Imaging Pixel Isolation Trenches Using (111) Sidewalls to Cut Dark Current
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Solution Overview
Problem
Dry etching in the formation of element isolation trenches in imaging devices can cause physical damage, leading to crystal defects that result in dark current and white spots.
Innovation Solution
The use of a (110) semiconductor substrate with a trench side surface etched to a (111) plane through crystal anisotropic etching, employing wet etching with an alkaline solution to minimize crystal defects, allowing for the reduction of dark current and white spots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dry etching is used to form the trench, then the trench can be formed with precise depth control, but crystal defects occur on the side surface and bottom surface causing dark current and white spots
Solution Approach 1:
The patent replaces the mechanical/physical dry etching process with a chemical wet etching process using alkaline solution. This substitution eliminates the physical damage and crystal defects caused by ion bombardment in dry etching, while still achieving precise trench formation through crystal anisotropic etching that exploits the directional etching rates of different crystal planes.
Solution Approach 2:
The patent changes the etching method parameter from physical (dry etching) to chemical (wet etching with alkaline solution). This parameter change fundamentally alters the etching mechanism from physical sputtering to chemical dissolution, thereby eliminating crystal defects while maintaining manufacturing precision through the inherent anisotropic etching characteristics of the alkaline solution on silicon crystal planes.
2Object-affected harmful factors
If wet etching with alkaline solution is used, then crystal defects are suppressed, but the etching process must exploit crystal anisotropy to achieve vertical sidewalls
Solution Approach 1:
The patent utilizes the crystal orientation parameter of the substrate ((110) plane) and the anisotropic etching characteristics of alkaline solutions to achieve vertical sidewalls. By carefully selecting the etching conditions and substrate orientation, the process exploits the different etching rates of various crystal planes to automatically form the desired trench geometry without additional complex process steps.
3Reliability
If the substrate is etched deeply to form isolation trenches, then pixel separation is improved, but physical damage to the trench surfaces increases
Solution Approach 1:
The patent replaces the mechanical/physical dry etching process with chemical wet etching using alkaline solution. This substitution eliminates the physical damage and crystal defects caused by ion bombardment, allowing deep trenches to be formed without increasing physical damage to the trench surfaces, thereby improving pixel separation while maintaining surface integrity.
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 effectively reduces dark current and white spots by suppressing crystal defects on the trench side surfaces, enhancing the performance and reliability of the imaging device.
Implementation Method 1
a trench in which at least a part of the side surface is the (111) plane can be formed by performing crystal anisotropic etching in which the (110) plane is easily etched and the (111) plane is hardly etched
Implementation Method 2
The crystal anisotropic etching described above can be performed by wet etching using an alkaline solution
Implementation Method 3
a plurality of sensor pixels that is provided on the first semiconductor substrate and performs photoelectric conversion
Data Source
AI summary
There is provided an imaging device capable of reducing dark current and white spots, and a manufacturing method for the imaging device. An imaging device includes a first semiconductor substrate, a plurality of sensor pixels that is provided on the first semiconductor substrate and performs photoelectric conversion, and a trench provided in a depth direction of the first semiconductor substrate from a first main surface of the first semiconductor substrate. The first semiconductor substrate is a (110) substrate in which the first main surface is a (110) plane. At least a part of a side surface of the trench is a (111) plane.