Image Sensor Rework via Segmented Capping Layer Etching
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Solution Overview
Problem
Conventional CMOS image sensor fabrication methods face challenges in completely removing the capping layer and microlenses, leading to defects that result in low product yield and high costs due to the inability to rework these components effectively.
Innovation Solution
A method involving a substrate with a pixel array and isolation structures, forming patterned metal layers, planarized layers, a color filter array, microlenses, and a capping layer, followed by an etching process to expose the patterned metal layer, which simplifies the fabrication and allows for reworking by reducing the need for photo lithography and avoiding incomplete removal or over-etching issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication methods are used to form a capping layer on microlenses, then the microlenses are protected, but the capping layer cannot be completely removed when defects are observed
Solution Approach 1:
The patent divides the capping layer into two distinct segments: a first capping layer (inorganic oxide layer) that provides protection and can be completely removed, and a second capping layer (organic layer) that provides additional protection and prevents adhesion. This segmentation allows the first capping layer to be selectively removed for reworking while the second layer remains to protect the microlenses during fabrication.
Solution Approach 2:
The patent changes the material parameters of the capping layer by using different materials for the first and second layers. The first capping layer uses inorganic oxide materials (such as silicon oxide, silicon nitride, or silicon oxynitride) that can be completely removed by etching, while the second capping layer uses organic materials that provide adhesion prevention and protection during subsequent processing steps.
2Ease of repair
If the capping layer is removed completely to allow reworking, then defects can be corrected, but the microlenses may be damaged or the removal may be incomplete
Solution Approach 1:
By segmenting the capping layer into removable and protective portions, the patent enables complete removal of the first capping layer through etching without exposing the microlenses to damage, while the second capping layer remains intact to continue providing protection.
Solution Approach 2:
The second capping layer acts as an intermediary protective layer that remains on the microlenses during the removal process of the first capping layer, preventing direct exposure and potential damage to the microlenses while allowing complete removal of the first layer.
3Manufacturing precision
If photo lithography is used to remove the capping layer, then the removal can be precise, but the process becomes complex and time-consuming
Solution Approach 1:
The patent replaces the photo lithography process with a direct etching process using etching solution or plasma. This substitution eliminates the need for photoresist coating, patterning, and development steps, significantly simplifying the fabrication process while maintaining precise removal of the first capping layer through selective etching.
4Reliability
If defects in color filter array or microlenses are detected after complete fabrication, then quality control is maintained, but the whole image sensor must be rejected
Solution Approach 1:
The patent enables the discarding and recovering approach by allowing selective removal of the first capping layer when defects are detected. Instead of rejecting the entire image sensor, the defective components can be reworked by removing the first capping layer, correcting the defects, and forming a new capping layer, thus recovering the value of the sensor.
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 method enhances product yield and reduces costs by enabling the reworking of image sensors, avoiding the rejection of whole units due to defects and minimizing the risks of incomplete removal or damage during the etching process.
Implementation Method 1
an etching step is performed to remove the capping layer and the second planarized layer in the opening, thereby exposing the patterned metal layer above the pad region
Data Source
AI summary
A method of fabricating an image sensor device is provided. First, a substrate comprising a pixel array region and a pad region is provided. A patterned metal layer and a first planarization layer having an opening exposing the patterned metal layer in the pad region are sequentially formed on the substrate. A color filter array is formed on the first planarization layer in the pixel array region. A second planarization layer is formed to cover the color filter array and filled into the opening. A plurality of microlens is formed above the color filter array on the second planarization layer. A capping layer is conformally formed on the microlens and the second planarization layer. An etching step is performed to remove the capping layer and the second planarization layer in the opening so as to expose the patterned metal layer in the pad region.