Plasma immersion ion implantation

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Knee joint in the PiiiD process with an ECR plasma source and a sputter magnetron with an Ag target

In the plasma immersion ion implantation is a vacuum process for most large-area implantation of ions in solid surfaces . It is therefore closely related to ion implantation . The most important feature is the direct introduction of the materials to be treated into a plasma , hence the term "immersion". Different synonymous terms or abbreviations are often used for the procedure, some of which are listed below:

  • Plasma Immersion Ion Implantation, PIII, P3I or PI³ for short; in English one speaks of p-triple-i or pi-cube
  • Plasma-based ion implantation, PBII
  • Plasma ion implantation, PII or PI² for short
  • engl. plasma ion immersion processing , PIIP
  • If the process is used in combination with simultaneous layer deposition (see PVD and CVD ), an "& D" (English. ... and deposition ) is often added, for example PIII & D.

Basic principle

The basic principle of plasma immersion ion implantation is to immerse a workpiece in a plasma and, by applying negative high-voltage pulses, pull ions out of the plasma and accelerate them towards the workpiece. As a result, the ions are implanted into the workpiece surface. During the high-voltage pulse, a so-called edge layer is formed , which supplies the ions and spreads out from the workpiece into the plasma. In the pulse pauses, the plasma regenerates around the workpiece so that ions are available again with the next high-voltage pulse.

In order to be able to operate plasma immersion ion implantation, a system is required that consists of the following basic parts:

  1. A vacuum vessel with a sample holder that is electrically insulated from the chamber wall and the necessary equipment for vacuum generation ( vacuum pumps , pressure measurement ). Typical working pressures for the PIII are in the range from 0.1 to 1  Pa . As a rule, higher pressures are avoided, as otherwise the risk of an electrical flashover increases. For the same reason, the geometry of the vacuum chamber and the insulation of the sample holder must be designed so that they can withstand voltages of several tens of  kV .
  2. A plasma source for generating the plasma as well as controllable gas flows. The gas or gas mixture used is selected depending on the type of ion desired. Typical examples are nitrogen for the implantation of nitrogen ions or ethyne for PIII & D of carbon layers. In principle, any methods can be used to generate the plasma. Accessible are capacitively or inductively coupled RF -Entladungen or microwave - ECR -Sources and magnetron or arc evaporator (engl. Arc evaporation ) for plasma generation from solids. Another possibility is through the high-voltage pulse even a plasma to ignite, this is called a pulsed glow discharge (Engl. Pulsed glow discharge , PGD).
  3. A high voltage pulse generator. Such a voltage source must be able to generate negative voltage pulses in the middle kilovolt range , which are as rectangular as possible . 1 kV is typical, but in individual cases up to 100 kV are generated. The pulse lengths are in the range of a few microseconds and repetition rates in the range of 1  kHz . Depending on the size of the workpiece and specimen holder, currents of a few 10–100  mA flow over the plasma over time, whereby the current peak when charging the approximately capacitive load can be up to several 100 A! This results in outputs in the kilowatt range. A special quality feature for high-voltage pulse generators are the switching times, especially the pulse rise time. The faster the pulse reaches the nominal voltage, the lower the proportion of low-energy ions.

literature

  • André Anders (Ed.): Handbook of plasma immersion ion implantation and deposition. Wiley, New York NY et al. a. 2000, ISBN 0-471-24698-0 .

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