Interconnect Corner Wettability Reduction via Alloy Formation
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Solution Overview
Problem
In semiconductor device manufacturing, the high wettability of copper with ruthenium at the interface of copper and ruthenium at the upper outer corners of metal features, known as triple points, leads to reliability issues such as copper migration and early failures due to the lack of copper recess, which is challenging to address with conventional dielectric materials and fabrication processes.
Innovation Solution
A method involving the formation of a recess in a dielectric layer with a first transition metal layer at the corners, followed by a second transition metal layer that lines the recess, allowing for a fill layer and subsequent annealing to form an alloy with reduced wettability, which is then polished to recess the copper, thereby reducing copper diffusion and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ruthenium liner is used to improve copper seed coverage and enhance copper fill, then copper wettability is improved, but copper migration and reliability issues occur at the triple points due to excessive wettability
Solution Approach 1:
The patent applies different materials with different wettability characteristics to different locations: ruthenium is used at the bottom and sidewalls where high wettability is needed for copper fill, while a titanium nitride barrier layer is used at the top corners where low wettability is needed to prevent copper migration. This local differentiation resolves the contradiction between needing high wettability for fill quality and low wettability to prevent migration.
Solution Approach 2:
The interconnect structure is segmented into different functional zones: the lower portion uses ruthenium for enhanced copper wettability and fill, while the upper corner portions use titanium nitride for barrier properties and migration prevention. This segmentation allows each zone to optimize its local properties without compromising the other.
2Reliability
If copper is plated to fill the recess completely, then interconnect continuity is ensured, but copper creeps over the ruthenium and migrates along the dielectric interface
Solution Approach 1:
The patent creates local quality differences by placing titanium nitride barrier material specifically at the top corner portions where copper migration occurs, while maintaining ruthenium at the bottom and sidewalls for continuous copper fill. This localized barrier prevents copper from creeping over the interface without compromising interconnect continuity.
3Ease of manufacture
If conventional dielectric materials are used, then manufacturing process is simple, but they cannot prevent copper diffusion and migration at the corner interfaces
Solution Approach 1:
The patent uses a composite interconnect structure combining ruthenium and titanium nitride barrier layers within the dielectric material. This composite approach provides both the structural integrity needed for manufacturing and the chemical barrier properties needed to prevent copper diffusion, resolving the contradiction between manufacturing simplicity and reliability.
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 method effectively reduces copper wettability at the corner interfaces, enhancing the reliability of interconnect structures by creating crevices that isolate copper from the dielectric surface, thereby improving time-dependent dielectric breakdown (TDDB) reliability and preventing copper migration.
Implementation Method 1
The substrate is annealed. The first transition metal layer and the second transition metal layer form an alloy portion proximate the corner portions during the annealing.
Implementation Method 2
The first transition metal layer and the second transition metal layer form an alloy portion proximate the corner portions during the annealing.
Implementation Method 3
The alloy portion has a lower wettability for a material of the fill layer than the second transition metal.
Data Source
AI summary
A method for forming an interconnect structure includes forming a recess in a dielectric layer of a substrate, forming a first transition metal layer in the recess on corner portions of the recess, and forming a second transition metal layer in the recess over the first transition metal layer to line the recess. The method further includes filling the recess with a fill layer and annealing the substrate so that the first transition metal layer and the second transition metal layer form an alloy portion proximate the corner portions during the annealing, the alloy portion having a reduced wettability for a material of the fill layer than the second transition metal. Additionally, the method includes polishing the substrate to remove portions of the fill layer extending above the recess.