| 摘要 |
1,197,641. Semi-conductor devices; discharge apparatus. HITACHI Ltd. 14 Sept., 1967, No. 41946/67. Headings H1K and H1X. An electric charge is provided permanently on the surface of an insulating film on a semiconductor substrate, thereby controlling the concentration of charge induced within the surface of the substrate by the ions present in the insulating film. The film may, for example, be of SiO 2 on a Si substrate, Si 3 N 4 or Al 2 O 3 , Ge or intermetallic compounds also being referred to as substrate materials. The charge may be applied by means of a corona discharge appartus comprising a central tungsten wire 7, Fig. 16, surrounded by an earthed cylindrical copper electrode 6 having a segment missing, the semiconductor substrate 3 carrying the film 4 being mounting on an earthed conducting plate 5. Charge of either polarity may be applied depending upon the application. The charge has been found to diminish to a certain level as a function of time after the initial charging-up process, and this partial discharge, which is believed to be due to the migration of positive impurity ions within the insulating film, can be speeded up by heating. A second charging process is followed by a very much smaller degree of discharge. The amount of charge on the insulating film may be controlled by means of an ionized atmosphere, produced for example by U.V. light or X-rays, and this method of control may be used to limit the charge to only part of the surface. The application of a layer of an anti-static agent or the inclusion of a phosphorus oxide, e.g. as a phosphosilicate glass, in the insulating film similarly may be used to control the charge. In one application a portion 29, Fig. 9, of the surface of the oxide layer 24 of a N-channel depletion mode MOS field effect transistor is provided with a positive charge to improve the drain current/gate voltage, characteristic. In the case of a P-channel enhancement mode device the charge applied is negative. PNP or NPN Si planar transistors having SiO 2 coatings may have their current gains increased by the application of permanent charges to the surfaces of the oxide coatings. The Specification includes a description of a method of testing the stability of a silicon oxide film on a Si substrate by measuring the capacitance/voltage characteristic of an MOS diode with various charges applied to the oxide surface. The electrode applied to the oxide in this case comprises a copper pipe having mercury applied to the end contacting the oxide. |
