Electric lamp and discharge devices – With positive or negative ion acceleration
Reexamination Certificate
2002-08-06
2003-08-26
Wells, Nikita (Department: 2881)
Electric lamp and discharge devices
With positive or negative ion acceleration
C313S361100, C250S3960ML, C250S298000, C315S500000, C315S507000, C315S111610
Reexamination Certificate
active
06611087
ABSTRACT:
BACKGROUND OF THE INVENTION
One aspect of the present invention relates to a system for depositing—e.g. “writing”—materials on a target while simultaneously monitoring—e.g. “reading”—the deposition process.
Beam Joining in a Magnetic Field
It is well known that passing beams of unfocussed charged particles through a magnetic field causes the constituent particles to separate according to particle charge-to-mass ratio and/or velocity. This is the basic principle of mass spectroscopy. A byproduct of the passage of such a beam through a magnetic field is the introduction of uncorrectable resolution-limiting aberrations to any subsequent images in the beam.
Rempfer and Mauck in a paper entitled Correction of Chromatic Aberration with an Electron Mirror, Optik Vol 92, No 1, (1992), disclosed that an image could be passed through a cylindrical magnetic turning field (CMTF) without limiting resolution if a real image were formed at the center of the magnetic field. In other words, the beam incident on the CMTF is focused at its center and thus may be refocused by a lens back to a single image without loss of resolution. Such a geometry is not useful for mass spectrometry because subsequent images in the beam are not easily separated by ion mass as they are in a system where the ions pass through a magnetic field substantially collimated. In other words, a mass spectrometry system uses an unfocused beam incident on the magnetic field. Then the beam normally passes through a lens and is separated into different ion masses.
FEI Company sells an XL800 Full Wafer Scanning Microscope which uses an ion beam for eroding—“machining”—a surface, and an electron beam for probing and monitoring the progress of erosion. The two beam-forming structures are separate but physically proximate one another.
Chromatic and Spherical Aberration Correction
Just as light beams passed through optical lenses will experience resolution-limiting spherical and chromatic aberrations, so beams of charged particles passed through electrostatic and electromagnetic lenses also include these aberrations, due primarily to two factors:
1. spherical aberrations are due to the failure of a lens to focus particles at different lateral distances from the axis thereof to the same point longitudinally on the axis, i.e., for a converging lens and particles incident upon the lens parallel to the axis, particles farther from the axis are focused nearer the lens than particles closer to the axis; and
2. chromatic aberration are due to the failure of a lens to focus particles of different energies to the same point on the axis.
Chromatic and spherical aberration may also be introduced into electron optical systems from the sources of the beams. Where energy aberration becomes significant, it can be reduced by passing the beam through an energy filter at the expense of reduced beam current.
Henneberg, U.S. Pat. No. 2,161,466, teaches that the aberrations of electrostatic mirrors have the opposite sign from those of electrostatic and electromagnetic lenses, and that such mirrors could in principle be used to correct spherical and chromatic aberrations of lens systems and beam sources. Rempfer and Mauck, Optik, 1992 discovered that incident and reflected beams of charged particles could be separated if the single homogenous beam is focused upon and passed through the geometric center of a substantially cylindrically symmetrical magnetic field, where the field is located at an image plane of a particle beam lens. In that system, two lenses were used to relay an image between each deflecting field, and small magnetic beam deflection angles were necessary in order to prevent magnetic field distortion effects. Unfortunately, such a system is complicated and the deflection angles are small. Further, small deflection angles cause distortion in the beam exiting the magnet.
Hereinafter, the term “incident beam” refers to a beam of charged particles which is directed toward an element which modifies it in some way.
Hereinafter, the term “reflected beam” or “exiting beam” refers to a beam of charged particles which has been modified in some way by interaction with some element.
Magnetic Deflection of 127 Degrees or 135 Degrees
Leboutet et al., U.S. Pat. No. 3,660,658, disclose a mass separator using a magnetic deflector system which deflects a charged particle beam at an angle of 90 degrees to its initial axis, and which also includes a magnetic deflector which deflects the beam at an angle of 127 degrees. The particle beam of Leboutet et al. passes through the turning magnetic field unfocussed. The Leboutet et al. device relies on the unfocussed nature of the beam to perform the mass separation.
Rose et al., U.S. Pat. No. 4,760,261, disclose an electron energy filter which operates at a preferred angle of 115 degrees. The geometry of Rose et al. incorporates a triangular-shaped magnet. Like Leboutet et al., Rose et al. depend upon separating all but those particles within a narrow selected energy range from a beam of particles having a wide spectrum of energies. Such a device is effective only when using unfocused beams.
Crewe, U.S. Pat. No. 5,336,891, discloses an aberration-free lens system which includes both magnetic and electrostatic components to obtain aberration-free imaging. All examples disclosed by Crewe (FIGS. 3
a-
3
i
) show deflections only of 45 degrees, 90 degrees, and 180 degrees.
Rose et al., U.S. Pat. No. 5,449,914, disclose an energy filter in which the beam is deflected four time at angles of 135 degrees. Rose et al. relies on an unfocused beam to perform its functionality.
Electrostatic Mirror Used with Magnetic Deflector
Wada, U.S. Pat. No. 5,254,417, discloses a reflection mask for producing reflected electrons from the surface of a substrate in a desired pattern. An electron beam is deflected by an electromagnetic field into an electrostatic mirror, from which it is reflected back into the field and deflected to continue in its former direction. Wada does not focus its incident or its reflected particle beams at the geometric center of the respective magnetic deflecting fields.
Rose et al., U.S. Pat. No. 5,319,207, disclose an electron beam passing through magnetic deflection fields B1/B2, deflected 90 degrees into a mirror, reflected back through the magnetic deflector, and deflected 90 degrees onto the object to be scanned. The magnetic deflector taught by Rose et al. is a complex device formed by a pair of circular magnetic poles having sufficient separation therebetween to allow one or more beams of charged particles to pass therethrough. Rose et al. focus their incident beam on the hypothetical diagonal symmetry plane 3 g of deflector 3, and their reflected beam on the hypothetical diagonal symmetry plane 3 h.
Combination of Electrostatic Mirror and Cylindrical
Magnetic Turning Field Rose et al., U.S. Pat. No. 5,319,207, further disclose an electron beam passing through magnetic deflection fields B1/B2, deflected 90 degrees into an electrostatic mirror, reflected back through a square magnetic deflector, and deflected 90 degrees onto the object to be scanned. Rose et al. focus their incident and reflected particle beams on hypothetical diagonal symmetry planes. Further, the deflector of Rose et al. is square, and has two magnetic fields which must be adjusted and balanced for strength.
What is desired, is a system for depositing—e.g. “writing”—materials on a target while simultaneously monitoring—e.g. “reading”—the deposition process.
SUMMARY OF THE INVENTION
The present inventions, in several aspects, overcome the aforementioned drawbacks of the prior art by providing a system for joining at least two beams of charged particles that includes directing a first beam along a first axis into a magnetic field. A second beam is directed along a second axis into the magnetic field. The first and second beams are turned, by interaction between the field and the first and second beams, into a third beam directed along a third axis.
In another aspect of the present invention a system separates at least two beams of charge
Chernoff Vilhauer McClung & Stenzel LLP
Coincident Beams Licensing Corporation
Wells Nikita
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