Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Patent
1991-06-21
1993-03-16
Anderson, Bruce C.
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
250358, 2504922, H01J 37317, G21K 510
Patent
active
051947480
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with a method and apparatus relating to ion implantation. In particular the invention relates to a method of an apparatus for presenting targets to an ion beam for ion implantation, and also relates to an overall method of and apparatus for implanting ions in a target element.
The invention relates in particular but not exclusively, to implanting ions of a preselected species, into a target element, for example the controlled introduction of a species into the surface layer of another material. The technique is important in semi-conductor technology where it is used in the manufacture of integrated circuits and other devices, particularly by modifying the conductivity of semi-conductor material by introducing chemical impurities into the material. The general background to the use of ion implantation in the manufacture of large scale integrated circuit chips is set out in published U.S. Pat. No. 4,578,589, having the same inventor as the present application.
An ion implantation apparatus normally consists of an ion source, an extraction system having an extraction electrode which accelerates the ions from the extraction slot in the ion source, an analysing magnet for the selection of the required ion species, acceleration stages before or after the analysing magnet, and a target region with means for producing relative scanning movement between the beam and the target, either by scanning the beam, or by moving the target.
There are a number of requirements for high dose implantation into semiconductors. The need for high current makes electrostatic beam scanning difficult because of space charge problems. Magnetic scanning of high energy, high mass beams requires large magnets, and scan frequencies tend to be limited by hysteresis and eddy current problems. The need to spread the large heat load, which is a direct consequence of the high dose, over a large number of wafers (in order to increase the implant time but still have high throughput) rules out single wafer implant. Hybrid scanning (beam scanning in one direction, mechanical scanning of the target in the other) is a partial solution to this problem, but the beam scan problems remain, although reduced in magnitude. Also, as the mechanical scan would logically be the slower of the two scan frequencies, the heat load spreading requirement is only partially addressed. Ideally the beam should pass in the fast scan direction over all the wafers in the batch before starting the next scan. Hybrid scanning does not in general achieve this.
As a consequence, mechanical scanning is generally considered to be the best solution to the problem, particularly when parallel scanning is required since parallel beam scanning is not easily achieved.
A number of different types of mechanical scanning are used, for example techniques which are known as linear mechanical scan, cylindrical carousel, Ferris wheel, racetrack carousel, and spinning disc. All these techniques have various drawbacks.
Linear mechanical scanning is a compact technique for large substrates. The problem is that it is inherently slow. The problem is not the speed of the scan but the time taken for reversal. High speed means that significant time and mechanical force are needed to achieve reversal. During reversal the beam is not being used; the technique is therefore inefficient at high scan speeds.
One particular problem to be addressed is the best way to implant large substrates. The implantation of flat computer and television screens is a particular requirement, but large area implantation is likely to be of general importance in the future. The presently available mechanical scanning techniques do not lend themselves to this requirement very well. It is an object of the present invention, at least in preferred embodiments, to provide a method of, and apparatus for, presenting a plurality of targets to an ion beam for ion implantation, particularly for use with large targets.
According to the present invention there is provided a method of presenting a plurali
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Anderson Bruce C.
Superion Limited
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