Patent Application
20150179327
1. Technical Field
The present disclosure relates to magnetic structures. More particularly, the present disclosure relates to adjusting the strength of a magnetic apparatus.
2. Description of the Background Art
A conventional technique for adjusting the strength of a magnet involves controlling a temperature of the magnet. For example, a temperature-controlled chuck may be used to heat a magnet array in a controllable manner. By adjusting the temperature of the array, the strength of the entire magnet array may be adjusted at the same time.
One embodiment relates to an apparatus for adjustment of local magnetic strength in a magnetic device. A stage holds the magnetic device, and a sensor measures a magnetic field at locations above the magnetic device so as to generate magnetic field data. A computer system detects a non-uniformity in the magnetic field from the magnetic field data and determines a location and a duration for application of a pulsed laser beam to correct the non-uniformity. A laser device applies the pulsed laser beam at said location for said duration.
Another embodiment relates to a method of adjusting local magnetic strength in a magnetic device. Steps of the method include: holding the magnetic device using a translatable stage; measuring a magnetic field using a sensor at locations above the magnetic device so as to generate magnetic field data; detecting a deviation in the magnetic field from the magnetic field data; determining a location and a duration for application of a pulsed laser beam to correct the deviation; and applying the pulsed laser beam at said location for said duration for adjustment of the local magnetic strength.
Another embodiment relates to a system for fine-tuning a magnet array with localized energy delivery. The system may be automated. The system includes: a translatable stage for holding and translating the magnet array; an inspection microscope for aligning a position of the magnet array; a sensor that measures a magnetic field at locations above the magnet array so as to generate magnetic field data; a computer apparatus that detects a deviation in the magnetic field from the magnetic field data; and a laser device that applies the pulsed laser beam to correct the deviation.
Other embodiments, aspects and features are also disclosed.
The present disclosure provides an innovative technique that does not use temperature control for adjusting local magnetic strength in a magnetic device. Rather, the technique uses laser pulses of a specific wavelength to provide targeted energy delivery. The targeted energy delivery effectively excites and/or distorts the lattice structure of the material to quench or reduce magnetism in the local vicinity of the delivered energy.
In one implementation, the wavelength may be related to absorption properties of the target magnetic material. The laser pulses may be of ultra-short duration to avoid excessive heating of the work piece that may adversely affect non-targeted magnetic domains. For example, research has found that, to adjust manganite material, the laser pulses may have a frequency above a terahertz and aduration on the order of 100 femtoseconds long.
In accordance with an embodiment of the invention, the presently-disclosed technique may be used in the manufacturing process for constructing a magnetic lens array. Using this technique, the magnetic lens array may be constructed to meet specifications so as to be used as a high-performance passive electron-optic element.
Meeting such specifications is difficult using conventional manufacturing processes because there are many sources that can introduce non-uniformity into the array. For example, machining tolerances may be not met, or there may be non-uniformities in the properties of the raw material, or there may be non-uniformity in the solenoid field used to charge the magnet array. In addition, it is often prohibitive to re-machine a magnetic part after magnetization of the part due to the difficult issue of removing magnetized particles.
The presently-disclosed technique provides for targeted delivery of light energy at a specified wavelength so as to adjust local magnetism without heating up the overall material of the work piece. By the local and direct application of energy to tune the magnetism of the work piece, this technique avoids issues relating to machining a magnetized part. By way of this technique, the peak field strengths and general lensing properties (such as astigmatism) may be adjusted to compensate for defects in the manufacturing process that may be unavoidable.
The magnetic lens array may be used, for example, as an electron-optics element in an electron beam column of an electron-beam imaging apparatus. The electron-beam imaging apparatus may be used, for example, for inspection and/or review of manufactured substrates. When peak field strength and/or astigmatism are corrected using the presently-disclosed technique, improved electron optics and imaging performance results.
In this illustrative example, the Bz field is shown as may be measured before adjustment 120. As depicted, the Bz field before adjustment 120 is shown to have a non-uniform peak 125 due to one lens 110 that is substantially higher than the peaks 127 due to other lenses 110 in the array. This non-uniform peak 125 indicates a non-uniformity in the corresponding lens 110 that may be corrected in accordance with an embodiment of the invention.
As further depicted, the non-uniform peak 125 may be shifted to one side of the expected location of the peak. A pulsed laser beam 130 of wavelength λ may be directed to a section of the corresponding lens 110 so as to make an adjustment 135 to the non-uniformity of the magnetic (B) fields. The Bz field after the adjustment 140 so as to correct the non-uniformity is illustrated.
In the illustrated example, the non-uniform peak 125 is shifted to the left side compared with the expected position of the peak relative to the corresponding lens 110. In this case, the pulsed laser beam 130 of wavelength λ may be directed to a section on the right side of the corresponding lens 110 so as to correct the non-uniformity.
An exemplary apparatus for detecting and correcting non-uniformities of a magnetic device is described below in relation to
As depicted, the apparatus 200 may include an XYZ stage 204 that holds the magnetic device 202. The XYZ stage 204 may be used to move the magnetic device 202 in the x, y, or z directions under control of a computer apparatus 212. An inspection microscope 210, which may be an optical microscope, may be used to image the magnetic device 202 for alignment and visual inspection. The microscope may have various illumination capabilities, such as for bright field and dark field imaging, for example.
A Hall sensor 206 may be positioned above the magnetic device 202. The stage 204 may be translated in x, y, and/or z directions under the Hall sensor 206 so as to measure the magnetic field at different locations above the magnetic device 202. The inspection microscope 210 may be used for aligning the magnetic device 202 relative to the hall sensor 206. Measurement data from the Hall sensor 206 may be provided to the computer apparatus 212. In other embodiments, other types of magnetic sensors may be used, such as, for example, magnetorestrictive sensors, giant magnetorestrictive sensors, and magneto optical Kerr effect sensors.
A laser device 208 may be positioned such that a pulsed laser beam may be directed at the magnetic device 202. In one implementation, the laser device 208 may have a controllable orientation so as to controllably change an incident angle of the pulsed laser beam that is directed to the magnetic device 202. The stage 204 may be translated in x, y, and/or z directions under the laser device 208 so that the pulsed laser beam may be directed to a desired location on the magnetic device 202. The inspection microscope 210 may be used for aligning the magnetic device 202 relative to the laser device 208 and for targeting the pulsed laser beam onto a desired location on the magnetic device 202.
The targeted location at which the pulsed laser beam impinges upon the magnetic device 202 may be imaged and observed using the inspection microscope 210. The inspection microscope 210 may also be used to visually inspect the magnetic device 202 for observable defects.
Per block 302, the magnetic device is held on a translatable stage. The magnetic device may be, for example, a magnet array 100 as described above. The stage may be, for example, an XYZ stage 204 as described above.
Per block 304, magnetic fields generated by the magnetic device may be measured. This step may involve using a Hall sensor (a sensor that uses the Hall effect) to measure the magnetic field at locations above the magnetic device. The magnetic device may be translated under the Hall sensor using the translatable stage, and the measurement data may be received, stored, and analyzed by a computer system.
Per block 306, a determination may be made of non-uniformities (i.e.
deviations) in the magnetic field to be corrected, if any. This determination may be made by the computer system or by an operator using the computer system. An example of a non-uniformity needing correction is discussed above in relation to
Per block 308, if it is determined that no non-uniformities need correction, then the method 300 may be done (complete). Otherwise, if it is determined that one or more non-uniformities need correction, then, per block 310, the method 300 may determine locations and durations for application of corrective laser pulses. This determination may be made by the computer system or by an operator using the computer system. For example, the location for application of corrective laser pulses may be determined from the location of the field non-uniformity, and the duration for application of corrective laser pulses at a particular location may be determined from the magnitude of the deviation needing correction.
Per block 312, corrective laser pulses may then be applied at the locations and for the durations determined in block 310. Thereafter, the method 300 may, optionally, loop back to block 304 and a further field check inspection may be performed so as to verify that the non-uniformity has been corrected or determine if any remaining non-uniformities still exist that need correction.
The present application claims the benefit of U.S. Provisional Patent Application No. 61/920,461, inventor John Gerling, filed Dec. 23, 2013, the disclosure of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61920461 | Dec 2013 | US |
