Image Sensor Lens Array Structure for Stress-Balanced Wafer Flatness
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Solution Overview
Problem
The manufacturing process of CMOS image sensors faces challenges such as substrate damage during lens array formation and stress imbalance between lens elements and the lens array, leading to wafer bending.
Innovation Solution
A manufacturing method that includes forming a lens layer with inclined sidewalls, a refill layer, and a cladding layer to reduce stress and prevent substrate damage, with specific etching and deposition processes to create micro-lenses or meta-surface lenses, and a bandpass filter layer to improve image sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a lens array is formed by etching process, then lenses can be created above photosensitive elements, but the substrate below the lens material is damaged
Solution Approach 1:
A refill layer is formed on the substrate before forming the lens array. This refill layer serves as a protective sacrificial layer that prevents etching damage to the substrate during lens array fabrication. The refill layer is positioned between the substrate and the lens array, and after the lens array is formed, the refill layer is removed through selective etching, leaving the substrate intact and undamaged.
2Adaptability or versatility
If elements are disposed above the lens array, then functional components are added, but stress imbalance occurs causing wafer bending
Solution Approach 1:
The cladding layer is formed with a specific refractive index that differs from surrounding materials, creating a localized optical pathway that guides light from the lens array to the photosensitive elements. This local quality modification in the cladding layer helps distribute stress more evenly across the wafer structure, preventing stress imbalance and wafer bending while maintaining element integration above the lens array.
3Ease of manufacture
If conventional etching is used to form lens array, then manufacturing process is simple, but substrate damage and stress imbalance occur
Solution Approach 1:
The refill layer acts as an intermediary sacrificial layer between the substrate and the lens array formation process. This intermediary layer allows the use of conventional etching processes to create the lens array while protecting the substrate from damage. The refill layer is selectively removed after lens formation, enabling simple manufacturing processes while maintaining substrate integrity and reliability.
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 method effectively reduces stress imbalance and prevents substrate damage, enhancing the optical performance and reliability of the image sensor by ensuring a smoother slope and better material coverage.
Implementation Method 1
the image sensor of the present disclosure has a smoother slopping to solve a stress imbalance at the boundary of a lens array and elements disposed above the lens array
Implementation Method 2
The lens layer is etched to transfer a pattern of the patterned hard mask layer to the lens layer such that a plurality of lenses are defined
Implementation Method 3
A bandpass filter layer having multiple films is conformally formed on the cladding layer and covers the substrate
Data Source
AI summary
A manufacturing method includes the following operations. A lens layer is formed above a substrate. A patterned hard mask layer is formed on the lens layer. The lens layer is etched to transfer a pattern of the patterned hard mask layer to the lens layer such that a plurality of lenses are defined, wherein the lens are micro-lenses or meta-surface lenses. A cladding layer is formed to cover the plurality of lenses and the substrate. Portions of the cladding layer are etched to form a first inclined sidewall and a second inclined sidewall, wherein the first inclined sidewall is above the second inclined sidewall, wherein a projection of the first inclined sidewall on the substrate is spaced apart from a projection of the second inclined sidewall on the substrate.