Deep Trench Isolation Structure for Defect-Free High-Aspect-Ratio Filling
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Solution Overview
Problem
As image pixel sizes and the spacing between neighboring image pixels shrink, it becomes challenging to gap fill material layers in Deep Trench Isolation (DTI) structures without defects, particularly for high aspect-ratio backside DTI structures in CMOS image sensors.
Innovation Solution
A method for fabricating semiconductor devices with DTI structures involves forming deep isolation trenches, depositing a hole accumulation layer, and using a two-step deposition process of isolation materials to fill the trenches, ensuring adequate electrical and optical isolation between photodiode doping regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If pixel sizes and spacing are reduced to increase integration density, then device miniaturization is achieved, but gap filling in DTI structures becomes defective
Solution Approach 1:
The isolation material deposition is segmented into multiple sequential steps (first isolation material layer, second isolation material layer) rather than attempting to fill the entire trench depth in a single step. This allows each deposition step to target specific depth ranges, ensuring complete and defect-free filling of high aspect-ratio trenches even as pixel dimensions shrink
Solution Approach 2:
The solution transitions from considering only the vertical depth dimension of the trench to incorporating the lateral deposition sequence dimension. By depositing isolation materials in multiple sequential layers from different starting points, the process achieves complete trench filling that accommodates reduced pixel spacing while maintaining manufacturing precision
2Device complexity
If single-step isolation material deposition is used, then process simplicity is maintained, but air gaps and defects remain in high aspect-ratio trenches
Solution Approach 1:
The deposition process is divided into multiple sequential steps with distinct isolation material layers. The first isolation material layer is deposited to a first thickness, then a second isolation material layer is deposited to a second thickness, ensuring complete trench filling without air gaps. This segmentation resolves the contradiction by prioritizing filling completeness over process simplicity
Solution Approach 2:
The first isolation material layer is deposited as a preliminary step before the second isolation material layer. This preliminary deposition establishes a foundation that prevents air gap formation and ensures subsequent layers adhere properly, thereby improving trench filling reliability while accepting increased process complexity
3Reliability
If thick isolation material layers are deposited to fill deep trenches, then isolation effectiveness is improved, but film stress-induced defects increase
Solution Approach 1:
The total isolation material thickness required for effective trench filling is segmented into multiple thinner layers (first isolation material layer and second isolation material layer). Each layer has reduced film stress compared to a single thick layer, preventing stress-induced defects while collectively providing the necessary electrical and optical isolation effectiveness
Solution Approach 2:
The deposition parameters are changed from single-step thick layer deposition to multi-step thinner layer deposition. By controlling the thickness of each individual layer and the sequence of deposition, the process achieves adequate isolation effectiveness while minimizing cumulative film stress and preventing defect formation
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 proposed method effectively gap-fills high aspect-ratio deep isolation trenches, reducing defects and improving yield by enclosing air gaps within the filling material and minimizing film stress-induced defects.
Implementation Method 1
depositing a hole accumulation layer on sidewalls of the deep isolation trenches
Implementation Method 2
depositing a first isolation layer on the hole accumulation layer, wherein the first isolation layer has a first thickness
Implementation Method 3
depositing a second isolation layer on the first isolation layer and exposed surfaces of the first filling material
Data Source
AI summary
Embodiments of the present disclosure relate to a structure, which includes a plurality of photodiode doping regions formed in a substrate, and a deep trench isolation (DTI) structure formed in the substrate, wherein the DTI structure separates photodiode doping regions, and the DTI structure comprises a first filling material defining an air gap therein. The first filling material includes a top, a sidewall, and a bottom. The structure also includes a first isolation layer surrounding and in contact with the top, the sidewall, and the bottom of the first filling material.