A static random access memory (SRAM) cell is given increased stability and latch-up
immunity by fabricating the PMOS load transistors of the SRAM cell to have a very
low drain/source dopant concentration. The drain/source regions of the PMOS load
transistors are formed entirely by a P-- blanket implant. The PMOS load transistors
are masked during subsequent implant steps, such that the drain/source regions
of the PMOS load transistors do not receive additional P-type (or N-type) dopant.
The P-- blanket implant results in PMOS load transistors having drain/source regions
with dopant concentrations of 1e17 atoms/cm3 or less. The dopant concentration
of the drain/source regions of the PMOS load transistors is significantly lower
than the dopant concentration of lightly doped drain/source regions in PMOS transistors
used in peripheral circuitry.