|
GaN MOCVD equipment is the most difficult expensive equipment in the blu-ray high-brightness LED production line. There are many devices need to be controlled, such as temperature control device, MFCs, pressure controllers, servo motors, pumps, dewpoint meter, purification and so on, so the control system is very complex. At present, GaN MOCVD control technology in our country is poor, in fact, it is the technical bottleneck in the chain of the semiconductor lighting industry, and has been the biggest obstacle of Chinese semiconductor lighting project.According to full investigation on foreign control technology of MOCVD equipment, a process control system based on computer is self-designed. The overall control strategy uses "host computer+PLC" two-layer control pattern: the host computer complete the tasks such as data management, data edition and graphical display; and communicates with PLC by the Ethernet card. PLC monitor and control all the field mounted instrument. Aiming at several key control problems in MOCVD, such as MO source transport control, disturbance-free gas switching, closed-loop pressure control and so on, some design programs are proposed.This article focuses on the issue of reactor temperature control, according to some heat transfer and control principles, pointes out some reasons to make this system difficult to control:(1) Control object is time-varying, temperature-varying, lagging in time; (2) The detected temperature is not equal to the temperature need to control. In view of these, mathematical models are built for the object in different temperature ranges using experiment approach, methods to revise temperature and assign heating power using experiments are proposed, fuzzy PID control method is proposed to use in this system. Simulation and experimental results show that fuzzy PID is superior to the traditional PID control in MOCVD temperature control, and can meet the control requirements.The article also introduced the development of hardware and software systems, including hardware configuration and selection, program designing, user interface development and so on. After more than two years of designing and manufacturing, more than 6 months of on-site commissioning and process testing, GaN MOCVD studied in this article has successfully produced GaN blu-ray LED chips, the technical indexes, process indexes and control function meet the contract requirements, the project has received good reputation from the expert group.
|