Introduction to Integrated Circuit Technology Fifth Edition Written by: Scotten W. Jones Introduction to Integrated Circuit Technology 1.0. Introduction At IC Knowledge LLC, 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 interact 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 objec- tive 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- Basic Definitions atomic particles that surround the nucleus of atoms. Electrons • Current - the flow of carry a fixed negative electric charge and the movement of elec- electrons carrying trons carries charge from one location to another - the flow of electric charge. electrons is referred to as electric current. Electric current is • Voltage - the force driven by a difference in potential from one location to another driving the flow of measured in volts. Electric current flows easily through materials current. that are conductors, and is blocked by materials that are insula- • Resistance - a mate- tors. The amount of resistance that a material presents to the flow rial’s resistance to of electric current is logically called resistance. Conductors have the flow of electric low resistance to the flow of current and insulators have current. extremely high resistance (essentially infinite until the voltage is • Conductor - a mate- so high that the material breaks down). For a given voltage, the rial that readily sup- higher the resistance the less current that will flow and the lower ports the flow of the resistance the higher the current that will flow. Conversely, electric current. for a given resistance, the higher the voltage the more current that • Insulator - a mate- will flow and the lower the voltage the less current that will flow. rial that blocks the flow of electric cur- 3.0. Electronic circuit elements rent. 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. Copyright © 2001 - 2012 IC Knowledge LLC, all rights reserved 2 Introduction to Integrated Circuit Technology An Integrated Circuit, or IC, is nothing more than a number of these components connected together as a circuit all formed on IC Circuit Elements the same substrate. • Resistors - resists current flow. 4.0. What is a Semiconductor? • Capacitors - stores charge. A semiconductor is a material that may act as a conductor or • Diodes - allows cur- as an insulator depending on the conditions. Diodes and transis- rent to flow in only tors are made with semiconductor material and resistors and one direction. capacitors may be made on or in semiconductor materials as well. • Transistor - As the scientific community began to understand semiconductor switches and or materials, the transistor and later the IC were invented (see “His- amplifies current. 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. 1) Starting substrate - 2) Wafer fabrication - 3) Wafer sort/test - silicon wafer fabricate IC’s test each IC, (purchased). on the wafer mark bad IC’s 5) Mark & class/final test - 4) Packaging - mark and final assemble IC’s test packaged product into packages 14003 Figure 1. IC manufacturing. Copyright © 2001 - 2012 IC Knowledge LLC, all rights reserved 3 Introduction to Integrated Circuit Technology 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 and 450mm wafers are currently in development). 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 - a) Wafer with flat b) Wafer with see figure 2b. р 150mm notchу 200mm Silicon wafers were at one time internally manufac- Figure 2. Silicon wafer orienta- tured by the IC companies who then fabricated circuits on tion indications. 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 memory such as DRAM and Flash. Copyright © 2001 - 2012 IC Knowledge LLC, all rights reserved 4 Introduction to Integrated Circuit Technology • Epitaxial wafers, silicon wafers with a single crystal silicon layer deposited on them. The deposited layer typically has Wafer Types different properties than the underlying raw wafer. Epitaxial • Raw - basic wafer layers allow the properties of the layer in which the devices used to make ICs. are formed to be more tailored than in a raw wafer and are • Epitaxial (Epi) - a widely used for the latest state-of-the-art Logic ICs. Epitaxial raw wafer with a wafer costs are 1.4 to 2.5 times the cost of a raw wafer. single crystal film • Silicon on Insulator (SOI) wafers - silicon wafers upon which deposited on it. an insulating layer is formed with a thin single crystal silicon • Silicon On Insula- layer on top of the insulating layer. SOI wafers reduce the tor (SOI) - a thin amount of power drawn by an IC when the circuit is switching single crystal silicon at high speed. SOI wafers costs are 4 to 15 times the cost of a film on an insulating raw wafer.