Image Sensor Bond Pad Planarization via CIAB Recessed Walls
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Solution Overview
Problem
The existing manufacturing process for image sensor dies, particularly the spin-on process for forming color filter and microlenses, results in inefficiencies, high costs, and planarity issues due to topography-related streaks and artifacts, leading to lower yield in imaging systems.
Innovation Solution
The process involves forming recessed color filter array-in-a-box (CIAB) wall structures with selective etching and chemical mechanical polishing to improve planarity, along with a light shielding layer grounded through the substrate, and the use of dielectric layers to create slots for color filter elements, allowing for efficient formation of image sensor dies with reduced optical crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a spin-on process is used to form color filter and microlenses, then the manufacturing process is simple and continuous, but the topography of bond pads and passivation layers creates streaks and artifacts resulting in lower yield
Solution Approach 1:
A planarization layer is formed over the bond pad and passivation layer structures before the spin-on process deposits color filters and microlenses. This preliminary planarization action creates a flat surface that eliminates topography-induced streaks and artifacts during the subsequent spin-on coating, thereby maintaining both manufacturing efficiency and optical quality
Solution Approach 2:
The planarization layer acts as an intermediary between the non-planar bond pad/passivation layer structures and the spin-on coating process. This intermediate layer absorbs the topography variations and provides a uniform surface for the color filter and microlens deposition, preventing defects while preserving the simplicity of the spin-on method
2Reliability
If bond pads are formed with standard passivation layers, then the bond pads are protected and can be wirebonded, but the topography creates issues during spin-on processes
Solution Approach 1:
The planarization layer is deposited over the bond pad and passivation structures before the color filter spin-on process. This preliminary action maintains the protective function of the passivation layers while simultaneously creating a flat surface that enables high-quality spin-on coating without streaks or artifacts
Solution Approach 2:
The planarization layer is selectively applied over the bond pad regions with non-planar topography, providing localized smoothing where needed while leaving other areas unchanged. This local quality adjustment resolves the conflict between bond pad protection and spin-on processability without affecting the entire wafer uniformly
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 enhances the manufacturing efficiency and yield of image sensor dies by improving planarity and reducing optical crosstalk, resulting in higher-quality imaging systems with improved performance.
Implementation Method 1
chemical mechanical polishing to improve planarity
Data Source
AI summary
An imaging system may include an image sensor die, which may be backside illuminated (BSI). A light shielding layer and a conductive layer may be formed in the image sensor die. First and second portions of the conductive layer may be electrically isolated, so that the second conductive portion may be coupled to other power supply signals through a bond pad region, while the light shield may be shorted to ground. Optionally, the first and second portions may both be coupled to ground. The light shield may also be shorted through the bond pad region in a continuous conductive layer. A through oxide via may be formed in the image sensor die to couple metal interconnect structures to the conductive layer. Color filter containment structures may be formed over active image sensor pixels on the image sensor die, which may be selectively etched to improve planarity.