Solid-State Image Sensor Pixel Isolation with Dual-Sided Trenches
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Solution Overview
Problem
Existing solid-state imaging elements face challenges in reliably separating pixels due to limitations in trench structure formation, impurity processing, and electric field intensification, leading to insufficient color separation and charge capacity.
Innovation Solution
A solid-state imaging element with a photoelectric converter separated by first and second separators formed in trenches from opposing surfaces, using N-type and P-type impurity layers formed by solid-phase diffusion, and a thermally-oxidized film, with the separators arranged parallel or perpendicular to the optical axis, and a method for manufacturing this element involving trench formation and impurity layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench structure is formed before photodiode formation to separate pixels, then pixel separation is improved, but the pixel transistor area is restricted and offset must be made in depth direction
Solution Approach 1:
The patent forms trenches from both the front surface and back surface of the semiconductor substrate, utilizing the depth dimension to achieve pixel separation without consuming lateral pixel transistor area. This dual-directional trench formation allows separators to extend through the substrate thickness, providing effective isolation while preserving in-plane area for transistor components.
2Ease of manufacture
If a trench structure is formed after photodiode formation to separate pixels, then manufacturing process is simplified, but high-heat treatment cannot be used and additional impurity processing is difficult
Solution Approach 1:
The patent performs impurity diffusion into the trench structures before photodiode formation, establishing the separator doping profile in advance. This preliminary impurity processing allows subsequent high-heat treatment during photodiode formation to simultaneously complete both photodiode doping and separator doping without requiring additional processing steps, thereby achieving both ease of manufacture and manufacturing precision.
3Quantity of substance
If N-type impurity is formed by ion implantation to create PN joint, then impurity can be introduced, but impurity expands in transverse direction and steep PN joint cannot be formed
Solution Approach 1:
The patent transitions from ion implantation to solid-phase diffusion for forming impurity layers in the trenches. Solid-phase diffusion allows precise control of impurity concentration profiles and diffusion depths by adjusting temperature and time parameters, preventing transverse expansion and enabling the formation of steep PN joints with well-defined boundaries at the trench interfaces.
4Device complexity
If single-sided trench structure is used to separate pixels, then manufacturing is simpler, but sufficient pixel separation cannot be achieved
Solution Approach 1:
The patent divides the pixel separation function into two segments: a first trench structure formed from the front surface and a second trench structure formed from the back surface. This segmentation allows each trench to be formed independently with optimized parameters, and their combined effect provides comprehensive pixel separation throughout the substrate thickness, achieving superior isolation effectiveness compared to a single-sided structure.
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 configuration allows for more reliable pixel separation and improved charge capacity, enhancing light shielding and reducing color mixture, even in pixels with thick silicon films.
Implementation Method 1
a first impurity layer formed of an N-type impurity and a second impurity layer formed of a P-type impurity are formed by solid-phase diffusion
Implementation Method 2
a thermally-oxidized film, with the separators arranged parallel or perpendicular to the optical axis
Data Source
AI summary
The solid-state imaging element includes a photoelectric converter, a first separator, and a second separator. The photoelectric converter is configured to perform photoelectric conversion of incident light. The first separator configured to separate the photoelectric converter is formed in a first trench formed from a first surface side. The second separator configured to separate the photoelectric converter is formed in a second trench formed from a second surface side facing a first surface. The present technology is applicable to an individual imaging element mounted on, e.g., a camera and configured to acquire an image of an object.