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Field inversion control for N-channel device integrated circuits

  • US 4,011,105 A
  • Filed: 09/15/1975
  • Issued: 03/08/1977
  • Est. Priority Date: 09/15/1975
  • Status: Expired due to Term
First Claim
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1. A method of making an N-channel MOS integrated circuit structure comprising the steps of:

  • providing a substrate of a P--type semiconductor material and forming a uniform thin oxide layer along a major surface of the substrate;

    ion-implanting a P-type dopant through the oxide layer to form immediately thereunder a uniform layer of P+-type semiconductor material extending along said major substrate surface;

    removing selected spaced-apart portions of the oxide layer and the underlying P+-type layer to leave a pattern of unimplanted active areas of the substrate spaced laterally by unremoved fields of oxide and underlying fields of P+-type material;

    forming a uniform thin oxide layer over the active substrate areas and forming a substantially thicker oxide layer over said fields;

    ion-implanting a P-type dopant through the thin oxide layer into the active substrate areas to form at said active areas layers of P-type semiconductor material whose resistivity is lower than that of the P--type substrate and higher than that of the P+-type fields; and

    forming N-channel MOS devices at least at selected ones of said layers of P-type material.

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