Wide aperature wien exb mass filter

a mass filter and wide aperture technology, applied in the field of mass filter for an ion beam system, can solve the problems of blurring of the focused beam at the target, increased repulsion, and inability to achieve the effect of wide optical apertur

Active Publication Date: 2012-10-18
FEI CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0013]A preferred ExB filter in accordance with the invention provides an adjustable electric field having components both parallel and perpendicular to the magnetic field. The adjustable electric field can compensate for the non-ideal configuration of the physical electrodes to provide a wide optical aperture. The adjustable electric field can also provide in some embodiments the capability for both X-Y beam deflection, which can be used for beam alignment. The adjustable electric field can also provide in some embodiments beam stigmation, which can be used for correcting some of the aberrations induced by the mass filter.

Problems solved by technology

This is impossible, however, since the electric and magnetic poles would physically interfere with each other.
Unavoidable energy spreads in the ion beams will, however, cause a blurring of the crossover along the mass dispersion axis, potentially resulting in blurring of the focused beam at the target.
Crossovers also have disadvantages—1) electrostatic repulsions are increased as the particles are brought closer together at the crossover itself, 2) the beam is generally smaller throughout the entire column due to the crossover, increasing the space-charge repulsions, and 3) sputter damage to the mass separation aperture is increased due to the higher beam current density at the mass separation aperture plate.
In a focused ion beam column without an intermediate crossover, the beam diameters are larger and the smaller optical aperture of a typical prior art mass filter may be more of a problem.
There are examples of ExB mass filters in the prior art having a wide optical aperture, but such prior art mass filters have other drawbacks.
5)—this makes the magnetic circuit relatively inefficient, requiring substantially increased permanent magnet strengths or magnetic coil excitations to achieve adequate B-field strengths in the physical aperture.
The Wien filter as described in this patent has no capability for applying deflecting fields along the magnetic field axis.
In addition there is no capability for applying a quadrupole electric field to stigmate the beam.

Method used

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  • Wide aperature wien exb mass filter
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Examples

Experimental program
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Effect test

example # 1

Example #1

Voltage Settings with No Deflection or Stigmation

[0035]In the case where only mass separation is desired, but no beam steering or stigmation, the voltages to the magnetic poles would be set as follows:

VB1=VD1=(LX2 / LX1)Vms

VB2=VD2=−(LX2 / LX1)Vms

[0036]Where the voltages on the electric poles would be:

VA=Vms

VC=−Vms

[0037]The value of Vms is chosen based on the electric field requirements for mass separation, in which the electric and magnetic forces on the ions are balanced for the ion species desired in the beam at the substrate, e.g., middle mass ions 140 in FIG. 1 being focused by lens 108 onto substrate 112.

[0038]The common-mode voltage of the overall Wien filter is set to 0 V in this example. If the voltage difference between the ion source and the Wien filter is Vaccel, then the energy of singly-ionized ions would be eVaccel passing through the Wien filter. For positive ions, this would correspond to the case of a positive Vaccel bias on the source relative to the bias...

example # 2

Example #2

Voltage Settings with Y-Axis Deflection but No Stigmation

[0040]In a second example where mass separation and Y-axis deflection are desired, the voltages to the magnetic poles would be set as follows:

VB1=(LX2 / LX1)Vms+VY

VB2=−(LX2 / LX1)Vms+VY

VD1=(LX2 / LX1)Vms−VY

VD2=−(LX2 / LX1)Vms−VY

[0041]Where the voltages on the electric poles would be:

VA=Vms

VC=−Vms

as was the case in example #1. The common-mode voltage of the Wien filter 200 is set to 0 V in this example. The Y-axis electrostatic deflection field is generated solely by the ±VY voltages applied to the two magnetic poles. By superposition, the effects of the (horizontal) electric field which is proportional to Vms, may be considered separately from the deflection effect of the (vertical) electric field which is proportional to VY. For the ion mass species which is selected to pass through the mass filter, e.g., middle mass ions 140 in FIG. 1, the net force on the middle mass ions 140 will be solely due to the Y-axis (vertic...

example # 3

Example #3

Voltage Settings with Stigmation but No Deflection

[0042]In a third example where mass separation and stigmation are desired, the voltages to the magnetic poles would be set as follows:

VB1=(LX2 / LX1)Vms−(LY / LX1)2Vstig

VB2=−(LX2 / LX1)Vms−(LY / LX1)2Vstig

VD1=(LX2 / LX1)Vms−(LY / LX1)2Vstig

VD2=−(LX2 / LX1)Vms−(LY / LX1)2Vstig

[0043]Where the voltages on the electric poles would be:

VA=Vms+Vstig

VC=−Vms+Vstig

[0044]As was the case in examples #1 and #2, Vms is the electric pole voltage needed for mass separation. The common-mode voltage of the overall Wien filter is set to 0 V in this example. The stigmation electrostatic quadrupole field is generated by the voltages applied to the electrostatic and magnetic poles which are proportional to Vstig—note that an (LY / LX1)2 scale factor for the voltages on the magnetic poles is used to compensate for different gap distances between the electric poles (2 LX gap) and the magnetic poles (2 LY gap)—the reason for the exponent of “2” in the stigmation ter...

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PUM

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Abstract

An ExB Wien mass filter provides an independently-adjustable electric field combined with the dipole electric field required for mass separation. The independently adjustable electric field can be used provide a larger optical aperture, to correct astigmatism and to deflect the beam in direction parallel and/or perpendicular to the magnetic field.

Description

[0001]This application claims priority from U.S. Provisional Application No. 61 / 476,135, filed Apr. 15, 2011, which is hereby incorporated by reference.TECHNICAL FIELD OF THE INVENTION[0002]The present invention relates to charged particle beam systems, and in particular, to a mass filter for an ion beam system.BACKGROUND OF THE INVENTION[0003]Some focused ion beam (FIB) columns are intended for use with ion sources that emit multiple ion species. In order to select only one of these ion species for the beam to be focused on a substrate, the FIB column will typically include a mass filter. One type of mass filter, a “Wien filter,” uses crossed electric and magnetic fields (ExB) to deflect unwanted ion species off-axis, thereby causing them to strike a mass-separation aperture and is also referred to as an “ExB filter.” The relative strengths of the electric and magnetic fields are set so that the desired ion species will pass through the mass filter undeflected, then through a mass-...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): H01J49/22H01J49/20
CPCH01J2237/31749H01J37/05
Inventor TUGGLE, DAVIDPARKER, N. WILLIAM
Owner FEI CO
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