Monocrystalline Silicon Wafer Gettering via Localized BMD Defects
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Solution Overview
Problem
Existing semiconductor wafers struggle to maintain high getter efficiency over long storage times, as they often lack sufficient BMD defects to effectively keep metallic impurities away from the surface.
Innovation Solution
A method involving the Czochralski method for pulling silicon single crystals, followed by specific thermal treatments in an NH3 and argon atmosphere to create a denuded zone (DZ) free of BMD defects and a region with high BMD defects, ensuring a high getter efficiency by controlling the V/G ratio and oxygen concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermal treatments are applied to produce BMD defects, then getter efficiency is improved initially, but getter efficiency deteriorates over long storage times due to impurity outdiffusion
Solution Approach 1:
The patent applies local quality by creating a non-uniform depth profile of BMD defects with specific local maxima at controlled depths (5-50 μm) from the front side. This spatial distribution ensures that gettering centers are positioned optimally to capture impurities diffusing from the surface, maintaining high getter efficiency (≥90%) even after long storage times without requiring additional thermal treatments.
Solution Approach 2:
The patent employs preliminary action by performing specific thermal treatments during the manufacturing process to pre-establish the desired BMD defect depth profile with local maxima. This preliminary configuration of gettering centers ensures that the wafer is pre-equipped to handle impurity outdiffusion during subsequent storage and processing, maintaining getter efficiency without needing corrective thermal treatments later.
2Reliability
If high density of BMD defects is created throughout the bulk, then gettering capability is improved, but formation of grown-in defects (COP defects, LPit defects) increases
Solution Approach 1:
The patent resolves this contradiction by applying local quality through a controlled depth profile of BMD defects featuring local maxima at specific depths (5-50 μm) rather than uniform distribution. This localized concentration of gettering centers provides effective gettering capability while avoiding supersaturation conditions that would lead to grown-in defects in other regions of the wafer bulk.
Solution Approach 2:
The patent uses parameter changes by precisely controlling the depth and density distribution of BMD defects through specific thermal treatment parameters (temperature, time, atmosphere). By adjusting these parameters to create local maxima at controlled depths, the patent achieves high gettering capability while maintaining defect-free regions, thus preventing the formation of harmful grown-in defects.
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 a DZ extending into the bulk and a region with BMD defects, maintaining a getter efficiency of at least 90% both immediately after production and after long storage, even under conditions that promote impurity outdiffusion.
Implementation Method 1
The Czochralski method comprises melting silicon in a crucible composed of quartz glass
Implementation Method 2
the single crystal grows at a phase boundary that has formed between the melt and the lower end of the seed crystal
Implementation Method 3
rapidly heating and cooling the substrate wafer in an atmosphere which substantially consists of NH3 and argon to a temperature of not less than 1165° C. and not more than 1180° C.
Implementation Method 4
slowly heating the rapidly heated and cooled substrate wafer from a temperature of not less than 500° C. and not more than 550° C. to a temperature of not less than 930° C. and not more than 1000° C.
Implementation Method 5
They form centers (gettering sites) which can bind, in particular, metallic impurities
Data Source
AI summary
The invention relates to a semiconductor wafer of monocrystalline silicon, and to a method for producing it. The semiconductor wafer has a zone, DZ, which is free of BMD defects and extends from a front side of the semiconductor wafer into the bulk of the semiconductor wafer, and a region having BMD defects which extends from the DZ further into the bulk of the semiconductor wafer. A silicon single crystal is pulled by the Czochralski method and processed to form a polished monocrystalline silicon substrate wafer. The substrate wafer is treated by rapidly heating and cooling the substrate wafer, slowly heating the rapidly heated and cooled substrate wafer, and keeping the substrate wafer at a specific temperature and over a specific period.