Introduction to Integrated Circuit Technology - IC Knowledge

1 Introduction to Integrated Circuit TechnologyFifth EditionWritten by: Scotten W. JonesIntroduction to Integrated Circuit TechnologyCopyright 2001 - 2012 IC Knowledge LLC, all rights IntroductionAt IC Knowledge LLC, we have found a wide diversity in our clients and web site visitorswith respect to their understanding of Integrated Circuit (IC) Technology . Some of the people weinteract with have a strong understanding of IC Technology , but there is also a substantial groupthat purchases or uses the Technology without a strong understanding. For the later group, wethough it would be useful to produce a basic Introduction to IC Technology , and that is the objec-tive of this have written this publication assuming no more technical background than a high schooleducation, and any technical terms will be defined when they are introduced. We have attemptedto provide a good high level overview of the Technology in this document, if you have questionsabout the content or would like to provide us with feedback, please e-mail us at Basic electronic conceptsElectronic circuits regulate and control the flow of electriccurrent.

2 Electric current is the flow of electrons, the tiny sub-atomic particles that surround the nucleus of atoms. Electronscarry a fixed negative electric charge and the movement of elec-trons carries charge from one location to another - the flow ofelectrons is referred to as electric current. Electric current isdriven by a difference in potential from one location to anothermeasured in volts. Electric current flows easily through materialsthat are conductors, and is blocked by materials that are insula-tors. The amount of resistance that a material presents to the flowof electric current is logically called resistance. Conductors havelow resistance to the flow of current and insulators haveextremely high resistance (essentially infinite until the voltage isso high that the material breaks down). For a given voltage, thehigher the resistance the less current that will flow and the lowerthe resistance the higher the current that will flow.

3 Conversely,for a given resistance, the higher the voltage the more current thatwill flow and the lower the voltage the less current that will flow. Electronic Circuit elementsElectronic circuits are made up of a number of elements usedto control current flow. There are a wide variety of different Circuit elements, but for the purposeof 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 wayvalve. Transistors, provides two major modes of action, one, a switch turning current flow on andoff, or two, act as an amplifier whereby an input current produces a larger output Definitions Current - the flow of electrons carrying electric charge.

4 Voltage - the force driving the flow of current. Resistance - a mate-rial s 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 TechnologyCopyright 2001 - 2012 IC Knowledge LLC, all rights reserved3An Integrated Circuit , or IC, is nothing more than a numberof these components connected together as a Circuit all formed onthe same What is a Semiconductor?A semiconductor is a material that may act as a conductor oras an insulator depending on the conditions. Diodes and transis-tors are made with semiconductor material and resistors andcapacitors may be made on or in semiconductor materials as the scientific community began to understand semiconductormaterials, the transistor and later the IC were invented (see His-tory of the IC at for more information).

5 Resistors and capacitors as individual components are commonlymade without the use of semiconductor materials but the ability to make them with semiconductormaterial made it possible to integrate them with diodes and transistors. Semiconductors may bemade more conductive by adding other impurity elements to the semiconductor material and theability to do this selectively, , add impurities to one part of a semiconductor material and not toother parts is what enables IC fabrication to take place. Areas of semiconductor material that arehighly 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 Integrated Circuit Manufacturing the highest level, the manufacture of ICs may be broken up into 5 major steps - see figure1. Figure 1. IC Circuit Elements Resistors - resists current flow. Capacitors - stores charge. Diodes - allows cur-rent to flow in only one direction.

6 Transistor - switches and or amplifies ) Starting substrate -silicon wafer(purchased).2) Wafer fabrication -fabricate IC son the wafer3) Wafer sort/test -test each IC,mark bad IC s4) Packaging -assemble IC sinto packages5) Mark & class/final test -mark and finaltest packaged product14003 Introduction to Integrated Circuit TechnologyCopyright 2001 - 2012 IC Knowledge LLC, all rights reserved4 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 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 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.

7 Wafer test will be discussed fur-ther in section 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 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 Silicon WafersFar 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'scrust and relatively easy to obtain and refine. Silicon is a semiconductor, although silicon hasbecome the dominant IC material not so much because it is a great semiconductor material, butrather 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 from100mm (4") to 300mm (12") in diameter (smaller sizes were used early in the development of theindustry but are now rarely used in production and 450mm wafers are currently in development).

8 Silicon wafers are highly polished - appearing mirror-like, extremely flat, and extremely cleanand 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 tomark how the crystal planes are oriented in the wafer andallow consistent alignment of various layers built up on thewafer - see figure 2a. 200mm (8") and 300mm (12") wafersuse a small notch in place of a flat because a flat takes awayan 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 onthem, but now virtually all IC manufacturers purchase thewafers 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 ) Wafer with flat150mm b) Wafer withnotch200mm Figure 2.

9 Silicon wafer orienta-tion to Integrated Circuit TechnologyCopyright 2001 - 2012 IC Knowledge LLC, all rights reserved5 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 tailored than in a raw wafer and are widely used for the latest state-of-the-art Logic ICs. Epitaxial wafer costs are to times the cost of a raw wafer. Silicon on Insulator (SOI) wafers - silicon wafers upon which an insulating layer is formed with a thin single crystal silicon layer on top of the insulating layer. SOI wafers reduce the amount of power drawn by an IC when the Circuit is switching at high speed. SOI wafers costs are 4 to 15 times the cost of a raw wafer. SOI is primarily used in low power and some high performance applications. We expect the use of SOI to increase and even become mainstream as linewidths continue to 3 illustrates the basicwafer manufacturing process steps are: Pull crystal ingot - a small seed of single crystal silicon is dipped into a crucible of molten silicon.

10 The crucible and seed are rotated in opposite direc-tions and the seed is slowly withdrawn from the crucible (figure 3a). Ingot grind - the silicon crystal ingot is ground to create a con-sistent diameter for the whole ingot (figure 3b). Saw off ingot ends - the two ends of the silicon ingot will not be usable and are sawn off using a diamond saw (figure 3c). Saw up the ingot into wafers - the Ingot is sawn up into wafers each approximately 1/2mm to 3/4mm in thickness (100mm to 300mm wafers) (figure 3d). Edge grind wafers - the edges of the wafers are ground to round off the sharp edges. Edge grinding minimizes chipping of the wafer edges during subsequent processing (figure 3e). Lap wafers - a process called lapping is used to flatten out the wafers and ensures the two wafer faces are parallel (figure 3f). Damage removal etch - a special wet etch is used to etch off the surface damage left from lap-ping (figure 3g).Wafer Types Raw - basic wafer used to make ICs.