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Fixed and variable threshold N-channel MNOSFET integration technique

  • US 3,978,577 A
  • Filed: 06/30/1975
  • Issued: 09/07/1976
  • Est. Priority Date: 06/30/1975
  • Status: Expired due to Term
First Claim
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1. The method of making fixed and variable threshold field effect transistors comprising the steps of:

  • providing a plurality of paired source and drain regions and at least one isolation region of n-type semiconductor material in a semiconductor material of p-type conductivity,providing a field dielectric structure over said source, drain and isolation regions comprising successive layers of silicon dioxide, aluminum oxide and silicon dioxide;

    selectively removing said field dielectric structure from the channel regions of a plurality of source and drain regions associated with fixed threshold transistors;

    growing a layer of silicon dioxide having a thickness of about 450 to 525 angstrom units in said channel regions of said fixed threshold transistors;

    selectively removing said field dielectric from the channel regions of a plurality of sorce and drain regions associated with variable threshold transistors;

    growing a layer of silicon dioxide having a thickness of about 31-34 angstrom units in said channel regions of said variable threshold transistors;

    depositing a layer of silicon nitride over said field dielectric structure and said silicon dioxide layers in said channel regions;

    depositing a layer of silicon dioxide over said silicon nitride layer; and

    depositing conductive metallurgy to interconnect said fixed and variable threshold transistors.

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