Monocrystalline Silicon Wafer Annealing for OSF-Resistant Strength
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Solution Overview
Problem
Existing semiconductor wafers made of monocrystalline silicon face challenges in maintaining mechanical robustness while avoiding the formation of OSF defects, which are promoted by high nitrogen concentrations.
Innovation Solution
A method involving the Czochralski growth of a single crystal silicon wafer, followed by specific rapid thermal annealing (RTA) treatments in controlled atmospheres to achieve a denuded zone and controlled nitrogen distribution, thereby enhancing mechanical robustness and preventing OSF defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nitrogen doping is performed during Czochralski crystal pulling to strengthen mechanical robustness, then the mechanical robustness of the semiconductor wafer is improved, but OSF defects (oxygen-induced stacking faults) are promoted in the interior of the wafer
Solution Approach 1:
The patent divides the wafer into two distinct regions with different nitrogen concentrations: an N+ region near the surface with high nitrogen concentration for mechanical strength, and an N region in the interior with low nitrogen concentration to avoid OSF defects. This spatial segmentation allows each region to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent applies local quality by creating a non-uniform nitrogen distribution where the nitrogen concentration varies with depth. The surface region receives nitrogen doping to enhance mechanical robustness, while the interior region maintains low nitrogen concentration to prevent OSF defect formation. This localized property assignment resolves the contradiction between strength and defect prevention.
2Length of stationary object
If RTA treatment is performed under argon atmosphere to create a denuded zone, then the DZ depth is increased, but the mechanical robustness of the semiconductor wafer is weakened due to oxygen loss
Solution Approach 1:
The patent performs nitrogen doping during crystal pulling before RTA treatment, establishing the nitrogen concentration profile in advance. This preliminary action ensures that when oxygen is subsequently removed during RTA to create the denuded zone, the mechanical robustness is already reinforced by the pre-established nitrogen distribution, particularly in the N+ region.
Solution Approach 2:
The patent changes the nitrogen concentration parameter through controlled doping during crystal pulling, creating a specific profile where nitrogen concentration is high near the surface and low in the interior. This parameter modification allows the wafer to withstand the mechanical weakening effect of oxygen loss during RTA while maintaining overall structural integrity.
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 produces semiconductor wafers with enhanced mechanical robustness and controlled bulk micro-defect formation, ensuring uniform BMD density and minimizing OSF defects across the wafer.
Implementation Method 1
growing a single crystal of silicon by the Czochralski (CZ) method
Implementation Method 2
axial temperature gradient G at the phase boundary between the single crystal and the melt
Implementation Method 3
phase boundary between the single crystal and the melt
Implementation Method 4
executing a first rapid thermal annealing (RTA) treatment of the semiconductor wafer at a first temperature
Implementation Method 5
oxygen under such conditions diffuses out in the vicinity of the surface
Implementation Method 6
the semiconductor wafer in the apparatus lies on a ring, and is rotated and exposed to thermal radiation from above
Data Source
AI summary
A semiconductor wafer of monocrystalline silicon is produced, in the following order: growing a single crystal of silicon by the CZ method; dividing off a wafer consisting completely of an N region, in which there are no agglomerates of silicon interstitials or vacancies having a diameter of more than 20 nm, and has an oxygen concentration of not less than 5.3×1017 atoms/cm3 and not more than 5.9×1017 atoms/cm3 and a nitrogen concentration of not more than 1.0×1012 atoms/cm3; executing a three separate rapid thermal annealing (RTA) treatments of the wafer at temperatures within different temperature ranges over different time periods in a different atmospheres of argon with and without ammonia.