Tri-Layer Passivation for Deep Trench Isolation
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Solution Overview
Problem
The manufacturing of CMOS image sensors with deep trench isolation (DTI) structures faces challenges such as lateral etching undercutting and crystalline defects, which increase dark current and result in white pixels, especially when etching depths exceed 1 micrometer, making uniform dopant implantation difficult.
Innovation Solution
A tri-layer passivation layer is formed using selective epitaxy, comprising a first undoped semiconductor layer, a doped semiconductor layer, and a second undoped semiconductor layer, with a baking process and cyclic-deposition/etch (CDE) process to reduce undercutting and repair defects, allowing uniform doping from top to bottom and controlling doping profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If etching depth is increased to achieve deeper isolation, then isolation effectiveness is improved, but lateral undercutting increases causing white pixels and dark current
Solution Approach 1:
The patent changes the chemical parameters of the etching process by introducing a sulfur-containing compound (such as H2S, DMS, or DMDS) into the etching atmosphere. This parameter change modifies the etching chemistry to reduce lateral undercutting while maintaining vertical etching depth, thereby achieving deep isolation without the harmful undercutting effect that would otherwise occur at increased etching depths.
Solution Approach 2:
The sulfur-containing compound acts as an intermediary substance during the etching process. It mediates between the etchant and the semiconductor material by forming a protective sulfur layer on the trench walls that prevents lateral etching attack while allowing vertical etching to proceed, thus eliminating the harmful undercutting that normally accompanies deep etching.
2Reliability
If etching depth exceeds 1 micrometer to improve isolation, then isolation depth is improved, but uniform dopant implantation becomes difficult
Solution Approach 1:
The patent modifies the etching process parameters by adding sulfur-containing compounds to the etching atmosphere, which creates a modified trench profile with reduced lateral undercutting. This parameter change results in more vertical trench walls that enable uniform dopant implantation even at depths exceeding 1 micrometer, as the dopant can now reach the trench bottom uniformly without being blocked by angled or undercut walls.
3Length of stationary object
If conventional etching is used to form deep trenches, then trench depth is achieved, but crystalline defects increase dark current
Solution Approach 1:
The sulfur-containing compound serves as an intermediary that protects the crystal structure during deep etching. By forming a protective sulfur layer on the trench walls, it prevents mechanical and chemical damage to the crystalline structure, thereby eliminating the generation of crystalline defects that would otherwise occur during conventional deep etching and subsequently increase dark current.
Solution Approach 2:
The patent converts the typically harmful effect of sulfur (which can contaminate semiconductors) into a beneficial protective layer during etching. The sulfur-containing compound forms a controlled protective layer on the trench walls that prevents crystal damage, thus converting what would normally be a contaminant into a protective intermediary that reduces crystalline defects and dark current.
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 reduces dark current, minimizes white pixels, and enhances performance by reducing undercutting and repairing crystalline defects, while allowing for uniform doping and controlled doping profiles, even in trenches with depths greater than 1 micrometer and high aspect ratios.
Implementation Method 1
A first undoped semiconductor layer is formed lining surfaces of the semiconductor substrate that define the trench. A doped semiconductor layer is formed over and lining the first undoped semiconductor layer in the trench. A second undoped semiconductor layer is formed over and lining the doped semiconductor layer in the trench. The first and second undoped semiconductor layers and the doped semiconductor layer are formed by epitaxy.
Implementation Method 2
A baking process and cyclic-deposition/etch (CDE) process to reduce undercutting and repair defects
Data Source
AI summary
A method for manufacturing a deep trench isolation (DTI) structure with a tri-layer passivation layer is provided. An etch is performed into a semiconductor substrate to form a trench. A first undoped semiconductor layer is formed by epitaxy lining surfaces of the semiconductor substrate that define the trench. A doped semiconductor layer is formed by epitaxy over and lining the first undoped semiconductor layer in the trench. A second undoped semiconductor layer is formed by epitaxy over and lining the doped semiconductor layer in the trench. A structure resulting from the method is also provided.