| 摘要 |
874,349. Semiconductor devices. STANDARD TELEPHONES & CABLES Ltd. May 27, 1960 [May 29, 1959], No. 18357/59. Class 37. A very small PN junction is made in a semiconductor wafer 1 by providing the wafer with both an oxide and a wax coating, positioning the wax to expose a small area of oxide, removing the exposed oxide and forming the PN junction in the exposed area. Fig. 1 (a) shows a silicon wafer which has been polished mechanically and on which is formed an oxide layer by heating the wafer in an atmosphere containing oxygen. The coating thickness is about 5000 Š and is determined by optical interference methods. The slice is coated with paraffin wax 3 (Fig. 1 (c)). A sewing needle of .018 inches diameter then punctures the wax 3 (Fig. 1 (d)) under spring control so that the wafer is not damaged. The oxide coating below the puncture is then removed by a hydrofluoric acid etch (Fig. 1 (e).), the size of the junction being determined not by the needle area but by the etching period. The remainder of the wax film is removed (Fig. 1 (f)) and the junction is formed by depositing a layer of boric acid 4 (Fig. 1 (g)) on the oxide and heating it for 1¢ hours at 1220‹ C. in an atmosphere of wet oxygen. Boron diffuses into the wafer to form the junction (Fig. 1 (h)) and electrical contact is made by evaporation of copper to which a lead wire may be soldered. The rest of the boric oxide and silicon oxide are removed by a hydrofluoric acid wash (Fig. 1 (i)). The oxide coating may be produced by an electrolytic etching process using acetic acid and can be removed by an acid vapour, spraying or floating in acid instead of total immersion. The Specification states that a ring-shaped electrode might be made by penetrating the wax with a thin-walled tube. |
