Silicon Single Crystal Dopant Supply Unit for Concentration Control

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Solution Overview

Problem

The existing CZ method for producing silicon single crystals faces challenges in precisely controlling the sublimation speed of dopants like arsenic and phosphorus, leading to variations in dopant concentration and resistance values, and an increased likelihood of crystal breakage during the pulling process, especially when high concentrations are used.

Innovation Solution

A dopant supply unit with a controlled heating mechanism that adjusts the sublimation speed of sublimable dopants, ensuring optimal introduction efficiency and concentration, and a blowing method that introduces dopants to the melt without submerging the tube, stabilizing the growth process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the dopant accommodation chamber is positioned higher above the melt to avoid interfering with the pulling mechanism, then the pulling process is smoother, but the sublimation speed of the dopant decreases and introduction efficiency is reduced

Engineering Contradiction:

Improvepulling process smoothnessVSAvoiddopant introduction efficiency

Core Design Contradiction:

Ease of operationVSProductivity

Solution Approach 1:

A carrier gas (inert gas such as argon) is introduced as an intermediary to transport the sublimed dopant from the accommodation chamber to the melt. The carrier gas flows through the supplying tube and carries the dopant vapor to the melt surface, enabling effective dopant introduction even when the accommodation chamber is positioned higher and does not directly contact the melt.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the dopant concentration in the melt is increased to produce low-resistivity N++ type silicon single crystals, then the electrical property is improved, but the likelihood of crystal breakage during pulling increases

Engineering Contradiction:

Improveelectrical property (low resistivity)VSAvoidcrystal integrity (resistance to breakage)

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The dopant is sublimed and introduced to the melt in advance before the crystal pulling process begins. By pre-doping the melt with the required concentration of dopant, the crystal grows with uniform dopant distribution throughout the pulling process, avoiding local concentration variations that could cause stress and breakage during pulling.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If radiant heat from the melt is used to sublime the dopant, then the process is simpler, but the sublimation speed varies and dopant concentration control becomes imprecise

Engineering Contradiction:

Improveheating system simplicityVSAvoiddopant concentration control

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The heating system is replaced from a mechanical/radiant heat approach to a controlled thermal field approach. Instead of relying on radiant heat from the melt, an independent heating system with controlled thermal fields is used to sublime the dopant at precise, controlled rates, enabling accurate control of dopant concentration in the melt.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 allows for precise control of dopant concentration and resistance values, reducing crystal breakage and ensuring stable growth of low-resistivity N++ type silicon single crystals by optimizing sublimation speed and introduction methods.

Implementation Method 1

heating the dopant in the accommodation chamber by radiant heat radiated from the melt to evaporate

Methodology Applied

Scientific EffectSublimation: Sublimation

Implementation Method 2

introducing, from the accommodation chamber to the melt, the dopant that has becomes the gas as a result of the evaporation

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentUS10294583B2Producing method and apparatus of silicon single crystal, and silicon single crystal ingot

Publication Date: 2019.05.21 SUMCO TECHXIV CORP

AI summary

The sublimation speed of dopant can be precisely controlled without being influenced by a change over time of intra-furnace thermal environment. A dopant supply unit equipped with an accommodation chamber and a supply tube is provided. A sublimable dopant is accommodated. Upon sublimation of the dopant within the accommodation chamber, the sublimed dopant is introduced into a melt. The dopant within the accommodation chamber of the dopant supply unit is heated. The amount of heating by means of heating means is controlled so as to sublime the dopant at a desired sublimation speed. The dopant is supplied to the melt so that the dopant concentration until the first half of a straight body portion of the silicon single crystal is in the state of low concentration or non-addition. After the first half of the straight body portion of the silicon single crystal is formed, the dopant is supplied to the melt so that every portion of the crystal is in the state where the dopant is added to a desired high concentration.