Flowable Oxide and HARP Cap STI for Channel Stress

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Solution Overview

Problem

In the semiconductor industry, particularly for small, densely packed CMOS transistors, achieving adequate channel stress within Shallow Trench Isolation (STI) regions becomes challenging as geometries shrink, requiring higher stress to maintain performance, and existing materials like porous oxides are not well-suited for semiconductor processing.

Innovation Solution

A method involving the formation of STI regions with a trench filled by a flowable oxide and capped with a HARP material, where both the oxide and cap layers are thermally cycled to impart mechanical stress on the semiconductor body, combining to create a greater net stress on the channel region while avoiding the limitations of using flowable oxide alone.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If flowable oxide is used to fill STI trenches, then stress can be imparted to enhance carrier mobility, but etch attack issues arise during processing

Engineering Contradiction:

Improvecarrier mobility enhancementVSAvoidetch attack susceptibility

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The HARP material acts as an intermediary protective layer between the flowable oxide and the etching environment. By depositing HARP over the flowable oxide-filled STI trenches, the patent creates a barrier that protects the porous oxide from etch attack during subsequent processing steps, while still allowing the flowable oxide to provide its stress induction function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If only HARP material is used to provide stress, then process compatibility is improved, but the amount of stress imparted to the channel region is insufficient

Engineering Contradiction:

Improveprocess compatibilityVSAvoidchannel stress magnitude

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The patent combines flowable oxide and HARP materials in a composite STI structure where each material contributes its strengths. The flowable oxide provides high stress induction capability to enhance carrier mobility, while the HARP material ensures process compatibility and structural stability. This composite approach overcomes the limitation of using HARP alone by incorporating the high-stress flowable oxide.

Inventive Principle:

Principle #40Composite materials

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 enhances carrier mobility by imparting greater stress to the channel region, improving transistor performance, and is more manufacturable than relying solely on HARP material, while preventing etch attack issues that arise with flowable oxide use.

Implementation Method 1

both the oxide and cap layers are thermally cycled to impart mechanical stress on the semiconductor body

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS7615840B2Device performance improvement using flowfill as material for isolation structures

Publication Date: 2009.11.10 INFINEON TECHNOLOGIES AG

AI summary

A trench is formed in the surface of a provided semiconductor body. An oxide is deposited in the trench and a cap is deposited on the oxide, wherein the combination of the cap and the oxide impart a mechanical stress on the semiconductor body.