Silicon Photosensor Array Trench Isolation on [110] Substrate
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Solution Overview
Problem
Existing CMOS silicon array photosensors face issues with crosstalk and leakage due to isolation trenches, leading to image blooming and increased dark current, which affects the accuracy of light exposure measurements.
Innovation Solution
The method involves forming isolation trenches in a [110]-oriented single-crystal silicon substrate using a combination of dry plasma etching and anisotropic wet etching, lining the trenches with boron-doped silicon and silicon dioxide, and filling them with tungsten, which reduces dark current and enhances trench depth and narrowness, thereby improving isolation between photodiodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolation trenches are formed to limit crosstalk and leakage between adjacent photosensors, then image blooming is reduced, but dark current increases and manufacturing complexity increases
Solution Approach 1:
The patent changes the crystallographic orientation parameter of the silicon substrate from conventional <100> to <110>, which fundamentally alters the etching behavior and enables the formation of deeper, narrower trenches with better isolation characteristics and reduced dark current
Solution Approach 2:
The patent employs a composite trench structure with multiple materials: silicon dioxide for the trench wall, silicon nitride for additional isolation, and tungsten for filling. This composite approach optimizes both isolation effectiveness and dark current reduction
2Reliability
If isolation trenches are formed to prevent image blooming, then isolation between photodiodes improves, but manufacturing process complexity increases
Solution Approach 1:
The patent combines dry plasma etching and wet chemical etching into a single trench formation process. The dry etch creates initial openings through the hard mask, while the wet etch completes the deep trench formation, achieving better isolation than either method alone
Solution Approach 2:
The patent utilizes the specific etching rate characteristics of <110> oriented silicon in wet chemical etchants, which etch this crystal orientation much slower than other orientations, enabling precise control of trench depth and shape
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 effectively reduces dark current and prevents image blooming, increasing the sensitivity and accuracy of low-light imaging by deeper and narrower trenches that better isolate photodiodes, allowing for more efficient light exposure measurement.
Implementation Method 1
performing an anisotropic wet etch through the openings in the hard mask layer
Implementation Method 2
the etch is performed in a solution of potassium hydroxide, tetramethylammonium hydroxide, and ethylenediamine-pyrocatechol-water
Implementation Method 3
dry plasma etching through the photoresist openings to form openings in the hard mask layer of locations for the trenches
Implementation Method 4
each cell including at least one photodiode... Exposure of the photodiode to light alters charge on the photodiode
Data Source
AI summary
A method for fabricating a photosensor array integrated circuit includes forming an isolation trench by a method comprising depositing a hard mask layer on a [110]-oriented single-crystal silicon substrate wafer, depositing, exposing, and developing a photoresist on the hard mask layer to define photoresist openings of locations for the trenches, dry plasma etching through the photoresist openings to form openings in the hard mask layer of locations for the trenches, and performing an anisotropic wet etch through the openings in the hard mask layer. In particular embodiments, the trenches are lined with P-type silicon, a silicon dioxide dielectric, and an additional oxide layer before being filled with tungsten.