Stepped Epitaxial Structures for Uniform BSI Image Sensor Surfaces

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Solution Overview

Problem

The challenge of controlling non-uniformity in the top surface profiles of epitaxial structures during the formation of BSI image sensors, particularly due to high temperature processes, which can lead to air gaps and damage from processing chemicals.

Innovation Solution

Formation of epitaxial structures in trenches with stepped or tapered sidewall profiles to prevent lateral expansion during high temperature processes, using methods like dry etching and selective epitaxial growth to maintain surface uniformity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high temperature processes are used to form epitaxial structures, then the epitaxial growth can proceed effectively, but non-uniformity in top surface profiles occurs leading to air gaps and damage

Engineering Contradiction:

Improveepitaxial structure qualityVSAvoidsurface profile uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by forming trenches with controlled sidewall profiles (stepped or tapered) before performing the high-temperature epitaxial growth. This pre-established geometric constraint prevents lateral expansion during the thermal process, ensuring uniform top surfaces while allowing effective epitaxial growth to occur.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the geometric parameters of the trench structure by creating stepped or tapered sidewall profiles instead of vertical walls. This parameter modification alters how the epitaxial material grows laterally, constraining expansion and maintaining surface uniformity throughout the high-temperature process.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If vertical sidewall trenches are used, then fabrication is simpler, but material laterally expands during high temperature processing causing non-uniformity

Engineering Contradiction:

Improvetrench fabrication simplicityVSAvoidmaterial dimensional stability

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The patent introduces asymmetry in the trench sidewall geometry by creating stepped or tapered profiles rather than symmetric vertical walls. This asymmetric design inherently restrains lateral material flow during thermal processing, maintaining dimensional stability while remaining manufacturable through standard semiconductor fabrication techniques.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The trench profile is predetermined and formed before epitaxial growth, establishing geometric constraints that will control material behavior during subsequent high-temperature processing. This preliminary structural design prevents lateral expansion without requiring complex real-time control during growth.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If high temperature processing is applied, then epitaxial growth is achieved, but processing chemicals can damage the structure through air gaps

Engineering Contradiction:

Improveepitaxial structure formationVSAvoidchemical damage from air gaps

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent establishes a chemically resistant trench profile (stepped or tapered) before air gaps can form during processing. This pre-configured geometric structure prevents the formation of air gaps that would otherwise allow processing chemicals to penetrate and damage the epitaxial material.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The constrained trench geometry acts as a protective structure that prevents harmful chemical ingress by eliminating air gap formation. This built-in protective design cushions the epitaxial structure against chemical damage during high-temperature processing.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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

Prevents material expansion and minimizes damage from processing chemicals, ensuring consistent interfaces and improved performance of BSI image sensors.

Implementation Method 1

using methods like dry etching and selective epitaxial growth

Methodology Applied

Scientific EffectDry etching:

Implementation Method 2

using methods like dry etching and selective epitaxial growth to maintain surface uniformity

Methodology Applied

Scientific EffectSelective epitaxial growth: Epitaxy

Data Source

PatentUS20250366231A1Epitaxial structures in image sensors

Publication Date: 2025.11.27 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor device with an image sensor and a method of fabricating the same are disclosed. The semiconductor device includes a substrate, a pixel region with a pixel structure, an isolation region with an isolation structure disposed adjacent to the pixel region, and a contact pad region with a pad structure disposed adjacent to the isolation region. The pixel structure includes an epitaxial structure, which includes an embedded portion with a stepped structure disposed in the substrate and a protruding portion extending above a top surface of the substrate. The pixel structure further includes a capping layer disposed on the protruding portion.