SiC Substrate Polytype Stacking for Low-Deformation Bonded Structures

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Solution Overview

Problem

The assembly of an active layer of polycrystalline SiC of 4H type and a support substrate of polycrystalline SiC creates interfaces with discontinuities in crystalline quality and crystal structure, leading to thermal deformation and loss of electrical conductivity.

Innovation Solution

A semiconductor structure is manufactured with a support substrate comprising a stack of a first layer of polycrystalline SiC mainly of polytype 3C and a second layer of polycrystalline SiC mainly of polytype 4H and/or 6H, and an active layer of single-crystal SiC bonded to the support substrate, thereby separating the interfaces of different crystalline qualities and polytypes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an active layer of single-crystal SiC is bonded to a support substrate of polycrystalline SiC, then the electrical conductivity is improved, but thermal deformation occurs due to discontinuities in crystal structure and thermal expansion coefficient

Engineering Contradiction:

Improveelectrical conductivityVSAvoidthermal deformation

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The support substrate is segmented into multiple layers with different polytypes (3C, 4H, 6H). The first layer (3C polytype) is positioned at the bonding interface with the active layer, while subsequent layers (4H and/or 6H polytypes) follow. This segmentation allows the interface to have matched thermal expansion coefficients (minimizing deformation) while maintaining good electrical conductivity through the doped 3C layer.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the support substrate are assigned different polytypes with specific properties. The 3C polytype layer at the interface provides optimal electrical conductivity and thermal match, while the 4H/6H polytype layers in the bulk provide mechanical strength and structural stability. Each layer is doped to exhibit good electrical conductivity, ensuring local optimization of both electrical and thermal properties.

Inventive Principle:

Principle #3Local quality

2Strength

If a bonding layer of doped silicon is used to bond the active layer to the support substrate, then the bonding strength is improved, but the manufacturing complexity and energy consumption increase due to high-temperature annealing requirements

Engineering Contradiction:

Improvebonding strengthVSAvoidmanufacturing process complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The invention extracts and eliminates the need for a separate bonding layer (such as doped silicon layers requiring high-temperature annealing at 1700-2000°C). Instead, the support substrate itself is designed with a 3C polytype layer that provides both bonding functionality and electrical conductivity, removing the extra manufacturing steps and reducing process complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The first layer of the support substrate (3C polytype) serves multiple functions simultaneously: it acts as the bonding interface to the active layer, provides good electrical conductivity through doping, and offers thermal expansion matching to prevent deformation. This multi-functionality eliminates the need for separate bonding layers and reduces manufacturing complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 minimizes the disadvantages related to the differences in crystalline quality and polytype at the interface, reducing thermal deformation and enhancing electrical conductivity, thus improving the performance and reliability of the semiconductor structure.

Implementation Method 1

Polycrystalline SiC substrates are commercially available in the 3C form. This is because this polytype can be obtained by chemical vapor deposition on a seed substrate

Methodology Applied

Scientific EffectChemical vapor deposition: Chemical Vapour Deposition

Implementation Method 2

the donor substrate is bonded to a support substrate of polycrystalline SiC, then the donor substrate is detached along the weakened zone so as to transfer the active layer onto the support substrate

Methodology Applied

Scientific EffectBonding: Welding

Data Source

PatentUS20250063784A1Process for the manufacture of a semiconductor structure comprising a polycrystalline silicon carbide substrate and an active layer of single-crystal silicon carbide

Publication Date: 2025.02.20 SOITEC SA

AI summary

A method of manufacturing a semiconductor structure, which includes a support substrate of polycrystalline silicon carbide and an active layer of single-crystal silicon carbide, involves:the formation of a support substrate including a stack of a first layer of polycrystalline SiC mainly of polytype 3C and of a second layer of polycrystalline SiC mainly of polytype 4H and/or 6H,the bonding of a donor substrate including an active layer of single-crystal SiC of polytype 4H or 6H to a face of polytype 4H and/or 6H of the support substrate, andthe transfer of the active layer onto the support substrate.