Thermal Stress Cleaving Single Crystal Substrate

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Solution Overview

Problem

The existing methods for slicing single crystal semiconductor wafers from boules result in significant material waste due to the saw blade kerf, leading to increased costs.

Innovation Solution

A method involving a parent single crystal substrate with a stress-mandrel having a higher thermal expansion coefficient than the substrate, bonded to the substrate and cooled to induce thermal stress, facilitating cleavage parallel to the major surface plane, thereby reducing material waste.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of substance

If sawing is used to slice single crystal semiconductor wafers from boules, then wafers can be obtained, but significant material waste occurs due to saw blade kerf

Engineering Contradiction:

Improvematerial wasteVSAvoidslicing process

Core Design Contradiction:

Loss of substanceVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical sawing system with a thermal stress-based cleaving system. By bonding a stress-mandrel with higher thermal expansion coefficient to the substrate and cooling the assembly, thermal stress induces cleavage along desired planes without mechanical contact, eliminating kerf waste entirely

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent utilizes differential thermal expansion between the stress-mandrel and substrate. The stress-mandrel has a higher coefficient of thermal expansion than the substrate, so upon cooling, the mandrel contracts more, generating tensile stress in the substrate that drives cleavage along low-index crystallographic planes

Inventive Principle:

Principle #37Thermal expansion

2Loss of substance

If cleaving is used to split substrates, then material waste is reduced, but the process requires precise control of stress and temperature

Engineering Contradiction:

Improvekerf lossVSAvoidcleavage control

Core Design Contradiction:

Loss of substanceVSManufacturing precision

Solution Approach 1:

The stress-mandrel serves as an intermediary that converts controlled thermal contraction into precise mechanical stress for cleavage. By controlling the cooling process and mandrel properties, the cleavage location and orientation are precisely determined without requiring complex force application mechanisms

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent controls cleavage by changing temperature parameters. By controlling the cooling rate and final temperature, the thermal stress magnitude is controlled, allowing precise initiation and propagation of cleavage fronts along desired crystallographic planes

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 method effectively reduces material waste by allowing the substrate to cleave into thinner wafers without the need for sawing, thereby minimizing kerf loss and associated costs, while enabling the formation of semiconductor devices like solar cells on both the major and cleaved surfaces.

Implementation Method 1

The stress-mandrel has a stress-mandrel coefficient of thermal expansion that is higher than the parent single crystal coefficient of thermal expansion. The method further includes bonding the stress-mandrel to the major surface and then cooling the parent single crystal substrate and the stress-mandrel sufficiently to initiate the cleaving

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10589445B1Method of cleaving a single crystal substrate parallel to its active planar surface and method of using the cleaved daughter substrate

Publication Date: 2020.03.17 SEMIVATION LLC

AI summary

A method of cleaving off a daughter single crystal substrate from a parent single crystal substrate includes providing a stress-mandrel and the parent a single crystal substrate. The parent single crystal substrate has a major surface and an edge surface that intersects the major surface. The major surface extends along a major surface plane. The stress-mandrel has a stress-mandrel coefficient of thermal expansion that is higher than the parent single crystal coefficient of thermal expansion. The method includes bonding the stress-mandrel to the major surface, and cooling the parent single crystal substrate and the stress-mandrel. The cooling of the parent single crystal substrate bonded to the stress-mandrel provides a thermal stress in the parent single crystal substrate sufficient to cleave the parent single crystal substrate. The cleaving extends substantially along a plane parallel to the plane of the major surface. In one embodiment the cleaved daughter substrate was used to make a photovoltaic cell.