Backside-Illuminated SPAD Layout With Full Deep Trench Isolation

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Solution Overview

Problem

SPADs configured for front side illumination suffer from degraded photon-detection probability for long wavelengths due to metal routing blocking and optical crosstalk, leading to reduced sensitivity and spatial resolution issues, particularly in applications requiring high safety and accuracy like automotive systems.

Innovation Solution

Implementing a semiconductor device with backside illumination and a full deep trench isolation (FDTI) structure, which includes shallow and deep trench isolation elements at the substrate's surfaces to reduce optical crosstalk, combined with reflective layers and metal grid structures to enhance light absorption and sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If front side illumination configuration is used, then device structure is simplified, but photon-detection probability degrades for long wavelengths due to metal routing blocking and optical crosstalk

Engineering Contradiction:

Improvedevice structureVSAvoidphoton-detection probability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent inverts the illumination direction from front side to back side. By illuminating the SPAD array from the back surface, incident light bypasses the metal routing layers that would otherwise block and scatter long wavelength photons, eliminating the fundamental conflict between simplified structure and detection reliability.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent introduces a vertical dimension solution by implementing full deep trench isolation (FDTI) structures that extend through the substrate thickness. This three-dimensional isolation approach separates adjacent pixel regions in the vertical dimension, effectively blocking optical crosstalk while maintaining the benefits of backside illumination.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If front side illumination is used, then manufacturing process is simpler, but optical crosstalk between neighboring SPADs increases

Engineering Contradiction:

Improvemanufacturing processVSAvoidoptical crosstalk

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent segments the substrate into isolated pixel regions using FDTI structures. These trenches physically divide the continuous substrate into discrete, optically isolated units, preventing light from one pixel from interfering with adjacent pixels while maintaining a relatively simple manufacturing process.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The FDTI structures act as intermediary elements between neighboring SPAD pixels. The trench isolation material serves as an optical barrier that mediates the interaction between adjacent pixels, blocking crosstalk while allowing each pixel to function independently.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If metal routing layers are present on front surface, then electrical connectivity is achieved, but light absorption and sensitivity are reduced for long wavelengths

Engineering Contradiction:

Improveelectrical connectivityVSAvoidlight absorption and sensitivity

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

By inverting the illumination direction to backside illumination, the patent allows light to enter the substrate from the rear surface and travel through the active detection region before reaching the metal routing layers. This reversal ensures that photons are absorbed by the SPAD junction before encountering the metal, maximizing sensitivity while maintaining electrical connectivity.

Inventive Principle:

Principle #13The other way round (Inversion)

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 FDTI structure improves photon-detection probability by approximately 30% and achieves high sharpness with a modulation transfer function greater than 50% at Nyquist frequency, suitable for infrared light applications.

Implementation Method 1

a single photo-generated carrier can trigger an avalanche multiplication process

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

trigger an avalanche multiplication process that causes current at an output of a photon detection cell to rapidly reach a final value

Methodology Applied

Scientific EffectAvalanche Breakdown: Avalanche Breakdown

Implementation Method 3

combined with reflective layers and metal grid structures to enhance light absorption and sensitivity

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS12453192B2Single-photon avalanche diode semiconductor device

Publication Date: 2025.10.21 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor device may include a single-photon avalanche diode (SPAD) arranged for illumination at a back surface of a substrate. The semiconductor device may include a full deep trench isolation (FDTI) structure between the SPAD and a neighboring SPAD of the semiconductor device. The FDTI may be associated with isolating the SPAD from the neighboring SPAD. The FDTI structure may include a shallow trench isolation (STI) element at the back surface of the substrate. The FDTI structure may include a deep trench isolation (DTI) element at a front surface of the substrate.