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Ion Beam Methods

IP.com Disclosure Number: IPCOM000237996D
Publication Date: 2014-Jul-24
Document File: 7 page(s) / 3M

Publishing Venue

The IP.com Prior Art Database

Abstract

Ion beam methods include a modified liquid metal ion source that reduces shorting caused by evaporated metals depositing on the source, a conjugate beam blanker for use with an energy filtered column, and a method of rapidly producing a fiducial for use in aligning a charged particle beam.

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Ion Beam Methods

Modified Liquid Metal Ion Source

            Liquid metal ion (“LMI”) sources are used in focused ion beam systems.   Ions are extracted from the liquid metal at the edge of a needle, and focused into a beam to process a sample.   A typical liquid metal ion source includes a glass base and two electrode posts extending from the glass base. Filaments connected to each of the electrode posts support a needle with an attached reservoir.  Liquid metal from reservoir migrates down the needle to replace the metal lost as ions are extracted.  A suppressor cap positioned over the other components of the LMIS and having a hole for extracting the ions suppresses the emission of ions away from the end of the needle.   Some LMISs use a pure metal, such as gallium or gold, whereas other LMIS use an alloy.  Gallium is a liquid at room temperature, while other metals used in the source must be heated to remain in a liquid phase during operation.  

While the goal is for all the metal to leave the LMIS from the end of the needle, some of the metal evaporates from the reservoir and other places along the needle.  Depending the duration and heating current, liquid metal ion material from the reservoir will be deposited on the LMI insulated glass base.  The thickness will eventually be thick enough that a short will occur between the filament leads and/or the suppressor.  This will be more prevalent of LMI emitters that require constant heating (Au, AuSi, AuGe, PdAsB, etc.).   

Moreover, after a period of 1 hour, the localized pressure around the emitter increases enough to cause excessive neutrals to escape through the suppressor hole. This has proven to be problematic resulting in large instabilities in the emission, although the mechanism is not clear. 

To solve the problem of shorting, a shield is provided between the reservoir and the glass base.   The shield prevents the build up of conductive material on the base and will lengthen the useful life of the emitter.  A hole provided in the glass base to vent the gas pressure, allowing the neutrals to be exhausted by the vacuum system.  

In the past, shorting to the suppressor was solved by a shadow feature where the base fits into the suppressor.  This has proven to be insufficient for LMI for the alloy sources which run at elevated temperatures and deposit significant thickness on the base.  The shadow size can be increased but it is margin with the real estate available with the present base diameter.  This solution is easily retrofitable to existing systems and also prevents the shorting of the filament leads.

CONJUGATE BLANKING USING ENERGY FILTER

Blanking is a method for turning the beam on and off using a “blanker” which deflects the beam such that it no longer passes into the lower lens, and thus does not reach the target.  Some system use a “Fast Beam Blanker” (FBB) which is a single-deflection high-voltage (typically between 100 and 200V...