Semiconductor Island Thickness Control via Bottom Oxidation

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Solution Overview

Problem

Existing methods for forming semiconductor regions of different thicknesses over insulating layers face challenges such as topology issues during lithographic and polishing operations, and the SIMOX process damages the semiconductor layer and does not adequately reduce crystal defects for high-performance transistors.

Innovation Solution

A process involving forming a patterned oxidation-resistant layer over a semiconductor layer, patterning to create semiconductor islands, and exposing them to an oxygen-containing ambient to oxidize the bottom surfaces while maintaining the top surfaces at the same elevation, thereby achieving different thicknesses without damaging the semiconductor layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If selective thinning of semiconductor layer is performed using masks and etching operations, then different thicknesses of semiconductor regions are achieved, but topology issues occur causing problems with lithographic operations (depth of focus) and polishing operations

Engineering Contradiction:

Improvesemiconductor region thicknessVSAvoidlithographic and polishing operations

Core Design Contradiction:

Manufacturing precisionVSEase of operation

Solution Approach 1:

Instead of removing material from the top surface to create thickness variations (selective thinning), the invention oxidizes the bottom surface of the semiconductor layer to create thickness variations. This inversion of the approach allows thickness differentiation without creating top surface topology variations, thereby avoiding lithographic and polishing problems while achieving the desired different semiconductor region thicknesses

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention introduces an oxidation-resistant layer as an intermediary element between the semiconductor layer and the oxidizing environment. This layer selectively protects certain regions during thermal oxidation, enabling precise control over which portions of the semiconductor layer are thinned without requiring direct mask-etch operations on the semiconductor layer itself, thus avoiding topology issues

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If SIMOX process is used to form thinner channel regions, then different thicknesses of semiconductor regions are achieved, but the semiconductor layer is severely damaged and crystal defect level is not reduced low enough for high-performance transistors

Engineering Contradiction:

Improvesemiconductor region thicknessVSAvoidcrystal defect level

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The invention replaces the mechanical impact-based SIMOX process with a thermal oxidation process. Instead of using high-energy oxygen ion implantation that causes severe lattice damage, the invention uses controlled thermal diffusion of oxygen through an oxidation-resistant layer to selectively thin the semiconductor layer. This substitution achieves the same thickness differentiation goal while maintaining crystal integrity and producing low defect levels suitable for high-performance transistors

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the processing parameters from high-energy ion implantation (SIMOX) to controlled thermal oxidation parameters including temperature (800-1200°C), oxidation time, and oxidation-resistant layer thickness. These parameter changes enable selective thinning through controlled material removal at the bottom surface while preserving the crystal structure and minimizing defects in the remaining semiconductor layer

Inventive Principle:

Principle #35Parameter changes

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 process allows for the formation of semiconductor islands of varying thicknesses with top surfaces at the same elevation, reducing complications in lithographic and polishing operations and enabling the creation of high-performance transistors with tailored electrical parameters.

Implementation Method 1

exposing the patterned oxidation-resistant layer, the semiconductor layer, and the oxidation-resistant material to an oxygen-containing ambient causes a first portion of the semiconductor layer along the first surface to be oxidized

Methodology Applied

Scientific EffectOxidation: Oxidation

Data Source

PatentUS7419866B2Process of forming an electronic device including a semiconductor island over an insulating layer

Publication Date: 2008.09.02 NXP USA INC

AI summary

A process of forming an electronic device can include forming a patterned oxidation-resistant layer over a semiconductor layer that overlies a substrate, and patterning the semiconductor layer to form a semiconductor island. The semiconductor island includes a first surface and a second surface opposite the first surface, and the first surface lies closer to the substrate, as compared to the second surface. The process can also include forming an oxidation-resistant material along a side of the semiconductor island or selectively depositing a semiconductor material along a side of the semiconductor island. The process can further include exposing the patterned oxidation-resistant layer and the semiconductor island to an oxygen-containing ambient, wherein a first portion of the semiconductor island along the first surface is oxidized during exposing the patterned oxidation-resistant layer, the semiconductor island, and the oxidation-resistant material to an oxygen-containing ambient.