Radiant energy – With charged particle beam deflection or focussing – With target means
Patent
1997-08-29
1999-12-07
Nguyen, Kiet T.
Radiant energy
With charged particle beam deflection or focussing
With target means
250396R, H01J 37244
Patent
active
059987952
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electron beam pattern-writing column.
Electron beam columns are used in electron beam pattern-writing or microfabrication machines which serve for writing on substrates, for example writing circuit patterns on masks coated with electron-sensitive resists (lithography) or direct writing of such patterns on wafers. It is common practice to utilise a high-energy beam with an electron acceleration potential of 50 to 100 kilo electron volts, or even more, to achieve good penetration of the resist and to minimise proximity effects arising from backscatter of secondary electrons by the substrate. However, the electron speed in high-energy beams is so high that the beams are relatively difficult to focus and deflect and electromagnetic lenses and electromagnetic deflecting systems are usually required for these purposes. If electrostatic lenses of the kind used in low-energy beams were to be considered, the potential of the focussing electrode in each such lens would have to be close to that of the beam emitter and the consequent demands of insulation and spacing would require the lenses to be very large.
A problem with electromagnetic lenses, however, is that they are bulky, heavy, consume a considerable amount of power and generate heat due to the excitation current in the lens coils. Each lens may have a heat output in the region of 30 to 40 watts, which can cause distortion of the beam column and thus lead to beam position error. This is highly detrimental in view of the criticality of tolerances in circuit writing on very small substrates. The effect of heat dissipation is controllable to some extent by water cooling via coolant channels in the column casing. Even with cooling it remains difficult to deal with changes in thermal influence when a lens is replaced by another with a different heat output. The change in thermal influence results in a change in the column performance.
In GB 522 195 there is disclosed a television cathode ray tube with a single upstream focussing lens and a downstream final lens serving for electron beam deflection. The beam electrons are accelerated after the deflection, but the beam remains a low-energy beam, undergoing merely a threefold increase from 6.5 to 20 keV. The amount of increase is critical and has to be kept below a value at which distortion of the television screen raster image occurs. Because only a single upstream focussing lens is present, specific problems connected with beam focussing, in particular lens spacing and insulation, do not have to be addressed. Moreover, a beam with a low final energy of the level referred to in GB 522 195 could not meet current demands with respect to pattern-writing accuracy and definition.
Electron beam apparatus usable for, inter alia, lithography purposes and incorporating electrostatic lenses is disclosed in EP-A 0 462 554. This apparatus, too, provides a low-energy beam and consequently is subject to the same limitations with respect to pattern-writing quality. The beam is accelerated during passage along the electron beam column of the apparatus but is decelerated at a final lens which contains a final electrode supplied with an acceleration voltage at least three times less than that supplied to a first electrode of the lens. Ultimately, there is only very low-energy beam action on a substrate on which pattern writing is to be carried out.
Apart from the beam electron accelerations performed in the apparatus described in these two documents, it is known to convert low-energy beams into high-energy beams in cathode ray tubes of oscilliscopes, but not for reasons of mitigating heat effect. Such tubes do not contain series of focussing lenses.
It is therefore the object of the present invention to provide an electron beam column which is suitable for extremely fine and accurate scanning, but in which the mentioned disadvantages of prior art columns, in particular heat output from focussing components and the accompanying need for cooling measures, can be eliminated or at least significantly r
REFERENCES:
patent: 4675524 (1987-06-01), Frosien et al.
Leica Microsystems Lithography Limited
Nguyen Kiet T.
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