Solid-Phase Boric Acid Doping in Single-Crystal Silicon Growth

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Solution Overview

Problem

Existing methods for producing single crystal silicon ingots face challenges in maintaining consistent resistivity due to dopant segregation, particularly with boron and phosphorous, leading to deviations from customer specifications and potential type-changes in the ingot.

Innovation Solution

A method using solid-phase boric acid as a dopant source to produce a boron-containing gas that is introduced into the silicon melt during ingot growth, counteracting phosphorous accumulation and maintaining resistivity through controlled doping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If phosphorous is added as a dopant to achieve target resistivity, then initial resistivity specification is met, but phosphorous accumulates in the melt causing resistivity to decrease and fall out of specifications

Engineering Contradiction:

Improveresistivity specification complianceVSAvoidresistivity consistency

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

Boron is added to the melt before ingot growth begins. This preliminary doping action establishes a boron reservoir in the melt that will continuously supply boron to the growing ingot, compensating for phosphorous accumulation throughout the growth process and maintaining resistivity specifications.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Boron is introduced as a counter-dopant to oppose the harmful effect of phosphorous accumulation. Since phosphorous has a low segregation coefficient (0.35) and accumulates in the melt, boron with a high segregation coefficient (0.8) is added in advance to compensate for this accumulation and prevent resistivity from falling out of specifications.

Inventive Principle:

Principle #9Preliminary anti-action

2Manufacturing precision

If boron is added to compensate for phosphorous accumulation, then resistivity can be maintained, but dopant segregation causes boron to be taken up more readily leading to type-changes

Engineering Contradiction:

Improveresistivity controlVSAvoidingot type consistency

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The doping process is made dynamic by continuously adjusting boron addition based on real-time monitoring of ingot resistivity and phosphorous concentration in the melt. This dynamic control allows the system to respond to changing conditions and maintain both resistivity specifications and type consistency throughout the growth process.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

A feedback control system monitors phosphorous accumulation and boron uptake during ingot growth, and adjusts dopant addition rates accordingly. This feedback mechanism prevents over-doping with boron that could cause type-changes while ensuring sufficient boron is added to maintain resistivity specifications.

Inventive Principle:

Principle #23Feedback

3Ease of operation

If solid-phase boric acid is used as dopant source, then dopant can be easily introduced and controlled, but additional equipment and process steps are required

Engineering Contradiction:

Improvedopant introduction easeVSAvoiddoping system complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

Boric acid serves as an intermediary dopant source that simplifies the doping process. Instead of directly adding elemental boron or complex boron compounds, boric acid is used as a stable, easily handled solid that decomposes in the melt to release boron, providing controlled doping while maintaining ease of operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The dopant is introduced in a different physical state (solid-phase boric acid) and chemical form than traditional dopants. This parameter change allows for easier handling and more controlled release of boron into the melt, simplifying the doping operation while requiring only moderate additional equipment.

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 ensures a larger portion of the ingot remains within resistivity specifications and prevents type-changes, utilizing a dopant source that is readily available and easy to use, with improved control over doping rates and reduced contamination risks.

Implementation Method 1

A boron-containing gas is produced from the solid-phase boric acid

Methodology Applied

Scientific EffectPhase change: Phase Change

Implementation Method 2

The boron-containing gas is contacted with a surface of the melt to cause boron to enter the melt as a dopant

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Data Source

PatentUS12435440B2Methods for producing a single crystal silicon ingot using boric acid as a dopant

Publication Date: 2025.10.07 GLOBALWAFERS CO LTD

AI summary

Methods for producing a single crystal silicon ingot are disclosed. The ingot is doped with boron using solid-phase boric acid as the source of boron. Boric acid may be used to counter-dope the ingot during ingot growth. Ingot puller apparatus that use a solid-phase dopant are also disclosed. The solid-phase dopant may be disposed in a receptacle that is moved closer to the surface of the melt or a vaporization unit may be used to produce a dopant gas from the solid-phase dopant.