from the passivation and glass layer deposited over the surface of the
die to protect it from mechanical damage and corrosion,
are also used for
components or structures in the active circuit from each other, and as
dielectric structures for MOS transistors, capacitors, and the like.
for dielectric layers include: 1)
for diffusion and ion implant processes; 2)
from doped oxides; 3)
of doped films to prevent dopant loss; 4)
of impurities; and 5) mechanical and chemical
oxide of silicon, is the
widely used dielectric in wafer fabrication. There are many ways
to grow silicon dioxide on the surface of silicon, but it is most
often done through a process known as
Thermal oxidation consists of exposing the silicon to
as water and oxygen at
temperatures. This process has good control over the thickness and
properties of the SiO2 layer.
1. Example of a
4-Stack Diffusion Furnace that
can be used
for Thermal Oxidation of SiO2
by which SiO2 is formed from silicon has been fully understood over the
years. A newly exposed silicon surface quickly oxidizes to form an
SiO2 film on its surface. As oxidation progresses, silicon is
and the SiO2 layer
moving the Si-SiO2 interface
into the silicon substrate.
process of thermal oxidation can be classified as either dry or wet
dry oxidation, the moxidizing agent is oxygen, and
is governed by the following reaction: Si (solid) + O2 (vapor) =
SiO2 (solid). In
the main oxidizing agent is water, and is governed by the following
reaction: Si (solid) + H2O (vapor) =
SiO2 (solid) + 2H2.
other commonly-used dielectric materials aside from SiO2.
Silicon dioxide doped with phosphorus (commonly referred to as P-glass,
or PSG) is used in many applications because it inhibits diffusion of
sodium impurities and exhibits a smooth topography. Adding boron
to PSG results in
glass (BPSG), which flows at lower temperatures than PSG (850C-950C for
BPSG versus 950C-1100C for PSG).
with enough oxygen content is also semi-insulating and has actually been
used in circuit passivation.
is an excellent moisture barrier while stoichiometric silicon nitride is
used in oxidation masks and for MOS gate dielectric.
dielectric layers are usually deposited by
(CVD). The layer material deposited depends on the
used during processing.
CVD system (left) and a
sputtering system (right) which may
be used for
depositing various dielectric layers
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