Avalanche Photodiode Diffusion Junction for Edge Breakdown Suppression

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Solution Overview

Problem

Avalanche photodiodes (APDs) face challenges in suppressing edge breakdown due to uneven electric fields, which is difficult to control reproducibly using existing methods like stepped diffusion profiles and floating guard rings, especially in thinner multiplication regions for high bandwidth applications.

Innovation Solution

The method involves selective area growth (SAG) with an in-situ etchant to create a tapered surface profile, reducing diffusion depth towards the outer edge and modifying the electric field, and a single diffusion process to form a diffusion junction, which suppresses edge breakdown without the need for precise calibration of diffusion profiles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If stepped diffusion profile and floating guard rings are used to suppress edge breakdown, then edge breakdown is suppressed, but manufacturing precision and reproducibility deteriorate due to difficulty in controlling p-n junction depth offset

Engineering Contradiction:

Improveedge breakdown suppressionVSAvoidp-n junction depth offset control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

A sacrificial layer is introduced as an intermediary element between the substrate and the active device structure. This sacrificial layer serves as a depth reference that automatically defines the p-n junction depth offset, eliminating the need for complex calibration processes. The sacrificial layer is removed after serving its purpose, leaving a precisely controlled depth offset without requiring multiple diffusion calibrations or precise etch depth control.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If double diffusion process is used to achieve stepped diffusion profile, then edge breakdown suppression is improved, but device complexity and manufacturing steps increase

Engineering Contradiction:

Improveedge breakdown suppressionVSAvoiddiffusion process steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention combines the functions of multiple diffusion steps into a single diffusion process. By using a sacrificial layer to pre-establish the depth reference, a single diffusion step can achieve the same edge breakdown suppression effect that previously required two separate diffusion steps with complex calibration. This merging reduces process complexity while maintaining reliability.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The sacrificial layer is deposited and patterned before the diffusion process, performing the preliminary action of defining the depth offset. This preliminary structuring allows the subsequent diffusion to proceed without complex real-time control, as the depth reference is already established. The sacrificial layer performs its function in advance and is then removed.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If wet chemical recess etching is used to create depth offset, then edge breakdown suppression is improved, but manufacturing precision deteriorates due to difficulty in controlling etch depth

Engineering Contradiction:

Improveedge breakdown suppressionVSAvoidetch depth control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The sacrificial layer is a temporary, disposable structure that is deposited, used to define the depth offset, and then removed. This disposable layer provides precise depth control during the process without requiring complex etch depth control, as its thickness can be precisely controlled during deposition. After serving its purpose as the depth reference, it is removed, leaving no residual impact on the final device.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

This approach effectively suppresses edge breakdown in APDs, maintaining high sensitivity and reliability across various APD designs, including those with thinner multiplication regions, by gradually reducing the electric field and preventing premature breakdown at device corners.

Implementation Method 1

performing selective area growth (SAG) with in-situ etchant on the low-doped region to grow a SAG structure

Methodology Applied

Scientific EffectIn-situ etching:

Implementation Method 2

diffusing through the SAG structure to form a second high-doped region in the low-doped region

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 3

APDs are a type of photodetector that provides internal gain through avalanche multiplication

Methodology Applied

Scientific EffectAvalanche multiplication: Avalanche Breakdown

Data Source

PatentUS11837681B2Method of fabricating an avalanche photodiode employing single diffusion

Publication Date: 2023.12.05 NAT RES COUNCIL OF CANADA

AI summary

An avalanche photodiode with a diffused junction and the method for its fabrication are disclosed. The method comprising forming, on a substrate, a first high-doped region and a low-doped region; performing selective area growth (SAG) with in-situ etchant on the low-doped region to grow a SAG structure; and diffusing through the SAG structure to form a second high-doped region in the low-doped region.