Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2003-01-08
2004-07-27
Wells, Nikita (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492100, C250S492300
Reexamination Certificate
active
06768125
ABSTRACT:
FIELD OF THE INVENTION AND DESCRIPTION OF PRIOR ART
The invention relates to a maskless particle-beam exposure apparatus for forming a pattern on a surface of a substrate by means of a beam of energetic electrically charged particles. More in detail, the invention relates to a pattern definition means and an exposure apparatus employing this pattern definition means. In particular, the pattern definition means is a device for defining a pattern in a particle-beam exposure apparatus, which device is adapted to be irradiated with a beam of electrically charged particles and let pass the beam only through a plurality of apertures. It comprises an aperture array means which has a plurality of apertures of identical shape defining the shape of beamlets permeating said apertures, and further a blanking means to switch off the passage of selected beamlets. This blanking means has a plurality of openings, each opening corresponding to a respective aperture of the aperture array means and being provided with a deflection means controllable to deflect particles radiated through the opening off their path to an absorbing surface within said exposure apparatus.
In other words, the particle beam is generated by an illumination system which produces a homocentric or preferentially telecentric beam of energetic particles; this beam illuminates a pattern definition (PD) means having an array of apertures which can be controlled so as to allow (‘switched on’) or deactivate (‘switched off’) the passage of particles of the beam through the respective aperture. The beam permeates the blanking aperture array through switched-on apertures, thus forming a patterned particle beam bearing a pattern information as represented by the spatial arrangement of the apertures that are switched on. The patterned beam is then projected by means of a particle-optical projection system onto the substrate where an image of the transparent apertures is thus formed.
One important application of exposure apparatus of this kind is in the field of particle-beam lithography used in semiconductor technology, as a lithography apparatus. In order to define a desired pattern on a substrate surface, such as a circuit layer to be defined on a silicon wafer, the wafer is covered with a layer of a radiation-sensitive photoresist. Then the desired structure is imaged onto the photoresist by means of a lithography apparatus. The photoresist thus patterned is partially removed according to the pattern defined by the previous exposure step, and is now used as a mask for further structuring processes such as etching. By repeating this scheme, complicated minute structures such as an integrated circuits can be formed.
Arai et al., U.S. Pat. No. 5,369,282, discuss an electron-beam exposure system using a so-called blanking aperture array (BAA) which plays the role of the pattern definition means. The BAA carries a number of rows of apertures, and the images of the apertures are scanned over the surface of the substrate in a controlled continuous motion whose direction is perpendicular to the aperture rows. The rows are aligned with respect to each other in an interlacing manner so that the apertures form staggered lines as seen along the scanning direction. Thus, the staggered lines sweep continuous lines on the substrate surface without leaving gaps between them as they move relative to the substrate, thus covering the total area to be exposed on the substrate. In the U.S. Pat. No. 5,369,282, the apertures of every second row align and the pitch between neighboring apertures in a row is twice the width of an aperture; in general, an alignment of rows is possible based on any number n, the pitch then being n times the width of an aperture. The BAA of Arai et al., which is designed for electron radiation only, employs a complicated connection circuitry in order to address the individual apertures. Furthermore, the fact that the beam is moved over the substrate offers problems, such as imaging aberrations, with the electro-optical imaging.
The article of I. L. Berry et al. in J. Vac. Sci. Technol. B15 (1997) pp. 2382-2386, describes a PD device comprising a “programmable aperture array” with an array of 3000×3000 apertures of 5 &mgr;m side length with an n=4 alignment of rows and staggered lines. The aperture array contains additional logic circuitry, thus implementing an electronic mask scanning system in which the pattern information is passed by means of shift registers from one aperture to the next within a row. The article proposes to use a 200× demagnification ion-optical system for imaging the apertures of the BAA onto the substrate, but does not point out how such a demagnification can be achieved.
There are several unresolved issues in the PD/BAA systems of Arai et al. and Berry et al. One of them is the damage done to the aperture array by particle irradiation endangering the lifetime of the array; this is a serious problem as the PD/BAA system contains delicate electronic circuitry. Another serious problem is the severe miniaturizing of the structures on the PD/BAA system, resulting in space scarcity.
SUMMARY OF THE INVENTION
The present invention sets out to overcome the above-mentioned shortcomings of the prior art. In particular, the basic layout of a PD device as proposed by Berry et al. shall be improved in an effective way.
This task is solved according to the invention by a pattern definition means wherein on the blanking and aperture array means, the apertures are arranged within a pattern definition field being composed of a plurality of staggered lines of apertures, wherein each of the lines comprises first segments which are free of apertures and second segments which each comprise a number of apertures spaced apart by a row offset (‘aperture fields’); this row offset is a multiple of the width of apertures, while the length of said first segments is greater than the row offset.
The apertures are typically arranged in the pattern definition field in a regular array which, perpendicular to the direction of the lines, repeats itself every n-th line, n≧2. This number can, for instance, be 3 or 4; also a value of 5 may be especially suitable.
In a preferred realization of the invention, the first segments of the lines are positioned adjacent to each other and form a storage field (or possible several storage fields) spanning the width of the pattern definition field. In this case, the lines may be (organizationally) ordered into groups, wherein the first segments of each group are divided along the direction of the lines into logic blocks, each of the logic blocks comprising controlling logic for a second segment of one of the lines of the group situated by the first segment.
Furthermore, the blanking means will preferably comprise buffer means for buffering information to control the deflection means associated with the apertures. These storage means are then located in the areas of the first segments.
A next aspect of the invention relates in particular to the problem to provide a PD system which, while containing a delicate (and thus expensive) circuitry, can stand a long lifetime despite the fact that it is exposed to severe irradiation from the lithography beam. This problem is met by a PD means wherein in front of the blanking means as seen in the direction of the particle beam, a cover means is provided having a plurality of openings, and each opening corresponds to a respective opening of the blanking means, the width of the openings of the cover means being smaller than the width of the openings of the blanking array means. The introduction of such a cover means removes the problem of irradiation of the blanking device but does not impede the definition of the patterned beam, in particular with respect to the shape of the beamlets and control of the pattern.
Preferably the cover means is realized as a unit other than the aperture array means. Furthermore, the aperture array means is preferably positioned after the blanking means as seen in the direction of the particle beam, and the abso
Buschbeck Herbert
Chalupka Alfred
Lammer Gertraud
Loeschner Hans
Nowak Robert
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
IMS Nanofabrication GmbH
Kalivoda Christopher M.
Wells Nikita
LandOfFree
Maskless particle-beam system for exposing a pattern on a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Maskless particle-beam system for exposing a pattern on a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Maskless particle-beam system for exposing a pattern on a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3226158