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Introduction to Integrated Circuit Technology Introduction to
Integrated Circuit
Technology
Fourth Edition
Written by: Scotten W. Jones Introduction to Integrated Circuit Technology
Copyright © 2001 - 2005 IC Knowledge LLC, all rights reserved
2
1.0. Introduction
At
IC Knowledge
, we have found a wide diversity in our clients and web site visitors with
respect to their understanding of Integrated Circuit (IC) technology. Some of the people we inter-
act with have a strong understanding of IC technology, but there is also a substantial group that
purchases or uses the technology without a strong understanding. For the later group, we though it
would be useful to produce a basic introduction to IC technology, and that is the objective of this
publication.
We have written this publication assuming no more technical background than a high school
education, and any technical terms will be defined when they are introduced. We have attempted
to provide a good high level overview of the technology in this document, if you have questions
about the content or would like to provide us with feedback, please e-mail us at info@icknowl-
edge.com.
2.0. Basic electronic concepts
Electronic circuits regulate and control the flow of electric
current. Electric current is the flow of electrons, the tiny sub-
atomic particles that surround the nucleus of atoms. Electrons
carry a fixed negative electric charge and the movement of elec-
trons carries charge from one location to another - the flow of
electrons is referred to as electric current. Electric current is
driven by a difference in potential from one location to another
measured in volts. Electric current flows easily through materials
that are conductors, and is blocked by materials that are insula-
tors. The amount of resistance that a material presents to the flow
of electric current is logically called resistance. Conductors have
low resistance to the flow of current and insulators have
extremely high resistance (essentially infinite until the voltage is
so high that the material breaks down). For a given voltage, the
higher the resistance the less current that will flow and the lower
the resistance the higher the current that will flow. Conversely, for
a given resistance, the higher the voltage the more current that
will flow and the lower the voltage the less current that will flow.
3.0. Electronic circuit elements
Electronic circuits are made up of a number of elements used
to control current flow. There are a wide variety of different circuit elements, but for the purpose
of this discussion the circuit elements will be restricted to the four most commonly used in ICs,
these are, resistors, capacitors, diodes and transistors. Resistors, provide a fixed amount of resis-
tance to current flow. Capacitors, store electric charge until discharged somewhat similar to a bat-
tery. Diodes, allow current to flow in one direction but not in the opposite direction, a one way
valve. Transistors, provides two major modes of action, one, a switch turning current flow on and
off, or two, act as an amplifier whereby an input current produces a larger output current.
Basic Definitions Current - the flow of
electrons carrying
electric charge. Voltage - the force
driving the flow of
current. Resistance - a mate-
rials resistance to
the flow of electric
current. Conductor - a mate-
rial that readily sup-
ports the flow of
electric current. Insulator - a mate-
rial that blocks the
flow of electric cur-
rent. Introduction to Integrated Circuit Technology
Copyright © 2001 - 2005 IC Knowledge LLC, all rights reserved
3
An Integrated Circuit, or IC, is nothing more than a number
of these components connected together as a circuit all formed on
the same substrate.
4.0. What is a Semiconductor?
A semiconductor is a material that may act as a conductor or
as an insulator depending on the conditions. Diodes and transis-
tors are made with semiconductor material and resistors and
capacitors may be made on or in semiconductor materials as well.
As the scientific community began to understand semiconductor
materials, the transistor and later the IC were invented (see His-
tory of the IC at www.icknowledge.com for more information).
Resistors and capacitors as individual components are commonly
made without the use of semiconductor materials but the ability to make them with semiconductor
material made it possible to integrate them with diodes and transistors. Semiconductors may be
made more conductive by adding other impurity elements to the semiconductor material and the
ability to do this selectively, i.e., add impurities to one part of a semiconductor material and not to
other parts is what enables IC fabrication to take place. Areas of semiconductor material that are
highly pure and therefore have little or no impurities act as insulators. This is the key to IC fabri-
cation and will be discussed further in the sections that follow.
5.0. Integrated Circuit Manufacturing Overview.
At the highest level, the manufacture of ICs may be broken up into 5 major steps - see figure
1.
Figure 1. IC manufacturing.
IC Circuit Elements Resistors - resists
current flow. Capacitors - stores
charge. Diodes - allows cur-
rent to flow in only
one direction. Transistor - switches
and or amplifies
current.
1) Starting substrate -
silicon wafer
(purchased).
2) Wafer fabrication -
fabricate ICs
on the wafer
3) Wafer sort/test -
test each IC,
mark bad ICs
4) Packaging -
assemble ICs
into packages
5) Mark & class/final test -
mark and final
test packaged product
14003 Introduction to Integrated Circuit Technology
Copyright © 2001 - 2005 IC Knowledge LLC, all rights reserved
4
The five major steps are:
1. Starting substrate - the starting substrate is purchased by virtually all major IC producers.
Starting substrates will be discussed further in section 6.0.
2. Wafer fabrication - the process of fabricating a numbers of ICs on the surface of the wafer
simultaneously. Wafer fabrication will be discussed further in section 8.0.
3. Wafer sort/test - each IC (referred to as a die) on the wafer surface is tested and the bad die are
marked with an ink dot or in an electronic map. The bad die are discarded after the wafer is
sawn up for packaging to save the cost of packaging bad die. Wafer test will be discussed fur-
ther in section 10.0.
4. Packaging - the wafer is sawn up into individual die and the good die are assembled into pro-
tective packages. Packaging will be discussed further in section 11.0
5. Mark and class/final test - in order to insure that the die were not damaged during packaging,
the packaged product is tested and marked with the product type. Final test will be discussed
further in section 12.0.
6.0. Silicon Wafers
Far and away the most common material for IC fabrication is silicon (there are other materi-
als in use, but only for small niche applications). Silicon is an abundant material in the earth's
crust and relatively easy to obtain and refine. Silicon is a semiconductor, although silicon has
become the dominant IC material not so much because it is a great semiconductor material, but
rather because it is relatively easy to work with.
The silicon used for IC fabrication has been highly purified, grown into nearly perfect crys-
tals and sliced up into discs, called wafers, less than a millimeter (mm) thick and anywhere from
100mm (4") to 300mm (12") in diameter (smaller sizes were used early in the development of the
industry but are now rarely used in production). Silicon wafers are highly polished - appearing
mirror-like, extremely flat, and extremely clean and particle free at the start of fabrication.
100mm (4"), 125mm (5") and 150mm (6") wafers typ-
ically have a flat section ground onto one or more edges to
mark how the crystal planes are oriented in the wafer and
allow consistent alignment of various layers built up on the
wafer - see figure 2a. 200mm (8") and 300mm (12" wafers
use a small notch in place of a flat because a flat takes away
an unacceptable amount of wafer area on the larger wafers -
see figure 2b.
Silicon wafers were at one time internally manufac-
tured by the IC companies who then fabricated circuits on
them, but now virtually all IC manufacturers purchase the
wafers from a third party.
There are three major types of silicon wafers currently in use for IC fabrication:
Raw wafers, silicon wafers without any additional processing. For state-of-the-art ICs raw
wafers are mainly used for DRAMs.
a) Wafer with flat
150mm
b) Wafer with
notch
200mm
Figure 2. Silicon wafer orienta-
tion indications. Introduction to Integrated Circuit Technology
Copyright © 2001 - 2005 IC Knowledge LLC, all rights reserved
5 Epitaxial wafers, silicon wafers with a single crystal silicon
layer deposited on them. The deposited layer typically has
different properties than the underlying raw wafer. Epitaxial
layers allow the properties of the layer in which the devices
are formed to be more t