Optical Sensor Trench Etch Through Dielectric Layers
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Solution Overview
Problem
Optical sensors with silicon photodiodes face challenges in efficiently capturing incident light due to uncontrolled reflections from multiple dielectric layers, leading to reduced light absorption and non-linear responsivity across various wavelengths.
Innovation Solution
A trench is etched through multiple dielectric layers to expose the silicon substrate, with a metal perimeter band acting as an etch stop, allowing for the deposition of an anti-reflection coating directly above the photodiode, thereby minimizing reflections and ensuring a smooth, flat surface for enhanced light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple layers of dielectric material are used over the silicon substrate, then the device complexity and integration are improved, but uncontrolled reflections occur leading to reduced light absorption and non-linear responsivity
Solution Approach 1:
A trench is etched through the dielectric layers to extract and remove the problematic dielectric material from above the photodiode, eliminating the source of uncontrolled reflections while preserving the integrated circuit structure
Solution Approach 2:
The anti-reflection coating is applied locally only within the trench region above the photodiode, providing targeted optical optimization without affecting the surrounding integrated circuit structures
2Reliability
If a trench is etched through dielectric layers to expose the substrate, then light absorption is improved, but the manufacturing process complexity increases
Solution Approach 1:
A metal perimeter band is formed as an etch stop before the trench etching process, providing a predefined termination point that simplifies the etching process and ensures consistent trench depth and positioning
Solution Approach 2:
The metal perimeter band acts as an intermediary element between the dielectric layers and the silicon substrate, serving as both a structural feature and an etch stop to control the trench formation process
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 significantly reduces uncontrolled reflections, achieving uniform responsivity across a range of wavelengths and maximizing light absorption by the photodiode, leading to improved sensitivity and performance of optical sensors.
Implementation Method 1
A metal perimeter band that is a portion of a metal plate etch stop surrounds the trench adjacent the trench wall
Implementation Method 2
Photodiodes convert an amount of incident light into an output electric current
Data Source
AI summary
In described examples an integrated circuit (IC) has multiple layers of dielectric material overlying at least a portion of a surface of a substrate. A trench is etched through the layers of dielectric material to expose a portion the substrate to form a trench floor, the trench being surrounded by a trench wall formed by the layers of dielectric material. A metal perimeter band surrounds the trench adjacent the trench wall, the perimeter band being embedded in one of the layers of the dielectric material.