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INTEGRATED CIRCUIT (IC) FABRICATION INTRODUCTION

• An Integrated circuits (ICs) are . • ICs form a branch of the which originated in the late 1950s. • At that time the military was interested in reducing the size of its electronic equipment to approx- 1/10th of its initial volume. EVOLUTION OF ICs

• Before the , assembly workers had to construct circuits by hand, soldering each component in place and connecting them with metal wires or they are assembled on PCB. These are discrete circuits. • The discrete circuits suffer from two main disadvantages- Large space & Reliability. • To meet the problems of space conservation & reliability, a new branch of electronics known as microelectronics was developed in the late 1950’s. The microelectronics deals with microcircuits. One type of such circuit is IC. Jack Kilby is probably most famous for his invention of the integrated circuit, for which he received the Nobel Prize in Physics in the year 2000. After his success with the integrated circuit Kilby stayed with and, among other things, he led the team that invented the hand-held . Photo: Texas Instruments

Kilby’s first chip Photo: Texas Instruments What is an integrated circuit? An integrated circuit is also known as IC, microcircuit, microchip, chip, or chip . It is a miniature that consists of devices, as well as passive components, that has been manufactured in the surface of a thin substrate of semiconductor material. ADVANTAGES OF ICs • Size- sub-micron vs. mm/cm. Systems are physically smaller, e.g.- cell phones. • IC provide better high frequency performance because of the reduced size of the components and of shorter lengths of connecting leads. • The IC is much more reliable due to absence of joints. • Low cost because a large no: of circuits or components cab be produced simultaneously on a small semi- conductor . • Speed & Power- Smaller size of IC components yield higher speed & lower power consumption due to smaller parasitic , resistances, . Silicon Wafer DISADVANTAGES OF ICs

• The & transformers cannot be fabricated. • & are limited in maximum value. • It is not possible to produce high power ICs ( greater than 10 W ). • If any component of the IC goes out of order, the whole IC has to be replaced by new one. ADVANCES IN ICs

• Among the most advanced integrated circuits are the or "cores", which control everything from to cellular phones to digital microwave ovens. Digital memory chips and ASICs are examples of other families of integrated circuits that are important to the modern information society. • While the cost of designing and developing a complex integrated circuit is quite high, when spread across typically millions of production units the individual IC cost is minimized. The performance of ICs is high because the small size allows short traces which in turn allows low power logic (such as CMOS) to be used at fast switching speeds. CLSSIFICATION OF ICs

• From fabrication point of view, ICs are- 1) Monolithic ICs 2) Thick & ICs 3) Hybrid ICs

• From functional point of view, ICs are- 1) Liner ICs 2) Digital ICs

Linear & Digital ICs

Opamp CMOS DIP IC

64-bit static RAM 2-input NAND IC Digital ICs • Digital ICs operate at only a few defined levels or states, rather than over a continuous range of signal amplitudes. • These devices are used in computers, networks, modems, and frequency counters. • The fundamental building blocks of digital ICs are logic gates, which work with binary data, that is, signals that have only two different states, called low (logic 0) and high (logic 1). Linear ICs

• Linear ICs have continuously variable output (theoretically capable of attaining an infinite number of states) that depends on the input signal level. As the term implies, the output signal level is a linear function of the input signal level. Ideally, when the instantaneous output is graphed against the instantaneous input, the plot appears as a straight line.

• Linear ICs are used as audio-frequency (AF) and -frequency (RF) amplifiers. The operational (op-amp) is a common device in these applications. Others are-linear regulators, active filters, phase locked loop, oscilators. Monolithic IC • The word ‘monolithic’ is derived from the Greek mono, meaning ’single’ and litho, meaning ’stone’. Thus monolithic circuit is built into a single stone or single crystal i.e. in monolithic ICs, all circuit components, (both active and passive) and their interconnections are formed into or on the top of a single chip of silicon.

• Commercially available ICs of this type can be used as amplifiers, regulators, crowbars, AM receivers, TV circuits, and computer circuits. Thick & Thin film ICs

• These devices are larger than monolithic ICs but smaller than discrete circuits.

• These ICs can be used when power requirement is comparatively higher.

• Therefore, commercially available thin- and thick- film circuits are combination of integrated and discrete components.

• The essential difference between the thin- and thick-film ICs is not their relative thickness but the method of deposition of film. Both have similar appearance, properties and general characteristics. Hybrid ICs

• A hybrid circuit serves as a component on a PCB in the same way as a monolithic integrated circuit; the difference between the two types of devices is in how they are constructed and manufactured. The advantage of hybrid circuits is that components which cannot be included in a monolithic IC can be used, e.g., capacitors of large value, wound components, crystals. LEVEL OF INTEGRATION

• Small-scale integration (SSI)-3 to 30 gates/chip or 100 /chip (e.g.-logic gates, flip-)

• Medium-scale integration (MSI)- 30 to 300 gates/chip or 100 to 1000 transistors/chip (counters, , adders)

• Large-scale integration (LSI)- 300 to 3000 gates/chip or 1000- 20,000 transistors/chip (8-bit up, ROM, RAM)

• Very large-scale integration (VLSI)- more than 3000 gates/chip or 20,000-100,00,00 transistors/chip (16 & 32-bit up)

• Ultra large-scale integration (ULSI)- more than 1 million (special processors- pentium processors, virtual reality , smart .) Basic Fabrication steps • Layer 1- Substrate upon which IC is built.(400um or 0.4mm) • Layer 2- Epitaxial layer. All active & passive components are fabricated within this layer.(5 to 25um) • Layer 3-Silicon dioxide i.e. insulation layer.(0.02-2um ) • Layer 4- Metallic layer of Al, used for obtaining interconnections b/w components.(~1um) Logic / Layout Design

• A logic is drawn to determine the electronic circuit required for the requested function. • Once the logic circuit diagram is complete, simulations are performed multiple times to test the circuit’s operation.

IC Production in short Clean Room • But let us first take a look at the special place where integrated circuits are produced - the clean room. Chip Production - in Detail

• Wafer Preparation • Epitaxial Growth • Insulating layer- Oxidation • Photolitography – Etching • • Metallization • Separating into chips • Mounting & Packaging

Wafer Fabrication

• A high-purity, single-crystal silicon called "99.999999999% (eleven-nine)" is grown from a seed to an ingot. • The wafers are generally available in diameters of 150 mm, 200 mm, or 300 mm, and are mirror-polished and rinsed before shipment from the wafer manufacturer.

Epitaxial Growth Insulation Layer & Photolithoraphy Photoresist Coating

1. A resin called "photoresist" is coated over the entire wafer. (~1μm thick coating.) 2. Photoresist is a special resin similar in behavior to photography films that changes properties when exposed to light. Masking/Exposure

• Placed over the photoresist-coated wafer, which is then irradiated to have the circuit diagram transcribed onto it. • An irradiation device called the "stepper" is used to irradiate the wafer through the mask with ultraviolet (UV) light.

Patterning: Development

• The photoresist chemically reacts and dissolves in the developing solution, only on the parts that were not masked during exposure (positive method). • Development is performed with an alkaline developing solution. • After the development, photoresist is left on the wafer surface in the shape of the mask pattern.

Diffusion Aluminium Metalization Dicing

• In back end processing, a wafer completed in front end processing is cut into individual IC chips and encapsulated into packages.

Mounting • After the IC chips are cut apart, they are sealed into packages. The IC chips must first be attached to a platform called the " frame“.

Characteristic Selection

• The packaged IC chips are tested and selected.

Printing and Lead Finish

• The final step of IC chip manufacturing is the printing onto the package surface and the finishing of leads. After this step, the IC chips are complete.

COMPONENTS ON MONOLITHIC IC

• Transistors APPLICATIONS OF ICs

• An IC can function as an amplifier, oscillator, , , ( RAM, ROM, flash) or , active filters, linear regulators. A particular IC is categorized as either linear (analog) or digital, depending on its intended application.

• Integrated circuits are also found in almost every modern electrical device such as cars, sets, CD players, cellular phones.

TYPES OF CHIPS • Dynamic Random Access Memory chips (DRAMs) - serve as the primary memory for computers • Microprocessors (MPUs) - act as the brains of computers. • Application Specific Integrated Circuits (ASICs) - are custom designed for very specific functions • Processors (DSPs) - process signals, such as image and sound signals or radar pulses. • Programmable memory chips (, EEPROMs, and Flash) - are used to perform functions that require programming on the chip. REFERENCES

• Electronic Devices And Circuits By Allen Mottershead • Electronic Devices And Circuits By Sanjeev Gupta • Linear Integrated Circuits By D.Roy.Choudhury, Shail B.Jain • http://google.com • http://wikipedia.com