Backside Grating Structure for Long Wavelength Light 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 absorption of long wavelength light without the manufacturing difficulties associated with thicker substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the substrate thickness is increased to improve absorption of long wavelength light, then quantum efficiency is improved, but manufacturing complexity increases
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 thin substrate for ease of manufacturing.
Solution Approach 2:
The grating structure introduces curved or angled surfaces that reflect light at multiple angles rather than straight-line propagation. This curvature in the light path creates extended traversal distances through the photodetector material, enhancing absorption efficiency for long wavelength light without requiring increased substrate thickness, thereby resolving the contradiction between quantum efficiency and manufacturing simplicity.
2Ease of manufacture
If the substrate is thinned to simplify manufacturing, then ease of manufacture is improved, but absorption of long wavelength light deteriorates
Solution Approach 1:
The grating structure compensates for the reduced substrate thickness by creating multiple reflection paths within the thin substrate. Light undergoes successive reflections at the grating surfaces, effectively increasing the optical path length and interaction distance with the photodetector material, thereby maintaining absorption efficiency despite the thinned substrate configuration that simplifies manufacturing.
Solution Approach 2:
The grating structure ensures continuous interaction between light and photodetector material through multiple reflections. Rather than a single-pass absorption opportunity in a thin substrate, the grating creates continuous light-material interaction paths, maintaining effective absorption of long wavelength light while preserving the manufacturing advantages of thin substrates.
3Reliability
If a grating structure is added to increase light propagation path, then absorption of long wavelength light is improved, but device complexity increases
Solution Approach 1:
The grating structure segments the substrate into multiple reflective zones that guide light through sequential reflections. This segmentation creates extended light paths without requiring a complete redesign of the entire device architecture. The segmented grating elements can be integrated into existing manufacturing processes, reducing the overall device complexity increase while achieving improved absorption efficiency.
Solution Approach 2:
The grating structure serves multiple functions simultaneously: it increases light propagation path length, enhances absorption of long wavelength light, and can be integrated with existing substrate and photodetector architectures. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in overall device complexity while achieving the desired absorption improvement.
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 detection of long wavelength light, maintaining high quantum efficiency while using a process-friendly thinned-down substrate, thereby enhancing the performance of BSI image sensors in low-light conditions.
Implementation Method 1
a grating structure on a backside of the thinned-down substrate. The grating structure reflects incident light multiple times in the substrate to induce a piecewise linear light propagation path
Implementation Method 2
A BSI image sensor comprises an array of photodetectors overlying an interconnect structure and configured to receive radiation on an opposite side as the interconnect structure
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.