Aging Fiber Control System of HVE-400 Ion Implanter Gets Digital Upgrade

The HVE-400 ion implanter, a workhorse machine built in the 1980s by High Voltage Engineering Europa B.V. for doping semiconductor materials with boron and phosphorus, has received a thorough electronic overhaul. Researchers report in EPJ Techniques and Instrumentation that they replaced the machine’s aging, fiber-optic control and monitoring system with a modern distributed centralized design run entirely from a single industrial computer. The upgrade was not cosmetic: years of continuous operation had degraded the original hardware to the point where it could no longer work stably, creating potential safety hazards for operators and maintenance staff.

The engineering challenge at the heart of the machine is high-voltage isolation. In the HVE-400, the ion source sits at a potential of 30 kV extraction voltage plus 400 kV acceleration voltage, and the extraction, initial focusing, and analysis deflection magnets all sit on the 400 kV high-voltage platform. The control system, however, lives at ground potential. Every control signal sent up to the platform and every measurement fed back down must cross that enormous potential difference without creating a conductive path, so the original design carried all signals through optical fiber cables after amplitude-frequency conversion on one end and optical-electric conversion on the other. Light carries the information; no wire ever bridges the gap.

The signals involved are numerous. Control signals for the ion source include the filament, anode, source magnetic field, heating oven, and gas inlet flow, all sent as continuously adjustable 0-10 V DC voltages from the ground terminal. In the return direction, the platform reports filament voltage and current, anode voltage and current, source magnetic field current, and heating oven current, with voltages modulated into 0-10 V signals and currents into 0-60 mV signals. In the original scheme, each of these data points demanded its own independent fiber and conversion system, with values set by manual adjustment knobs and displayed on separate instrument panels, a decentralized single-point approach that multiplied hardware and failure points.

The new architecture, informed by a review of relevant literature, keeps multi-mode fiber for high-voltage isolation but replaces the point-to-point sprawl with modular components from Advantech. Two optical fiber communication loops divide the workload: one loop handles everything at the full 400 + 30 kV potential of the ion source, carrying control signals for the filament, anode, source magnetic field, heating furnace, and gas flow along with their measurement feedback; the other loop serves components at the 400 kV platform, transmitting control signals for the extraction voltage, analysis magnet, and focusing power supply together with their voltage, current, and status feedback.

The hardware chain is built from standard industrial modules. An industrial control computer with a graphical interface connects through two USB data conversion interfaces, and two ADAM-4541 photoelectric conversion modules translate between RS-485 electrical signals and optical signals at each end of the fibers. On the control side, ADAM-4024 four-channel digital-to-analog modules convert incoming RS-485 digital commands back into analog voltages for the controlled devices. On the monitoring side, ADAM-4017 eight-channel analog-to-digital modules collect analog voltage signals from platform instruments and convert them to RS-485 digital form. A relay module, the ADAM-4060, provides switch control used for the coarse adjustment of the analysis magnet. Because each module carries a preset address and channel number, a single fiber can now serve multiple devices, a decisive simplification over the one-signal-one-fiber past.

The control software, written in Delphi and running on Windows 7, concentrates all control and monitoring functions into two graphical panels, one for the ion source and one for the high-voltage platform, with Start, Init, Pause, and Exit buttons. Before starting, operators verify that software settings match the hardware, checking USB port numbers and setting port communication parameters to 9600, n, 8, 1. Module addresses and channel numbers can be reconfigured in the program, and linear calibration of each signal can be performed through a setup menu so that control values and measured feedback match the actual physical ranges. Saved parameters reload automatically at the next experiment run.

Safety and convenience features are built into the workflow. The Init command resets all control signal input values to zero, preventing the values of a previous experiment from being sent directly to the hardware when a new run begins, without disturbing the configuration settings. Once conditions are stable, the Pause button locks all control input boxes and adjustment arrows against accidental touches, and pressing Start restores normal operation. If the computer crashes, automatically saved parameters are reloaded on restart, allowing the implanter to continue running under the settings in effect before the failure. At the end of an experiment, control signals are restored to zero before Exit closes the session.

The most scientifically interesting improvement concerns how the machine selects the ions to implant. Ions extracted from the source contain a mixture of species, and the analyzing magnet bends ions of different mass-to-charge ratios through a 90-degree path into the acceleration tube. The mass-to-charge ratio follows the relation M/q = kB²/V, where M is the ion mass number, q the charge number, V the extraction voltage, B the magnetic field strength, and k a calibration coefficient. In the original implanter this calculation was performed in hardware by a mass number calculation box that collected the extraction voltage and the magnetic field measured by a HALL probe, computed M/q with two LH0094CD calculation modules and an adjustment potentiometer, and displayed the result on a digital tube after fiber transmission.

Experiments revealed that the circuit in that calculation box was faulty and its mass number display inaccurate, so the team abandoned the hardware result. Instead, the extraction voltage, magnetic field strength, and feedback magnet current are now transmitted directly to the computer, where the mass number is calculated in software in two independent ways: M1 from the magnetic field B, and M2 from the magnet current I, exploiting the proportionality between field and current in a uniform magnet. The calibration coefficients k1 and k2 can be determined at any time during operation using known ions such as 40Ar+ and 14N+, far more convenient than adjusting a potentiometer inside the high-voltage chamber. The charge state q can be set as an independent parameter in the interface, and displaying M directly is more intuitive than M/q.

The dual calculation proved its worth immediately. During testing, the HALL probe signal was indeed found to have problems, but because the software can compute the mass number from the magnet current alone, mass analysis continued even while the probe was unreliable. Using BF3 gas as the ion source, the team recorded a scanning mass spectrum plotting ion beam current, measured in the target chamber in microamps, against mass-to-charge ratio, and could identify ions of different types and charge states along with residual impurity ions in the gas. Once the HALL probe was repaired, the two mass number calculations showed good consistency after calibration. According to the authors, the upgraded system now offers digital operation, centralized control, high reliability, strong anti-interference capability, fast communication, and easy operation, qualities well suited to the strong magnetic, strong electric, and high-voltage environment of an ion implanter.

Subject of Research: Digital upgrade of the high-voltage-isolated fiber control and monitoring system of an HVE-400 ion implanter

Article Title: Update of high voltage isolation control and monitoring system for HVE-400 ion implanter

Article References: Li, C., Sun, X., Liu, Z., Guo, C., & Li, X. (2024). Update of high voltage isolation control and monitoring system for HVE-400 ion implanter. EPJ Techniques and Instrumentation, 11(1), Article 4. https://doi.org/10.1140/epjti/s40485-024-00110-2

Image Credits: AI Generated

DOI: 10.1140/epjti/s40485-024-00110-2

Keywords: ion implanter, high voltage isolation, fiber optics, control system, semiconductor doping, industrial automation, mass spectrometry, HALL probe, data acquisition, instrumentation upgrade, Update, high