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CHEMICAL ETCHING OF LaB6-CATHODES

IP.com Disclosure Number: IPCOM000062480D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Bug, U: AUTHOR [+2]

Abstract

Implementation of Critical Koehler Illumination (C.K.I.) in E-beam lithography tools requires LaB6-cathodes with outstanding surface quality. Disclosed is a fabrication technique for such cathodes. The ideal LaB6-cathode for C.K.I. is a perfect single crystal confined in size and shape by crystal planes of high symmetry (represented by low indices) defining a truncated pyramid (frustrum). The present technique utilizes a single crystal LaB6-cathode already shaped as a truncated cone by means of conventional grinding techniques. The size of the flat top, the cone angle and the crystal orientation are crucial parameters determining size and shape of the cathode after treatment. Crucial process parameters are cathode temperature Tc, reactor gas pressure p and ionization voltage vi .

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CHEMICAL ETCHING OF LaB6-CATHODES

Implementation of Critical Koehler Illumination (C.K.I.) in E-beam lithography tools requires LaB6-cathodes with outstanding surface quality. Disclosed is a fabrication technique for such cathodes. The ideal LaB6-cathode for C.K.I. is a perfect single crystal confined in size and shape by crystal planes of high symmetry (represented by low indices) defining a truncated pyramid (frustrum). The present technique utilizes a single crystal LaB6-cathode already shaped as a truncated cone by means of conventional grinding techniques. The size of the flat top, the cone angle and the crystal orientation are crucial parameters determining size and shape of the cathode after treatment. Crucial process parameters are cathode temperature Tc, reactor gas pressure p and ionization voltage vi . All together they have impact on the emission current ie . Its variation in time is useful for leading the process. Depending on the choice of parameters, the dry etching process exhibits an isotropic or an anisotropic character. For finishing LaB6-cathodes the anisotropic process (preferential etching) is the proper choice. The cathode crystal heated up to Tc l emits electrons which become accelerated by vi . They generate positive ions in the reactor gas which impact onto the crystal, eroding the surface and poisoning the electron emission. At a critical pressure Pmin and at the parameter set (Tc l, Pmin) the ions preferentially attack the surface of t...