Design The Control System Of LPCVD (Low Pressure Chemical Vapor Deposition) Equipment

This thesis describes an imported LPCVD(low pressure chemical vapor deposition) equipment whose type is ACS514. It consists of three sets of furnace tube system. The equipment uses ammonia, SiH2Cl2, TEOS and SiH4 etc special gas. The LPCVD equipment failure rate was high. The statistics of the equipment fault revealed that fault about control system of this equipment was most high and it was the 38% of total failure. In order to reduce the fault rate of the equipment, improve the stability and reliability of the equipment, the control system of this equipment was needed to redesign.The design of this thesis was done on the ACS514 equipment. Most parts of the control system of this equipment were removed, and only a few parts were retained. Reserved parts comprised a heating trigger parts and some intelligent control units. The ACS514 equipment circuits were analyzed, and the input and output of the equipment were been counted. The PLC modules were selected, the input and output points of PLC modules were defined, and some pins connection diagrams about PLC modules were drawed. And the control modes of LPCVD equipment were determined. In order to simplify the communication between microcomputer and PLC, some variables of the V storage area were defined. PLC was used to control the temperature, the PLC PID instruction wizard was used to generate the PID temperature control procedures, and the PID parameters self-tuning function was used to determine the PID parameters. The trapezoid diagram and sequence control method were used to design the PLC user programs, including the subroutine and semi automatic sequence control program. The Lab VIEW software was used to design of the equipment control software in microcomputer. NI 485 communication card was used to Connect the microcomputer and the PLC, and the card is PCI interface communication card with isolation function.In this thesis, when designing the hardware of a LPCVD equipment control system, it was designed of the thermocouple signal conditioning interface board, according to the temperature control requirements. In the thermal couple interface circuit board diagram, it was used of the 5B47 isolation and signal conditioning of R type thermocouple signal. The output of the 5B47 signal was connected to an amplification adjustable amplifier, then was connected to a differential element SN7518 which converted the signal into a differential signal. In this design, the signal has an better anti-interference ability. Vacuum degree gradual change often appeared in vacuum chamber of a LPCVD equipment, it was caused by that the wall of the vacuum tube has been deposited on some reaction product, which caused vacuum tube tapering. In this thesis, it was installed of a pressure controller in the control system design. This measure improved the furnace tube vacuum stability when processing, and improved the uniformity of the batches prodcuts, then improved the quality of the products. It was added of the pressure sensor for furnace tube, which strengthened the protection of boat motor control board, then reduced the LPCVD equipment failure rate.The equipment had runned for six months time in control of the new control system, and the equipment failure rate was obviously reduced. The equipment failure rate reduced from an average of 5 times a month to 2 times a month. The maintenance cost of equipment reduced from a monthly average of 6000 yuan to a monthly average of 3000 yuan. It reduced from ± 1.2 to℃ ± 1 ℃ of the equipment furnace tube constant temperature zone temperature fluctuation range.