Multilayer SiC Seed Structure for Low-Stress PVT Growth

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Solution Overview

Problem

The use of monocrystalline seeds in conventional PVT processes for growing SiC single-crystals is hindered by intrinsic stresses, leading to reduced quality and increased dislocation densities in the grown crystals, which do not meet the demands of high-quality semiconductor substrates.

Innovation Solution

A multilayer seed composed of multiple monocrystalline layers is designed to counteract internal stresses by selecting layers with complementary stress parameters, such as bow, warp, and thickness, and orienting them to cancel out stress effects, resulting in a virtually stress-free growth surface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single monocrystalline seed is used in conventional PVT processes, then the crystal growth process is simple and straightforward, but intrinsic stresses in the seed lead to reduced crystal quality and increased dislocation densities

Engineering Contradiction:

Improvecrystal qualityVSAvoidseed structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The seed is divided into multiple monocrystalline layers (first seed layer, second seed layer, etc.) with different stress characteristics. Each layer is selected to have specific bow and warp parameters that complement each other, allowing the layers to counteract intrinsic stresses when stacked together, thereby improving crystal quality without requiring a completely new seed design approach

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent creates a composite seed structure by stacking multiple monocrystalline layers with different stress profiles. This composite approach combines layers with positive bow values, negative bow values, and various warp characteristics to achieve a net stress-free state, effectively using composite material principles to resolve the stress-quality contradiction

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If multiple monocrystalline layers are stacked to counteract internal stresses, then crystal quality and reduced dislocation densities are achieved, but the seed selection and assembly process becomes more complex

Engineering Contradiction:

Improvesubstrate qualityVSAvoidseed production ease

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent systematically varies key parameters of individual seed layers including bow values (positive and negative), warp values, and thicknesses. By selecting layers with specific parameter combinations and stacking them in predetermined sequences, the design achieves stress compensation while providing a standardized methodology for seed production that balances precision requirements with manufacturing feasibility

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If monocrystalline seeds with intrinsic stresses are used, then the seed structure is simple and easy to handle, but the grown single-crystals exhibit high dislocation densities and reduced quality

Engineering Contradiction:

Improveseed handling easeVSAvoidintrinsic stress effects

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful intrinsic stresses present in individual monocrystalline layers into a beneficial effect by strategically stacking layers with opposing stress characteristics. The bow and warp stresses that would normally degrade crystal quality are instead used to counterbalance each other, transforming individual layer defects into a collective stress-free structure that improves overall crystal quality

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

The multilayer seed enables the growth of high-quality SiC single-crystals with reduced dislocation densities and improved substrate quality by mitigating the negative impact of intrinsic stresses, aligning with the demands of the semiconductor industry.

Implementation Method 1

each of the at least two seed layers is adapted to counter-act the respective internal stresses from each other

Methodology Applied

Scientific EffectStress counteraction:

Implementation Method 2

The basic principle of a PVT process lies in sublimating a suitable source material into a gas phase and depositing the species (e.g. SiC, Si2C, SiC2) present in the gas phase

Methodology Applied

Scientific EffectSublimation: Sublimation

Implementation Method 3

bulk SiC single-crystals are grown using physical vapor transport (PVT) processes

Methodology Applied

Scientific EffectPhysical vapor transport: Physical Vapour Deposition

Data Source

PatentUS20250313988A1Multilayer Seed for Single-Crystal Growth, Method of Producing a Multilayer Seed, Use of the Multilayer Seed in a PVT Process for Growing a Single-Crystal and PVT Process Using the Same

Publication Date: 2025.10.09 SICRYSTAL GMBH

AI summary

The present invention provides a multilayer seed which is designed such as to offer a virtually unstressed surface onto which a single-crystal can grow without the negative impact of the internal stress carried by monocrystalline seeds, in particular at the high temperatures conventionally used in sublimation processes. The multilayer seed for growing a single-crystal comprise at least two seed layers, wherein each of the at least two seed layers is a monocrystalline layer characterized by one or more parameters associated with a respective degree of internal stress. The one or more parameters are selected such that the at least two seed layers are adapted to counter-act the respective internal stresses from each other.