R.D. Rathmell

Production MeV ion implanters for energies from 200 keV to 4 MeV

Abstract Two ion implantation systems using electrostatic accelerators to produce MeV beams for production processing of wafers will be discussed. One system, the Model MV-T30, using a 1 MV tandem accelerator was first installed in May 1983. Subsequent models of this system have been upgraded to provide an order of magnitude higher current than the first unit. The changes responsible for this improved performance will be discussed. The second system, Model MV-H20, using a 2 MV single ended accelerator is still under development and its performance to date will be reviewed.

A high stability accelerator for ion beam diagnostics in a tokamak

Abstract A 2 MV single ended accelerator has been developed for probing a Tokamak plasma with a heavy ion beam. This high current Pelletron is designed to deliver up to 200 μA of 2 MeV Tl+ for plasma diagnostics. Stringent energy stability requirements have led to the development of an improved accelerator voltage control system incorporating a capacitive tank liner. The special design features and performance of this system will be discussed.

Improved voltage performance of the Oak Ridge 25URC tandem accelerator

Abstract Installation of compressed geometry acceleration tubes and associated changes in the corona voltage grading system have resulted in significant improvement in voltage performance of the Oak Ridge 25URC tandem accelerator. Details of the final phase of this work and initial tests on the modified accelerator are provided.

Developments in small electrostatic accelerators (invited)

Today’s application for small accelerators are spin‐off technologies of nuclear physics research. Many of these applications have gained such wide utility that accelerators are developed specifically for them. This paper will review the new generation of small electrostatic accelerators which are being built as diagnostic and production tools.

Tests of compressed geometry acceleration tubes in the Oak Ridge 25URC tandem accelerator

Abstract In an effort to improve further the voltage performance of the Oak Ridge 25URC accelerator, the original acceleration tubes will be replaced with NEC compressed geometry acceleration tubes. In this paper, we report on tests in the 25URC accelerator of two prototype compressed geometry acceleration tube designs. One of the designs utilizes a novel aperture which provides enhanced electron and ion trapping.

Tests of compressed geometry NEC acceleration tubes

Abstract Tests have been performed in the 3 MV Pelletron test machine at NEC on a compressed geometry tube which increases the insulating length of the tube by eliminating the heated electrode assemblies (∼ 2.5 cm thick) at the end of each tube section. Some insert electrodes are changed to provide some trapping of secondary ions. The geometry tested provided an 18% increase in live ceramic in the tube. The compressed geometry tube allowed a terminal voltage of 3.55 MV on the 3 MV column at normal gradients of 30.3 kV/tube gap. The tube was also conditioned to more than 4 MV and remained stable in voltage with few sparks and with low X-ray levels for days at about 4 MV. This same performance could be achieved with or without arc discharge cleaning.

Hydrogen arc discharge cleaning of accelerator tubes

Abstract Accelerator tubes manufactured by NEC were cleaned by the hydrogen arc discharge method and tested on the NEC 3 MV test accelerator. We will discuss the results of this testing program. Generally, we confirm the favorable experience previously obtained by Korschinek et al. [1]. The familiar microdischarges exhibited by normal tubes are largely eliminated in arc discharge cleaned tubes. Thus, the arc discharge process has the same observable effect as voltage conditioning. This result suggests that the hydrogen discharge is effective in removing carbon and hydrocarbons from the surface of the accelerator tube.

Design considerations of MeV implanters

Abstract Two ion implantation systems using electrostatic accelerators to produce MeV beams for production processing of wafers will be described. One system uses a tandem accelerator with a 1 MV terminal rating to produce beams of 750 keV to 3 MeV. The other uses a single ended accelerator with a 2 MV terminal rating to provide an energy range of 300 keV to 2 MeV. Both systems use electrostatic scanning and a serial cassette to cassette wafer handler for fully automated wafer processing. The advantages and limitations of these two systems will be compared.

A new accelerator tube and column for a horizontal 8 MV tandem

Abstract A horizontal 8 MV tandem is being installed in an existing tank at Kyoto University in Japan. This NEC Model 8UDH is the largest horizontal Pelletron® constructed to date. The terminal is charged by two Pelletron chains. The acceleration tube is a metal and ceramic construction made into tube sections with a length of 30 cm each. This tube design adds 27% more live ceramic than in the standard NEC tube design, which had heated apertures in 5 cm long shorted regions every 20 cm. The column structure and tube design are reviewed.

The VP 7-200 batch-processing wafer handler

Abstract A new batch-processing end station for ion implantation has been developed for wafers of 100–200 mm diameter. It utilizes a spinning disk with clampless wafer support. All wafer transport is done with backside handling and is carried out in vacuum. Maximum throughputs range from 175 wafers/hour for 200 mm wafers to 221 wafers/hour for 100 mm wafers. This end station incorporates a new dose control scheme which is able to monitor the incident particle current independently of the charge state of the ions. This technique prevents errors which may be caused by charge exchange between the beam and the residual gas. The design and features of this system will be reviewed and the performance to date will be presented.