Czochralski Silicon Ingot Defect Control via v/G Ratio
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Solution Overview
Problem
The Czochralski process for growing single crystal silicon ingots often results in agglomerated intrinsic point defects, such as vacancies and self-interstitials, which can severely impact the quality and yield of semiconductor materials, particularly due to the formation of defects like D-defects, A-defects, and oxygen clusters, which are challenging to quantify and control.
Innovation Solution
A process is developed to control the growth velocity and axial temperature gradient during the Czochralski method, ensuring the ratio of v/G varies radially by less than ±30% over a significant portion of the ingot, and specific cooling rates are applied to minimize the formation of agglomerated intrinsic point defects, creating an axially symmetric region with reduced or eliminated edge rings of defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Czochralski process is used to grow single crystal silicon ingots, then single crystal material is produced, but agglomerated intrinsic point defects (vacancies and self-interstitials) form and severely impact material quality
Solution Approach 1:
The patent applies parameter changes by precisely controlling the ratio of crystal pull rate (v) to axial temperature gradient (G) to maintain it within a critical range during growth. This parameter control prevents excessive supersaturation of point defects, thereby suppressing the formation of agglomerated defects while still producing high-quality single crystal silicon material.
Solution Approach 2:
The patent implements preliminary action by controlling the temperature field and growth conditions during the crystal growth process to prevent the formation of agglomerated defects before they can develop. By maintaining appropriate thermal gradients and pull rates throughout growth, the patent preemptively avoids defect formation rather than attempting to correct it afterward.
2Reliability
If the crystal pull rate and temperature gradient are controlled to reduce point defect agglomerates, then defect formation is minimized, but the process complexity increases
Solution Approach 1:
The patent employs feedback control by continuously monitoring and adjusting the crystal pull rate and temperature gradient to maintain their ratio within the critical range. This feedback mechanism ensures that defect formation is minimized while providing a systematic approach to managing process complexity through controlled parameter adjustment rather than uncontrolled variation.
3Productivity
If rapid cooling is applied to solidify the crystal, then growth time is reduced, but agglomerated point defects increase due to supersaturation
Solution Approach 1:
The patent applies dynamics by implementing a variable cooling rate strategy that adapts to different stages of crystal growth. During initial growth, slower cooling rates are used to prevent supersaturation and defect formation. As growth progresses and the crystal structure stabilizes, the cooling rate can be increased to improve productivity without compromising quality.
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 single crystal silicon ingots and wafers with significantly reduced agglomerated intrinsic point defects, enhancing the quality and yield of semiconductor materials by minimizing defect formation and improving the radial uniformity of defect distribution.
Implementation Method 1
the temperature field in the vicinity of the melt/crystal interface drives the recombination of the point defects providing driving forces for their diffusion from the melt/crystal interface—where they exist at their respective equilibrium concentrations—into the crystal bulk
Implementation Method 2
the temperature field in the vicinity of the melt/crystal interface drives the recombination of the point defects providing driving forces for their diffusion
Implementation Method 3
polycrystalline silicon ('polysilicon') is charged to a crucible and melted, a seed crystal is brought into contact with the molten silicon, and a single crystal is grown by slow extraction
Implementation Method 4
a single crystal is grown by slow extraction
Data Source
AI summary
The present invention relates to a single crystal silicon ingot or wafer wherein the lateral incorporation effect of intrinsic point defects has been manipulated such that the formation of agglomerated intrinsic point defects and/or oxygen precipitate clusters in a ring extending radially inward from about the lateral surface of the ingot segment is limited.