Bond Pad Structure Adhesion Structures Stress Management
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Solution Overview
Problem
Adhesion failure and stress-related issues in bond pads of power devices, such as DMOS and IGBT, due to defects in field oxide and mismatched thermal expansion properties of material layers, leading to potential high current conditions and device destruction.
Innovation Solution
A bond pad structure featuring a first oxide layer with adhesion structures and a second oxide layer, along with a barrier layer and a metal layer, where the adhesion structures have reduced contact area with the oxide layer to minimize defect-induced failures and a structured metal layer surface to manage lateral stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polysilicon layer is formed between the metal layer and field oxide to improve adhesion and absorb stress, then adhesion and stress absorption are improved, but the probability of high current condition due to localized thinning defects increases
Solution Approach 1:
The bond pad structure is segmented into multiple functional layers: field oxide layer, polysilicon layer, barrier layer, and metal layer. Each layer performs a specific function, with the polysilicon layer segmented into discrete regions that provide adhesion and stress absorption while limiting defect propagation.
Solution Approach 2:
The polysilicon layer acts as an intermediary between the field oxide and metal layer, providing chemical compatibility and stress absorption. The barrier layer serves as an additional intermediary to prevent direct contact between metal and defective oxide regions, reducing high current risk while maintaining adhesion benefits.
2Reliability
If a diffusion barrier layer such as Ti/TiN or TiW is formed between the aluminum metal layer and SiO2 field oxide to prevent silicon diffusion, then silicon diffusion is prevented, but adhesion to SiO2 becomes poor leading to peeling or separation
Solution Approach 1:
The polysilicon layer serves as an intermediary that provides both good adhesion to SiO2 and compatibility with the barrier layer. This mediator layer ensures strong bonding between the field oxide and the diffusion barrier system, preventing peeling while maintaining diffusion prevention capabilities.
Solution Approach 2:
The bond pad structure uses a composite material system consisting of field oxide, polysilicon, barrier layer, and metal layer. Each material is selected for its specific properties, and their combination creates a structure that simultaneously achieves adhesion, diffusion prevention, and stress management that individual materials cannot provide alone.
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
Enhances adhesion and durability of bond pads, reducing the likelihood of current-induced failures and improving reliability by minimizing contact area with defects and controlling lateral stress.
Implementation Method 1
The polysilicon layer absorbs external thermo-mechanical stress and improves durability against stress in a vertical direction relative to a surface of the metal layer
Implementation Method 2
Diffusion barrier layers such as a titanium (Ti), titanium nitride (TiN) or titanium tungsten (TiW) are effective at preventing the diffusion of silicon into the aluminum metal layer
Data Source
AI summary
A bond pad structure includes a first oxide layer that overlies a substrate. A plurality of adhesion structures are formed over the first oxide layer. A second oxide layer is formed over the plurality of adhesion structures and the first oxide layer. Each one of a plurality of contact openings formed within a surface region of the second oxide layer includes one or more sides and is aligned over at least a portion of a top surface of a corresponding one of the plurality of adhesion structures. A barrier layer is formed within the surface region that is over the second oxide layer and within the plurality of contact openings and over the at least a portion of the top surface of the corresponding ones of the plurality of adhesion structures. A metal layer is formed over the barrier layer.