Semiconductor Pad Thickness Control for Wire Bonding Splash Out
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Solution Overview
Problem
When copper wires are bonded to aluminum electrodes in semiconductor devices, there is a risk of 'splash out,' where part of the electrode material is excluded and can damage the insulating film, potentially impairing the reliability of the semiconductor device due to increased electrical resistance and miniaturization challenges.
Innovation Solution
The method involves forming a pad with a laminated structure of conductive layers, including aluminum, and using a specific etching process to expose the aluminum film in a way that reduces the thickness in the wire bonding area, minimizing splash out and maintaining sufficient thickness for low electrical resistance, along with an optional conductive adhesive layer to enhance bonding strength and reduce ultrasonic energy impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire is bonded to aluminum electrode, then bonding cost is reduced compared to gold wire, but splash out occurs and damages insulating film
Solution Approach 1:
The aluminum electrode is segmented into two regions with different thicknesses: a thicker region for low electrical resistance and a thinner region for wire bonding. This segmentation allows the bonding area to minimize splash out while the thicker region maintains electrical conductivity.
Solution Approach 2:
Different regions of the aluminum electrode are given different local properties: the wire bonding region has reduced thickness to minimize splash out, while other regions maintain sufficient thickness for low electrical resistance. This local quality differentiation resolves the contradiction between preventing splash out and maintaining conductivity.
2Reliability
If aluminum electrode thickness is reduced to minimize splash out, then insulating film damage is reduced, but electrical resistance increases
Solution Approach 1:
The electrode structure is segmented into multiple regions with different thicknesses. The thinner region is specifically located at the wire bonding area to reduce splash out, while thicker regions are maintained in other areas to ensure low electrical resistance, thus resolving the contradiction through spatial differentiation.
Solution Approach 2:
The electrode exhibits non-uniform local quality with varying thickness across different regions. The local thickness at the bonding region is optimized to minimize splash out, while other regions maintain sufficient thickness for electrical conductivity, achieving both protection and low resistance simultaneously.
3Ease of manufacture
If uniform aluminum electrode thickness is used, then manufacturing is simplified, but splash out damages insulating film during wire bonding
Solution Approach 1:
Instead of uniform thickness, the electrode is segmented into different thickness zones. This can be achieved through selective etching or deposition processes that create the thickness variation, balancing manufacturing complexity with improved reliability by preventing splash out damage.
Solution Approach 2:
The electrode structure incorporates local quality variations where the thickness is specifically adjusted at the bonding region. This localized modification targets the problem area without requiring complete redesign of the entire electrode, maintaining reasonable manufacturing simplicity while improving 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 approach improves the reliability of semiconductor devices by reducing splash out, minimizing damage to the insulating film, and maintaining low electrical resistance, even with miniaturization, thereby enhancing the operational stability and efficiency of the semiconductor device.
Implementation Method 1
etching the part of the pad exposed from the insulating film to expose the first conductive layer
Implementation Method 2
when a wire including copper (Cu) is used, that is, when a wire including copper is bonded to an electrode (pad) including aluminum
Data Source
AI summary
A pad formed in a semiconductor chip is formed such that a thickness of an aluminum film in a wire bonding portion is smaller than that of an aluminum film in a peripheral portion covered with a protective film. On the other hand, a thickness of a wiring formed in the same step as the pad is larger than that of the pad in the wire bonding portion. The main conductive film of the pad in the wire bonding portion is comprised of only one layer of a first aluminum film, while the main conductive film of the wiring is comprised of at least two layers of aluminum films (the first aluminum film and a second aluminum film) in any region of the wiring.