Epitaxial Wafer Defect Reduction via Oxygen Precipitation Control
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Solution Overview
Problem
The challenge is to manufacture epitaxial wafers with diameters of 300 mm to 450 mm that have a high intrinsic gettering effect and few epitaxial defects, while also maintaining high productivity and a wide process margin, as existing methods struggle with contamination and defect generation due to metal impurities and oxygen-induced stacking faults.
Innovation Solution
The method involves slowly cooling silicon single crystals through a temperature region of 800 to 600°C during the pulling step, followed by pre-annealing to increase the density of oxygen precipitate nuclei, which are then turned into bulk microdefects that act as gettering sites, thereby reducing epitaxial defects and enhancing the intrinsic gettering effect. This process sets the oxygen concentration within a specific range to prevent defect generation and ensures a high-quality epitaxial wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rapid cooling is applied to suppress oxygen precipitation nuclei, then epitaxial defects are reduced, but intrinsic gettering effect is insufficient
Solution Approach 1:
The patent applies preliminary action by performing a specific heat treatment process before epitaxial growth to intentionally generate and stabilize oxygen precipitation nuclei. The heat treatment conditions (temperature range, time, and atmosphere) are carefully controlled to create sufficient nuclei that will serve as gettering sites during subsequent processing, ensuring both defect reduction and effective intrinsic gettering
2Manufacturing precision
If high-temperature heat treatment is applied to form epitaxial layer, then epitaxial layer is formed, but oxygen precipitation nuclei are reduced and annihilated
Solution Approach 1:
The patent performs preliminary heat treatment to generate oxygen precipitation nuclei before the high-temperature epitaxial growth process. These pre-formed nuclei are stabilized through controlled cooling and atmosphere management, ensuring they survive the subsequent high-temperature epitaxial layer formation without being completely annihilated
Solution Approach 2:
The patent carefully controls parameters including heat treatment temperature (specific range), holding time, and atmosphere composition to optimize the balance between forming sufficient oxygen precipitation nuclei and maintaining conditions that allow these nuclei to survive subsequent high-temperature epitaxial processing
3Productivity
If device integration degree is increased, then device performance is improved, but metal impurity contamination increases
Solution Approach 1:
The patent converts the harmful effect of metal impurities into a beneficial outcome by utilizing intrinsic gettering. Oxygen precipitation nuclei are intentionally created and positioned to act as traps that actively capture and immobilize metal impurities that contaminate during high integration device processing, thereby protecting the active device regions from harmful contamination effects
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 results in epitaxial wafers with a high intrinsic gettering effect, reduced epitaxial defects, and improved productivity, as evidenced by a low defect density and increased BMD density, which effectively reduces leak current and enhances the lifetime of the wafers.
Implementation Method 1
the silicon single crystal is slowly cooled while passed through a temperature region of 800 to 600°C in 250 minutes or less and 180 minutes or more during the pulling step
Implementation Method 2
the grown silicon single crystal is subjected to pre-annealing prior to formation of an epitaxial layer on the surface of a silicon wafer, for 10 minutes to 4 hours at a predetermined temperature within a temperature region of 650 to 900°C in an inert gas atmosphere to thereby grow BMDs as a gettering sink
Data Source
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AI summary
A method for manufacturing an epitaxial wafer includes: a step of pulling a single crystal from a boron-doped silicon melt in a chamber based on a Czochralski process; and a step of forming an epitaxial layer on a surface of a silicon wafer sliced from the single crystal. The single crystal is allowed to grow while passed through a temperature region of 800 to 600°C in the chamber in 250 to 180 minutes during the pulling step. The grown single crystal has an oxygen concentration of 10 x 1017 to 12 x 1017 atoms/cm3 and a resistivity of 0.03 to 0.01 Ωcm. The silicon wafer is subjected to pre-annealing prior to the step of forming the epitaxial layer on the surface of the silicon wafer, for 10 minutes to 4 hours at a predetermined temperature within a temperature region of 650 to 900°C in an inert gas atmosphere. The method is to fabricate an epitaxial wafer that has a diameter of 300 mm or more, and that attains a high IG effect, and involves few epitaxial defects.