Abstract
Performance enhancement of the Surrey 400 keV ion implanter has been successfully implemented by upgrading the ion optics and installing a computerised telemetry system. Ion optics improvements include redesigning the mass analyser system and designing and installing a double electrostatic quadrupole lens. Telemetry enhancements entailed designing and installing an "intelligent" multiplexer system within the high voltage terminal and connecting this system to computers at earth potential using only two (Down- and Up-link) fibre optic lines. This new system solved the problem of frequent failures caused by current discharges. Other telemetry improvements included: upgrading all data acquisition and conversion head units especially those monitoring the critical parameters; standardising the design of voltage-to-frequency (V/F) head units and installing these as boxed modules; and, increasing the number of telemetry channels (from 15 to 22) to monitor the (original 15 plus the seven newly developed) sub-systems within the high voltage terminal. Upgrading of the machine optics and electronics not only remedied several of the shortcomings of the original machine, but also worked to produce an equipment with better operational characteristics. Currently, the implanter is capable of resolving ion species with masses up to 241 amu, which enables selected isotopes from across the periodic table to be ion implanted. Ray tracing simulations show that the machine now has a much-improved beam transport efficiency with a smaller and more symmetric beam spot at the target. Experiments using 100 keV Ar+ showed that the beam spot is 5mm x 3mm as against 35mm x 20mm in the old system. At the same time, the implanter has a reliable telemetry system which efficiently links together all of its sub-systems within the high voltage terminal. Performance measurements showed that there has been a significant improvement in channel accuracies (from 1% to at least 0.3%) as well as an increase in its measurement speed, being at least five times faster. The best indicator of implanter reliability, however, is that since the commissioning of both optics and electronics improvements in 1988, there has been no reported telemetry breakdown. This not only provides substantial savings in machine maintenance and repairs, but, also increased the productivity of the implanter. These improvements in hardware have made the machine more amenable to and worthy of computer control. To ensure tighter control and to enhance the reliability of the implanter, a distributed computer control system for the automatic control of the whole implanter has also been designed. Within this control configuration, three types of applications software have been developed, tested and subsequently implemented to control the Beam Generation and Analysis sub-systems. These Assembly code programmes provide the operator with real-time information which enable him to conduct fault diagnosis, parameter calibration, and, on a day to day basis, perform the setting up and control of the implanter. In the future, the software can be expanded and integrated into the final algorithm needed to implement the closed-loop computer control of the implanter. Full automation will further enhance the implanter's performance and reliability. In summary, major improvements have been made to the 400 kV high current implanter at the University of Surrey. This has greatly enhanced the purity of the beam at the target and the reliability of the machine. As a result, this project serves to enhance the quality of research in the field of ion implantation technology within the Department. It also contributes to ongoing research in the development of implanter telemetry and control systems.