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Ion implantation for an emitter is usually performed at low energy and high dose, primarily because of the need for shallow emitter depth and high surface concentration.
English (United States)
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Ion Implantation of Emitter Region Through Thick Oxides
Ion implantation for an emitter is usually performed at low energy and high
dose, primarily because of the need for shallow emitter depth and high surface
Present technology uses a nitride layer in which all contact windows are
defined. By blocking out all other areas except where the emitter diffusion is
required, the oxide underneath can be etched out. This process presents no
problem when the oxide thickness in the area to be etched out on top of the base
area is of the order of 800 Angstroms.
Thicker oxide layers are sometimes used for lower defect levels, less land
capacitance and other reasons. A potential emitter-base passivation problem
exists when using such thicker oxide layers.
A wet etch to define the emitter area through the oxide layer and into the
silicon base causes undercutting of the oxide layer at the nitride edges. Since
ion implantation is masked out by the nitride overhang, there is no implantation in
the undercut area. In subsequent process steps metal is evaporated on the
wafer, filling the undercut, and covering all of the emitter area. The metal may
also cover part of the base area which can be exposed by the undercut. This
results in emitter base shorts. The structure produced is illustrated in Fig. 1,
which is not to scale.
In the improved process of this article the emitter base shorts are eliminated
by a modification of the nitride etch step. In this process react...