Multi-Layer Bonding Pad Structure for Wire Bond Stress Reduction
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Solution Overview
Problem
Conventional integrated circuit bonding pads are prone to cracking or damage due to high stress from wire bonding, and achieving thicker bonding pads using typical semiconductor processes is challenging due to the unavailability of thicker resist materials.
Innovation Solution
A method involving the deposition of a first metal layer, patterning to form a lower bonding pad layer, conformally depositing a passivation layer, forming an opening, and adding a second metal layer to create an upper bonding pad layer, resulting in a thicker bonding pad structure with increased thickness range of 8.5-9.5 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of bonding pads is increased to reduce wire bond stress, then the reliability of the bonding pad improves, but the manufacturing complexity increases due to the unavailability of thicker resist materials in typical semiconductor processes
Solution Approach 1:
The bonding pad is divided into multiple layers (first metal layer, second metal layer) deposited at different stages. The first metal layer is deposited and patterned to form a lower bonding pad layer, then a passivation layer is deposited, and finally a second metal layer is deposited and patterned to form an upper bonding pad layer. This segmentation allows the total bonding pad thickness to exceed the thickness of any single resist layer used in the patterning process.
Solution Approach 2:
The bonding pad structure transitions from a single-layer planar structure to a multi-layer vertical structure. By adding the passivation layer between the first and second metal layers, the design extends into the vertical dimension, achieving greater total thickness while using standard-thickness resist materials for each patterning step.
2Length of stationary object
If a thicker resist is used to etch openings for thicker bonding pads, then the bonding pad thickness can be increased, but such thicker resist is not currently available and/or is not supported in typical semiconductor processes
Solution Approach 1:
Instead of using one thick resist layer that is unavailable in standard processes, the patterning is segmented into multiple steps using standard-thickness resist materials. The first metal layer is patterned using a first resist, then after depositing the passivation layer, the second metal layer is patterned using a second resist. This allows each resist to be within the thickness range supported by typical semiconductor processes while achieving a total bonding pad thickness of 8.5-9.5 μm.
Solution Approach 2:
The first metal layer and its patterning are completed before depositing the passivation layer and forming the passivation opening. This preliminary action allows the first bonding pad layer to be established with standard resist thickness, and then the second metal layer is added later to increase the total thickness without requiring thick resist materials.
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
The solution effectively increases the thickness of bonding pads to 8.5-9.5 μm, reducing the risk of cracking and damage while being compatible with standard semiconductor processes, enhancing the reliability of integrated circuits.
Implementation Method 1
depositing a first metal layer over a bonding pad support layer
Implementation Method 2
conformally depositing a passivation layer over the lower bonding pad layer
Data Source
AI summary
A bonding pad for an integrated circuit is formed by a stack of bonding pad layers. A lower bonding pad layer is supported by a bonding pad support layer. A passivation layer extends over the lower bonding pad layer and includes a passivation opening at a portion of an upper surface of the lower bonding pad layer. An upper bonding pad layer rests on said passivation layer and in the passivation opening in contact with the lower bonding pad layer.