Recessed Color Filter Array Planarity via Fill Material
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Solution Overview
Problem
Current methods for planarizing color filter arrays in solid-state imagers are ineffective when the recess depth exceeds the thickness of the color filter film, as chemical mechanical planarization (CMP) is no longer applicable, leading to imperfect planarity and optical issues.
Innovation Solution
A method involving forming layers over a photo-conversion device, etching a trench for the color filter, filling with photoresist material, planarizing, and etching back to achieve uniform thickness, allowing for improved planarity and reduced stack height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the CFA is lowered into a recessed area to reduce pixel stack height, then the micro-lens and CFA can be brought closer to the photosensor, but the typical CMP planarization method is no longer applicable when the recess depth exceeds the CFA film thickness
Solution Approach 1:
The patent introduces an intermediary material (fill material such as spin-on-glass, BPSG, or photoresist) to fill the recessed area beneath the CFA. This fill material acts as a mediator that enables planarization of the CFA surface without requiring the CFA to be fully supported by the trench walls, thus solving the planarity issue when recess depth exceeds CFA thickness
Solution Approach 2:
The patent changes the physical parameters of the recessed area by filling it with material having different mechanical properties than the original substrate. This allows the CFA to be planarized on top of the fill material, achieving the required surface flatness for optical performance while maintaining the recessed configuration
2Adaptability or versatility
If the CFA is placed in a recessed area, then the angular acceptance range for incoming light is enhanced, but optical crosstalk and color artifacts may occur without proper planarity
Solution Approach 1:
The fill material serves as an optical intermediary that maintains the recessed configuration for enhanced angular acceptance while providing a planar surface for the CFA. This prevents optical crosstalk and color artifacts by ensuring proper alignment and positioning of the CFA relative to the micro-lens and photosensor
3Manufacturing precision
If CMP is used for planarization in shallow recesses, then the CFA surface can be flattened, but this method becomes ineffective when the recess depth exceeds the CFA film thickness
Solution Approach 1:
The patent solves the planarization problem by adding a dimensional element - the fill material layer - beneath the CFA. This creates a new structural dimension that supports the CFA and enables planarization processes to work effectively even in deep recesses where traditional CMP would fail
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 ensures uniformity and reduces optical crosstalk by placing the micro-lens closer to the photosensor, enhancing the angular acceptance range for incoming light and minimizing color artifacts.
Implementation Method 1
the typical method of planarizing, i.e., chemical mechanical planarization (CMP), is no longer directly applicable to improve the planarity of the CFA on the pixel array
Data Source
AI summary
A method and apparatus for improving the planarity of a recessed color filter array when the recessed region or trench depth exceeds the thickness of the color filter film. The method includes the steps of coating the entire wafer with an additional coating material after applying the CFA, then planarizing that resist layer using CMP and then using a dry etch to transfer that planar surface down as far as required to achieve a planar color filter with a uniform thickness.