Boron-Doped Silicon Substrate Defect Reduction via v/G Control
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Solution Overview
Problem
Epitaxial wafers often suffer from surface defects in the silicon substrate that propagate into the epitaxial layer, leading to grown-in defects such as epi-stacking faults and hillocks, which worsen with increasing epitaxial layer thickness, necessitating methods to reduce these nuclei.
Innovation Solution
A method involving boron-doped silicon substrates where the growth velocity and axial temperature gradient are controlled to maintain a specific ratio (v/G) and dwell time within a controlled temperature range to minimize defects, with boron concentrations between 2.8×10^18 and 8.0×10^18 atoms/cm^3, ensuring reduced grown-in nuclei for epitaxial defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thicker epitaxial layer is deposited to cover substrate defects, then the coverage of defects is improved, but the size of epitaxial defects is enlarged due to growth along crystallographic planes
Solution Approach 1:
The patent changes the chemical composition parameter by introducing boron doping at specific concentrations (2.8×10^18 to 8.0×10^18 atoms/cm³) to modify the growth behavior of silicon atoms during epitaxial deposition. This parameter change suppresses the formation of large defects by altering the crystallization kinetics, allowing thicker layers to be grown without proportionally increasing defect sizes
Solution Approach 2:
The patent utilizes control of phase transition conditions during epitaxial growth by maintaining specific temperature ranges and growth velocities. By controlling the solidification phase transition of silicon from liquid to crystal, the method minimizes defect formation while achieving adequate coverage of substrate defects
2Productivity
If the growth velocity is increased to improve productivity, then the production rate is improved, but the ratio v/G increases leading to more grown-in nuclei
Solution Approach 1:
The patent introduces boron doping as a chemical parameter change that decouples the relationship between growth velocity and defect formation. The boron atoms modify the growth mechanism such that higher velocities can be achieved without proportionally increasing the v/G ratio, thereby maintaining low defect densities while improving productivity
Solution Approach 2:
Boron atoms act as an intermediary that mediates between the growth velocity parameter and the defect formation process. The dopant atoms interfere with the normal growth kinetics in a controlled manner, allowing faster growth rates while suppressing the formation of grown-in nuclei through modified crystal lattice incorporation
3Manufacturing precision
If the axial temperature gradient is increased to improve crystal quality, then the manufacturing precision is improved, but the growth velocity must be reduced maintaining low productivity
Solution Approach 1:
The patent changes the chemical composition parameter by adding boron doping, which allows the system to operate at higher growth velocities even with increased temperature gradients. The dopant modifies the thermal and kinetic properties of the growing crystal, enabling simultaneous achievement of high crystal quality and productivity
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 controlled boron doping and growth parameters significantly reduce the number of epitaxial defects, resulting in substrates suitable for epitaxial growth with minimal or no grown-in defects, enhancing the quality of epitaxial layers.
Implementation Method 1
A silicon seed crystal is contacted with the doped silicon melt. The silicon seed crystal is withdrawn to grow a single crystal silicon ingot
Implementation Method 2
an axial temperature gradient, G, is controlled during the growth of the segment
Data Source
AI summary
Methods for preparing single crystal silicon substrates for epitaxial growth are disclosed. The methods may involve control of the (i) a growth velocity, v, and/or (ii) an axial temperature gradient, G, during the growth of an ingot segment such that v/G is less than a critical v/G and/or is less than a value of v/G that depends on the boron concentration of the ingot. Methods for preparing epitaxial wafers are also disclosed.