Fluorinated Amorphous Layer for Mesa Photodiode Dark Current Reduction
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Solution Overview
Problem
Mesa-type photodiodes with super-lattice structures in image sensors experience high dark current due to native oxides formed on the side surfaces, which deteriorate the signal-to-noise ratio.
Innovation Solution
A method involving the growth of stacked semiconductor layers with a super-lattice structure, followed by forming a fluorinated amorphous layer on the side surfaces exposed to fluorine plasma and then a passivation film containing an oxide, which reduces the dark current by minimizing the oxide layer on the side surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passivation film is formed on the side surface of the mesa structure to protect it, then the side surface is protected, but dark current is generated at the interface between the super-lattice structure and the passivation film
Solution Approach 1:
A fluorinated amorphous layer is introduced as an intermediary between the super-lattice structure and the passivation film. This intermediate layer prevents direct contact between the semiconductor super-lattice and the passivation film, thereby eliminating the dark current generation at their interface while still providing protection to the side surface.
Solution Approach 2:
The harmful oxide layer that forms on the side surface during exposure to atmosphere is removed by treating with fluorine plasma. This extraction of the harmful oxide prevents it from causing dark current when the passivation film is subsequently formed.
2Ease of manufacture
If the side surface of the mesa structure is exposed in the atmosphere until the passivation film is formed, then the passivation film can be formed on the side surface, but native oxides are unintentionally formed on the side surface generating dark current
Solution Approach 1:
Fluorine plasma treatment is performed as a preliminary action before forming the passivation film. This treatment removes native oxides and deposits a fluorinated amorphous layer in advance, preventing dark current generation when the passivation film is subsequently formed on the side surface.
Solution Approach 2:
The exposure to atmosphere that causes harmful oxide formation is converted into a benefit by subsequently treating with fluorine plasma. The fluorine plasma not only removes the harmful oxides but also deposits a beneficial fluorinated amorphous layer that serves as an effective barrier against 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
The approach effectively suppresses dark current at the interface between the passivation film and the fluorinated amorphous layer, improving the signal-to-noise ratio of image sensors.
Implementation Method 1
growing a stacked semiconductor layer on a principal surface of a substrate, the stacked semiconductor layer including a light-receiving layer having a super-lattice structure
Implementation Method 2
forming a mesa structure on the substrate by etching the stacked semiconductor layer using the mask
Implementation Method 3
forming a fluorinated amorphous layer on the side surface of the mesa structure by exposing the substrate product in fluorine plasma
Implementation Method 4
forming a passivation film containing an oxide on the side surface of the mesa structure
Data Source
AI summary
A method for producing a semiconductor light receiving device includes the steps of growing a stacked semiconductor layer on a principal surface of a substrate, the stacked semiconductor layer including a light-receiving layer having a super-lattice structure, the super-lattice structure including a first semiconductor layer and a second semiconductor layer that are stacked alternately; forming a mask on the stacked semiconductor layer; forming a mesa structure on the substrate by etching the stacked semiconductor layer using the mask so as to form a substrate product, the mesa structure having a side surface exposed in an atmosphere; forming a fluorinated amorphous layer on the side surface of the mesa structure by exposing the substrate product in fluorine plasma; and after the step of forming the fluorinated amorphous layer, forming a passivation film containing an oxide on the side surface of the mesa structure.