Halosilane-Assisted SiC PVT Growth for Boron Removal
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Solution Overview
Problem
The challenge is to reduce the unintentional boron content in silicon carbide (SiC) crystals to achieve semi-insulating properties with higher resistivity, as conventional growth methods struggle to eliminate boron impurities from graphite crucibles effectively, leading to suboptimal electrical parameters in SiC-based devices.
Innovation Solution
A dynamic reactive atmosphere is used during SiC sublimation growth, comprising an inert carrier gas and a halosilane gas, such as tetrahalosilane, which reacts with boron to form volatile boron halides that are removed through the permeable crucible wall, while hydrogen is added to minimize silicon loss and chemical attack on the crystal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional PVT growth methods are used, then SiC crystals can be grown, but unintentional boron impurities from graphite crucibles contaminate the crystals, reducing electrical resistivity
Solution Approach 1:
The patent extracts and removes boron impurities from the growth system by reacting them with halosilane gas to form volatile boron halides that are pumped away, thereby separating the harmful boron from the growing SiC crystal
Solution Approach 2:
The patent introduces halosilane gas as an intermediary substance that mediates between the boron impurity and the removal system. The halosilane reacts with boron to form volatile compounds that can be easily removed, thus facilitating the elimination of boron without directly contacting or damaging the SiC crystal
2Manufacturing precision
If halosilane gas is introduced to remove boron, then boron acceptor concentration is reduced, but silicon loss and chemical attack on crystal may increase
Solution Approach 1:
The patent carefully controls the concentration of halosilane gas in the reaction atmosphere and adjusts other atmospheric parameters (such as adding hydrogen) to optimize the removal of boron while minimizing silicon loss and chemical attack on the crystal
Solution Approach 2:
The patent uses a composite gas atmosphere consisting of halosilane combined with hydrogen and inert gases. This composite atmosphere provides multiple functions: halosilane reacts with boron, hydrogen prevents oxidation and reduces silicon volatility, and inert gases maintain atmospheric stability, thereby achieving boron removal while protecting the crystal
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 significantly reduces unintentional boron acceptor concentrations below 7·10^15 cm^-3, resulting in SiC crystals with resistivity above 10^7 Ohm·cm, enhancing the quality and electrical parameters of semi-insulating SiC substrates.
Implementation Method 1
a halosilane gas, such as tetrahalosilane, which reacts with boron to form volatile boron halides
Implementation Method 2
removed through the permeable crucible wall
Implementation Method 3
heating the interior of the growth crucible such that a temperature gradient forms between the source material and the seed crystal, the source material is heated to a sublimation temperature and the temperature gradient is sufficient to cause sublimated source material to be transported to the seed crystal
Implementation Method 4
a temperature gradient forms between the source material and the seed crystal
Implementation Method 5
hydrogen is added to minimize silicon loss and chemical attack on the crystal
Data Source
AI summary
In a physical vapor transport growth technique for silicon carbide a silicon carbide powder and a silicon carbide seed crystal are introduced into a physical vapor transport growth system and halosilane gas is introduced separately into the system. The source powder, the halosilane gas, and the seed crystal are heated in a manner that encourages physical vapor transport growth of silicon carbide on the seed crystal, as well as chemical transformations in the gas phase leading to reactions between halogen and chemical elements present in the growth system.