Epitaxial Wafer Surface Roughness Control via Oxynitride Removal

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Solution Overview

Problem

Existing methods for producing epitaxially coated semiconductor wafers using rapid thermal anneal (RTA) treatments face issues with surface roughness and the formation of defects like localized light scatterers (LLS) due to nitriding effects, which impair the quality of the epitaxial layer.

Innovation Solution

A method involving a two-stage precipitation-thermal treatment and an RTA process in an argon and ammonia atmosphere, followed by removal of the oxynitride layer and polishing, to control the denuded zone depth and BMD nuclei density, while minimizing surface roughness and defect formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If RTA treatment is applied to produce BMD nuclei in the bulk, then the density of BMD nuclei increases, but the surface roughness of the epitaxial layer increases and LLS defects are formed

Engineering Contradiction:

Improvedensity of BMD nucleiVSAvoidsurface roughness of epitaxial layer

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent segments the thermal treatment process into two distinct stages: a first RTA treatment at 900-1100°C for 1-30 minutes to generate BMD nuclei, followed by a second RTA treatment at 1150-1200°C for 1-30 minutes to reduce surface roughness and eliminate LLS defects. This segmentation allows each stage to optimize for its specific purpose without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs periodic thermal action with two distinct temperature phases. The first phase (900-1100°C) periodically generates BMD nuclei, while the second phase (1150-1200°C) periodically reduces surface roughness. This periodic action at different temperature levels enables sequential achievement of both high BMD nuclei density and low surface roughness.

Inventive Principle:

Principle #19Periodic action

2Quantity of substance

If RTA treatment is applied to increase BMD nuclei density, then more vacancies are injected to support nucleation, but the thermal loading causes slip in the crystal lattice and increases surface roughness

Engineering Contradiction:

Improvedensity of BMD nucleiVSAvoidcrystal lattice stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The patent segments the thermal treatment into two stages with different temperature ranges and durations. The first stage (900-1100°C, 1-30 minutes) is optimized for vacancy injection and BMD nuclei formation, while the second stage (1150-1200°C, 1-30 minutes) is optimized for crystal lattice stabilization and surface roughness reduction, preventing slip.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the thermal parameters (temperature and time) between two distinct treatment stages. By adjusting temperature from 900-1100°C to 1150-1200°C and controlling duration for each stage, the process optimizes vacancy injection during the first stage and crystal lattice stabilization during the second stage, resolving the contradiction between nucleation and stability.

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

The method achieves a polished epitaxial layer with reduced surface roughness and controlled BMD nuclei distribution, maintaining high peak density while minimizing defects and surface irregularities, thereby enhancing the quality of the semiconductor wafer.

Implementation Method 1

A thermal treatment by means of momentary rapid heating and cooling is also called RTA treatment (rapid thermal anneal)

Methodology Applied

Scientific EffectRapid thermal anneal (RTA):

Implementation Method 2

momentary rapid heating and cooling of the semiconductor wafer in an atmosphere having a nitriding effect injects vacancies

Methodology Applied

Scientific EffectVacancy injection:

Implementation Method 3

A two-stage precipitation-thermal treatment and an RTA process

Methodology Applied

Scientific EffectPrecipitation: Precipitation

Implementation Method 4

an epitaxial layer composed of silicon having a polished surface

Methodology Applied

Scientific EffectMechanical polishing:

Data Source

PatentUS10483128B2Epitaxially coated semiconductor wafer, and method for producing an epitaxially coated semiconductor wafer

Publication Date: 2019.11.19 SILTRONIC AG

AI summary

Epitaxial wafers with a high concentration of BMD nuclei or developed BMDs just below a denuded zone, and having low surface roughness, are produced by forming an oxynitride layer on a purposefully oxidized epitaxial layer by a short RTA treatment in a nitriding atmosphere, removing the oxynitride layer, and then polishing the epitaxial surface.