Deep Trench Isolation Shrinkage via Protective Sleeve Etching
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Solution Overview
Problem
Deep trench isolation (DTI) structures in semiconductor devices face contamination issues due to the dissociation of functional layer materials during etching, which degrades the isolation and optical properties, leading to reduced performance in photovoltaic devices.
Innovation Solution
A protective capping layer and sleeve are used to limit the dissociation of contaminants from the functional layer during the formation of DTI structures, with a two-step etching process where the first etch stops before fully removing the functional layer and a conformal protective sleeve is applied to prevent further contamination during the second etch, ensuring cleaner sidewalls and improved trench filling with dielectric or tungsten materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a deep trench is etched through the functional layer to form DTI structure, then isolation between pixels is improved, but contaminant dissociation from the functional layer increases causing sidewall contamination
Solution Approach 1:
The etching process is segmented into two distinct steps: a first etch that creates an initial trench and a second etch that completes the deep trench formation. This segmentation allows for intermediate protective measures to be applied, specifically forming a protective sleeve after the first etch and before the second etch, thereby preventing contaminant dissociation during the most critical etching phase while still achieving the required isolation.
Solution Approach 2:
A protective sleeve is formed preliminarily during the first etch step, before the second etch step begins. This protective sleeve acts as a barrier that prevents contaminants from dissociating from the functional layer during the second etch. The protective action is established in advance, before the harmful contaminant dissociation can occur during the deep trench completion phase.
2Ease of manufacture
If the first etch removes the functional layer completely to form the trench, then trench filling is simplified, but contaminant dissociation increases degrading isolation and optical properties
Solution Approach 1:
The trench formation is segmented into two etching steps with an intermediate protective sleeve formation. The first etch creates the initial trench structure, the protective sleeve is formed to prevent contamination, and the second etch completes the trench. This segmentation maintains manufacturing complexity while dramatically improving sidewall cleanliness, resolving the contradiction between ease of manufacture and manufacturing precision.
Solution Approach 2:
A protective sleeve is introduced as an intermediary element between the etching process and the functional layer. This protective sleeve mediates the interaction by preventing direct contact between the etchant and the functional layer during the second etch step, thereby preventing contaminant dissociation while still allowing the trench to be formed and filled.
3Device complexity
If no protective measures are used during etching, then process complexity is reduced, but optical crosstalk increases due to contaminant diffusion
Solution Approach 1:
The etching process is divided into two steps with an intermediate protective sleeve formation. While this increases process steps, it dramatically reduces optical crosstalk by preventing contaminant diffusion. The segmentation allows for a relatively simple protective sleeve formation step that provides substantial protection against optical crosstalk, making the increased complexity worthwhile.
Solution Approach 2:
The protective sleeve serves as an intermediary barrier that prevents contaminant diffusion from the functional layer into the trench sidewalls during the second etch step. This intermediary protection directly addresses optical crosstalk by maintaining clean sidewalls, which are critical for optical isolation between pixels, thereby justifying the additional process step.
4Reliability
If the protective sleeve extends to the bottom of the trench, then sidewall protection is maximized, but trench filling volume increases reducing device density
Solution Approach 1:
The protective sleeve is designed with local quality - it provides maximum protection where most needed (along the sidewalls during etching) while minimizing unnecessary material at the trench bottom. The sleeve can be configured to extend partially or fully along the sidewalls depending on the specific contamination risk, allowing optimization between protection and volume. This local quality approach ensures protection is applied precisely where it prevents contaminant dissociation without unnecessarily increasing trench fill volume.
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 solution effectively prevents contaminant diffusion into the semiconductor substrate, enhancing the isolation and optical properties of photovoltaic devices by maintaining cleaner sidewalls and increasing quantum efficiency through reduced optical crosstalk and improved radiation absorption.
Implementation Method 1
a protective capping layer and sleeve are used to limit the dissociation of contaminants from the functional layer during the formation of DTI structures
Implementation Method 2
with a two-step etching process where the first etch stops before fully removing the functional layer
Implementation Method 3
a conformal protective sleeve is applied to prevent further contamination during the second etch
Implementation Method 4
When incident radiation from an image is absorbed near a depletion region of the p-n junction, an electron-hole pair is created. The electron is drawn to cathode and the hole is drawn to the anode to produce a photocurrent.
Data Source
AI summary
Some embodiments of the present disclosure relate to a method in which a functional layer is formed over an upper semiconductor surface of a semiconductor substrate, and a capping layer is formed over the functional layer. A first etchant is used to form a recess through the capping layer and through the functional layer. The recess has a first depth and exposes a portion of the semiconductor substrate there through. A protective layer is formed along a lower surface and inner sidewalls of the recess. A second etchant is used to remove the protective layer from the lower surface of the recess and to extend the recess below the upper semiconductor surface to a second depth to form a deep trench. To prevent etching of the functional layer, the protective layer remains in place along the inner sidewalls of the recess while the second etchant is used.