Radiant energy – Ion generation – Field ionization type
Patent
1997-04-18
1999-08-10
Anderson, Bruce C.
Radiant energy
Ion generation
Field ionization type
3133621, H01J 2700
Patent
active
059362510
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to the field of liquid metal ion sources, in which ions are produced from a supply metal which covers a point made of a refractory metal.
By applying an intense electrical field, under vacuum, between this point and an extraction electrode, there is emission of ions according to a field evaporation mechanism. This emission is localised at the apex of the point. The size of the emissive area is of the order of a few nm.sup.2 for an emission current of about 2 .mu.A.
These sources are used in focused ion beam machines which play an increasingly important part in the techniques of microelectronic fabrication.
At present, these machines almost exclusively use ion sources of liquid gallium metal. The use of lighter ions is interesting since it allows the size of ionic probes to be reduced. This allows the resolution of existing machines to be increased, by simply changing the source. Furthermore, for implantation applications, a light element is interesting since it penetrates more deeply into the material than a heavy element, at equal energy.
2. State of the Art
The article by Bell et al. that appeared in the "Journal of Applied Physics", Vol. 53, No. 7, July 1982, pp. 4602 to 4605 described a source of aluminium ions made up of a graphite point fixed onto a tungsten heating filament. The graphite point is surface treated by deposition of a film of titanium. In effect, the graphite is relatively resistant to attack by liquid aluminium, but it is difficult to wet it with such a liquid. The use of a film of titanium allows this problem to be resolved. The source has the shape illustrated in FIG. 1, where reference number 2 designates the graphite point, which has, at its base a cylindrical part. A heating filament 4, made of tungsten, passes through this cylindrical part. Heating of the point 2 is obtained by the heat released by a Joule effect in the filament.
This type of source has the advantages, on the one hand of simplicity, and on the other hand, of compactness since the graphite point has a diameter of about 0.8 nm, for a length of 2 mm.
Nevertheless, a certain number of disadvantages are observed with it. Firstly, the assembling and the positioning of the graphite point on a filament whose diameter is less than 0.2 mm are very delicate and indeed uncertain. The assembly lacks mechanical stability, which causes thermal drifting that is incompatible with applications in the field of microelectronics. On the other hand, heating of the emissive area is poorly controlled. The greater the thermal power used by the source, the more the thermal drift due to radiation to the environment is increased. This consequently, can modify the mechanical centring of the emissive point with respect to a target or with respect to an extraction electrode. This centring influences the direction of the emission of the ions and is inaccessible during operation. Its variation leads therefore to a loss of precision; in the context of use in the field of microelectronics, the resolution of the etched structures obtained with such a source is affected to a considerable extent. Another problem is the limited life of the source. In effect, the reserve resolution of the etched structures obtained with such a source is affected to a considerable extent. Another problem is the limited life of the source. In effect, the reserve of liquid supply metal is small and cannot be used in its entirety.
Document WO 86/06210 describes another type of ion source, that includes a point and a heating element in the form of a tape. A hole in the heating tape allows a molten liquid to flow in the direction of the point.
DESCRIPTION OF THE INVENTION
This invention seeks to resolve the problems mentioned above.
The object of the invention is a liquid metal ion source including a cylindrical rod made of a conductive and refractory material, extended by a point made of refractory material, intended to be covered by a liquid supply metal, characterised in that the assembly made up by the cylindrical
REFERENCES:
patent: 4318030 (1982-03-01), Jergenson
patent: 4328667 (1982-05-01), Valentian et al.
patent: 4551650 (1985-11-01), Noda et al.
patent: 4617203 (1986-10-01), Jergenson
patent: 4638210 (1987-01-01), Jergenson
patent: 4774413 (1988-09-01), Okubo et al.
patent: 5153440 (1992-10-01), Yasaka
patent: 5399865 (1995-03-01), Umemura et al.
Ishitani et al; "Carbon Needle Emitter for Boron and Aluminum Ion Liquid-Metal-Ion Sources"; May 1982; pp. L277-L278; Japanese Journal of Applied Physics, vol. 21, No. 5.
Bell et al; "The emission characteristics of an aluminum liquid metal ion source"; Jul. 1982; pp. 4602-4605; Journal of Applied Physics, vol. 53, No. 7.
Ben Assayag Gerard Jacques
Gierak Jacques
Anderson Bruce C.
Centre National de la Recherche Scientifique
LandOfFree
Liquid metal ion source does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid metal ion source, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid metal ion source will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1122307