Crystal Growth Front Thermal Gradient In-Situ Determination
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Solution Overview
Problem
Conventional Czochralski crystal growth processes struggle to accurately monitor and adjust thermal gradients at the crystal growth front in real-time, leading to defects and inconsistencies in semiconductor crystal production due to reliance on pre-determined gradients and post-pull analysis, which cannot correct for gradual changes or human errors during the process.
Innovation Solution
A method and apparatus that modulate the crystal pull speed with a periodic term to induce small diameter changes, allowing for real-time temperature gradient estimation using frequency selective algorithms, enabling in-situ adjustments of process parameters like the melt gap to maintain desired thermal gradients during crystal growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CZ process control methods are used with pre-determined temperature gradients, then the process setup is simple, but the manufacturing precision of crystal diameter and quality is degraded due to inability to correct gradual changes and setup errors
Solution Approach 1:
The patent applies periodic modulation to the crystal pull speed, introducing a small sinusoidal variation at frequency ω. This periodic action creates corresponding periodic variations in crystal diameter that can be detected and used to infer temperature gradient information in real-time, enabling active monitoring without adding complex measurement hardware.
Solution Approach 2:
The patent implements a feedback control system where the modulated diameter signal is processed to extract temperature gradient information, which then feeds back to adjust the pull speed or heating power. This closed-loop feedback enables real-time correction of temperature gradient deviations, improving crystal diameter control precision.
2Reliability
If real-time temperature gradient monitoring is implemented, then the manufacturing precision and quality control are improved, but the device complexity and measurement system requirements increase
Solution Approach 1:
The patent makes the crystal diameter itself serve as the temperature gradient indicator. By monitoring the naturally occurring diameter variations induced by pull speed modulation, the system uses the crystal's own geometric parameter as the sensor, eliminating the need for separate temperature measurement devices at the growth front.
Solution Approach 2:
The patent introduces diameter modulation as an intermediary that couples the controllable pull speed parameter with the difficult-to-measure temperature gradient parameter. The diameter variations act as a mediator that translates thermal gradient information into measurable geometric changes.
3Loss of time
If post-pull material analysis is used to adjust process parameters, then the measurement method is simple, but the loss of time and inability to correct defects during growth increases
Solution Approach 1:
The patent performs temperature gradient measurement and correction actions during the crystal growth process itself, rather than after completion. By continuously monitoring diameter variations and adjusting parameters in real-time, the system prevents defect formation before it occurs, eliminating the time loss associated with post-growth analysis and correction.
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
Enables real-time determination and control of temperature gradients, improving crystal diameter control, morphological stability, and reducing micro-defects by allowing for immediate adjustments during the growth process, thereby enhancing the quality and consistency of semiconductor crystals.
Implementation Method 1
Temperature gradients are important crystal growing process parameters that affect crystal diameter control, crystal morphological stability in heavily doped crystal growing, and bulk crystal micro-defects
Data Source
AI summary
A method and apparatus for growing a semiconductor crystal include pulling the semiconductor crystal from melt at a pull speed and modulating the pull speed by combining a periodic pull speed with an average speed. The modulation of the pull speed allows in-situ determination of characteristic temperature gradients in the melt and in the crystal during crystal formation. The temperature gradients may be used to control relevant process parameters that affect morphological stability or intrinsic material properties in the finished crystal such as for instance the target pull speed of the crystal or the melt gap, which determines the thermal gradient in the crystal during growth.