Cobalt-Aluminum Metal Caps for Copper Electromigration Control
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Solution Overview
Problem
Copper interconnects in semiconductor devices face challenges with electro-migration, as they tend to form voids and extrusions, leading to open or short circuits, and traditional methods like cobalt caps diffuse and lose their effectiveness.
Innovation Solution
A method involving the formation of a barrier layer, a liner layer, a seed layer, and a cobalt-aluminum alloy cap layer, where the substrate is exposed to cobalt and aluminum precursors to prevent cobalt diffusion and enhance adhesion, thereby improving electro-migration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cobalt cap layer is used to improve adhesion and electro-migration resistance, then electro-migration performance is improved, but cobalt diffusion occurs and the cap layer loses its effectiveness
Solution Approach 1:
A ruthenium liner layer is introduced as an intermediary between the copper fill and the cobalt cap layer. This liner prevents direct contact and diffusion between cobalt and copper while maintaining the adhesion benefits of the cobalt cap, thus resolving the contradiction between improving electro-migration resistance and preventing cobalt diffusion
Solution Approach 2:
The structure combines multiple materials (copper fill, ruthenium liner, cobalt cap) into a composite interconnect structure. Each material performs its specific function: copper provides conductivity, ruthenium provides a diffusion barrier and adhesion promotion, and cobalt provides electro-migration resistance, collectively resolving the technical contradiction
2Manufacturing precision
If a ruthenium liner layer is used to promote copper reflow and achieve voids-free gap-fill, then gap-fill quality is improved, but copper moves easily on the liner layer resulting in electro-migration failure
Solution Approach 1:
The ruthenium liner provides different properties at different interfaces: at the copper-ruthenium interface, it promotes reflow for voids-free filling, while at the ruthenium-cobalt interface, it prevents cobalt diffusion. The addition of cobalt cap layer provides localized electro-migration resistance where needed, resolving the contradiction between gap-fill quality and electro-migration resistance
3Ease of manufacture
If conventional copper filling is used to form interconnects, then manufacturing simplicity is maintained, but voids form during copper filling leading to open circuits
Solution Approach 1:
The ruthenium liner layer is deposited beforehand on the trench walls before copper filling. This preliminary action promotes copper reflow during filling, ensuring voids-free gap-fill without complicating the manufacturing process. The liner is applied once and provides continuous protection during subsequent filling operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The cobalt-aluminum alloy cap layer effectively reduces cobalt migration, enhancing the electro-migration performance and reliability of copper interconnects by maintaining adhesion and preventing voids and extrusions.
Implementation Method 1
selectively forming a cobalt-aluminum alloy cap layer on the barrier layer, the liner layer, the seed layer, and the metal fill by exposing the substrate to a cobalt-containing precursor and an aluminum-containing precursor
Implementation Method 2
overburdening the feature using an electroplating process
Data Source
AI summary
Embodiments of the present disclosure are related to improved methods for forming an interconnect structure in a substrate. In one implementation, the method includes forming a barrier layer on exposed surfaces of a feature in a dielectric layer, forming a liner layer on the barrier layer, forming a seed layer on the liner layer, forming a metal fill on the seed layer by a metal fill process and overburdening the feature using an electroplating process, performing a planarization process to expose a top surface of the dielectric layer, and selectively forming a cobalt-aluminum alloy cap layer on the barrier layer, the liner layer, the seed layer, and the metal fill by exposing the substrate to a cobalt-containing precursor and an aluminum-containing precursor.