Freestanding Epitaxial Layer Release by Thermal Pillar Breakage

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing methods for producing substrates for electric or electronic components face challenges in achieving freestanding epitaxial layers without mechanical or chemical post-processing, particularly due to thermal stress-induced bowing and cracking during cooling, especially when using different materials with varying thermal expansion coefficients.

Innovation Solution

A method involving patterning a substrate into an array of pillars, followed by high-temperature epitaxial growth, and utilizing the differential thermal contraction of the substrate and epitaxial layer to induce pillar breakage during cooling, allowing the epitaxial layer to separate spontaneously from the substrate without mechanical or chemical intervention.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If heteroepitaxy is performed on planar substrates to achieve thick epitaxial layers, then film thickness increases and quality improves, but thermal stress causes extended cracking and bowing

Engineering Contradiction:

Improvefilm thicknessVSAvoidcrack-free continuous film

Core Design Contradiction:

Length of moving objectVSReliability

Solution Approach 1:

The substrate surface is segmented into an array of micrometric pillars with pitch between 1-10 micrometers. This segmentation allows the epitaxial layer to grow continuously across the pillar array while the substrate is divided into discrete support points, enabling thick film growth without extended cracking by localizing thermal stress at pillar interfaces rather than across the entire film-substrate interface.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the substrate is patterned in micrometric pillar arrays to accommodate thermal misfit, then bowing and cracking are reduced, but mechanical or chemical post-processing is required to achieve freestanding layers

Engineering Contradiction:

Improvereduced bowing and no cracksVSAvoidpost-processing steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The aspect ratio of the pillars (height to lateral dimension) is quantitatively tailored to specific parameter ranges that enable spontaneous pillar breakage during cooling. By optimizing pillar dimensions and spacing, the thermal stress accumulated during cooling naturally exceeds the mechanical strength of the pillars, causing them to break and release the epitaxial layer as freestanding structures without requiring additional mechanical or chemical post-processing steps.

Inventive Principle:

Principle #35Parameter changes

3Length of moving object

If high aspect ratio pillars are used to support thick epitaxial layers, then thermal stress is accommodated, but pillar breakage during cooling prevents freestanding layer formation

Engineering Contradiction:

Improveepitaxial layer thicknessVSAvoidspontaneous separation

Core Design Contradiction:

Length of moving objectVSEase of operation

Solution Approach 1:

The thermal stress that normally causes cracking and bowing is converted into a beneficial force by designing pillars with optimized aspect ratios. During cooling, the accumulated thermal stress causes the pillars to break at controlled locations, and this breakage mechanism spontaneously releases the epitaxial layer from the substrate, achieving both thick layer formation and automatic freestanding structure creation without additional processing.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 enables the production of freestanding epitaxial layers with reduced bowing and cracking, suitable for use in electric, electronic, or optoelectronic components, by leveraging the thermal stress-induced breaking of pillars to achieve a self-separation process.

Implementation Method 1

the cooling induces a breaking of the pillars (110) due to a differential shrinkage of the epitaxial layer (200) and of the substrate (100)

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Data Source

PatentUS12581872B2Method for producing a freestanding and stress-free epitaxial layer starting from a disposable substrate patterened in etched pillar array

Publication Date: 2026.03.17 PILEGROWTH TECH SRL

AI summary

The method provides for the growth of an epitaxial layer (200) made of a first semiconductor material on a substrate (100) made of a second semiconductor material; the materials are different and have different CTEs; the method comprises the steps of: A) patterning the substrate (100) by an etching process so to form an array of pillars (110), the pillars (110) being laterally spaced from each other and having a top section (112) larger than a bottom section (114) and/or intermediate sections (116), B) depositing the second semiconductor material on top of the pillars (110) at a growth temperature so to form an epitaxial layer (200) generated by vertical and lateral growth, and C) inducing breaking of the pillars (110) by cooling the substrate (100) and the epitaxial layer (200) below the growth temperature.