Composite Interconnect Wires for Lower RC Delay and Electromigration
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Solution Overview
Problem
As integrated circuit features are scaled down, interconnect delay due to resistive-capacitance (RC) delay becomes significant, and reliability is affected by electromigration, with refractory metals increasing resistivity and resistance, and diffusion barriers affecting wire properties like capacitance.
Innovation Solution
The formation of interconnect wires with cores of lower resistivity materials (e.g., copper, aluminum) surrounded by jackets of higher resistivity materials (e.g., tungsten, cobalt) provides a diffusion barrier and reduces electron scattering, thereby minimizing RC delay and electromigration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If refractory metals are used in interconnect fabrication to reduce electromigration, then reliability is improved, but resistivity increases and RC delay worsens
Solution Approach 1:
The patent employs composite interconnect structures combining copper cores with refractory metal jackets (tungsten, cobalt, or ruthenium). The copper core provides low resistivity for signal transmission, while the refractory metal jacket provides electromigration resistance. This composite approach resolves the contradiction by integrating materials with complementary properties rather than using a single material that must compromise between these competing requirements.
Solution Approach 2:
Different portions of the interconnect structure are assigned different material properties optimized for their specific functions. The core region uses copper for low resistivity and high conductivity, while the outer jacket region uses refractory metals for electromigration resistance and diffusion barrier properties. This local differentiation allows each region to excel at its primary function without being constrained by the limitations of a uniform material.
2Productivity
If feature size is scaled down to increase density, then productivity is improved, but RC delay increases and reliability deteriorates
Solution Approach 1:
The copper-refractory metal composite structure enables continued scaling by providing a solution that simultaneously addresses the worsening RC delay and electromigration issues that arise at smaller dimensions. The low-resistivity copper core becomes increasingly important as cross-sectional area decreases, while the refractory metal jacket maintains reliability despite reduced feature sizes.
3Reliability
If diffusion barriers are deposited on interconnect walls to reduce electromigration, then reliability is improved, but wire capacitance properties are adversely affected
Solution Approach 1:
The refractory metal jacket itself serves as the diffusion barrier, eliminating the need for separate barrier layers. The jacket material (tungsten, cobalt, or ruthenium) naturally provides diffusion resistance to prevent electromigration, while being in direct contact with the copper core to provide this protection without introducing additional dielectric interfaces that would increase capacitance.
4Productivity
If feature size is scaled down to increase density, then productivity is improved, but electromigration becomes more prominent
Solution Approach 1:
The composite structure with refractory metal jacket provides robust electromigration resistance that becomes increasingly critical as feature sizes decrease. The jacket protects the copper core from ion transport and material redistribution that are exacerbated at smaller dimensions, enabling continued scaling while maintaining 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
This configuration reduces interconnect delay and enhances reliability by lowering resistive-capacitance delay and mitigating electromigration, while maintaining acceptable wire properties.
Implementation Method 1
cores exhibiting relatively lower resistivity than the jackets... reduces electron scattering, thereby minimizing RC delay
Implementation Method 2
diffusion barriers have been deposited on the side and bottom walls of openings in interlayer dielectrics containing the interconnects
Implementation Method 3
Electromigration is understood as the transport of material due to movement of ions in a conductor
Data Source
AI summary
A dielectric layer and a method of forming thereof. An opening defined in a dielectric layer and a wire deposited within the opening, wherein the wire includes a core material surrounded by a jacket material, wherein the jacket material exhibits a first resistivity ρ1 and the core material exhibits a second resistivity ρ2 and ρ2 is less than ρ1.