Bronze Contact Structure to Mitigate Semiconductor Undercut
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Solution Overview
Problem
Undercutting during the formation of conductive contacts on semiconductor dies can increase impedance and degrade the mechanical integrity of the contact structure, primarily due to galvanic corrosion differences between sputtered seed copper and electroplated copper.
Innovation Solution
A method involving the formation of a titanium or titanium tungsten barrier layer, a tin seed layer, and a copper structure on a semiconductor die, followed by heating to form a bronze material between the barrier layer and the copper structure, and subsequent removal of exposed seed and barrier layers to mitigate undercutting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If sputtered seed copper is used versus electroplated copper, then deposition speed is improved, but undercutting increases due to galvanic corrosion
Solution Approach 1:
A tin seed layer is introduced as an intermediary material between the sputtered copper and the barrier layer. This tin layer acts as a sacrificial sacrificial layer that etches faster than copper, preventing undercutting of the copper structure while allowing rapid copper deposition. The tin layer is subsequently removed, leaving the copper structure protected from galvanic corrosion-induced undercutting.
Solution Approach 2:
The invention changes the material parameter of the seed layer from copper to tin, which has different etching characteristics. Tin etches faster than copper in the etching process, which reverses the galvanic corrosion effect and prevents undercutting. This parameter change (material composition) resolves the contradiction between fast deposition and undercutting control.
2Reliability
If barrier layer is removed to expose copper structure, then electrical conductivity is improved, but mechanical integrity deteriorates due to undercutting
Solution Approach 1:
The tin seed layer serves as a protective intermediary during the barrier layer removal process. When the barrier layer is etched away, the tin layer remains as a protective cap over the copper structure, preventing undercutting and maintaining mechanical integrity. After barrier layer removal, the tin layer is selectively removed, achieving both electrical conductivity improvement and mechanical integrity preservation.
Solution Approach 2:
The tin seed layer is placed beforehand as a cushioning layer that prevents damage to the copper structure during subsequent processing steps. This sacrificial layer absorbs the mechanical stress and chemical etching that would otherwise cause undercutting, ensuring the copper structure maintains its mechanical integrity throughout the fabrication process.
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 described method reduces undercutting and maintains low impedance coupling between the copper structure and the conductive features, enhancing the mechanical integrity and electrical performance of the contact structures.
Implementation Method 1
heating the seed layer and the copper structure to form a bronze material between the barrier layer and the copper structure
Implementation Method 2
undercutting during formation of the conductive contacts on the semiconductor die can increase the impedance and/or degrade the mechanical integrity of the conductive contact structure. Undercut issues can result from faster etching away of sputtered seed copper versus electroplated copper of a die contact pillar or post due to galvanic corrosion
Data Source
AI summary
Described examples provide microelectronic devices and fabrication methods, including fabricating a contact structure by forming a titanium or titanium tungsten barrier layer on a conductive feature, forming a tin seed layer on the barrier layer, forming a copper structure on the seed layer above the conductive feature of the wafer or die, heating the seed layer and the copper structure to form a bronze material between the barrier layer and the copper structure, removing the seed layer using an etching process that selectively removes an exposed portion of the seed layer, and removing an exposed portion of the barrier layer.