Formation of elements of a vertical bipolar transistor is described, in
particular a vertical npn transistor formed on a p-type substrate.
Accordingly, an improved method not limited by constraints of
photolithography, and an ensuing device made by such methods, is
described. A temporary spacer (e.g., an oxide spacer) is deposited over a
dielectric separation layer. The temporary spacer and dielectric
separation layers are then anisotropically etched, forming a dielectric
"boot shape" on a lower edge of the dielectric separation layer. An area
within this non-photolithographically produced boot region defines an
emitter contact window. Since the boot tip is formed through deposition
and etching techniques, the emitter window is automatically aligned
(i.e., self-aligned) with an underlying base region. Feature sizes are
determined by deposition and etching techniques. Consequently,
photolithography of small features is eliminated.