Backside Epitaxial Isolation With Hard Mask Gate Protection

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Solution Overview

Problem

As semiconductor technology advances, the continuous shrinkage of circuit cells leads to undesired merging of epitaxial regions in semiconductor devices, such as source/drain regions of field-effect transistors, necessitating effective methods to isolate these regions without adverse effects on the gate structures.

Innovation Solution

A semiconductor fabrication method involving the formation of hard mask features over gate structures on the front side of the wafer, followed by etching the epitaxial layer from the back side to isolate merged source/drain features, while protecting the gate structures from etching damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the epitaxial layer is etched from the back side to isolate merged source/drain features, then the merging of epitaxial regions is prevented, but the gate structures may be damaged by etching

Engineering Contradiction:

Improveisolation of source/drain regionsVSAvoidintegrity of gate structures

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

Hard mask features are formed over the gate structures on the front side of the wafer before the back-side etching process. This preliminary protective action ensures that when the epitaxial layer is etched from the back side, the gate structures are already shielded and cannot be damaged by the etchant

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The hard mask features serve as an intermediary protective layer between the etchant and the gate structures. This intermediary element allows the etching process to proceed on the back side while the hard mask absorbs or blocks the etching action, preventing it from reaching and damaging the gate structures on the front side

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If circuit cells are continuously shrunk to advance semiconductor technology, then device density and integration are improved, but undesired merging of epitaxial regions occurs

Engineering Contradiction:

Improvedevice densityVSAvoidseparation of epitaxial regions

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The solution segments the processing approach by performing etching from the back side of the wafer rather than from the front. This segmentation allows the epitaxial regions to be isolated while the gate structures remain protected on the front side, enabling continued circuit shrinkage without merging issues

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of etching from the conventional front side where gate structures are exposed, the method inverts the approach by etching from the back side of the wafer. This inversion allows the epitaxial regions to be separated while the gate structures are protected, enabling continued scaling without merging

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS12107011B2Method for fabricating a semiconductor device

Publication Date: 2024.10.01 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

During a front side process of a wafer, a hard mask layer is formed under a metal portion of a semiconductor device, and an epitaxial layer is deposited to form epitaxial portions of the semiconductor device. In a back side process of the wafer to cut the epitaxial layer, the metal portion is covered and protected by the hard mask layer from damages during etching of the epitaxial layer.