabricating advanced electronic devices.
• Achieving void-free filling in deep, high-aspect-ratio structures remains a significant challenge.
• Understanding factors limiting deposition depth and process robustness is essential for practical applications.

Purpose of the Study:

• To extend superconformal gold electrodeposition to deeper device architectures.
• To investigate factors constraining void-free processing in high-aspect-ratio trenches.
• To explore the robustness and uniformity of the bottom-up filling process.

Main Methods:

• Employed an extreme variant of superconformal electrodeposition using a bottom-up approach.
• Utilized a near-neutral electrolyte (Na3Au(SO3)2 + Na2SO3) with Bi3+ additive.
• Filled diffraction gratings with trenches up to 305 microm deep and aspect ratios (AR) below 20.

Main Results:

• Successfully achieved void-free gold filling in trenches significantly deeper (up to 305 microm) than previously reported.
• Demonstrated a linkage between accelerated deposition start and void-free filling, suggesting transport limitations.
• Confirmed fully dense, void-free gold structures using electron microscopy, electron backscatter diffraction, and X-ray transmission.

Conclusions:

• The superconformal electrodeposition process is robust and scalable for void-free filling of deep trenches.
• Self-passivation inherent in the process ensures highly uniform gold profiles across large gratings.
• This work advances the capability for fabricating complex, high-density electronic components.