Disclosed is a semiconductor device, such as a semiconductor memory device,
having structure wherein invasion of minority carriers from the
semiconductor substrate into components of the device, formed on the
substrate, can be avoided. The semiconductor memory device can be an SRAM
or DRAM, for example, and includes a memory array and peripheral circuit
on a substrate. In one aspect of the present invention, a buried layer of
the same conductivity type as that of the substrate, but with a higher
impurity concentration than that of the substrate, is provided beneath at
least one of the peripheral circuit and memory array. A further region can
extend from the buried layer, for example, to the surface of the
semiconductor substrate, the buried layer and further region in
combination acting as a shield to prevent minority carriers from
penetrating to the device elements. As a second aspect of the present
invention, first carrier absorbing areas (to absorb minority carriers) are
located between the memory array and the switching circuit of the
peripheral circuit, and second carrier absorbing areas are provided to
surround input protective elements of the device. As a third embodiment of
the present invention, a plurality of isolation regions of the same
conductivity type are provided, with unequal voltages applied to these
isolation regions, or unequal voltages applied to the substrate, on the
one hand, and to these isolation regions, on the other.
