Titanium Tungsten Liner for Copper Interconnects
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Solution Overview
Problem
Stress migration failure in copper interconnects due to fast diffusion at the interface between copper wires and nitride capping layers, leading to void formation and circuit failure, is not effectively addressed by existing solutions which either introduce unwanted resistance variability, sputter damage, or nitrogen poisoning.
Innovation Solution
A nitride-free interface is created using a sputtered titanium and tungsten liner, with a pure titanium layer forming an alloy with copper and a pure tungsten layer, preventing vacancy diffusion and nitrogen poisoning, thereby enhancing adhesion and avoiding circuit failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a titanium liner is formed on the copper wire, then vacancy diffusion is prevented, but nitrogen poisoning occurs at the Ti/Cu interface
Solution Approach 1:
A tungsten layer is introduced as an intermediary between the titanium liner and the copper wire. This tungsten barrier prevents nitrogen from reaching the Ti/Cu interface, thereby eliminating nitrogen poisoning while preserving the vacancy diffusion prevention properties of the titanium layer.
2Reliability
If via liner re-sputtering is performed to gouge the copper wire, then a tantalum to copper interface is achieved, but sputter damage is induced into the copper wire
Solution Approach 1:
The harmful sputtering process is completely removed from the fabrication sequence. Instead of using re-sputtering to create the interface, the invention employs a deposited titanium liner that naturally forms a high-quality interface with the copper wire during the standard deposition process, thereby achieving interface quality without inducing sputter damage.
3Reliability
If a titanium nitride liner is used, then the via-to-wire interface is protected, but nitrogen is present at the copper interface inducing adhesion problems
Solution Approach 1:
A pure tungsten layer is introduced as an intermediary between the titanium nitride liner and the copper wire. This tungsten barrier prevents nitrogen from the TiN layer from reaching the copper interface, thereby maintaining interface protection while eliminating adhesion problems caused by nitrogen presence at the Cu interface.
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 titanium-tungsten liner provides a robust, nitride-free interface that suppresses void nucleation at the via-to-wire interface, improving adhesion and preventing electrical discontinuity, thus enhancing the reliability of copper interconnects in semiconductor structures.
Implementation Method 1
a pure titanium layer forming an alloy with copper
Implementation Method 2
A nitride-free interface is created using a sputtered titanium and tungsten liner
Data Source
AI summary
Approaches for providing a liner at a via-to-wire interface are provided. A method includes: forming a via opening that exposes an upper surface of a copper wire; forming a titanium liner on the upper surface of the wire; forming a tungsten liner on the titanium liner; and forming a via on the second liner in the via opening.