A semiconductor memory device having a thyristor is manufactured in a
manner that makes possible self-alignment of one or more portions of the
thyristor. According to an example embodiment of the present invention, a
gate is formed over a first portion of doped substrate. The gate is used
to mask a portion of the doped substrate and a second portion of the
substrate is doped before or after a spacer is formed. After the second
portion of the substrate is doped, the spacer is then formed adjacent to
the gate and used to mask the second portion of the substrate while a
third portion of the substrate is doped. The gate and spacer are thus used
to form self-aligned doped portions of the substrate, wherein the first
and second portions form base regions and the third portion form an
emitter region of a thyristor. In another implementation, the spacer is
also adapted to prevent formation of salicide on the portion of the
thyristor beneath the spacer, self-aligning the salicide to the junction
between the second and third portions. In addition, dimensions such as
width and other characteristics of the doped portions that are used to
form a thyristor can be controlled without necessarily using a separate
mask.
