Epitaxial Layer Segmentation for Fast Turn-Off in LIGBTs

Solution Overview

Problem

Integrated circuit devices with two carriers, such as LIGBTs, have a relatively long turn-off time due to minority carrier recombination, which limits their application and increases power consumption.

Innovation Solution

A multiple layer substrate is created by forming epitaxial layers with varying carrier concentrations over a device wafer, using chemical vapor deposition, to improve device performance by reducing turn-off time without compromising breakdown voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If a single layer substrate is used, then the device structure is simple, but the turn-off time is long due to minority carrier recombination

Engineering Contradiction:

Improveturn-off timeVSAvoidsubstrate structure

Core Design Contradiction:

Duration of action of moving objectVSDevice complexity

Solution Approach 1:

The substrate is divided into multiple epitaxial layers with different carrier concentrations (first epitaxial layer with higher carrier concentration, second epitaxial layer with lower carrier concentration). This segmentation allows different regions to perform different functions: the first layer provides fast recombination for reduced turn-off time, while the second layer maintains breakdown voltage, thereby resolving the contradiction between fast switching and device simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the substrate are given different local properties through varying carrier concentrations in different epitaxial layers. The first epitaxial layer has higher carrier concentration optimized for rapid minority carrier recombination, while the second epitaxial layer has lower carrier concentration optimized for electrical breakdown resistance. This local quality differentiation enables the substrate to simultaneously achieve fast turn-off time and maintain structural simplicity.

Inventive Principle:

Principle #3Local quality

2Duration of action of moving object

If the carrier concentration is increased to improve recombination efficiency, then the turn-off time is reduced, but the breakdown voltage may be compromised

Engineering Contradiction:

Improveturn-off timeVSAvoidbreakdown voltage

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

The substrate is divided into multiple epitaxial layers with different carrier concentrations (first epitaxial layer with higher carrier concentration, second epitaxial layer with lower carrier concentration). This segmentation allows different regions to perform different functions: the first layer provides fast recombination for reduced turn-off time, while the second layer maintains breakdown voltage, thereby resolving the contradiction between fast switching and device simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the substrate are given different local properties through varying carrier concentrations in different epitaxial layers. The first epitaxial layer has higher carrier concentration optimized for rapid minority carrier recombination, while the second epitaxial layer has lower carrier concentration optimized for electrical breakdown resistance. This local quality differentiation enables the substrate to simultaneously achieve fast turn-off time and maintain structural simplicity.

Inventive Principle:

Principle #3Local quality

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 higher carrier concentration in the epitaxial layers enhances recombination efficiency, redistributes the electric field, and reduces turn-off time while maintaining device breakdown voltage, thereby improving device performance.

Implementation Method 1

forming epitaxial layers with varying carrier concentrations over a device wafer, using chemical vapor deposition

Methodology Applied

Scientific EffectChemical vapor deposition: Chemical Vapour Deposition

Implementation Method 2

Two carrier devices have the recombination of minority carriers when the devices are turning off

Methodology Applied

Scientific EffectCarrier recombination:

Data Source

PatentUS10002761B2Method for forming a multiple layer epitaxial layer on a wafer

Publication Date: 2018.06.19 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A substrate for an integrated circuit includes a device wafer having a raw carrier concentration and an epitaxial layer disposed over the device wafer. The epitaxial layer has a first carrier concentration. The first carrier concentration is higher than the raw carrier concentration.