Backside CMOS Image Sensor Isolation for Lower Dark Current
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Solution Overview
Problem
Complementary metal-oxide-semiconductor (CMOS) image sensors face challenges in improving dark current and white pixel performance due to various factors affecting photodiodes, leading to blemished pixels and white spot defects.
Innovation Solution
A method for manufacturing a CMOS image sensor involving the formation of a semiconductor structure with an epitaxial layer, a barrier layer, and densified high-aspect-ratio process (HARP) oxide isolation features, which includes ion implantation, annealing, and chemical mechanical polishing to create a photodiode with reduced dark current by preventing plasma-induced damage and ensuring stringent gap-fill requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photodiode fabrication is used, then manufacturing process is simple, but dark current increases and white pixel defects occur
Solution Approach 1:
The patent applies preliminary action by performing ion implantation to create a protective layer in the epitaxial layer before forming the isolation features. This protective layer is prepared in advance to prevent plasma-induced damage during subsequent isolation formation processes, thereby reducing dark current and preventing white pixel defects before they can occur.
Solution Approach 2:
The patent introduces a protective layer as an intermediary element between the epitaxial layer and the isolation features. This protective layer acts as a mediator that prevents direct interaction between plasma and the epitaxial layer during isolation formation, thereby eliminating the harmful effects of plasma-induced damage while allowing the isolation features to be formed properly.
2Manufacturing precision
If plasma processing is used for isolation formation, then gap-fill requirements are met, but plasma-induced damage occurs causing blemished pixels
Solution Approach 1:
The patent applies beforehand cushioning by forming a protective layer in the epitaxial layer prior to the plasma processing step. This protective layer serves as a cushion or barrier that absorbs or prevents the harmful effects of plasma exposure, allowing the plasma processing to proceed for gap-fill purposes without causing damage to the underlying epitaxial layer that would result in blemished pixels.
3Reliability
If dopant diffusion is not prevented, then manufacturing process is simple, but photodiode performance deteriorates
Solution Approach 1:
The patent applies preliminary action by performing ion implantation to create a protective layer before isolation feature formation. This protective layer is prepared in advance to control dopant diffusion during subsequent processing steps, thereby maintaining photodiode performance without requiring complex additional process steps.
Solution Approach 2:
The protective layer acts as an intermediary that controls and regulates dopant diffusion during the isolation feature formation process. It prevents uncontrolled diffusion that would deteriorate photodiode performance while allowing the manufacturing process to remain relatively simple.
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 method effectively reduces dark current and prevents blemished pixels, enhancing the performance of CMOS image sensors by maintaining the integrity of the epitaxial layer and preventing dopant diffusion, thereby improving image quality.
Implementation Method 1
growing an epitaxial layer on the substrate
Implementation Method 2
implanting dopants into the epitaxial layer around a sidewall of the trench to form a protective layer
Implementation Method 3
performing an annealing operation to densify the oxide layer to form a densified oxide layer
Data Source
AI summary
The present disclosure provides a method of manufacturing a semiconductor structure of a CMOS image sensor. The method includes providing a substrate; growing an epitaxial layer on the substrate; forming a barrier layer on the epitaxial layer; forming a trench extending into the epitaxial layer; oxidizing the epitaxial layer to form a liner layer; defining a region of a photodiode and a first dopant thickness; implanting dopants into the epitaxial layer around a sidewall of the trench to form a protective layer with a second dopant thickness less than the first dopant thickness; forming an oxide layer in the trench; performing an annealing operation to densify the oxide layer to form a densified oxide layer, wherein the protective layer, expanded from the second dopant thickness to a third dopant thickness less than the first dopant thickness, is kept spaced from the region; and forming the photodiode in the region.