Czochralski Silicon Neck Pulling to Reduce Center Dislocations
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Solution Overview
Problem
Existing methods for pulling low-resistivity single silicon crystals using the Czochralski process fail to effectively eliminate dislocations, particularly in highly doped silicon crystals, leading to center defects.
Innovation Solution
A three-stage neck pulling process is employed, with a rapid tapering of the first section, a controlled slow pull of the second section, and an increased velocity in the third section, accompanied by adjustments in heating power and magnetic field application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a neck is pulled at a constant low pulling velocity to eliminate dislocations, then dislocation elimination is improved, but productivity deteriorates due to excessively long processing time
Solution Approach 1:
The neck pulling process is divided into three distinct sections with different pulling velocities: first section at velocity v1 for initial dislocation elimination, second section at reduced velocity v2 (<0.2 mm/min) for prolonged dislocation elimination without excessive time loss, and third section at increased velocity v3 (>2 mm/min) to restore productivity. This segmentation allows each section to serve a specific function in eliminating dislocations while minimizing overall processing time.
Solution Approach 2:
The pulling velocity is varied periodically through the three sections rather than maintaining a constant velocity. The velocity profile oscillates between low (second section) and high (third section) values, creating a periodic action pattern that achieves dislocation elimination during low-velocity phases while recovering productivity during high-velocity phases.
2Reliability
If the pulling velocity is reduced to eliminate center dislocations in highly doped crystals, then dislocation elimination is improved, but the processing time increases significantly
Solution Approach 1:
The neck is divided into three sections where only the second section uses the time-consuming low velocity (v2 < 0.2 mm/min) necessary for center dislocation elimination. The first and third sections use higher velocities, so the overall time loss is limited to one segment rather than the entire neck pulling process.
Solution Approach 2:
The low pulling velocity is applied locally only to the second section of the neck where it is most needed for eliminating center dislocations, rather than applying it uniformly to the entire neck. This localized application minimizes the time penalty while achieving the desired dislocation elimination effect.
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
Significantly reduces the frequency of dislocations to below 1%, ensuring high-quality monocrystalline silicon production.
Implementation Method 1
The Czochralski process comprises the pulling of a single crystal from a melt which is contained within a crucible
Implementation Method 2
the concentration of germanium in the single crystal ought to be linked, within certain limits, to the concentration of boron
Data Source
AI summary
Single silicon crystals having a resistivity of ≤20 mΩcm are pulled by the Czochralski process from a melt, by a method of pulling a first section of a neck at a first velocity whereby the diameter of a first section of the neck, with respect to the diameter of a seed crystal, tapers at a rate of ≤0.3 mm per mm neck length to a diameter of not more than 5 mm;pulling a second section of the neck at a pulling velocity of <0.2 mm/min for not less than 3 min, without the diameter increasing to more than 5.5 mm; andpulling a third section of the neck at a third pulling velocity of >2 mm/min.