Electron beam evaporator having beam spot control

#The present invention relates in general to electron beam evaporators and more particularly to such evaporators having beam spot control.

#Heretofore, it has been proposed to employ one pair of auxiliarly pole piece structures projecting inwardly from a pair of main pole piece structures of an electron beam evaporator to provide a magnetic lens for adjusting or controlling the beam spot size at the crucible target. It was also suggested that the auxiliary pole piece structures take the form of magnetically permeable screws which would be axially translatable for adjusting the beam spot size. Such an electron beam evaporator structure is disclosed in U.S. Pat. No. 3,483,417 issued Dec. 9, 1969.

#It is also known from the prior art to provide a pair of inwardly directed pole piece portions outside of the curved electron beam path for defocusing the electron beam and thus increasing its spot size to increase the rate of evaporation at the higher input powers to the electron gun. Distributing the electron beam energy over a greater area of the surface of the evaporant also minimizes the possibility of ejection of large particles of the evaporant materials, a common problem with sublimable evaporants such as Si, SiO.sub.z, C.sub.r and the like.

#FIG. 1 is a top elevational view, partly in schematic form, of an electron beam evaporator incorporating features of the present invention,

#FIG. 2 is a side elevational view of the structure of FIG. 1 taken along line 2--2 in the direction of the arrows,

#FIG. 3 is a schematic sectional view of a portion of the structure of FIG. 1 taken along line 3--3 in the direction of the arrows and showing the focusing and defocusing forces on an electron stream produced by a magnetic lens,

#Referring now to FIGS. 1 and 2 there is shown an electron beam evaporator 11 having features of the present invention. The electron beam evaporator 11 includes a solid block 12 of thermally conductive metallic material, as of copper. The opposite sides of the conductive block 12 are recessed at 13 and 14 to receive magnetic pole piece structures or plates 15 and 16, as of magnetic alloy permeable or ferromagnetic material. The pole piece structures 15 and 16 are energized with magnetic flux by means of a transversely directed permanent magnet 17 interconnecting the pole pieces 15 and 16 and passing through a transverse bore 18 in the copper block 12.

#A conical recess 19 in the upper side of the copper block 12 serves as a crucible 21 for containing a material 22 to be evaporated. Water coolant channels, not shown, course through the copper block for cooling same in use.

#A thermionic directly heated filamentary cathode emitter 23 is contained in the block body structure 12 and the block is recessed at 24 to hold an acclerating anode structure not shown. The anode, located in close proximity to cathode 23 is operated at ground potential and which cooperated with a high negative potential, as of -6 to -14 kV, applied to the filamentary cathode 23 for projecting a ribbon shaped beam of electrons 25 from the cathode 23 through the recess 24 and into an arcuate beam path to the crucible 21. The electrical potential applied between the filamentary cathode 23 and the recessed walls 24 of the body and anode, in cooperation with a strong transverse magnetic field produced between the planar pole structures 15 and 16 causes the beam 25 to take the arcuate path to the crucible. In addition, the fringing magnetic field over the top surface of the block 12 has a certain curvature while facilitates lateral focusing of the electron beam 25 into the crucible 21.