GB854202A - Improvements in or relating to the treatment of solid bodies with liquids - Google Patents

Abstract

854,202. Electrolytic etching. MORLE, C. W. (Philco Corporation). July 8, 1957, No. 21526/57. Class 41 A method of treating a body 10 of semiconductive material, e.g. a germanium wafer, with a liquid, e.g. a solution of an electrolyte, comprises forming a drop 18 of the liquid with one surface of the drop exposed to atmosphere and the other contacting the body 10, feeding liquid to the inner part of the drop, and maintaining a gaseous current around the drop 18 in such a manner as to propel liquid of the exposed surface away from the body surface 10. The liquid may be an aqueous solution of sodium nitrate, sodium chloride, sodium sulphate, potassium nitrate, or nitric acid. A pump 17 delivers the electrolyte solution 14 through a flexible conduit 16 to an inner nozzle 12 having a central tube 32 from which the solution issues to contact the wafer 10, either in the form of a drop 18 or as a self-supporting jet. A vacuum pump 20 applies suction through conduits 21, 23 to an outer co-axial nozzle 13, whereby solution, after contacting the wafer 10, is withdrawn through the nozzle 13 and passed by the conduit 23 to a closed reservoir 22. An electrode 30, e.g. of stainless steel, supplies current to the solution, the wafer 10 being suitably connected in circuit as indicated. A gas trap 31 is provided above the electrode 30. In operation, the rate of the pumps 17, 20 is adjusted to give a bubble at the outlet of the tube 32, liquid being continuously supplied to and taken from the bubble, and the wafer 10 contacted by the bubble, e.g. by accelerating the pump 17 or by pinching the tube 16, e.g. through a relay-operated device 40. The liquid then spreads outwardly over the surface of the wafer 10 to take up a stable position. Electrolysing current is passed, e.g. for up to 20 seconds, and the etching promoted by the application of light. The thickness of the etched portion of the wafer 10 may be measured electronically e.g. by a thin wire sensing electrode 37 connected to a circuit unit 39. Electroplating may be initiated by reversing the polarity of the electrolysing circuit. In a modification, the electrolyte contacts the wafer 10 in the shape of a jet which spreads out on contacting the wafer, the constructional details of the apparatus being as described above, except for the omission of the device 40. Reference has been directed by the. Comptroller to Specification 805,291.