The Ion Source

The Ion Source Magnetic FilterRF Cable ConnectorHigh Vacuum Feed ThroughVacuum Variable CapacitorNetworkMagnetic FilterRF AntennaExtraction ElectrodeSuppression ElectrodeGround ElectrodeExtraction Electrode AssemblyMagnet OrientationPermanent MagnetsMagnetic Cusp LinesRF AntennaGas Inlet FittingMatching Transfomer
 
 
 Introduction
The Ion Implanter
The Vacuum system 
The Ion Source 
The Ion Beam
 Glossary
The Faraday 
Matching Network
The Magnet 
Boron Trifluoride
Charge Neutralization
 References
 
 
 
 

The Ion Source has arrays of permanent magnets to produce a multi-cusp magnetic field in regions remote from the plasma grid and the RF antenna, for largely confining the plasma by lengthening the path of ionising electrons and reducing their drift to the walls. The ion source has a chamber which is short in length, relative to its transverse dimensions, and the RF antenna is at an even shorter distance from the plasma grid, which contains one or more extraction apertures. RF electric field coupled into the plasma chamber maintains a low pressure (10-2 --- 10-3 Torr) discharge. Positive ions are expelled from the discharge by a negatively biased Extraction electrode. United States Patent 4,793,961
 
 
More infomation on Ion Sources and ion source technology.
 

The Magnetic Filter in an ion source reduces the production of undesired ion species and improves the ion beam quality. High-energy ionizing electrons are confined by the magnetic filter to an ion source region, where the high-energy electrons ionize gas molecules. One embodiment of the magnetic filter uses permanent magnets oriented to establish a magnetic field transverse to the direction of travel of ions from the ion source region to the ion extraction region. In another embodiment, low energy 16 eV electrons are injected into the ion source to dissociate gas molecules and undesired ion species into desired ion species. United States Patent 4,447,732
 
 

 
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Multi-cusp Magnetic Field:  The density of a plasma is dictated by the balance between production and loss processes, with the added restriction that to maintain neutrality the ion charge and electron charge densities must be equal. Energetic electrons, which are more useful for ionisation, are more easily lost to the chamber walls than the slower ions unless steps are taken to return the fast electrons to the plasma. It would also be of advantage to allow slow electrons with less than the minimum ionisation energy to escape thus reducing the possibility of electron-ion recombination. A strong multipole magnetic field surrounding the plasma volume meets these requirements.
 

Permanent Magnets Samarium-cobalt about 1.5 killoGauss.
 
 

The Antenna is supported by the base has a metallic radio frequency conducting segment mounted directly within the gas confinement chamber to deliver ionizing energy into the gas ionization zone. United States Patent 5,661,308
 
 
 

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The Source Gas flow is from 1 to 10 sccm to sustain the plasma between pressure zones within the source, which operates between 1x 10-5 Torr and 1x 10-4 Torr in the chamber depending upon the pumping capacity of the vacuum system for that particular operating gas. Beam current varies according to the pumping speed and the capacitance of the vacuum system. Typical injection beam current is a between a few milliamps and ninty milliamps depending on the gas flow rate and RF power.
 

The Matching Network:  The antenna and source are connected via a matching network including first and second variable capacitors and a step down transformer to maximize power transferred to the load and tuning a load. The values of the first and second variable capacitor are varied simultaneously until the best impedance match between the impedances seen looking into and out of output terminals of the RF. generator is attained.
 
 

TheElectrode Assembly is bounded in close proximity to the ion source. The extraction electrode is used for extracting positively charged ions from the source. Ions exiting the source combine downstream to form a broad beam which is used for ion beam treatment of a silicon wafer. Individual electrodes in close proximity to the extraction electrode can be biased to either inhibit or allow backstreaming of neutralizing electrons from beam portions close to the source back to the extraction electrode. Insulators separates beam portions in close proximity to the extraction electrode to inhibit beam crosstalk and an additional suppression electrode common to all beam portions is controllably biased to further enhance control over beam portion intensity. In a typical application, the beam is a circular beam and intensity control is maintained to assure common intensity for a given radii from the beam center. United States Patent 5,218,210
 

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 Introduction
The Ion Implanter
The Vacuum system 
The Ion Source 
The Ion Beam
 Glossary
The Faraday 
Matching Network
The Magnet 
Boron Trifluoride
Charge Neutralization
 References
 


 
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This page is sponsored by Case Technology Inc. since 5/1/98.

Updated 6/6/99.