Optical: systems and elements – Lens – With support
Reexamination Certificate
1999-09-22
2001-02-06
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With support
C250S3960ML
Reexamination Certificate
active
06185054
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to forming circuit patterns in semiconductor wafers using electron beam lithography and, more particularly, to an apparatus and method for mounting a ceramic ferrite pole piece in an electromagnetic lens of an electron beam system used in such lithography.
Pole pieces must be located accurately within an electromagnetic lens. Ferrite is a magnetic ceramic, and a pole piece made of ferrite is the focusing part of the lens. It is critical that the pole piece be centered in the lens so that an electromagnetic field which focuses the electron beam is centered. In conventional electron beam systems, the centering of the ceramic ferrite pole piece is accomplished by inserting the pole piece into a metal centering plate having an opening whose diameter is larger by only a very small tolerance than the outer diameter of the pole piece. Ferrite pole pieces are fragile, and the close tolerance between the pole piece and the centering plate subjects the pole piece to chipping and even breaking during assembly and disassembly. The pole pieces must be removed sometimes for maintenance and then replaced. This increases the exposure of the pole piece to chipping and breaking. Although external chipping does not pose a serious problem in itself, it can lead to the breaking of a pole piece. The ferrite used for the pole pieces is expensive and has a long manufacturing lead time.
SUMMARY OF THE INVENTION
By the present invention, ferrite pole pieces are accurately centered within electromagnetic lenses of electron beam systems without chipping or breaking of the pole pieces.
In order to achieve this advantage, an opening through a centering plate of an electron beam system is made larger than is conventional, and a steel mounting ring is fixed around the pole piece and then secured to the centering plate. The mounting ring has an inner diameter sufficiently greater than the outer diameter of the pole piece that a gap is present and chipping is not a problem. An epoxy adhesive is applied to the inner diameter of the mounting ring, particularly in annular grooves provided for that purpose, and the pole piece is inserted in the opening through the mounting ring and centered using shims.
The mounting ring has a flange extending radially outward, and diametrically opposed alignment apertures are defined through the flange. When the epoxy adhesive has cured, the assembly of the pole piece and the mounting ring is inserted into the opening through the centering plate such that the flange overlies the centering plate, and the alignment apertures in the flange are aligned with corresponding apertures in the mounting plate. Precision dowel pins only slightly smaller in diameter than the diameter of the alignment apertures are inserted through the aligned apertures of the mounting ring and the centering plate for precise positioning of the pole piece assembly. Screws are inserted through the other aligned apertures to fix the assembly to the mounting plate. When the centering apertures are aligned, fastener openings spaced around the ring are aligned with corresponding fastener openings in the centering plate, so that fasteners can be inserted to secure the mounting ring to the centering plate.
REFERENCES:
patent: 5338939 (1994-08-01), Nishino et al.
patent: 5382800 (1995-01-01), Nishino et al.
patent: 5629526 (1997-05-01), Nakasuji
patent: 5900667 (1999-05-01), Veneklasen et al.
International Business Machines - Corporation
Mack Ricky
Shannon John P.
Venable
LandOfFree
Apparatus and method for mounting pole piece in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for mounting pole piece in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for mounting pole piece in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2610943