Radiant energy – With charged particle beam deflection or focussing – Magnetic lens
Reexamination Certificate
1998-11-05
2001-02-27
Anderson, Bruce C. (Department: 2881)
Radiant energy
With charged particle beam deflection or focussing
Magnetic lens
C250S305000, C313S361100
Reexamination Certificate
active
06194730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic lens for focusing the beams of charged particles, more particularly of ions, which have at least two electrodes being designed as an electric conductor with a ring-shaped section, the inner edge of which is essentially circular, whereas each electrode is connected to a power supply, can be connected to an electric potential and is fastened on a holding device.
2. Description of the Prior Art
Electrostatic lenses are used in particle optical systems and may be used for multi-various applications. Of particular interest is the application of ion beam lithography used in structure semiconductors. In the case of ion beam lithography, an ion beam pictures the structures of a shadow mask on a wafer in a usually reduced picture. In order to produce a well defined picture of the mask structures on the wafer with the help of the ion beam, the ion beam is led through an imaging system in which a number of electrodes held at different electrostatic potentials are combined into electrostatic lenses.
Due to the extraordinarily high requirements expected in the production of semiconductors, the electrostatic field in ion beam lithography has to be very accurately defined in the areas traversed by the ion beam. The efficiency of such a physical system is thus essentially dependent on the fact that the actual electrostatic fields are corresponding with the set points. This means that on one hand, the shape of the electrodes—which is usually radial symmetric—and their spacing is “perfect” and, on the other hand, that all the parts of the projection system have to be “perfectly” aligned. The production of such a “perfect” system is implying considerable measures and costs. Furthermore, in case of a defect or a change in shape or alignment of the electrodes, for example, due to environmental factors, the repair or realignment of the system is particularly difficult.
If, during the mounting of an ion beam lithography installation, inaccuracies in production or misalignments are making their appearance, the image will be faulty also. Thanks to electric or magnetic multipole fields, the correction of image distortions is possible and well known to those skilled in the art.
In U.S. Pat. No. 2,919,381, multipole electrodes are used to correct image distortions. Such a multipole electrode is divided into sectors functioning as partial electrodes and having their own power supply. In feeding potential differences between the partial electrodes of a multipole electrode, a multipole field is being produced that corrects partially the different image distortions.
U.S. Pat. No. 4,963,748 teaches combining multipole electrodes longitudinally, thus further improving the image accuracy, as well as electrodes having a rotationally symmetrical basic shape and presenting, among others, advantages in manufacturing techniques.
In a multipole electrode of the type mentioned above, each partial electrode has to be connected individually to a supply point and has to be triggered by it. This may imply considerable measures. Moreover, the potential difference between adjacent partial electrodes may lead to big field intensities which are occurring particularly on the edges of the partial electrode of an essentially rotationally symmetrical electrode.
SUMMARY OF THE INVENTION
The present invention provides a type of electrodes which concede, adjust and correct processes on the electrostatic field even after installation, particularly after initiation of the particle optical system, so that the image, in the case of a lithography installation of the mask on the wafer is provided at the required quality.
Further, the present invention provides an electrostatic lens of the type mentioned above in which at least one of the electrodes is composed of sector areas succeeding one another along the periphery of an electrode, whereas
each sector area is covering one predetermined angle area of the periphery,
the sector areas are electrically connected to one another,
sector areas are linked to the holding device via at least one adjusting element per sector area, and
the position of said sector areas may be adjusted independent of the other sector areas by means of the adjusting elements during operation of the electrostatic lens.
This solution, thanks to the change of position of the sector areas of the electrode, allows influence on the spatial distribution of the electric potential without having to change the potentials of the partial electrodes and the possibilities regarding the approachable multipole fields remain the same. The mechanical precision adjusting of the electrodes or of the partial electrodes needs no more to be done during the assembly of the lithography installation. It may be postponed until after initiation and may be amended later on at any time when needed, even during operation.
In one preferred embodiment of the invention, the sector areas are each covering an angle area of the periphery with each angle area having the same size. This facilitates the production of the electrode elements whereas, thanks to the thus achieved symmetry, the control of the field distributions becomes far less complicated.
In order to achieve an effective influence on the electric potential, it is propitious if the sector areas whose position are adjustable, are adjustable by means of the adjusting elements at least in a radial direction.
For an accurate definition not only of the position but also of the alignment of the sector areas, it is moreover advantageous if the sector areas, whose positions are adjustable, are assigned at least two adjusting elements each and they are arranged in a longitudinal direction relative to one another.
It is hereby particularly advantageous if the sector areas, whose position are adjustable, are additionally adjustable by means of the adjusting elements at least in their tilting relative to the longitudinal axis of the electrostatic lens.
In another embodiment of the invention each sector area is advantageously linked to the holding device via at least one adjusting element and is adjustable in its position by means of at least one adjusting element during operation of the electrostatic lens, irrespective of the other sector areas.
In still another advantageous embodiment that additionally tolerates the influence on the potential distribution in a z direction sector areas are longitudinally divided into segments, whereas
each segment is occupying a predetermined longitudinal area,
the segments are connected to the common power supply,
segments are linked to the holding device via at least one adjusting element, and
the position of said segments is individually adjustable by means of the adjusting elements during operation of the electrostatic lens.
In one embodiment, the sector areas and/or segments are mechanically separated. This facilitates among others their mechanical motion relative to each other.
In another embodiment, the sector areas and/or the segments are advantageously mechanically connected to one another on the inner surface of the electrode by electric connections, so that potential unsteadiness along said inner surface is avoided.
In a particularly preferred embodiment, an electrode cross-section with periodically variable thickness is provided, whereas each sector area is extending from one thickness minimum to the next one.
REFERENCES:
patent: 5869838 (1999-02-01), Stengl
patent: 5929452 (1999-07-01), Yoshitake et al.
Chalupka Alfred
Stengl Gerhard
Anderson Bruce C.
IMS-Ionen Mikrofabrikations Systeme GmbH
Vigil Thomas R.
Wells Nikita
LandOfFree
Electrostatic lens does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrostatic lens, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrostatic lens will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593914