Research On Diameter Control Method Of Silicon Single Crystal Under Constant Pulling Velocity Process

The rapid development of the integrated circuit and photovoltaic industry has put forward higher requirements on the important indicators of silicon singl e crystals,such as the size and micro-defects.At the same time,it has also challenged the growth control of silicon single crystals.At present,the Czochralski method(Cz method)is the main method for growing large-size,high-quality silicon single crystals.In the crystal growth process of the Cz method,the crystal diameter control is an important control target.In the traditional crystal growth control structure,due to the frequent change of the crystal pulling velocity,it is easy to cause the generation of micro defects in the crystal,while the constant pulling velocity crystal growth process makes It is possible to realize the growth of perfect silicon single crystal.Therefore,it is of great value and practical significance to study the crystal diameter control under the constant pulling velocity process.Cz method silicon single crystal growth is a dynamic time-varying process with complex physical changes,multi-field and multi-phase coupling,uncertain model,large lag and nonlinearity,and the mechanism model based on a large number of assumptions is difficult to be practically applied.In order to establish a stable and reliable crystal growth process model,this paper builds a hybrid model of the crystal growth process based on data and mechanisms,including data-driven thermal field temperature model and pulling dynamics model.Among them,based on the VMD-LSTM-ELM nonlinear integrated modeling method,the thermal field temperature model between the heater power and the thermal field temperature is constructed;The pulling dynamics model is based on the mathematical relationship between the thermal field temperature and the crystal diameter at the meniscus during crystal growth.Based on the mixed model of the crystal growth process established above,this paper proposes a crystal diameter data-driven control method under constant pulling velocity process,namely model-free adaptive sliding mode predictive control(MFASMPC).The purpose of introducing sliding mode control is to enhance the robust performance of the crystal diameter prediction controller.On this basis,a novel double closed-loop control scheme for the crystal diameter is designed.Taking the thermal field temperature as the intermediate variable,the v/G criterion is introduced into the outer-loop control(v is the pulling velocity and G is the axial temperature gradient at solid-liquid interface),in order to achieve the diameter control of silicon single crystals that meet the requirements of low defects.The results of simulation experiments based on industrial data show that the proposed thermal field temperature based on VMD-LSTM-ELM has excellent predictive performance and generalization ability,and can provide accurate thermal field temperature prediction values for the pulling dynamics model,ensuring the establishment of The mixed model of the crystal growth process meets the requirements of crystal diameter control.In addition,the crystal diameter MFASMPC algorithm based on the hybrid model of the crystal growth process can not only achieve accurate control of the desired diameter,but also effectively suppress the influence of external disturbances,and has excellent control performance and good robustness.At the same time,the designed double closed-loop control scheme can not only meet the crystal diameter control target requirements,but also ensure that the v/G of the entire control process is within a reasonable range.