Method of making dense flash EEPROM cell array and peripheral supporting circuits formed in deposited field oxide with sidewall spacers

A method of constructing a plurality of memory cells across a surface of a semiconductor substrate, comprising the steps of:

• forming a plurality of parallel elongated strips of field oxide with walls substantially perpendicular to said substrate surface, said field oxide strips being elongated in a first direction along said substrate surface and spaced apart in a second direction to form openings therebetween, said first and second directions being substantially orthogonal with each other,
• forming a first plurality of parallel elongated strips of polysilicon over said field oxide strips and extending into said openings, said first plurality of polysilicon strips being elongated in said second direction and spaced apart in said first direction, thereby exposing portions of the field oxide strips and openings which lie between the polysilicon strips,
• removing by a dry etch process at least a portion of the field oxide strips that are exposed between the first polysilicon strips, and
• implanting ions into the surface of the substrate in regions positioned between the first polysilicon strips including locations where the field oxide strips extending therebetween have been removed, said implanted regions being elongated in the second direction.