Bond Pad Moisture Barrier Structure for Polyimide Wicking
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Solution Overview
Problem
Polyimide interlayer insulators in semiconductor integrated circuits act as a wick, drawing moisture and causing metal migration between bond pads and other components, leading to short circuits under high humidity and stress conditions.
Innovation Solution
A moisture barrier is created by forming a trench between polymer interlevel dielectric layers and applying a topcoat insulation layer that is impervious to moisture, preventing moisture migration and metal migration along the interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyimide is used as an interlayer insulator, then the insulator provides electrical isolation between metal layers, but it acts as a wick to draw moisture and transport it to bond pads, causing metal migration and short circuits
Solution Approach 1:
The patent divides the interlayer insulator into two distinct parts: a polyimide layer that provides electrical isolation, and a separate moisture barrier layer (such as silicon nitride or parylene) that prevents moisture absorption. This segmentation allows each layer to perform its specific function without the harmful wicking effect of polyimide transporting moisture to bond pads.
Solution Approach 2:
The patent employs a composite structure combining polyimide with a moisture barrier material. The polyimide provides flexible electrical isolation and stress relief, while the moisture barrier layer (silicon nitride, parylene, or other impermeable materials) prevents moisture ingress. This composite approach maintains the advantages of polyimide while eliminating its moisture-wicking drawback.
2Ease of manufacture
If polyimide is used as an interlayer insulator, then the structure remains simple and manufacturing is straightforward, but moisture migration along the interface causes metal migration and short circuits between bond pads
Solution Approach 1:
The moisture barrier layer is formed beforehand, either as an underlayer beneath the polyimide or as an overlayer above it, before the complete stack is assembled. This preliminary placement of the moisture barrier prevents moisture from reaching the polyimide-polymer interface where metal migration would occur, addressing the reliability issue without complicating the manufacturing sequence.
Solution Approach 2:
The moisture barrier layer acts as an intermediary between the polyimide interlayer insulator and the external environment (moisture). This intermediate layer blocks moisture transport along the interface, preventing metal migration and short circuits while allowing the polyimide to maintain its electrical isolation function.
3Reliability
If the trench is formed to space the polymer interlevel dielectric layers from metal layers, then moisture migration along the interface is inhibited, but the device structure becomes more complex
Solution Approach 1:
The trench physically segments and separates the polymer interlevel dielectric layers from the metal layers, creating a gap that interrupts the continuous interface pathway for moisture migration. This segmentation approach provides an effective moisture barrier while maintaining a relatively simple structural concept that can be integrated into existing fabrication processes.
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 solution effectively prevents short circuits by isolating bond pads from moisture and metal migration, enhancing the reliability of semiconductor devices without increasing manufacturing costs or size.
Implementation Method 1
a topcoat insulation layer disposed over the one or more metal layers and one or more polymer interlevel dielectric layers, the top coat insulation layer being impervious to moisture
Implementation Method 2
the trench inhibits migration of moisture along the interface to the one or more metal layers
Implementation Method 3
polyimide acts as a wick to draw moisture from outside and transport it to sensitive elements on the ICs
Data Source
AI summary
A semiconductor die includes a substrate layer, one or more metal layers disposed over the substrate layer, and a pair of polyimide layers disposed over the substrate so that they define an interface therebetween. One or both of the pair of polyimide layers have a trench that separates the interface from the one or more metal layers. The trench can be formed by etching the polyimide layer(s). A topcoat insulation layer is disposed over the one or more metal layers and polyimide layers. The topcoat insulation layer is impervious to moisture and the trench inhibits migration of moisture along the interface to the one or more metal layers, thereby preventing metal migration from the one or more metal layers along the interface.