What exactly is a semiconductor? If you don’t know, you’re not alone. For something that powers nearly all electronic devices, this is our most commonly asked question.
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The process of manufacturing semiconductors or integrated circuits (commonly called ICs or chips) typically consists of hundreds of steps, during which hundreds of copies of an integrated circuit are formed on a single wafer.
Generally, the process involves the creation of 8 to 20, and frequently more, patterned layers on (and into) the wafer, ultimately forming the complete integrated circuit. This layering process creates (interconnected) electrically active regions on the semiconductor wafer surface.
Silicon Wafer Manufacturing
Semiconductor manufacturing begins with production of the wafer, i.e., a thin, round slice of a semiconductor material varying in size 6 inches to 12 inches in diameter. The finished wafer is approximately 15 mil thick. The materials are primarily silicon; however, gallium arsenide, silicon carbide, germanium, and others undergo similar processes. Purified polycrystalline silicon is created from sand, one of the most abundant materials available on our planet, is heated to a molten liquid. In a process similar to repeatedly dipping a wick in wax to make a candle, a small piece of solid silicon (seed) is dipped in molten liquid. As the seed is slowly withdrawn (by mechanical means) from the melt, the liquid quickly cools to form a single crystal ingot.
This cylindrical crystal ingot is then ground to a uniform diameter. A diamond saw blade slices the ingot into thin wafers. The cut wafers are then processed through a series of machines where they are ground (optically) smooth and chemically polished.
The wafers are now ready to be sent to the wafer fabrication area fab, where they are used as the foundation for manufacturing integrated circuits (ICs).
The heart of any semiconductor manufacturing business is the fab, where the integrated circuit is formed on the wafer. The fabrication process, which takes place in an environmentally controlled clean room, involves a series of principle repetitive steps described below. Typically, it takes from 10-30 days, but frequently much longer, to complete the fabrication process.
Thermal oxidation–wafers are pre-cleaned using high-purity deionized water and various low-particulate chemicals, a must for high-yield production. The silicon wafers are heated to approximately 1000 c and exposed to ultra-pure oxygen in the oxidation furnace. Under carefully controlled conditions, a silicon dioxide insulator film of uniform thickness is formed on the surface of the wafer.
Patterning–masking is used to protect one area of the wafer while working on another. This process is referred to as photolithography. A photo resist, light-sensitive film is spin-coated onto the wafer, giving it characteristics similar to a photographic film. A (micro) aligner aligns the wafer to a glass mask and then projects an intense ultraviolet light through the mask, exposing the photo resist with the mask pattern, thereby transferring the image from the mask into the light-sensitive film.
Etching–the wafer image is then developed (like a photo negative). The exposed photo resist is chemically removed and baked to harden the remaining photo resist pattern, which now is no longer light sensitive. It is then exposed to a chemical wet solution or plasma (gas discharge) so that areas not covered by the hardened photo resist are etched away. The remaining photo resist is now removed using either wet or plasma chemistry. The wafer is optically inspected to assure that the image transfer from the mask to the top silicon layer is correct, and then goes on to the next step.
Doping/diffusion–atoms with one less electron than silicon (such as boron) or one more electron than silicon (such as phosphorus) are introduced into the area exposed by the etch process, to alter the electrical character (conductivity) of the silicon. These areas are called p type or n type, respectively, which reflects their conducting characteristics.
Complete front end layer— Repeating the above steps: the thermal oxidation, masking, etching, and doping steps are repeated many times until the last “Front end” layer is completed (all active devices have been formed).
Dielectric deposition and metallization–following completion of the “Front end,” the individual devices are interconnected “Backend” (like on a pc board) using a series of alternating metal depositions, dielectric films, with their respective patterning. Current semiconductor fabrication includes as many as 5 to 7 metal layers for logic, and fewer for memory, separated by dielectric layers (insulators).
Passivation–after the last metal is patterned, a final insulating layer (passivation) is deposited to protect the circuit from damage and contamination. Openings are etched in this film to allow access to the top metal later by electrical probes and subsequent wire bonds.
Electrical test–an automatic, computer-driven test system checks for functionality of each chip on the wafer. Chips that do not pass the test are marked for automatic rejection. For simpler devices a mechanical probe is used.
Assembly–a diamond saw slices the wafer into single chips. Sizes can vary from 1 x 1 mm to 10 x 10 mm. The rejected chips are discarded and the remaining chips are visually inspected under a high-power microscope before packaging.
Each chip is then assembled into an appropriate package that provides the contact leads for the chip. In one type of interconnect a wire bonding machine attaches wires, a fraction of the width of a human hair, to the leads of the package. The packaged chip is tested again prior to delivery to the customer. Alternatively, the chip can be assembled in a ceramic package for certain high-performance applications.
A 300mm wafer is 12 inches in diameter. When using a chip that is 1 square centimeter, a 300mm wafer includes approximately 706 chips. The 300mm wafer has 2.25 times the wafer area than a 200mm wafer or 8 inches, a higher clean room utilization efficiency, and a reduced defect density that will lower die cost. It’s also much cheaper to manufacture.
Terms of Measurement:
Micron: A micron is a metric unit of linear measure, which equals one-millionth of a meter. The diameter of a human hair is about 100 microns. Today’s semiconductors have line etched at 0.048 microns.
Nanometer: A nanometer is a metric unit of linear measure, which equals one-billionth of a meter. The semiconductor industry is now using nanometer as opposed to “microns” because the conversion is easier as it eliminates the need for decimals. For example, .13 microns is equal to 130 nanometers.
What is Moore’s Law?
Gordon Moore made his famous observation in 1965, just four years after the first planar integrated circuit was discovered. The press called it “Moore’s Law” and the name has stuck. In his original paper, Moore observed an exponential growth in the number of transistors per integrated circuit and predicted that this trend would continue.
Who is Gordon Moore?
Gordon E. Moore is currently Chairman Emeritus of Intel Corporation. Moore co-founded Intel in 1968, serving initially as Executive Vice President. He became President and Chief Executive Officer in 1975 and held that post until elected Chairman and Chief Executive Officer in 1979. He remained CEO until 1987 and was named Chairman Emeritus in 1997.
Moore is widely known for “Moore’s Law,” in which he predicted that the number of transistors the industry would be able to place on a computer chip would double every couple of years. In 1995, he updated his prediction to once every two years. While originally intended as a rule of thumb in 1965, it has become the guiding principle for the industry to deliver ever-more-powerful semiconductor chips at proportionate decreases in cost.
Moore earned a B.S. in Chemistry from the University of California at Berkeley and a Ph.D. in Chemistry and Physics from the California Institute of Technology. He was born in San Francisco, Calif., on January 3, 1929.
He is a director of Gilead Sciences Inc., a member of the National Academy of Engineering, and a Fellow of the IEEE. Moore also serves on the Board of Trustees of the California Institute of Technology. He received the National Medal of Technology from President George Bush in 1990.
The SIA was pleased to honor Dr. Gordon E. Moore with its first-ever SIA Lifetime Achievement Award in November, 2002.
Monthly sales in the semiconductor industry tend to fluctuate greatly within a quarter and throughout the year, based on seasonal demand and business patterns. The SIA uses a three-month-moving average as a “smoothing technique” to avoid confusion when looking at the data in terms of single months, which can make the data look distorted with sales spiking and dropping off from month to month.
Industry term for third and fourth generation wireless mobile communications networks.
Analog-to-Digital Converter. This device is what all digital imaging systems use to get real-world pictures from a TV camera, for example into a computer.
Circuit board or other hardware in Data Terminal Equipment (DTE) that provides the physical interface to the communications network.
Analog is a continuous signal, measuring features that are difficult to break into digital components, such as pressure, temperature, voltage, current and air and water-flow. The circuits are used in products that involve sound (radios, TVs) and pressure (automotive air bags, anti-lock brakes).
One ten-billionth of a meter. Some chip layers are only 100 angstroms thick.
Application Specific Integrated Circuits. Designed to suit a customer’s particular requirement, as opposed to DRAMs or microprocessors, which are general-purpose semiconductors.
Application Specific Integrated Circuits
Designed to suit a customer’s particular requirement, as opposed to DRAMs or microprocessors, which are general-purpose semiconductors.
A step in semiconductor manufacturing in which the chip (die) is either encased in a plastic, ceramic or other package or assembled directly on a printed circuit board.
Application-Specific Standard Products. An integrated circuit that performs functions for a single application.
An analog measure derived from the difference between the highest and lowest frequency on a carrier wave. Also used to describe the amount of data that can be sent through a given communications circuit.
Bipolar Complementary Metal Oxide Semiconductors. This relatively new process combines both bipolar and CMOS technologies on the same chip, yielding products with the benefits of both technologies.
Characteristic of having only two states, such as current on and current off. The binary number system uses only ones and zeros.
A type of transistor noted for its speed where a flow of both conduction electrons and holes determine the device characteristics.
The basic unit of all digital communications. A bit is a “1” or “0” in a binary language.
A wireless Personal Area Network (PAN) technology from the Bluetoothtm Special Interest Group, founded in 1998 by Ericsson, TBM, Intel, Nokia and Toshiba. It is an open standard for short-range transmission of digital voice and data between mobile and desktop devices.
Originally described the frequency bandwidth of analog circuits. The term has evolved to specify 56 KBps, then 1.5 Mbps capability.
A sphere of 60 carbon atoms in an arrangement that looks like a soccer ball. A popular name for a buckminsterfullerene (named after Buckminster Fuller, inventor of the geodesic dome). This nanostructure’s unique properties could be useful in nanotechnology.
A data unit of eight bits.
Computer-Aided Design. Sophisticated, computerized workstations and software used to design integrated circuit chips.
Code Division Multiple Access, also called Spread Spectrum, a term for a form of digital spread spectrum cellular phone service that assigns a code to all speech bits, sends a scrambled transmission of the encoded speech over the air and reassembles the speech into its original format. CDMA has up to 20 times the capacity of analog cellular service and is best known for its superior call quality and long battery life.
An individual integrated circuit built in a tiny, layered rectangle or square on a silicon wafer.
The sterile rooms where chips are fabricated. The air in these rooms is thousands of times cleaner than in a typical hospital operating room.
Same as printed circuit board. A board with microprocessors, transistors and other electronic components. Also called a circuit card.
Complementary Metal Oxide Semiconductors. Combine both positive- and negative-channel transistors on the same circuit design. CMOS circuits consume relatively low amounts of power.
A chemical or structural irregularity that degrades the product. Defects can affect the product over time or interfere with manufacturing the chip correctly. Common causes of defects are flakes from skin or cosmetics, and droplets from a person’s sneeze.
The method of representing information as numbers with discrete (non-continuous) values, usually expressed as a sequence of binary digits (ones and zeros).
A single integrated circuit (or chip) cut from the wafer on which it was manufactured.
Cellular communications technology. Transmitting digital data with over 15 times the capacity of analog technology with significantly less static, loss/interruption of the signal when passing between cells and connection problems because of congested relays.
Digital Subscriber Line. A technology that increases the digital speed of ordinary phone lines by a substantial factor over common dial-up modems. Offers symmetrical and asymmetrical operation. Asymmetrical versions (ADSL, RADSL, VDSL, etc.) provide higher downstream transmission than upstream and are better suited for Internet usage and video on demand applications. Symmetric DLS (HDLS, SDSL, IDSL, etc.) provide the same speed in both directions. All DSL have distance limitations of around two or three miles between the telephone company’s central office and the customer site.
Digital Signal Processing (DSP)
Digital circuits designed to address a broad class of problems in signal reception and analysis that have traditionally been solved using analog components. DSP is used to enhance, analyze, filter, modulate or otherwise manipulate standard analog functions, such as images, sounds, radar pulses, and other such signals by analyzing and transforming wave-forms (e.g., transmitting data over phone lines via modem).
A signal and switching device that allows current in one direction and blocks it in the opposite direction. One use: regulating load voltages.
A device that contains one active element, such as a transistor or diode, although a hybrid might contain more than one active element. In comparison, an integrated circuit could contain billions of active elements on a single chip.
Dynamic Random Access Memory. A type of memory component. “Dynamic” means the device’s memory cells must be recharged periodically. Information stored in the memory cells is accessed randomly. Memory is a key component of most electronic products.
A wafer fabrication process in which exposed areas of silicon are bombarded with chemical impurities to alter the way the silicon conducts electricity in those areas.
Electron Beam refers to a machine that produces a stream of electrons that can be used to expose photoresists directly on a wafer or on a mask. Electron-beam lithography is a microprinting technique.
Electronically-Erasable Programmable Read-Only Memory.
A computer chip that controls the function of its product. While embedded processors sometimes refer to the type of chips used in simple electronic toys, “talking” greeting cards and similar consumer products, they are also high-functioning microcontrollers that are the brains of products such as laser printers.
The removal of selected portions of materials to define patterned layers on chips.
Erasable Programmable Read Only Memory. Allows stored information to be erased by exposure to ultraviolet light.
A local area network used for connecting computer, printers, workstations, terminals, servers and other computer hardware within the same company. Ethernet operates over twisted wire and over coaxial cable at speeds up to 10 million bits per second (Mbps).
Extreme Ultraviolet Technology
A technology for extending ultraviolet lithography by manufacturing a lens with concave and convex mirrors. This type of manufacturing allows the lens to focus patterns on a chip that are too small to be lithographed.
The fabrication facility, or fab, is the manufacturing plant where the front-end process of making semiconductors on silicon wafers is completed. The package and assembly (back end) stages are typically completed at other facilities.
A semiconductor company with no wafer fabrication capability.
A faster form of EPROM that permits more erase/write cycles. Flash memory allows large amounts of non-volatile program memory.
The Focus Center Research Program has six Focus Centers that are university centers leading a consortium of other universities in researching a particular challenge to the long-term advancement of semiconductor technologies.
A factory that manufactures semiconductor chips on wafers. Usually used to denote a facility that is available on a contract basis to companies that do not have wafer fab capability of their own, or that wish to supplement their own capabilities.
Gallium Arsenide. A III-V compound semiconductor material used for making optoelectronic devices and high-frequency ICs. GaAs has a higher electron mobility than silicon, thus having the capability of producing higher-speed devices. III-V refers to the third and fifth columns of the periodic table.
A semi-custom chip. The integrated circuit is preprocessed to the first interconnect level. The remainder of the interconnect is customized to meet specific requirements of the customer.
Integrated Circuit. A chip etched or imprinted with network or electronic components such as transistors, diodes and resistors along with their interconnections.
Institute of Electrical and Electronics Engineers. A world-wide engineering publishing and standards-making body for the electronics industry.
Integrated Circuit (IC)
Semiconductor chip in which many active or passive elements are fabricated and connected together on a continuous substrate, as opposed to discrete devices, such as transistors, resistors, capacitors and diodes that exist individually.
One way that the surface of a chip is transformed. It is a method that fires beams of charged atoms at the surface of the wafer. The high level of energy of these ions allows them to penetrate the silicon to produce the desired doping effect.
International Technology Roadmap for Semiconductors. ITRS is an international effort involving industry, government and academic experts to identify technical barriers that must be overcome to continue semiconductor technology advances.
Local Area Network. A communications network that serves users within a confined geographical area, and made up of servers, workstations, a network operating system and a communications link.
A stamped or etched metal frame, usually connected to the bonding pads of a die by wire bonding, that provides external electrical connections for a packaged electrical device.
The size range within which an object falls; e.g. nanscale, millimeter scale.
From the root “litho” meaning “stone” and “graph” meaning “writing”. Lithography is the transfer of a pattern or image from one medium to another, as from a mask to a wafer. If light is used to effect the transfer, the term “photolithography” applies. “Microlithography” refers to the process as applied to images with features in the micrometer range.
Large Scale Integration. The art of putting tens of thousands of transistors into a single integrated circuit.
A unit of measure equaling about 3.3 feet.
Similar to a standard cell but larger. Macro cells contain predefined circuit elements that may be selected and arranged to create a custom or semi-custom integrated circuit more easily than through design. Designers building ASICs use macro and standard cells.
A microcontroller is a stand-alone device that performs computer functions within an electronic system without the need of other support circuits. A microcontroller contains memory functions, unlike a microprocessor; which is typically paired with a chip that provides memory. Microcontrollers are used in TVs, VCRs, microwave ovens and automobile engines.
A metric unit of linear measure which equals one millionth of a meter or one thousandth of a millimeter. A thousand times bigger than a nanometer. The diameter of a human hair is about 100 microns. Today’s semiconductors have lines etched at 0.065 microns.
A device that works with a micro-controller or microprocessor. Microperipherals are used in modems, ISDN and ethernet lines, in imaging equipment such as printers, computer mice and keyboards.
A central processing unit (CPU) fabricated on one or more chips, containing the basic arithmetic, logic and control elements required by a computer for processing data. Micro-processor also refers to an integrated circuit that accepts coded instructions, executes the instructions and delivers signals that describe its internal status.
One thousandth of a meter. About 4/100 inch.
A class of ICs that have traditionally been considered analog semiconductors. They can also be defined as anything that combines analog and digital circuitry-and that includes many ASICs and DSPs.
Any system with atomically precise electronic devices of nanometer dimensions, especially if made of discrete molecular parts rather than the continuous materials found in today’s semiconductor devices.
In 1965 Intel co-founder Gordon Moore predicted that the number of transistors (and capacity) that can be squeezed onto a chip would double every 18 months. If this trend continued, he reasoned, computing power would rise exponentially with each new generation of chips. His published observation holds to this day.
Metal Oxide Semiconductor Field Effect Transistor. A device that does not require as much power as bipolar devices because of its insulation. The term can be applied either to transistors in an IC or to discrete power devices. MOSFETs are easier to manufacture than bipolar devices and are a building block in the fabrication of CMOS chips.
A nanoscale crystal whose size, shape and atomic composition are carefully controlled to yield specific properties, like absorption of specific wavelengths of light.
A metric unit of linear measure which equals one billionth of a meter. A leading edge semiconductor today has line widths of 65 nanometers.
The size range of objects studied by nanotechnologists.
The ability to see, measure and make objects that are within the same tiny size scale as atoms and molecules. The nanotechnology realm can be defined as being between 0.1 nanometer (about the size of a hydrogen atom) and 100 nanometers (about the size of a virus).
A tube of nanoscale dimensions, but most frequently referring to carbon nanotubes. These tubes, which are stronger and lighter than steel, can have varying electrical properties with applications in computing, materials manufacturing and biotechnology.
A storage device whose contents are preserved when its power is off. Storage using magnetic disks or tape is normally non-volatile. Some semiconductor memories (ROM, EPROM, Flash memory) are non-volatile while other semiconductor memories (static RAM and especially dynamic RAM) are normally volatile but can be made into non-volatile storage by permanently connecting a (rechargeable) battery.
Negative-channel Metal Oxide Semiconductor. NMOS was the preferred technology for making leading-edge chips in the 1970’s and early 1980’s.
A device that is responsive to or that emits or modifies light waves. Examples are LEDs, optical couplers, laser diodes, and photo detectors.
The protective container or housing for an electronic component or die, with external terminals to provide electrical access to the components inside. Packages provide for power and signal distribution, power dissipation, and physical and chemical protection of the circuits.
Printed Circuit Board. Flat material on which electronic components are mounted. Also provides electrical pathways that connect components.
Personal Digital Assistant
Programmable Logic Device. A digital IC that can be programmed by the user to perform a wide variety of logical operations. FPGAs and CPLDs are classes of PLDs.
A class of nanocrystals that emit varying colors of light depending on their size. They can be used to label different biological structures.
Random Access Memory. May be written to, or read from, any address location in any sequence. Also called a read/write memory, RAM stores digital bits temporarily and can be changed rapidly as required. RAM constitutes the basic read/write storage element in computers.
Radio Frequency. The rage of electromagnetic frequencies above the audio range and below the visible light. All broadcast transmission, from AM radio to satellites, falls into this range, between 30KHz to 300GHz.
Read Only Memory. Permanently stores information used repeatedly, such as tables of data, characters for electronic displays, etc. A popular type known as PROM is programmable in the field with the aid of programmer equipment. Programmed data stored in ROM is often called firmware.
An international reference document of requirements, potential solutions, and their timing for the semiconductor industry. It identifies needs and encourages innovative solutions to meet future technical challenges, and provides an ongoing emphasis on obtaining consensus industry drivers, requirements, and technology timelines.
The ability of an entity such as a living cell to make a copy of itself. Theoretically, nanotechnologists could invent self- replicating devices.
The ability of objects to assemble themselves into an orderly structure. Routinely seen in living cells, this is a property that nanotechnology may extend to inanimate matter.
This is the generic name for discrete devices and integrated circuits that can control the flow of electrical signals. Silicon is the basic material on which semiconductors are fabricated.
Electronic functions that enhance the representations of physical or electrical phenomena. Temperature, pressure, vibration, acceleration and flow are examples of physical properties that rely on signal processing enhancements. The detection and conversion of RF, X-ray or ultrasonic energy into images and sound is another form of signal processing.
Refers to the electronic properties of crystalline material, as opposed to vacuum and gas-filled tubes that transmit electricity. Compared with earlier vacuum-tube devices, solid-state components are smaller, less expensive, more reliable, use less power and generate less heat.
Static Random Access Memory. Is an integrated circuit similar to a DRAM that requires no constant refreshing or recharging. It retains stored information as long as power is applied to the computer, hastening information-retrieval process time. In contrast to ROM, SRAM is still volatile and will lose its contents when the power is switched off. SRAM is usually faster than DRAM but usually costs more per bit because each bit requires several transistors. It is used for the most speed-critical parts of a computer or other circuit.
Predefined circuit elements that may be selected and arranged to create a custom or semi-custom integrated circuit more easily than through design. Designers build ASICs using standard cells.
The body or base layer of an integrated circuit, onto which other layers are deposited to form the circuit. The substrate is usually silicon, although sapphire is used for certain applications, particularly military, where radiation resistance is important. The substrate is originally part of the wafer from which the die is cut. It is used as the electrical ground for the circuit.
A device used to produce high-energy X-rays that can inscribe features on a chip potentially as small as 100 nanometers.
System on a Chip
A chip that is a self-contained system, including processing, memory and input-output functions.
An electronic device capable of amplifying electronic signals similar to the vacuum tube but made from a semiconductor material such as silicon or germanium.
Very Large-Scale Integration. The art of putting hundreds of thousands of transistors onto a single quarter-inch integrated circuit.
A slang term for wafer fabrication facilities, ultra clean factories wherein silicon wafers are produced.
A thin slice, typically 10-30 mils thick, sawed from a cylindrical ingot (boule) of extremely pure, crystalline silicon, typically six to eight inches in diameter. Arrays of ICs or discrete devices are fabricated in the wafers during the manufacturing process.
The lithographic process for transferring patterns to a silicon wafer. The electromagnetic radiation used is X-ray, rather than visible radiation.
Yield refers to the percentage or absolute number of defect-free die on a silicon wafer or of packaged units that pass all device specifications. Because it costs the same to process a wafer with 10% good die and 90% good die, eliminating defects and improving yield become the critical variable in determining the cost per chip.