Thick Bond Pad for Cavity Image Sensor
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Solution Overview
Problem
Chips with cavity packages face a conflict between thin top wiring layers for high light sensitivity and thick bond pads for low resistance connections, as thin top wiring layers result in high resistance connections due to small cross-sectional areas.
Innovation Solution
A method involving a substrate with vias through inter layer dielectric, multiple conductive layers with varying thicknesses, a polymer layer with a cavity, and an optically transparent layer to form a thick bond pad while maintaining sensitivity, including depositing a silicon nitride layer, etching, and forming a second conductive layer with a thinner thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If thin top wiring layers are used to maximize light sensitivity, then light sensitivity is improved, but connection resistance increases due to small cross-sectional area
Solution Approach 1:
The top wiring layer is segmented into two distinct layers: a thin upper layer (less than 1 micron) for light sensitivity and a thick lower layer (1 micron or more) for low resistance connections. This segmentation allows each layer to optimize its function independently, resolving the contradiction between sensitivity and connection quality.
Solution Approach 2:
The wiring structure transitions from a single-layer two-dimensional configuration to a multi-layer three-dimensional configuration. By stacking conductive layers at different heights (z-dimension), the invention achieves both thin profile for sensitivity and sufficient cross-sectional area for low resistance through vertical stacking.
2Reliability
If thick bond pads are used to reduce connection resistance, then connection resistance is improved, but light sensitivity decreases due to larger cross-sectional area blocking light
Solution Approach 1:
The bond pad structure is segmented vertically into a thin upper portion and a thick lower portion. The thin upper portion minimizes light blocking while the thick lower portion provides low resistance electrical connection, allowing both requirements to be satisfied simultaneously in different spatial zones.
Solution Approach 2:
Different regions of the conductive structure have different thicknesses optimized for their specific functions: the upper regions near the light path are kept thin for sensitivity, while lower regions for electrical connection are made thick for low resistance. This local quality variation resolves the global contradiction.
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 approach allows for improved connectivity with lower resistance while maintaining the thin top wiring layers' sensitivity, enabling finely spaced and narrow wires, and protecting cavity components.
Implementation Method 1
depositing a silicon nitride layer over an inter layer dielectric (ILD)
Implementation Method 2
etching the silicon nitride layer with a fluorine-based etch
Data Source
AI summary
Disclosed herein an image sensor chip, including a substrate having at least one via extending through at least one inter layer dielectric (ILD); a first conductive layer over the ILD, wherein the first conductive layer has a first thickness; a second conductive layer over the first conductive layer, wherein the second conductive layer has a second thickness of less than the first thickness; a polymer layer over the second conductive layer, the polymer layer including a cavity; a plurality of cavity components in the cavity; and protective layer contacting the polymer layer and covering the cavity.