The evolution of ICs
The manufacturing of integrated circuits
Electronics – Integrated circuits
Prof. Márta Rencz, Gergely Nagy
BME DED
October 8, 2012
The evolution of ICs
The manufacturing of integrated circuits
Moore’s law I.
IC production is one of the fastest growing industries.
Gordon Moore made a prediction in 1965, that the number
of transistors integrated on one chip would double every
18-24 month (exponential growth).
He thought it would stand for the next decade, it’s still true
today.
The 1 million transistors per chip barrier was broken through
in the 80’s:
1971: Intel 4004 – 2800 transistors, clock frequency: 1 MHz
2001: Intel P4 – 42 million transistors, clock frequency: 2 GHz
2011: Xeon Westmere-EX – 2.6 billion transistors, 10 cores, 30
MB L3 cache
More than Moore: growth of an even higher rate is possible
by using 3D structures (e.g. in RAMs)
The evolution of ICs
The manufacturing of integrated circuits
Moore’s law II.
The original figure showing the prediction in Moore’s paper
The evolution of ICs
The evolution of microprocessors
The manufacturing of integrated circuits
The evolution of ICs
The evolvement of DRAM capacity
The manufacturing of integrated circuits
The evolution of ICs
Trends in technology: the roadmaps
The ITRS roadmaps always
contain the latest
predictions and directions of
the development.
They are created by the
leaders of the industry.
The manufacturing of integrated circuits
The evolution of ICs
The predicted rate of the decrease
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The evolution of ICs
The increase in dissipation density
The manufacturing of integrated circuits
The evolution of ICs
The manufacturing of integrated circuits
Planar technology
The word planar implies that the devices are fabricated on
the surface of the silicon wafer in a 2D structure.
The basis is the silicon ingot made up of monocristalline
silicon.
The ingot is sliced into wafers:
diameter: 2-12”
width: 0.25-0.7 mm
A wafer can contain thousands of ICs that are manufactured
at the same time.
The evolution of ICs
Si ingots and wafers today
The manufacturing of integrated circuits
The evolution of ICs
The manufacturing of integrated circuits
Parties and clean rooms
During the manufacturing
process the wafers undergo the
steps in groups called parties.
A party is put in a furnace in
the picture at the top.
The photo at the bottom shows
a clean room where the
manufacturing steps are
performed. IC technology
requires a very high degree of
cleanness.
The evolution of ICs
The manufacturing of integrated circuits
The steps of IC manufacturing
The basic steps of IC manufacturing are
doping,
deposition of a layer,
selective removal of a layer,
lythography.
These entire process is made up these steps.
The evolution of ICs
The manufacturing of integrated circuits
Doping
Doping: is the materials engineering process by which the
electrical properties of the semiconductor are changed.
It is used to introduce elements of a different type to the
target material. The elements need to occupy the place of
silicon atoms in the crystalline lattice.
Every p-n junction is created using doping:
the diode,
the B-E and B-C junctions of a BJT,
the source and drain electrodes of an MOS FET.
Ways to perform doping:
diffusion,
ion implantation.
The evolution of ICs
The manufacturing of integrated circuits
Diffusion I.
Atomic diffusion in solids: atoms at the proximity of the
silicon wafer diffuse into the crystalline by thermally-activated
movement.
The silicon and the dopant atoms change places.
The process is driven by the concentration gradient.
The speed of diffusion can be increased by elevating the
ambient temperature – it is usually done at 1000 ◦ C.
Selectivity: the areas where diffusion is unwanted are covered
by SiO2 – the oxide is used as a mask.
The evolution of ICs
The manufacturing of integrated circuits
Diffusion II.
The doping density is inhomogeneous: the volumes close
to the surface have a higher density of dopants.
The doping density degrades exponentially with the distance
from the surface.
Dopants diffuse horizontally as well (though not at the same
speed), which results in a doped volume that is wider than the
aperture on the mask.
Density profile: is the density distribution created by
diffusion. It defines the operation of the device.
The stability of this step is a key factor in IC technology.
The evolution of ICs
The manufacturing of integrated circuits
Ion implantation
Ion implantation: ions of a material are accelerated in an
electrical field and impacted into another solid.
Advantages:
It is done at room temperature (no need to warm up the
material to high temperatures).
The horizontal movement is much smaller than with diffusion.
Downsides:
The crystalline structure is demaged by the high speed ions
crashing into the material.
Thermal annealing is needed for demage recovery.
The evolution of ICs
The manufacturing of integrated circuits
The deposition of material layers
Chemical or physical methods tha create a layer at the top of
the silicon surface.
Oxidation: the production of SiO2 on top of silicon in oxygen
ambience at 1000 ◦ C.
SiO2 is used for several purposes throughout the technology:
1
2
3
used as a mask in technology steps,
used to insulate between devices (field or thick oxide),
used as a dielectric in MOS FETs (thin oxide).
The evolution of ICs
The manufacturing of integrated circuits
Epitaxy
Epitaxy refers to the deposition of a crystalline overlayer on a
crystalline substrate, where the overlayer is in registry with the
substrate. In other words, there must be one or more
preferred orientations of the overlayer with respect to the
substrate for this to be termed epitaxial growth. The overlayer
is called an epitaxial film or epitaxial layer.
Epitaxy is performed at 1200 ◦ C and with gaseous precursors.
It is used to grow a film which is more pure than the
substrate and to fabricate layers having different doping
levels.
The evolution of ICs
The manufacturing of integrated circuits
Molecular beam epitaxy
It is performed in high vacuum and yields a very slow
deposition rate (< 1000 nm/s).
It allows a precise control of the thickness of each layer, down
to a single layer of atoms.
The behavior of very thin layers differ greatly of that of big
volumes due to quantum effects.
The evolution of ICs
The manufacturing of integrated circuits
Chemical Vapour Deposition (CVD)
In the gaseous ambience above the wafer a set of chemical
reactions take place.
One of the outputs of these reactions is the solid material that
is deposited on the surface.
CVD is used mostly to create insulators, passivating layers and
polysilicon.
The evolution of ICs
The manufacturing of integrated circuits
Physical Vapour Deposition (PVD)
It is used mostly to deposit metal layers.
Several methods exist to performe PVD:
Vacuum evaporation:
metal is vaporized at a high temperature in vacuum,
the substrate is kept cool → metal atoms converge to its
surface.
Ion plating:
ions accelerated by an electric field bombard the source,
as a result, metal particles break free and fall to the
semiconductor where a metal layer is created.
The evolution of ICs
The manufacturing of integrated circuits
The removal of layers
The removal of layers is done by etching.
The chemical and physical reactions that are used for etching
are usually selective, which means that they etch some
materials while leaving others intact.
The surface is covered with materials that can mask against
th etchants.
The patterns are created using lithography.
Types:
wet etching: using a
liquid etchant,
dry etching: using
plasma as the etchant.
The evolution of ICs
The manufacturing of integrated circuits
Lithography I.
Lithography creates the patterns.
A special agent called photoresist is deposited on the surface:
when exposed to light, a photoresist changes its chemical
properties and becomes soluble or non-soluble by etchants,
if the photoresist is exposed to light through a mask, it
changes its properties in a pattern.
After the exposure, the parts of the resist that are soluble are
etched away, which leaves a protective layer over the wafer
where the etching is unwanted.
The evolution of ICs
The manufacturing of integrated circuits
Lithography II.
The fabrication of a MOS FET’s source and drain:
The evolution of ICs
The manufacturing of integrated circuits
Lithography III.
The oxide masks against doping.
The evolution of ICs
The manufacturing of integrated circuits
Masks
Every step needs a different mask.
20-30 masks are needed to fabricate a modern IC.
IC design is basicly mask design.
Designers actually draw some of the masks, while others can
be deduced from them.
One chip’s layout is created (reticle) and that is projected
onto the wafer at the right positions.
A very large fraction of the price of an IC is that of the masks.
Quite often the masks need to be created at a technology with
a higher resolution than that of the IC.
At the 32 nm technology the price of a mask set is $1 million.
The evolution of ICs
The manufacturing of integrated circuits
Individual steps
Steps that are performed on a big number of chips at the
same time are economic (oxidation, etching, doping, etc).
There are steps that need to be performed on individual
chips – these are very expensive:
bonding,
packaging.
When the circuits are ready, the wafer needs to be sawed
apart to cut out the individual chips:
The evolution of ICs
The manufacturing of integrated circuits
Packaging I.
Gold wire bonding:
the contacts of the IC and the pads of the package are
connected with gold wires.
Flip-chip packaging:
the pads and the contacts are connected by soldering,
it is similar to the way surface mounted devices are soldered to
the printed circuit boards,
the solder balls are placed in position and then melted by heat.
The evolution of ICs
The manufacturing of integrated circuits
Packaging II.
Modern packaging is a great challange.
The maximum power of a connection is
limited.
The power needed by modern ICs is large.
Thus many connections are needed in a
very fine grid.
The evolution of ICs
The manufacturing of integrated circuits
The steps of MOS IC fabrication I.
The simplified cross-section and layout of an MOS transistor:
The evolution of ICs
The steps of MOS IC fabrication II.
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The evolution of ICs
The steps of MOS IC fabrication III.
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The evolution of ICs
The steps of MOS IC fabrication IV.
The manufacturing of integrated circuits