Segmented Epitaxial Growth for CIS Quantum Efficiency
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Solution Overview
Problem
The existing methods for forming doped epitaxial layers in contact image sensors result in poor photolithography and dry etching morphologies due to thick photoresist and hard masks, leading to inefficient ion implantation and restricted quantum efficiency, especially for near infrared/infrared applications.
Innovation Solution
A method involving multiple cycles of epitaxial growth, trench isolation, and ion implantation, where each cycle forms deep and shallow trench isolations through a large-thickness doped epitaxial layer, reducing the need for thick photoresist and hard masks, thereby improving morphology and quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the epitaxial layer is thickened to improve quantum efficiency for near infrared/infrared applications, then the quantum efficiency is improved, but the photolithography and dry etching morphologies become poor due to the required thick photoresist
Solution Approach 1:
The patent divides the single thick epitaxial layer formation into multiple sequential epitaxial growth steps (first, second, and optionally third epitaxial layers). Each growth step is followed by isolation trench formation and ion implantation. This segmentation allows each photoresist layer to be applied to a thinner substrate, improving photolithography and etching morphologies while achieving the total thickness needed for high quantum efficiency through cumulative growth.
2Reliability
If the implantation depth is increased to improve quantum efficiency, then the quantum efficiency is improved, but the photoresist thickness increases causing poor photolithography morphology and lag problems
Solution Approach 1:
The patent segments the deep ion implantation process into multiple shallower implantation steps. Each implantation step operates on a thinner accumulated epitaxial layer, allowing the use of thinner photoresist that maintains good photolithography morphology. The cumulative effect of multiple implantation steps achieves the desired total implantation depth for high quantum efficiency without the lag problems associated with single deep implantation.
3Reliability
If the isolation depth is deepened to improve quantum efficiency, then the quantum efficiency is improved, but thick photoresist or hard mask is required causing poor etching morphology
Solution Approach 1:
The patent divides the deep isolation trench formation into multiple sequential steps, each creating partial depth. After each epitaxial growth step, isolation trenches are formed to the current depth of the epitaxial layer. This segmented approach allows each etching step to work with thinner photoresist, maintaining good etching morphology, while the cumulative isolation depth achieves the level needed for high quantum efficiency.
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 performance of contact image sensors by maintaining good photoresist and etching morphologies, allowing for higher quantum efficiency and smaller pixel sizes, suitable for near infrared/infrared applications.
Implementation Method 1
performing first epitaxial growth on a wafer to form a first epitaxial layer
Implementation Method 2
performing first ion implantation to the epitaxial layer
Data Source
AI summary
The disclosure discloses a method for forming a doped epitaxial layer of contact image sensor. Epitaxial growth is performed in times. After each time of epitaxial growth, trench isolation and ion implantation are performed to form deep and shallow trench isolation running through a large-thickness doped epitaxial layer. Through cyclic operation of epitaxial growth, trench isolation and ion implantation, the photoresist and hard mask required at each time do not need to be too thick. In the process of trench isolation and ion implantation, the photoresist and etching morphologies are good, such that the lag problem of the prepared contact image sensor is improved. By forming the large-thickness doped epitaxial layer by adopting the method for forming the doped epitaxial layer of the contact image sensor, a high-performance contact image sensor applicable to high quantum efficiency, small pixel size and near infrared/infrared can be prepared.