Copper Wire Bonding with In-Situ Plasma Oxide Removal
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Solution Overview
Problem
Copper surfaces in semiconductor chip bonding pads are prone to oxidation, leading to unreliable adhesion and increased electrical resistance in wire bonding, resulting in manufacturing defects and device malfunctions.
Innovation Solution
Atmospheric Pressure Plasma Jet (APPJ) treatment is used in-situ to clean surface contaminants from copper-based bonding pads before and during wire bonding, eliminating the need for additional metal layers like gold and ensuring oxide-free interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If copper bonding pads are used without additional metal layers, then processing costs are reduced, but oxide formation occurs leading to poor adhesion and increased electrical resistance
Solution Approach 1:
The patent applies preliminary plasma treatment to the copper bonding pad surface before wire bonding to remove oxides and create a clean, reactive surface. This preliminary action prevents oxide formation during subsequent processing steps, enabling direct copper-to-wire bonding without additional protective metal layers like gold or nickel, thus reducing cost while maintaining reliable adhesion
Solution Approach 2:
The patent changes the surface state of the copper pad through plasma treatment, transforming it from an oxidized, non-reactive state to a clean, reactive state with improved surface energy. This parameter change in surface condition enables direct bonding without additional metal layers, reducing processing cost while ensuring reliable adhesion and low electrical resistance
2Device complexity
If copper bonding pads are used without additional metal layers, then processing complexity is reduced, but oxide formation leads to manufacturing defects
Solution Approach 1:
The plasma treatment is performed as a preliminary step before wire bonding to completely remove oxides from the copper surface. This preliminary surface preparation ensures that subsequent bonding occurs on a pristine copper surface, eliminating the need for complex multi-layer metal structures and preventing manufacturing defects related to oxide contamination
Solution Approach 2:
The patent replaces the mechanical/physical approach of depositing additional metal layers (gold, nickel) to protect copper surfaces with a chemical/plasma-based approach that actively removes oxides and creates a bonding-ready surface. This substitution simplifies the metal layer structure while maintaining high bonding quality through surface activation
3Reliability
If in-situ plasma treatment is applied during wire bonding, then oxide-free interfaces are ensured, but processing time is increased
Solution Approach 1:
The patent implements continuous plasma treatment that operates throughout the wire bonding process rather than as a separate discrete step. The plasma source remains active during wire placement and bonding, continuously removing any oxides that form during the process and maintaining a reactive copper surface, thus ensuring oxide-free interfaces without significant time penalty
Solution Approach 2:
The plasma treatment is applied in periodic pulses synchronized with the wire bonding process steps. Plasma is activated during critical bonding phases and can be temporarily suspended during wire feed or positioning, providing oxide protection when needed while minimizing overall processing time extension
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 method provides reliable wire bonding with improved adhesion and reduced electrical resistance, enhancing the stability and performance of semiconductor devices while reducing processing costs by eliminating the need for gold plating.
Implementation Method 1
a plasma treatment process is performed on a copper-containing surface of a chip bonding pad (48) on the semiconductor chip (40) in the low-oxygen ambient (29) by directing a plasma jet (P) to the chip bonding pad (48)
Implementation Method 2
Copper surfaces in semiconductor chip bonding pads are prone to oxidation, leading to unreliable adhesion and increased electrical resistance in wire bonding
Data Source
AI summary
A bonded assembly may be formed by: providing a substrate and a semiconductor chip in a low-oxygen ambient having an oxygen partial pressure that is lower than 17 kPa; disposing the semiconductor chip on the substrate; performing a plasma treatment process on a copper-containing surface of a chip bonding pad on the semiconductor chip in the low-oxygen ambient by directing a plasma jet to the chip bonding pad; and attaching a bonding wire to the semiconductor chip and to the substrate such that a first end of the bonding wire is attached to the copper-containing surface and a second end of the bonding wire is attached to a substrate bonding pad on the substrate.