Non-Reactive Al-Cu Interconnect Stack with TiN Barrier
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Solution Overview
Problem
Aluminum-based interconnects in semiconductor devices face challenges with low electrical conductivity and electromigration resistance, which are improved by doping with copper and using specific crystal orientations, but conventional non-reactive metal stacks without annealing result in poor electromigration lifetime and hillock formation.
Innovation Solution
A non-reactive metal interconnect stack is formed by depositing an aluminum-containing layer over a TiN barrier layer, with a Ti layer on top, and annealing at a temperature below the deposition temperature to prevent chemical reactions and hillock formation, while maintaining good electromigration properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum-based interconnects are doped with copper and deposited on (111) crystal orientation to improve electromigration resistance, then electromigration lifetime is enhanced, but chemical reactions at the Ti/Al interface occur leading to hillock formation and poor yield
Solution Approach 1:
A TiN barrier layer is introduced between the Ti seed layer and the Al-Cu interconnect layer to prevent direct chemical reaction and hillock formation, while still allowing the Al-Cu layer to maintain good electromigration properties through proper crystal orientation
Solution Approach 2:
The deposition temperature is optimized to balance between achieving good crystal orientation for electromigration resistance and preventing excessive chemical reaction that would cause hillock formation. The annealing temperature is also controlled to be below the deposition temperature to avoid reaction while maintaining EM properties
2Strength
If a sintering process is used to react Al and Ti layers at the interface in a reactive metal stack, then bond strength is improved, but chemical reactions cause hillock formation and reduced manufacturing yield
Solution Approach 1:
The TiN barrier layer serves as an intermediary that prevents direct reaction between Ti and Al-Cu, eliminating hillock formation while maintaining adequate interface adhesion through the barrier layer's bonding characteristics
Solution Approach 2:
The potential harmful chemical reaction between Ti and Al is converted into a beneficial controlled reaction at the TiN barrier interface, which provides adequate adhesion without the harmful effects of direct Ti-Al reaction such as hillock formation
3Reliability
If annealing is performed at high temperature to improve electromigration properties, then EM resistance is enhanced, but chemical reactions increase causing hillock formation
Solution Approach 1:
The TiN barrier layer acts as a mediator that allows annealing at temperatures sufficient to improve electromigration resistance through crystal orientation, while preventing the barrier layer from reacting with the Al-Cu layer and forming hillocks
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 approach enhances electromigration resistance and yield by minimizing chemical reactions and preventing hillock formation, resulting in improved reliability and reduced shorts between metal interconnect lines.
Implementation Method 1
The metal interconnect layer is annealed at a maximum annealing temperature that is less than the first temperature
Data Source
AI summary
A method of fabricating an integrated circuit (IC) includes depositing an aluminum-containing metal interconnect layer at a first temperature over a semiconductor device having a plurality of transistors. The metal interconnect layer is annealed at a maximum annealing temperature that is less than the first temperature. The metal interconnect layer is patterned after the annealing, thereby interconnecting the transistors.