Semiconductor Photodetector Epitaxial Shielding Layer
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Solution Overview
Problem
Existing semiconductor photodetector devices face issues with unwanted backside illumination causing signal distortions due to charge carrier drift, which existing solutions attempt to mitigate through additional process steps and coatings, risking mechanical damage to fragile substrates.
Innovation Solution
A semiconductor photodetector device with an epitaxial shielding layer acting as a pnp bipolar transistor, where a trench is formed to short the substrate and epitaxial layers, preventing charge carrier drift by grounding generated carriers, eliminating the need for non-transparent coatings and reducing mechanical risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a non-transparent coating is applied to protect against backside illumination, then protection against unwanted light is improved, but the risk of mechanical damage to the fragile substrate increases
Solution Approach 1:
The patent replaces the mechanical approach of applying non-transparent coatings on the substrate backside with an electrical/electronic approach using an epitaxial shielding layer. This shielding layer is formed during the semiconductor fabrication process through epitaxial growth, creating a doped semiconductor layer that electrically screens the active photodetector region from unwanted backside illumination effects, thereby avoiding mechanical coating processes that could damage the fragile substrate.
Solution Approach 2:
The epitaxial shielding layer is formed during the semiconductor fabrication process, before the fragile thin substrate membrane is created and before any subsequent processing steps. This preliminary formation of the shielding structure eliminates the need for later deposition and patterning of non-transparent coatings on the finished device, preventing mechanical damage risks.
2Object-affected harmful factors
If additional process steps including non-transparent coating and patterning are used, then protection against unwanted illumination is improved, but the device complexity and fabrication difficulty increase
Solution Approach 1:
The patent merges the formation of the shielding layer with the standard semiconductor epitaxial growth process. The shielding layer is created as an integrated part of the semiconductor layer structure during epitaxial growth, combining the shielding function with the existing fabrication process rather than adding separate coating and patterning steps.
Solution Approach 2:
The epitaxial shielding layer serves multiple functions: it provides electrical screening from backside illumination, maintains compatibility with bipolar and CMOS processes, and is formed using standard semiconductor fabrication techniques. This multi-functionality reduces the need for additional specialized process steps.
3Object-affected harmful factors
If additional process steps including non-transparent coating and patterning are used, then protection against unwanted illumination is improved, but the manufacturing time and productivity decrease
Solution Approach 1:
The shielding layer is formed during the epitaxial growth process, which occurs early in the semiconductor fabrication sequence before the fragile thin substrate membrane is created and before subsequent processing steps. This eliminates the need for additional deposition, lithography, and patterning steps that would extend manufacturing time.
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
Effectively blocks undesired ambient light illumination, enhancing photodetector operation by preventing charge carrier diffusion and reducing fabrication risks through an integrated epitaxial structure.
Implementation Method 1
These layers act as a pnp bipolar transistor in a closed state
Implementation Method 2
These charge carriers drift partially toward the active area and thus cause distortions of the output signal
Implementation Method 3
unwanted backside illumination can create free carriers in the substrate
Implementation Method 4
An electric conductor is arranged in the trench to short the substrate, the epitaxial layer and the further epitaxial layer wherein a metallization in the trench forms the electric conductor
Data Source
AI summary
The semiconductor photodetector device comprises a substrate (1) of semiconductor material of a first type of electric conductivity, an epitaxial layer (2) of an opposite second type of electric conductivity, a further epitaxial layer (3) of the first type of electric conductivity and photodetectors (4). The epitaxial layer functions as a shielding layer for charge carriers (e-, h+) generated by radiation that is incident from a rear side opposite the photodetectors.