Six-transistor SRAM semiconductor structures and methods of fabrication

A semiconductor structure for a cross-coupled PNP and NPN bipolar transistors and an adjoining access transistor comprising:

• a first conductivity type semiconductor substrate having an upper surface;
• an isolation region extending into the substrate from the upper surface defining first and second adjoining pockets of first conductivity type semiconductor material, each of the first and second pockets having an upper surface and extending to a buried layer of opposite conductivity type at a bottom of each pocket;
• in the first pocket:
• a shallow well region of opposite conductivity type extending from the upper surface into the pocket over a first portion of the pocket, but not extending over a second portion of the pocket and not extending to the buried layer;
• a first field effect transistor gate disposed over some of the first portion and some of the second portion;
• a second field effect transistor gate spaced apart from the first field effect transistor gate, the second field effect transistor gate being disposed only over some of the first portion;
• first and second regions of first conductivity type disposed on opposing sides of the first gate and a first side of the second field effect transistor gate;
• a first region of opposite conductivity type disposed on an opposing side of the second gate;
• in the second pocket:
• an access transistor coupled to the cross-coupled PNP and NPN bipolar transistors;
• and
• electrical connections to each of the first and second regions of first conductivity type disposed on opposing sides of the first gate and the first side of the second field effect transistor gate and to the first region of opposite conductivity type on the opposing side of the second gate.