Dual Isolation Structures for Semiconductor Pixel Arrays
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Solution Overview
Problem
Shallow trench isolation (STI) processes in semiconductor imaging devices introduce lattice defects and stress-induced defects at vertical surfaces, leading to increased dark current and reverse bias leakage due to the accumulation of electron hole pairs at the interface between the substrate and isolation structures, which affects the efficiency and reliability of photodiodes.
Innovation Solution
The method involves forming dual isolation structures, including a protruding isolation structure that extends from the surface and an embedded isolation structure within the substrate, using selective etching and deposition techniques to reduce the interaction between the depletion region and damaged vertical surfaces, thereby minimizing dark current effects. This is achieved by creating a cleaner interface and reducing the area of contact between the depletion region and the isolation structures, which are used as self-aligned masks for doping to form the p-n junction at a distance from the substrate surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shallow trench isolation (STI) is used to isolate pixels and devices, then electrical isolation between adjacent structures is improved, but dark current and reverse bias leakage increase due to lattice defects at vertical surfaces
Solution Approach 1:
The isolation structure is divided into two distinct segments: a first isolation structure extending from the surface into the substrate, and a second isolation structure embedded within the substrate. This segmentation allows each structure to perform isolation functions while minimizing their individual harmful effects on dark current generation.
Solution Approach 2:
Different regions of the isolation structure are designed with different properties: the first isolation structure uses a material with a first band gap, while the second isolation structure uses a material with a second band gap. This local quality differentiation optimizes the electrical characteristics in different spatial zones to reduce dark current while maintaining isolation effectiveness.
2Reliability
If STI is used to provide physical and electrical barrier, then device isolation is improved, but lattice defects and stress-induced defects are introduced at vertical surfaces
Solution Approach 1:
The first isolation structure acts as an intermediary between the surface and the second isolation structure. It provides a transition zone that reduces the direct interaction between the depletion region and the substrate surface, thereby minimizing lattice defects and stress-induced defects while maintaining the necessary physical and electrical barrier.
Solution Approach 2:
The dual isolation structure employs composite materials with different band gap characteristics. The first isolation structure material and the second isolation structure material are selected to create a composite system that optimizes both isolation performance and defect reduction, leveraging the complementary properties of different materials.
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 dual isolation structure approach reduces dark current and processing costs by minimizing the formation of dangling bonds and stress-related dislocations, enhancing the reliability and efficiency of photodiodes by reducing electron hole pair accumulation and improving channel control.
Implementation Method 1
using selective etching and deposition techniques to reduce the interaction between the depletion region and damaged vertical surfaces
Implementation Method 2
During the STI process, a number of lattice defects, such as dangling bonds and stress-induced defects, may be introduced at vertical surfaces 130 in the substrate 101
Implementation Method 3
As voltage is applied, the depletion region 129 extends toward the vertical surfaces 130 in the substrate 101 in the vicinity of the oxide material of the STI
Implementation Method 4
Accumulation of electron hole pairs resulting from damaged vertical surfaces 130 in the substrate 101 may have detrimental effects on the function of the photodiode
Data Source
AI summary
A semiconductor structure with dual isolation structures is disclosed. The semiconductor structure may include a protruding isolation structure in a pixel array region of a substrate and an embedded isolation structure in a peripheral device region of the same substrate. A region of the protruding isolation structure extends from an upper surface of the substrate, while another region of the protruding isolation structure may, optionally, be embedded within the substrate. The embedded isolation structure is formed within the substrate and includes an upper surface that is substantially coplanar with the upper surface of the substrate. A method of forming the semiconductor structure with dual isolation structure is also disclosed.