Semiconductor Pad Multilayer Structure Crack Prevention
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Solution Overview
Problem
Semiconductor devices with aluminum or aluminum alloy metal interconnects face mechanical stress issues during wire bonding, leading to cracks in the bonding pad or interlayer insulating film, especially when using copper wires due to the higher hardness of copper compared to gold and aluminum.
Innovation Solution
A multilayer pad structure is formed by a first metal layer, an insulating layer with an opening, a second metal layer with a thickness smaller than the insulating layer, and a third metal layer, enhancing mechanical strength and reducing crack occurrence without adding new processes to standard manufacturing methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper bonding wire is used to join to the bonding pad, then electrical connection and signal transmission are improved, but mechanical stress increases causing cracks in the bonding pad or insulating film
Solution Approach 1:
The bonding pad is constructed as a composite structure with a first pad layer (Al or Al alloy) and a second pad layer (Cu or Cu alloy) with different material properties. The Cu layer provides high electrical conductivity for reliable electrical connection, while the Al layer provides mechanical strength to withstand the stress from copper wire bonding, thus resolving the contradiction between electrical performance and mechanical strength.
Solution Approach 2:
The bonding pad is segmented into two distinct layers with different functions: the first pad layer serves as the mechanical support structure formed on the semiconductor substrate, while the second pad layer provides the electrical connection interface. This segmentation allows each layer to be optimized for its specific function, enabling the pad to withstand mechanical stress while providing reliable electrical connection.
2Ease of manufacture
If the second pad layer thickness is reduced to avoid additional thinning processes, then manufacturing complexity is reduced, but mechanical strength may be compromised
Solution Approach 1:
The thickness of the second pad layer is precisely controlled within a specific range (0.5-2.0 μm) to achieve the optimal balance between mechanical strength and manufacturing simplicity. This parameter optimization ensures that the Cu layer is thin enough to eliminate the need for additional thinning processes like CMP, while still providing sufficient electrical conductivity and structural integrity to support wire bonding without compromising pad strength.
Data Source
AI summary
The manufacturing method of a semiconductor device can improve the mechanical strength of a pad more than before, and suppress the occurrence of a crack. The manufacturing method of a semiconductor device includes: forming a first pad constituted by a first metal layer; forming an insulating layer on the first pad; providing an opening portion in the insulating layer by removing the insulating layer on at least a partial region of the first pad; forming a second pad constituted by a second metal layer in the opening portion of the insulating layer so as to have a film thickness that is smaller than the film thickness of the insulating layer; and forming a third pad constituted by a third metal layer on the second pad.