Welded silicon member

#Parts of the invention described herein were made by employees of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

#1. Field of the Invention

#The invention relates generally to welding. In particular, the invention relates to welding together two silicon workpieces.

#FIG. 1 is an isometric view of a silicon wafer tower which may be fabricated using the invention.

#FIG. 2 is an schematic illustration of a first embodiment of the welding apparatus and method of the invention.

#FIG. 3 is a schematic cross-sectional view of a inert gas welding head.

#A first embodiment of the invention is schematically illustrated in FIG. 2 for joining together two silicon bars 20, 22 butted together along a seam 24. The support structure is not illustrated but is conventional. Anode contacts 26, 28 are formed on the neighboring ends of the two bars 20, 22, and cathode contacts 30, 32 are formed on the other ends of the bars 20, 22. The two anode contacts 30, 32 are electrically tied to each other. A first DC heater power supply 34 has its negative terminal connected to the anode contact 26 of the first silicon bar 20, and a second DC heater power supply 36 has its negative terminal connected to the anode cathode contact 28 of the second silicon bar 22. The positive terminals of both power supplies 34, 36 are commonly connected to the two cathode contacts 30, 32. Both heater power supplies 34, 36 may be standard commercial DC welding power supplies. A single heater power supply 34 may be used if proper control is available to assure that nearly equal currents flow through the two silicon bars 20, 22. It is also possible in some circumstances to supply current to only one of the bars and rely upon thermal conduction and radiation to also heat the other one. If the bars have smooth sides and are tightly clamped together, sufficient electrical and thermal conductance between the two bars will distribute a single heating current between the bars.

#A DC welding power supply 38 has its positive terminal connected to both the cathode contacts 30, 32 and its negative terminal connected to the tungsten inert gas (TIG) head 40. The TIG head 40 has a structure schematically illustrated in FIG. 3. A power supply lead 42 penetrates a shroud 44 and terminates in a tungsten tip 46 positioned above the weld spot. When the welding power supply 28 is electrically biased sufficiently with respect to the underlying workpiece, an arc 50 is formed between the tungsten tip 46 and the more positively biased workpiece. The arc 50 is very hot and can easily melt the underlying workpiece. An inert gas such as argon is supplied from a gas source 48 into the shroud 44 and surrounds the arc 50 with an inert shield to prevent the weld from becoming contaminated.

#An alternative but related welding head is configured for plasma arc welding. A small flow of arc gas is flowed through an orifice adjacent the tungsten tip 46 to form the arc plasma. A shielding gas is flowed through an outer nozzle assembly encircling the tungsten tip 46 and arc gas orifice to shield the arc and weld zone. The arc gas may be the same as the shielding gas and may include one or more of the noble gases, particularly helium and argon, and may additionally include nitrogen and/or hydrogen in proportions selected to optimize the weld. The plasma is initiated by an internal low-current pilot arc between the electrode and the arc orifice. The pilot arc ionizes the arc gas to ignite the primary arc between the electrode and the workpiece. The operation of this equipment may be manual or automated.