BSI Photodetector Grating Structure for Long-Wavelength Absorption
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Solution Overview
Problem
Backside illumination (BSI) image sensors with thinned-down silicon substrates face challenges in absorbing long wavelengths of light, such as near-infrared light, due to their thin thickness, resulting in low quantum efficiency, and increasing substrate thickness complicates manufacturing.
Innovation Solution
Incorporating a grating structure on the backside of the thinned-down substrate that reflects incident light multiple times, increasing the light propagation path and enhancing the detection of long wavelength light without the manufacturing challenges associated with thicker substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the substrate thickness is increased to improve long wavelength light absorption, then quantum efficiency for long wavelength light is improved, but manufacturing complexity and difficulty increase
Solution Approach 1:
The patent introduces a grating structure that adds a spatial dimension to light propagation. Instead of increasing substrate thickness (one dimension), the grating creates multiple reflection paths within the existing thin substrate plane, effectively increasing the optical path length without increasing physical thickness. This dimensional approach allows light to traverse a longer distance through the photodetector material, improving absorption of long wavelength light while maintaining the manufacturing advantages of thin substrates.
Solution Approach 2:
The grating structure introduces curved or angled surfaces that redirect light paths. The periodic modulation of the grating creates multiple internal reflections, bending the light path multiple times as it passes through the substrate. This curvature in the light path increases the effective interaction length between light and photodetector material, enhancing quantum efficiency for long wavelength detection without requiring increased substrate thickness.
2Ease of manufacture
If the substrate is thinned to simplify manufacturing, then ease of manufacture is improved, but light absorption for long wavelengths deteriorates
Solution Approach 1:
The grating structure compensates for the reduced substrate thickness by creating multiple reflection paths within the thin substrate. Light enters the thin substrate and undergoes multiple internal reflections off the grating structures, effectively increasing the optical path length. This allows the thin substrate to achieve the same light absorption performance as a much thicker substrate would provide, maintaining ease of manufacture while improving long wavelength detection.
Solution Approach 2:
The grating structure ensures continuous interaction between light and photodetector material by creating multiple reflection events. Instead of a single-pass straight trajectory that would require thick substrate for adequate absorption, the light continuously interacts with the photodetector material through multiple bounces off the grating, maximizing absorption efficiency within the thin substrate volume.
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 grating structure significantly improves the quantum efficiency for long wavelength light detection, allowing for high performance in low-light conditions while maintaining the manufacturing advantages of a thin substrate.
Implementation Method 1
a grating structure on a backside of the thinned-down substrate, the grating structure reflecting incident light multiple times in the substrate to lengthen a propagation path of the incident light
Implementation Method 2
A BSI image sensor comprises an array of photodetectors overlying an interconnect structure and configured to receive radiation
Data Source
AI summary
Some aspects of the present disclosure relate to a method. In the method, a semiconductor substrate is received. A photodetector is formed in the semiconductor substrate. An interconnect structure is formed over the photodetector and over a frontside of the semiconductor substrate. A backside of the semiconductor substrate is thinned, the backside being furthest from the interconnect structure. A ring-shaped structure is formed so as to extend into the thinned backside of the semiconductor substrate to laterally surround the photodetector. A series of trench structures are formed to extend into the thinned backside of the semiconductor substrate. The series of trench structures are laterally surrounded by the ring-shaped structure and extend into the photodetector.