Control Of Crystal Growth Processes Research Articles

Numerical Modeling and Control of the Dynamic Single Silicon Crystal Growth Process

A new control strategy combing the Finite Element Method (FEM) with the control method is proposed to study the control of crystal growth process in this article. In the proposed control strategy, the crystal diameter control loop and the crystal temperature control loop are designed respectively to meet the requirements on crystal diameter and crystal temperature distribution. In the crystal diameter control loop, a bio-heuristic model based PID controller is designed to control crystal diameter. In the crystal temperature control loop, considering the undetectable characteristic of temperature distribution inside crystal, the control of crystal temperature distribution is transformed into the control of a key monitoring point in crystal and the constraint of crystal temperature gradient, and a model reference adaptive temperature controller is designed to achieve the control of the monitoring point temperature. Simulation results show that the crystal diameter and the temperature of the monitoring point are controlled well. Furthermore, the internal temperature distribution inside crystal is constrained within a reasonable range, avoiding the excessive thermal stress and dislocation defects. The proposed control strategy solves the problem of the traditional crystal growth system which cannot control crystal temperature, providing a new way for growing high-quality single silicon crystal.

レーザー光による結晶化現象の制御

レーザー光による結晶化現象の制御

APPLICATION OF MATHEMATICAL MODEL FOR SUPPORT OF CRYSTAL GROWTH PROCESS IN MULTIZONE THERMAL INSTALLATIONS

A system for control of crystal growth process in the multizone thermal installation with an integrated mathematical model is developed. Experimental information on both temperature distribution and powers of the heating elements as well as calculation data about the form of crystallization front have been used as input information for the control system. Consecutive correction of controller setpoints of multizone thermal installation during crystal growth process based on calculated data is aiming at deviation reduction between crystal growth rate and container moving rate.

OPTICAL MONITORING OF CZOCHRALSKI CRYSTALS GROWTH FROM HIGH-TEMPERATURE MELT

Problems of optical monitoring of melt level and diameter of a crystal growing from high-temperature melt by Czochralski technique are considered. Investigations results performed in Institute of Automatics and Electrometry of the Siberian Branch of the Russian Academy of Science at vision system construction to control the automatic growth installations are presented. Such system consists of laser triangulation sensor used to measure the melt level in a crucible and also of digital vision system to control the diameter of growing crystal. Metrological problems important to control of crystal growth process caused by nonstationarity and variations of melt surface curvature and also by parallax of crystallization zone image formed by optical projection system are analyzed. Joint measurements of melt level andcrystal diameter are discussed allowing to eliminate a systematic measurement error caused by melt rotation.

Modelling control of crystal growth processes

The goal of this paper is to describe an efficient cost-effective mathematical modelfor controlling the Czochralski crystal growth process. We first consider the governing equations for a class of MHD problems. We then choose the use of an externally applied magnetic field as a control mechanism. We examine theoretical and numerical results applicable to the optimal control of evolutionary magnetically conducted flows. The appropriate state equations are derived. First-order necessary conditions are examined. Next, we develop numerical methods for solving the necessary conditions of optimality, and alternative cost-efficient algorithms are discussed. Finally, these results are used to design a control strategy for the Czochralski crystal growth process.

Investigations into growth of semiconductor crystals with high microhomogeneity of properties under microgravity simulating conditions

The updated version of the Bridgman method ensuring a reduced level of thermal convection in a melt under terrestrial conditions is presented. Automated control of crystal growth process has been realized for this method. Crystallization took place at programmable heat removal from a melt. Striation-free germanium single crystals, doped with gallium, with high microhomogeneity of properties were grown. Effect of vibrations, applied to a melt, on microhomogeneity of dopant distribution in a crystal was investigated. There were made theoretical calculations of heat and mass transfer processes in a melt for different values of the radial temperature gradient on the upper boundary with a fixed vertical temperature gradient in a melt. Level of vibrational actions capable of bringing about formation of growth striation in single crystals grown under space conditions has been estimated on the basis of ground-based experiments.

Optimal control of crystal growth processes

This work focuses on the optimal control of two typical processes in the context of industrial crystal growth. First, the annealing of bulk GaAs crystals is considered and an optimal control problem is solved in order to find optimised heating profiles for the furnace. A reduced order model for the annealing furnace has been developed in order to speed up the optimisation algorithm. As a second application, our control algorithm is used to optimise a VGF-process for growing GaAs crystals: the growth rate of the GaAs crystal is maximised under side conditions for the resulting thermal stress.

Control of Crystal Growth Processes by Block-Copolymers

In crystallization processes from solution, parameters like crystal habit, grain size, grain size distribution, concentration and type of impurities/dopants can be controlled by addition of admixtures. Amphipolar diblock-copolymers (DBCP's) are shown to have unique effects on crystallization processes from solution. With polyethylene oxide)-block−poly(methacrylic acid) (PEO-b-PMAA) as admixture in concentrations in the 100 ppm range, control of nucleation density and crystallization of calcium carbonate (CaCO3) is possible. Crystal growth perpendicular to {hk0}-faces of calcite is retarded, whereas the growth perpendicular to {104}-faces remains undisturbed. In the case of growth of zincite (ZnO), the grain size distribution is narrowed and crystal growth in [001]-direction is slowed down. To explain the special effect of the DBCP's on crystal growth, a simple model is proposed.

Aspects Refering to the Control of Crystal Growth Process by Electrically Modifying the Interface Tension

Aspects Refering to the Control of Crystal Growth Process by Electrically Modifying the Interface Tension