Semiconductor Bonding Pad Structure for Cu Wire Corrosion Control
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Solution Overview
Problem
Semiconductor elements with switching circuits, such as MOSFETs or IGBTs, face issues like cracking of the semiconductor layer and corrosion at the boundary between the electrode and the bonding wire when a Cu bonding wire is used, leading to bonding failures.
Innovation Solution
A semiconductor element design featuring a metal layer, including Ni, Pd, and Au layers, electrically connected to the wiring layer and partially overlapping with the surface protection film, acts as a pad for bonding wires, with underlying layers like TiW to mitigate orientation effects and prevent peeling, and a surface protection film with openings that enclose the wiring layer, reducing thermal stress and irregularities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Cu bonding wire is used to bond to the Al wiring layer, then bonding cost is reduced, but the semiconductor layer cracks and corrosion occurs at the boundary between the electrode and bonding wire
Solution Approach 1:
A metal layer containing Ni is introduced as an intermediary between the Al wiring layer and the Cu bonding wire. This intermediate metal layer prevents direct contact between Al and Cu, eliminating galvanic corrosion while maintaining electrical connectivity and bonding reliability.
Solution Approach 2:
The electrode structure uses a composite material approach by combining Al wiring layer with a Ni-containing metal layer. This composite structure leverages the advantages of both materials: Al for electrical conductivity and Ni for corrosion resistance against Cu bonding wires.
2Reliability
If a metal layer containing Ni is formed instead of the electrode to prevent corrosion, then bonding reliability improves, but irregularities occur on the metal pad surface
Solution Approach 1:
The surface protection film is selectively formed only in regions where irregularities occur on the metal pad surface, while leaving other regions exposed. This local application approach corrects surface irregularities in specific areas without affecting the overall bonding functionality or electrical performance.
Solution Approach 2:
A surface protection film is introduced as an intermediary layer between the Ni-containing metal layer and the bonding wire. This film fills in surface irregularities and provides a flat bonding surface, ensuring reliable wire bonding while maintaining the underlying Ni layer's corrosion resistance.
3Stability of the object's composition
If the surface protection film opens are enlarged to enclose the wiring layer, then thermal stress is reduced, but the contact area between metal layer and bonding wire decreases
Solution Approach 1:
The surface protection film openings are strategically sized and positioned to provide adequate enclosure of the wiring layer for thermal stress relief, while maintaining sufficient exposure of the metal layer for bonding. The local geometry is optimized to balance these competing requirements.
Solution Approach 2:
The surface protection film provides partial enclosure of the wiring layer rather than complete coverage. This partial action is sufficient to reduce thermal stress while maintaining adequate bonding contact area, avoiding the extremes of full enclosure or no enclosure.
Data Source
AI summary
A semiconductor element includes: an element body including an obverse surface facing a first side in a thickness direction z; a wiring layer formed on the obverse surface and electrically connected to the element body; an insulating layer covering the obverse surface and the wiring layer, and including a first opening overlapping with the wiring layer as viewed in the thickness direction z; a surface protection film covering the insulating layer, and including a second opening overlapping with the wiring layer and the first opening as viewed in the thickness direction z; a metal layer overlapping with the first opening and the second opening, and also overlapping with the surface protection film as viewed in the thickness direction, and a mitigation layer (underlying layer) provided between the wiring layer and the metal layer. A first material of the mitigation layer is less affected by an orientation of the wiring layer than a second material of a portion of the metal layer located closest to the wiring layer.