Ion implanter

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Ion implanters are machines that bombard materials with charged particles ( ions ) and introduce them into a substrate ( ion implantation ) in order to change the material properties.

Structure & functionality

Ion implantation facility.

All ion implanters consist of an ion source , an acceleration system (ion accelerator), an extraction aperture , a mass and energy separation of the ions, a scanning system and a chamber for processing the wafers .

It is implanted in silicon and other semiconductors such as B. gallium arsenide (GaAs), a III-V compound semiconductor .

The gas is ionized in the ion source . The ion source consists of a heating wire against which the dopant gas flows. For implanting substances that occur as solids (e.g. beryllium), a so-called "vaporizer" can be used in some implanters, with which solid dopants can be evaporated. The ionized dopants are then pre-accelerated (usually a few 10 kV) before the ion beam reaches the magnet for mass / energy separation. After the selection magnet, there is a post-acceleration of up to a few megavolts. The entire process takes place in an ultra-high vacuum , which is usually generated with turbo molecular pumps or cryopumps .

Elements that can act as acceptors, such as boron and indium , or donors, such as phosphorus and arsenic , serve as dopants . The examples relate to silicon as the material to be doped. These elements are often not used in their elemental form, but bound in gaseous or solid form (powder):

Classification

A distinction is made between the following basic types of implanters in semiconductor production:

  • Medium current implanter with implant currents from 1 µA to 5 mA at energies from 10 keV to 200 keV
  • High current implanter with implant currents from 100 µA to 30 mA at energies from 80 keV to 200 keV
  • Low-energy implanters with implant currents from 1 mA to 20 mA at energies from 0.2 keV to 80 keV
  • High-energy implanter with implant currents from 10 µA to 1 mA at energies from 200 keV to 5 MeV and higher (up to 10 MeV)

The limits mentioned here are only a rough guide and the information varies from literature to literature, cf. In addition, modern, commercially available systems have a usable power or energy area that covers two or three of the aforementioned areas. For a specific application - based on the general requirements for a given energy and dose (ions per area) - more than one type of system is often considered. Based on comparable implantation profiles, economic aspects are then also given a higher priority, so that a process with a high dose ( > 5the14 ions per square centimeter) is preferably carried out on high-current implanters, since a significantly short process time is required here compared to medium-current implanters (approximately linear increase with the decrease in the ion current).

Furthermore, implanters can be classified according to their handling equipment :

  • Batch machines (several wafers are processed at the same time)
  • Single wafer machines (the wafers are processed one after the other)

Batch machines have long been the common type. Several wafers (often 13) are placed on a rotating carrier and driven through the ion beam at high rotational speeds (up to 1200 / min). With the introduction of 200 mm wafers, single wafer machines, in which a single wafer is held on an electrostatic carrier ( chuck ), became attractive . In addition to process cost savings, single wafer machines enable more even doping over the wafer surface thanks to a different way of guiding the ion beam and, due to the smaller space requirement of the single wafer holder, higher tilts (up to 60 °) and better angular accuracy. When manufacturing on 300 mm wafers, almost no batch systems are used any more, because on the one hand it is difficult to achieve the necessary tolerance requirements and the systems are simply too large (and too expensive, floor space in a clean room is costs) .

See also

Individual evidence

  1. Bernd Schmidt, Klaus Wetzig: Ion Beams in Materials Processing and Analysis . Springer, 2012, ISBN 3-211-99355-X , pp. 74 .
  2. Axcelis Celebrates Shipment of 300th GSD / HE Series Implanter Marking Over 15 Years. Axcelis Technologies, June 22, 2011, accessed July 22, 2020 (press release ).
  3. a b Lis K. Nanver, Egbert JG Goudena: Ion implantation . In: Wiley Encyclopedia of Electrical and Electronics Engineering . American Cancer Society, 1999, ISBN 978-0-471-34608-1 , doi : 10.1002 / 047134608X.W7021 .
  4. Sami Franssila: Introduction to Microfabrication . John Wiley & Sons, 2010, ISBN 978-1-119-99189-2 , pp. 177 .
  5. ^ Mel Schwartz: New Materials, Processes, and Methods Technology . CRC Press, 2010, ISBN 978-1-4200-3934-4 , pp. 647-649 .
  6. Michael Nastasi, James W. Mayer: Ion Implantation and Synthesis of Materials . Springer, 2006, ISBN 978-3-540-45298-0 , pp. 214 .