Czochralski Crystal Diameter Control via Heat Shield Gap
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Solution Overview
Problem
Conventional crystal pulling methods in the Czochralski process often result in non-optimal crystal homogeneity and diameter consistency due to fluctuations in melting convection and melt level changes, leading to incomplete defect annihilation and diameter fluctuations, which are critical issues for semiconductor production.
Innovation Solution
A control algorithm that maintains a constant crystal pulling rate by adjusting the annular gap height between the crystal and the heat shield, using the existing crucible heater's irradiation to regulate heat input, while using closed-loop control circuits to compensate for melting convection and melt level changes, thereby optimizing the temperature gradient and defect recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the crystal pulling rate is adjusted to regulate crystal diameter, then the crystal diameter consistency is improved, but the crystal homogeneity deteriorates due to changing temperature gradient ratio
Solution Approach 1:
The control system is segmented into two independent control loops: one controlling crystal diameter via heat shield position, and another controlling crystal homogeneity via pulling rate. This separation allows each parameter to be optimized independently without compromising the other.
Solution Approach 2:
The heat shield position serves as an intermediary control variable that affects crystal diameter without directly impacting the temperature gradient ratio. By using the heat shield as a mediator, the system can adjust diameter while maintaining optimal conditions for defect annihilation.
2Stability of the object's composition
If additional heating elements are added to regulate temperature gradient, then the crystal homogeneity is improved, but the device complexity increases
Solution Approach 1:
The existing crucible heater is made multi-functional by controlling not only the melt temperature but also the temperature gradient in the crystal through coordinated control with the heat shield position. This eliminates the need for additional heating elements while achieving the same effect.
Solution Approach 2:
The system uses its existing components (crucible heater and heat shield) in a coordinated manner to achieve temperature gradient control, rather than relying on external or additional heating elements. The crucible heater serves both melting and gradient control functions.
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 ensures a homogeneous and largely defect-free crystal with a consistent diameter, reducing production rejects by maintaining a uniform temperature gradient and crystal pulling rate, even in the presence of thermal fluctuations, without the need for additional heating elements.
Implementation Method 1
using the existing crucible heater's irradiation to regulate heat input
Implementation Method 2
By varying the annular gap height, the inward radiation of heat onto the crystal can be regulated
Implementation Method 3
a crystal is pulled from a hot melt, with the atoms of the melt taking their place at the lower end face of the crystal in a lattice structure
Implementation Method 4
the vertical temperature gradient in the crystal
Data Source
AI summary
A method for pulling a cylindrical crystal from a melt by a crystal pulling unit includes measuring an actual value of a diameter of the crystal at a surface of the melt, comparing the actual value with a setpoint value for the diameter of the crystal, and setting a height of the annular gap as a function of a deviation between the actual value and the setpoint value using a first controller which has a first readjustment time.