Ion implantation for semiconductor devices

World Abstracts on Microelectronics and Reliability Automatic registration in an electron-beam lithographic system. D. E. DAVIS, R. D. MOORE, M. C. WILLIAMS and O. C. WOODARD.I B M Jl Res. Dev. 21, (6) 498 (November 1977). In the fabrication of integrated circuits, electronbeam systems are increasingly used to directly expose circuit patterns on resist-covered semiconductor wafers. These systems are made attractive by their inherent capability for writing patterns at high resolution, which eliminates the need for the masks used in optical exposure systems. To compete economically in production, electronbeam systems must attain a high level of wafer throughput. To achieve this, the system must be fully automated and spend the minimum of time in performing overhead functions such as various calibrations, pattern registration, and mechanical positioning of the wafers. This paper describes pattern registration, a process by which the circuit patterns required at a particular level of device fabrication are mapped to those of the preceding level. It discusses the considerations taken as basic in designing an accurate, high-speed registration process for a production-type electron-beam exposure system. This automatic registration system operates in 150milliseconds per integrated circuit chip, allowing the system to achieve a throughput of 2000 5-mm chips per hour with overlay error of less than 0.75 pm (3a). The operation of this system, its performance characteristics, and measurements of its pattern-matching accuracy are presented. Ion implantation for semiconductor devices. R. J. DUCHYNSKI. Solid St. Technol. p. 53 (November 1977). Ion implantation is a new technique to introduce precisely con-

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trolled impurities (doping agents) into silicon to change the silicon's electrical characteristics. The ion dose is a direct measure of the actual number of atoms implanted in a unit area. Implantation is accomplished by ionizing gas at a source and drawing ions into a high-intensity beam. The ions are extracted at a high voltage, and a magnetic field exerted on charged particles separates them into several beams according to the masses of the particles. A lens catches a selected beam and accelerates it before the beam hits a target--one silicon wafer out of 50 wafers. The beam is spread uniformly over the surface of the wafer by a rotating mechanical scan. The ion dose and the uniform scan provide significantly better doping control over a large-dose range, compared to previous doping methods. These methods included chemical or furnace deposition of an impurity followed by either a high temperature redistribution or a drive-in diffusion. Ion implantation offers room-temperature operation, a wider range of masking materials, a wider range of impurities, and elimination of chemical problems. Ion milling for semiconductor production processes. DR L. D. BOLLINGER. Solid St. Technol. p. 66 (November 1977). Work with ion milling is increasing as solid state devices progress towards finer geometries. This article discusses the advantages of ion milling and what is required of an ion beam system. The problems involved in scaling up from a laboratory system to a production system are considered. The development of a large diameter ion beam system with production wafer handling is described.