Method of making thin oxide portions particularly in electrically erasable and programmable read-only memory cells

A method for producing an EEPROM cell comprising the steps of:

• defining an active area on a doped silicon substrate by growing gate oxide regions;
• depositing a first layer of radiation-sensitive material on a the active area and gate oxide regions;
• masking portions of the first layer of radiation-sensitive material layer;
• removing unmasked portions of the first layer of radiation-sensitive material layer, leaving protective portions of the first layer of radiation-sensitive material on the active area and on the gate oxide regions;
• heavily doping the active area to form defined heavily doped regions;
• removing the protective portions of the first layer of radiation-sensitive material;
• diffusing heavily doped drain regions;
• growing a first oxide layer on the active area;
• depositing a second layer of radiation-sensitive material on the gate oxide regions and first oxide layer;
• masking the portions of the second layer of radiation-sensitive material;
• removing unmasked portions of the second layer of radiation-sensitive material, leaving an opening in a central portion of the active area defined on either side by protective portions of the second layer of radiation-sensitive material;
• lightly doping the active area to form a defined lightly doped region;
• removing a portion of the first oxide layer within the opening;
• removing the protective portions of the second layer of radiation-sensitive material;
• growing a second oxide layer on the active area, simultaneously yielding gate oxide regions over the defined heavily doped regions and a tunnel oxide region over the defined lightly doped region;
• depositing a layer of polysilicon on the second oxide layer and gate oxide regions;
• masking portions of the polysilicon layer;
• and
• removing unmasked portions of the polysilicon layer, yielding a floating gate electrode.