Bonding Pad Metal Structure for Power-Cycling Crack Resistance
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Solution Overview
Problem
Semiconductor devices face limitations in power cycling capabilities due to mechanical constraints and thermal expansion issues at the wire to pad interface, leading to potential cracks and reduced reliability.
Innovation Solution
A semiconductor device structure incorporating a dielectric layer between the wiring metal layer and the bonding pad metal layer, with the bonding pad metal layer composed of at least 50% aluminum, and a dielectric layer thickness ranging from 1% to 30% of the wiring metal layer thickness, allowing for electrical connection through openings and improved mechanical tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire bonds are used for interconnection, then electrical connection is achieved, but current density is limited due to material heat up and thermal expansion
Solution Approach 1:
The bonding pad metal layer is segmented into multiple sub-layers (first bonding pad metal layer, second bonding pad metal layer, third bonding pad metal layer) with different materials and functions. This segmentation allows each layer to be optimized for specific purposes: current carrying, mechanical bonding, and stress management, thereby resolving the contradiction between power handling and reliability.
Solution Approach 2:
The bonding pad structure uses composite materials with different properties at different layers. The first bonding pad metal layer uses high-conductivity material (e.g., pure aluminum or copper) for current carrying, while the second and third layers use materials optimized for bonding strength and stress management. This composite approach enables the system to handle higher current densities while maintaining reliability under power cycling.
2Reliability
If mechanical parameters of pad and wire are fixed, then manufacturing simplicity is maintained, but maximum energy application is limited ensuring robust interconnect
Solution Approach 1:
The bonding pad is divided into multiple functional layers, each with specific thickness ratios (second layer thickness: 10-50% of first layer; third layer thickness: 1-10% of first layer). This segmentation enables independent optimization of each layer's mechanical properties while maintaining overall structural robustness for high energy handling.
Solution Approach 2:
The invention changes the mechanical parameters of the bonding pad by introducing multiple layers with different material compositions and thickness ratios. This allows tuning of the overall mechanical properties (hardness, bonding strength, stress distribution) to achieve robust interconnect capable of withstanding maximum energy application during power cycling.
3Area of stationary object
If bond feet density increases to shrink device size, then area is reduced, but wire bond material heat up and thermal expansion increase
Solution Approach 1:
The multi-layer bonding pad structure with composite materials provides enhanced thermal management. The first layer uses high-conductivity material to efficiently conduct heat away from the bond feet, while the subsequent layers provide thermal buffering and stress management. This enables higher bond feet density without excessive temperature rise.
Solution Approach 2:
The second and third bonding pad metal layers act as intermediary structures between the wire bond and the substrate. These intermediate layers provide thermal buffering and stress distribution, reducing the direct thermal and mechanical impact on the wire bond material, thereby enabling higher density interconnections.
4Power
If aluminum content in bonding pad is increased, then electrical conductivity is improved, but mechanical hardness decreases
Solution Approach 1:
The bonding pad is segmented into layers with different aluminum contents. The first bonding pad metal layer has high aluminum content (≥50%, preferably ≥80%) for optimal electrical conductivity and current carrying. The second and third layers have reduced aluminum content or use different materials to provide the necessary mechanical hardness and bonding strength. This segmentation resolves the contradiction between conductivity and hardness.
Solution Approach 2:
The bonding pad structure uses composite materials where the first layer is high-purity aluminum or aluminum alloy for conductivity, while the second and third layers use materials with different properties (such as copper, aluminum-copper alloy, or other metals) to provide mechanical strength. This composite approach enables the system to achieve both high electrical conductivity and adequate mechanical hardness.
Data Source
AI summary
A method of manufacturing a semiconductor device includes forming a wiring metal layer structure; forming a dielectric layer structure arranged directly on the wiring metal layer structure; and forming a bonding pad metal layer structure arranged, at least partially, directly on the dielectric layer structure, wherein a layer thickness of the dielectric layer structure ranges from 1% to 30% of a layer thickness of the wiring metal layer structure, wherein the wiring metal layer structure and the bonding pad metal structure are electrically connected through openings in the dielectric layer structure.