Initiating with a consistently doped silicon wafer, the
manufacture of ICs requires thousands of consecutive procedure steps. One of
the most crucial procedure steps utilized in the semiconductor manufacture are:
Lithography
Lithography is
utilized to move a pattern from a photomask to the surface of the wafer. The
gate area of a metal–oxide–semiconductor transistor is specified by a certain
pattern. The pattern details are recorded on a layer of photoresist that is
used on the top of the wafer. While exposed to light (commonly UV) or an
additional source of lighting (e.g. X-ray), the photoresist alters its physical
properties. The photoresist is either produced by (dry or wet) etching or by
conversion to volatile substances via the exposure itself. The pattern
specified with mask is either gotten rid of or stayed after development,
relying when the type of resist is negative or positive. The produced
photoresist could function as an etching mask for the underlying layers.
Etching
Etching
is made use of to eliminate material precisely to produce patterns. The pattern
is specified by the etching mask, due to the fact that the parts of the
material, which must remain, are guarded by the mask. The unmasked material can
be eliminated either by wet or dry etching. Wet etching is highly isotropic
that controls its application and the etching time can be managed difficultly.
Wet etching isn't fit to transmit patterns with sub-micron feature dimension
due to of the so-called under-etch effect. Wet etching has a high selectivity
(the etch rate highly relies on the material) and it doesn't harm the material.
Beyond dry etching is very anisotropic yet minimal selective. It is a lot more
capable for transmitting small structures.
Deposition
A wide range of layers of various materials
need to be deposited throughout the Integrated Circuit manufacture procedure. The 2 crucial deposition techniques are the physical vapor
deposition and the chemical vapor
deposition. Throughout accelerated gas ions sputter particles from a
sputter target in a minimal pressure plasma chamber. The concept of is a
chemical reaction of a gas mixture on the substrate surface at high temps. The
requirement of high temperature levels is one of the most restricting aspect
for using chemical vapor deposition. This trouble can be prevented with plasma
enhanced chemical vapor deposition (PECVD), where the chemical reaction is
increased with radio frequencies as opposed to high temperature levels. A
crucial factor for this procedure is the consistency of the deposited material,
particularly the layer density. Chemical vapor deposition has a much better
harmony compared to physical vapor deposition.
Chemical
Mechanical Planarization
Procedures like deposition, oxidation, or
etching, which customize the topography of the wafer surface lead to a
non-planar surface. Chemical mechanical planarization is made use of to plane
the wafer surface with a chemical slurry. A planar surface is essential for
lithography because an appropriate pattern transfer. Chemical Mechanical
Planarization allows indirect pattering, since the material elimination
constantly initiates on the highest possible areas of the wafer surface. This
implies that at specified lower lying areas like a trench the material can be
left. Along with the deposition of non-planar layers, Chemical Mechanical
Planarization is an efficient procedure to develop IC structures.
Oxidation
Oxidation is a
procedure that transforms silicon on the wafer right into silicon dioxide. The
chemical reaction of silicon and oxygen currently initiates at normal
temperature level yet quits after a really thin native oxide film. For a
reliable oxidation rate the wafer need to be settled to a furnace with oxygen
or water vapor at raised temps. Silicon dioxide layers are utilized as high
quality insulators or masks for ion implantation. The capacity of silicon to
create good silicon dioxide is a vital factor, why silicon is still the
dominating component in Integrated Circuit manufacture.
Ion
Implantation
Ion implantation is
the leading procedure to present dopant impurities right into crystalline
silicon. This is done with an electrical field that increases the ionized atoms
or particles to ensure that these particles penetrate right into the target
material till they come to rest due to connections with the silicon atoms. Ion
implantation has the ability to regulate specifically the distribution and dose
of the dopants in silicon, since the penetration deepness depends upon the
kinetic energy of the ions which is relative to the electric field. The dopant
dose are regulated by differing the ion source. After ion implantation the
crystal structure is harmed that means worse electric properties. An additional
trouble is that the implanted dopants are electrically inactive, since they are
founded on interstitial sites. After ion implantation a thermal procedure step
is essential that fixings the crystal damages and activates the dopants.
Diffusion
Diffusion is the
flow of impurity atoms in a semiconductor product at high temperature levels.
The driving pressure of diffusion is the concentration gradient. There is a
wide variety of diffusivities for the different dopant species, that depend
upon how easy the particular dopant impurity could move with the material.
Diffusion is used to anneal the crystal deficiencies after ion implantation or
to present dopant atoms right into silicon from a chemical vapor source. In the
last instance the diffusion time and temp figure out the deepness of dopant penetration.
Diffusion is made use of to form the source, channel, and drain areas in a MOS
transistor. Diffusion could also be an undesirable parasitical effect, due to
the fact that it happens throughout all high temperature level procedure steps.
