Christofle

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Christofle is a manufacturer of fine silver flatware and home accessories based in France since 1830. They are renowned for their sterling, silverplate and stainless flatware. Among Christofle's product lines are silver picture frames, crystal vases and glassware, porcelain dinnerware and silver jewelry. Christofle is also well known for their silver holloware.

Artists and designers such as Man Ray, Jean Cocteau, Gio Ponti, Andre Putman, Martin Szekely, Ito Morabito (Ora-to) and Richard Hutten are among those whose creations have been made by Christofle. freeze dried rose petals

The origins of Christofle date to 1830 when jeweler Charles Christofle assumed management of a jewelry workshops pertaining to his wife's family. Christofle today is under the control and ownership of the Christofle family, the current generation being represented by Maurizio Borletti. Christofle was publicly-traded until 1998, when Borletti and others took the firm private. glow cups

Christofle manufactures their products in France and in Brazil, and they are sold worldwide through 75 Pavillon Christofle retail stores and also through 400 department stores and specialty shops. lighted ice cubes

References

Style on a Silver Platter, India Today, 2/28/08

Christofle: A Legend Revisited, Diplomat, June 2006

External links

Wikimedia Commons has media related to: Christofle

Official website

Christofle Hotel Division, Table De France, North America

This French corporation or company article is a stub. You can help Wikipedia by expanding it.

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Categories: Companies established in 1830 | Companies of France | French silversmiths | French company stubs

Phone fraud

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Types of frauds

Fraud against users

Frauds against users by phone companies mini tape dispenser

Cramming is the addition of charges to a subscriber's telephone bill for services which were neither ordered nor desired by the client, or for fees for calls or services that were not properly disclosed to the consumer. These charges are often assessed by dishonest third-party suppliers of data and communication service that phone companies are required, by law, to allow the third-party to place on the bill. heavy duty stapler

Slamming is any fraudulent, unauthorized change to the default long-distance/Local carrier or DSL internet service selection for a subscriber's line, most often made by dishonest vendors desirous to steal business from competing service providers. Main article: Telephone slamming. auto tape dispenser

Fraud against customers by third parties

PBX dial through (hi) can be used fraudulently by placing a call to a business and then requesting to be transferred to "9-0" or some other outside toll number. (9 is normally an outside line and 0 then connects to the utility's operator) The call appears to originate from the business (instead of the original fraudulent caller) and appears on the company's phone bill. Trickery (such as impersonation of installers and telco personnel "testing the system") or bribery and collusion with dishonest employees inside the firm may be used to gain access.

Autodialers may be used for a number of dishonest purposes, including telemarketing fraud or even as War dialing. War dialers take their name from a scene in the early-1980's movie WarGames in which a 'cracker' programs a home computer to dial every number in an exchange, searching for lines with auto-answer data modems. Sequential dialing is easy to detect, pseudo-random dialing is not. One more recent variant involves claiming to be a customer-owned coin-operated telephone (COCOT) vendor, connecting an autodialer to what should have been a payphone line, dialing an assorted series of toll-free "wrong numbers" (such as +1-800 in US, which effectively reverses the charges) and then demanding that the called parties reimburse the fraudulent COCOT provider for the cost of "calls received from a payphone".

Autodialers are also used to make many short duration calls, mainly to mobiles, leaving a missed call number which is either premium rate or contains advertising messages. Knowns as Wangiri from Japan where it originated.

Dialer programs containing malware or malicious code have been used to cause personal computers to disconnect from an existing legitimate local provider and instead dial into a premium (usually overseas) number. The first of these used a Moldovan phone number[citation needed].

Pre-pay telephone cards and "calling cards" are also very vulnerable to fraudulent use; these cards contain a number or passcode which can be dialed in order to bill worldwide toll calls to the card. Anyone who obtains the passcode can dishonestly misuse it to make or to resell toll calls.

809 scams take their name from the former +1 (809) area code which used to cover most of the Caribbean nations (it has since been split into multiple new area codes, adding to the confusion). The numbers *look* like Canadian or US telephone numbers but turn out to be costly, overpriced international calls. Entire Caribbean 'phone exchanges (such as +1-876-HOT-...) numbers in Jamaica, plus numbers in Antigua, Montserrat and a number of other Caribbean or overseas countries) are used to bypass consumer protection laws which govern premium numbers and phone sex operations such as +1-900 or 976 services in the victim's home country. Other variants on this scheme involve leaving messages on pagers or making bogus claims of being a relative in a family emergency to trick users into calling the foreign numbers, then attempting to keep the victim on the line as long as possible in order to incur the cost of an expensive foreign call.

The 10xxx or 1010xxx codes used to select an alternate long-distance carrier on a per-call basis were also widely misused by phone sex scammers and spammers in the early days of competitive long distance; the phone-sex operations would misrepresent themselves as alternate long-distance carriers to evade consumer protection measures which prevent US 'phone subscribers from losing local or long-distance service due to calls to +1-900 or 976 premium numbers. This practice has largely been replaced by the misuse of numbers in former +1-809 countries or other overseas numbers as cash-strapped governments in many poorer nations are willing to condone the practice.

Telemarketing fraud takes a number of forms; much like mail fraud, solicitations for the sale of goods or investments which are never delivered or worthless and requests for donations to bogus unregistered charities are not uncommon. Callers often prey upon sick and elderly persons; scams in which a caller attempts to obtain banking or credit card information also frequently occur. One other variant

involves calling a number of business offices, asking for model numbers of various pieces of office equipment in use (such as photocopiers) and then sending unsolicited shipments of supplies for the machines then billing the victims at artificially inflated prices.

Verizon, at the customer's request, will put a Cramming Block on the customer's account, that prevents third parties from adding charges. To obtain the free Cramming Block call Verizon customer service.

Fraud against phone companies

Fraud by phone companies against one another

Interconnect fraud involves the falsification of records by telephone carriers in order to deliberately miscalculate the money owed by one telephone network to another. This affects calls originating on one network but carried by another at some point between source and destination.

Refiling is a form of interconnect fraud in which one carrier tampers with CID (caller-ID) or ANI data to falsify the number from which a call originated before handing the call off to a competitor. Refiling and interconnect fraud briefly made headlines in the aftermath of the Worldcom financial troubles; the refiling scheme is based on a quirk in the system by which telcos bill each other - two calls to the same place may incur different costs because of differing displayed origin. A common calculation of payments between telcos calculates the percentage of the total distance over which each telco has carried one call to determine division of toll revenues for that call; refiling distorts data required to make these calculations.

Fraud against the phone company by users

Subscription fraud: for example, signing up with a bogus name, or no intention to pay

Frauds against the phone company by third parties

Phreaking involves obtaining knowledge of how the telephone network operates, which can be used (but isn't always) to place unauthorised calls. The history of phone phreaking shows that many 'phreaks' used their vast knowledge of the network to help telephone companies. There are, however, many phreaks that use their knowledge to exploit the network for personal gain, even today. In some cases social engineering has been used to trick telco employees into releasing technical information. Early examples of phreaking involved generation of various control tones, such as a 2600 hertz blue box tone to release a long-distance trunk for immediate re-use or the red box tones which simulate coins being inserted into a payphone. These exploits no longer work in many areas of the telephone network due to widespread use of digital switching systems and out-of-band signaling. There are, however, many areas of the world where these control tones are still used and this kind of fraud is still continuing to happen.

A more high-tech version of the above is switch reprogramming, where unauthorized "back door" access to the phone company's network or billing system is used to allow free telephony. This is then sometimes resold by the 'crackers' to other customers.

Payphones have also been misused to receive fraudulent collect calls; most carriers have turned off the feature of accepting incoming calls or have muted the payphones internal ringing mechanism for this very reason.

Cloning (telephony) has been used as a means of copying both the electronic serial number and the telephone number of another subscriber's 'phone to a second (cloned) 'phone. Airtime charges for outbound calls are then mis-billed to the victim's cellular 'phone account instead of the perpetrator's. Cordless phones are often even less secure than cellphones, though there are a number of security issues currently affecting cellular phones. There are a number of other privacy concerns with mobile and cordless 'phones; a scanner radio may intercept analogue conversations in progress.

Frauds against the phone company by phone company employees

This section requires expansion.

See also

Caller ID spoofing

Credit card fraud

Dial tapping

Internet fraud

Mail fraud

Mobile phone spam

Vishing

Wire fraud

External links

State-by-State Comparison of Cramming Laws plus recommended course of action for affected consumers

Find and Report Trouble callers

Billing World article: Telecom Fraud on the Rise

Lasar's Letter on the Federal Communications Commission: FCC slams 13 telcos for slamming--exonerates three

Identify Fraudulent Charges in Your Phone Bill guide from non-profit consumer group on identifying and disputing fraudulent charges

16 Ways You Can be Phone Scammed a list of the most popular phone scams.

OFCOM: Problems with your landline phone: slamming - advice from the British communications regulator

Daily Mail: Phone scam hits thousands

The Guardian: When slamming the phone prompts a row

The Guardian: Orange slammed as users see red - concerns over data protection by British mobile telecom suppliers

Bell Canada Fraud Control Centre

Categories: FraudHidden categories: Articles with limited geographic scope | USA-centric | All articles with unsourced statements | Articles with unsourced statements from February 2007 | Articles to be expanded from May 2008 | All articles to be expanded

Polyphenism

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Definition

A polyphenism is a biological mechanism that causes a trait to be polyphenic. For example, crocodiles possess a sex-determining polyphenism, and therefore their gender is a polyphenic trait.

When polyphenic forms exist at the same time in the same panmictic (interbreeding) population they can be compared to genetic polymorphism. With polyphenism the switch between morphs is environmental, but with genetic polymorphism with the determination of morph is genetic. These two cases have in common that more than one morph is part of the population at any one time. This is rather different from cases where one morph predictably follows another during, for instance, the course of a year. In essence the latter is normal ontogeny where young forms can and do have different forms, colours and habits to adults. prescription swimming goggles

The discrete nature of polyphenic traits differentiates them from traits like weight and height, which are also dependent on environmental conditions but vary continuously across a spectrum. When a polyphenism is present, an environmental cue causes the organism to develop along a separate pathway, resulting in distinct morphologies; thus, the response to the environmental cue is ll or nothing. The nature of these environmental conditions varies greatly, and includes seasonal cues like temperature and moisture, pheromonal cues, kairomonal cues (signals released from one species that can be recognized by another), and nutritional cues. blade table tennis

Examples of Polyphenism table tennis paddle

Sex determination

Sex-determining polyphenisms allow a species to benefit from sexual reproduction while permitting gender ratios other than unity. This is beneficial to the species because a large female-to-male ratio maximizes reproductive capacity. However, temperature-dependent sex determination (as seen in crocodiles) limits the range in which a species can exist, and makes the species susceptible to endangerment by changes in weather pattern. Temperature-dependent sex determination has been proposed as an explanation for the extinction of the dinosaurs.

Population-dependent and reversible sex determination, found in animals such as the blue wrasse fish, have less potential for failure. In the blue wrasse, only one male is found in a given territory: larvae within the territory develop into females, and adult males will not enter the same territory. If a male dies, one of the females in his territory becomes male, replacing him. While this system ensures that there will always be a mating couple when two animals of the same species are present, it could potentially decrease genetic variance in a population, for example if the females remain in a single male's territory. Furthermore, this system is inherently unstable on a small scale because a single mutation causing a fish to remain permanently male would spread quickly through the population (due to high female availability) and might eventually cause loss of females in the species, and therefore extinction.

The caste system in insects

The caste system of insects enables eusociality, the division of labor between non-breeding and breeding individuals. A series of polyphenisms determines whether larvae develop into queens, workers, and in some cases soldiers. In the case of the ant, P. morrisi, an embryo must develop under certain temperature and photoperiod conditions in order to become a reproductively-active queen. This allows for control of the mating season, but like sex determination, limits the spread of the species into certain climates. In bees, royal jelly provided by worker bees causes a developing larva to become a queen. Royal jelly is only produced when the queen is aging or has died. This system is less subject to influence by environmental conditions, yet prevents unnecessary production of queens.

Seasonal pigmentation changes

Polyphenic pigmentation is adaptive for insect species that undergo multiple mating seasons each year. Different pigmentation patterns provide appropriate camouflage throughout the seasons, as well as alter heat retention as temperatures change. Because insects cease growth and development after eclosion, their pigment pattern is invariable in adulthood: thus, a polyphenic pigment adaptation would be less valuable for species whose adult form survives longer than one year. Birds and mammals, however, are capable of continued physiological changes in adulthood, and some display reversible seasonal polyphenisms, such as coat color in the Arctic fox.

Predator-Induced Polyphenisms

Predator-induced polyphenisms are advantageous because they allow the species to develop in a more reproductively-successful way in a predator absence, but to otherwise assume a more defensible morphology. However, this advantageous polyphenism can quickly become neutral or a disadvantage if the predator evolves to stop producing the kairomone to which the prey responds. For example, the fly larvae that feed on Daphnia cucullata (a water flea) release a kairomone that Daphnia can detect. When the fly larvae are present, Daphnia grow large helmets that protect them from being eaten. However when the predator is absent, Daphnia have smaller heads and are therefore more agile swimmers.

Cannibalistic Polyphenism

The spadefoot toad polyphenism maximizes its reproductive capacity in temporary desert ponds. While the water is at a safe level, the tadpoles develop slowly on a diet of other opportunistic pond inhabitants. However, when the water level is low and desiccation is imminent, the tadpoles develop a morphology (wide mouth, strong jaw) that permits them to cannibalize. Cannibalistic tadpoles receive better nutrition and thus metamorphose more quickly, avoiding death as the pond dries up.

Evolution of Polyphenisms

A mechanism has been proposed for the development of polyphenisms:

A mutation results in a novel, heritable trait.

The trait frequency expands in the population, creating a population on which selection can act.

Pre-existing (background) genetic variation in other genes results in phenotypic differences in expression of the new trait.

These phenotypic differences undergo selection; as genotypic differences narrow, the trait becomes:

Genetically fixed (non-responsive to environmental conditions)

Polyphenic (responsive to environmental conditions)

Evolution of novel polyphenisms through this mechanism has been demonstrated in the laboratory. Suzuki and Nijhout used an existing mutation (black) in a monophenic green hornworm (M. sexta) that causes a black phenotype. They found that if larvae from an existing population of black mutants were raised at 20C, then all the final instar larvae were black; but if the larvae were instead raised at 28C, the final instar larvae ranged in color from black to green. By selecting for larvae that were black if raised at 20C but green if raised at 28C, they produced a polyphenic strain after thirteen generations.

This fits the model described above because a new mutation (black) was required to reveal pre-existing genetic variation and to permit selection. Furthermore, the production of a polyphenic strain was only possible because of background variation within the species: two alleles, one temperature-sensitive and one stable, were present for a single gene upstream of black (in the pigment production pathway) before selection occurred. The temperature-sensitive allele was not observable because at high temperatures, it caused an increase in green pigment in hornworms that were already bright green. However, introduction of the black mutant caused the temperature-dependent changes in pigment production to become obvious. The researchers could then select for larvae with the temperature-sensitive allele, resulting in a polyphenism.

See also

Phenotypic switching

References

^ Noor MA, Parnell RS, Grant BS (2008). "A Reversible Color Polyphenism in American Peppered Moth (Biston betularia cognataria) Caterpillars". PLoS ONE 3 (9): e3142. doi:10.1371/journal.pone.0003142. PMID 18769543. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0003142. 

^ Woodward, D.E. and Murray, J.D. (1993). On the effect of temperature-dependent sex determination on sex ratio and survivorship in crocodilians. Proc. R. Soc. Lond. [B] 252:149-155.

^ Ford E.B. 1975. Ecological genetics. 4th ed, Chapman & Hall, London

^ Woodward, D.E. and Murray, J.D. (1993). On the effect of temperature-dependent sex determination on sex ratio and survivorship in crocodilians. Proc. R. Soc. Lond. [B] 252:149-155.

^ Gilbert, S.F. (2003). Developmental Biology, 7 edn (Sunderland, Massachusetts, Sinauer Associates, Inc.). pp.731.

^ Gilbert, S.F. (2003). Developmental Biology, 7 edn (Sunderland, Massachusetts, Sinauer Associates, Inc.). pp.732

^ Abouheif, E., and Wray, G.A. (2002). Evolution of the gene network underlying wing polyphenism in ants. Science 297, 249-252.

^ Braendle, C., and Flatt, T. (2006). A role for genetic accommodation in evolution? Bioessays 28, 868-873.

^ Gilbert, S.F. (2003). Developmental Biology, 7 edn (Sunderland, Massachusetts, Sinauer Associates, Inc.). pp.727.

^ Gilbert, S.F. (2003). Developmental Biology, 7 edn (Sunderland, Massachusetts, Sinauer Associates, Inc.). pp.735.

^ Storz, B.L. (2004). Reassessment of the environmental mechanisms controlling developmental polyphenism in spadefoot toad tadpoles. Oecologia 141, 402-410.

^ Braendle, C., and Flatt, T. (2006). A role for genetic accommodation in evolution? Bioessays 28, 868-873.

^ Suzuki, Y., and Nijhout, H.F. (2006). Evolution of a polyphenism by genetic accommodation. Science 311, 650-652.

Note: The seventh edition of Gilbert's Developmental Biology is available online: DevBio.

Categories: Biology | Subfields and areas of study related to evolutionary biology | Evolutionarily significant biological phenomena | Population ecologyHidden categories: Unclassified articles missing geocoordinate data | All articles needing coordinates

Semiconductor device fabrication

China Product


History

When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacturing. As devices became more integrated, cleanrooms became even cleaner. Today, the fabs are pressurized with filtered air to remove even the smallest particles, which could come to rest on the wafers and contribute to defects. The workers in a semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination.

In an effort to increase profits, semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, such as Europe, Israel, and Asia. It is a global business today. solar blankets

The leading semiconductor manufacturers typically have facilities all over the world. Intel, the world's largest manufacturer, has facilities in Europe and Asia as well as the U.S. Other top manufacturers include STMicroelectronics (Europe), Analog Devices (US), Atmel (US/Europe), Freescale Semiconductor (US), Samsung (Korea), Texas Instruments (US), GlobalFoundries (Germany, Singapore, future New York fab in construction), Toshiba (Japan), NEC Electronics (Japan), Infineon (Europe), Renesas (Japan), Taiwan Semiconductor Manufacturing Company (Taiwan), Fujitsu(Japan/US), NXP Semiconductors (Europe), Micron Technology (US), Hynix (Korea) and SMIC (China). rockwool insulation

Wafers extruded polystyrene

Main article: wafer (semiconductor)

A typical wafer is made out of extremely pure silicon that is grown into mono-crystalline cylindrical ingots (boules) up to 300 mm (slightly less than 12 inches) in diameter using the Czochralski process. These ingots are then sliced into wafers about 0.75 mm thick and polished to obtain a very regular and flat surface.

Once the wafers are prepared, many process steps are necessary to produce the desired semiconductor integrated circuit. In general, the steps can be grouped into two areas:

Front-end processing

Back-end processing

Processing

In semiconductor device fabrication, the various processing steps fall into four general categories: deposition, removal, patterning, and modification of electrical properties.

Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer. Available technologies consist of physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and more recently, atomic layer deposition (ALD) among others.

Removal processes are any that remove material from the wafer either in bulk or selectively and consist primarily of etch processes, either wet etching or dry etching. Chemical-mechanical planarization (CMP) is also a removal process used between levels.

Patterning covers the series of processes that shape or alter the existing shape of the deposited materials and is generally referred to as lithography. For example, in conventional lithography, the wafer is coated with a chemical called a photoresist. The photoresist is exposed by a stepper, a machine that focuses, aligns, and moves the mask, exposing select portions of the wafer to short wavelength light. The unexposed regions are washed away by a developer solution. After etching or other processing, the remaining photoresist is removed by plasma ashing.

Modification of electrical properties has historically consisted of doping transistor sources and drains originally by diffusion furnaces and later by ion implantation. These doping processes are followed by furnace anneal or in advanced devices, by rapid thermal anneal (RTA) which serve to activate the implanted dopants. Modification of electrical properties now also extends to reduction of dielectric constant in low-k insulating materials via exposure to ultraviolet light in UV processing (UVP).

Many modern chips have eight or more levels produced in over 300 sequenced processing steps.

Front-end processing

Front-end processing refers to the formation of the transistors directly on the silicon. The raw wafer is engineered by the growth of an ultrapure, virtually defect-free silicon layer through epitaxy. In the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built. One method involves introducing a straining step wherein a silicon variant such as silicon-germanium (SiGe) is deposited. Once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility. Another method, called silicon on insulator technology involves the insertion of an insulating layer between the raw silicon wafer and the thin layer of subsequent silicon epitaxy. This method results in the creation of transistors with reduced parasitic effects.

Gate oxide and implants

Front-end surface engineering is followed by: growth of the gate dielectric, traditionally silicon dioxide (SiO2), patterning of the gate, patterning of the source and drain regions, and subsequent implantation or diffusion of dopants to obtain the desired complementary electrical properties. In memory devices, storage cells, conventionally capacitors, are also fabricated at this time, either into the silicon surface or stacked above the transistor.

Back-end processing

Metal layers

Once the various semiconductor devices have been created they must be interconnected to form the desired electrical circuits. This back end of line (BEOL, the latter portion of the wafer fabrication, not to be confused with back end of chip fabrication which refers to the package and test stages) involves creating metal interconnecting wires that are isolated by insulating dielectrics. The insulating material was traditionally a form of SiO2 or a silicate glass, but recently new low dielectric constant materials are being used. These dielectrics presently take the form of SiOC and have dielectric constants around 2.7 (compared to 3.9 for SiO2), although materials with constants as low as 2.2 are being offered to chipmakers.

Interconnect

Synthetic detail of a standard cell through four layers of planarized copper interconnect, down to the polysilicon (pink), wells (greyish) and substrate (green).

Historically, the metal wires consisted of aluminium. In this approach to wiring often called subtractive aluminium, blanket films of aluminium are deposited first, patterned, and then etched, leaving isolated wires. Dielectric material is then deposited over the exposed wires. The various metal layers are interconnected by etching holes, called vias, in the insulating material and depositing tungsten in them with a CVD technique. This approach is still used in the fabrication of many memory chips such as dynamic random access memory (DRAM) as the number of interconnect levels is small, currently no more than four.

More recently, as the number of interconnect levels for logic has substantially increased due to the large number of transistors that are now interconnected in a modern microprocessor, the timing delay in the wiring has become significant prompting a change in wiring material from aluminium to copper and from the silicon dioxides to newer low-K material. This performance enhancement also comes at a reduced cost via damascene processing that eliminates processing steps. In damascene processing, in contrast to subtractive aluminium technology, the dielectric material is deposited first as a blanket film, and is patterned and etched leaving holes or trenches. In single damascene processing, copper is then deposited in the holes or trenches surrounded by a thin barrier film resulting in filled vias or wire lines respectively. In dual damascene technology, both the trench and via are fabricated before the deposition of copper resulting in formation of both the via and line simultaneously, further reducing the number of processing steps. The thin barrier film, called copper barrier seed (CBS), is necessary to prevent copper diffusion into the dielectric. The ideal barrier film is as thin as possible. As the presence of excessive barrier film competes with the available copper wire cross section, formation of the thinnest continuous barrier represents one of the greatest ongoing challenges in copper processing today.

As the number of interconnect levels increases, planarization of the previous layers is required to ensure a flat surface prior to subsequent lithography. Without it, the levels would become increasingly crooked and extend outside the depth of focus of available lithography, interfering with the ability to pattern. CMP (chemical mechanical planarization) is the primary processing method to achieve such planarization although dry etch back is still sometimes employed if the number of interconnect levels is no more than three.

Wafer test

The highly serialized nature of wafer processing has increased the demand for metrology in between the various processing steps. Wafer test metrology equipment is used to verify that the wafers haven't been damaged by previous processing steps up until testing. If the number of dieshe integrated circuits that will eventually become chips etched on a wafer exceeds a failure threshold (ie. too many failed dies on one wafer), the wafer is scrapped rather than investing in further processing.

Device test

Main article: wafer testing

Once the front-end process has been completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly. The proportion of devices on the wafer found to perform properly is referred to as the yield.

The fab tests the chips on the wafer with an electronic tester that presses tiny probes against the chip. The machine marks each bad chip with a drop of dye. The fab charges for test time; the prices are on the order of cents per second. Chips are often designed with estability features such as "built-in self-test" to speed testing, and reduce test costs.

Good designs try to test and statistically manage corners: extremes of silicon behavior caused by operating temperature combined with the extremes of fab processing steps. Most designs cope with more than 64 corners.

Die preparation

Main article: die preparation

Once tested, the wafer is scored and then broken into individual die -- wafer dicing. Only the good, unmarked chips go on to be packaged.

Packaging

Main article: integrated circuit packaging

Plastic or ceramic packaging involves mounting the die, connecting the die pads to the pins on the package, and sealing the die. Tiny wires are used to connect pads to the pins. In the old days, wires were attached by hand, but now purpose-built machines perform the task. Traditionally, the wires to the chips were gold, leading to a ead frame (pronounced eed frame) of copper, that had been plated with solder, a mixture of tin and lead. Lead is poisonous, so lead-free ead frames are now mandated by ROHS.

Chip-scale package (CSP) is another packaging technology. A plastic dual in-line package, like most packages, is many times larger than the actual die hidden inside, whereas CSP chips are nearly the size of the die. CSP can be constructed for each die before the wafer is diced.

The packaged chips are retested to ensure that they were not damaged during packaging and that the die-to-pin interconnect operation was performed correctly. A laser etches the chip name and numbers on the package.

List of steps

This is a list of processing techniques that are employed numerous times in a modern electronic device and do not necessarily imply a specific order.

Wafer processing

Wet cleans

Photolithography

Ion implantation (in which dopants are embedded in the wafer creating regions of increased (or decreased) conductivity)

Dry etching

Wet etching

Plasma ashing

Thermal treatments

Rapid thermal anneal

Furnace anneals

Thermal oxidation

Chemical vapor deposition (CVD)

Physical vapor deposition (PVD)

Molecular beam epitaxy (MBE)

Electrochemical Deposition (ECD). See Electroplating

Chemical-mechanical planarization (CMP)

Wafer testing (where the electrical performance is verified)

Wafer backgrinding (to reduce the thickness of the wafer so the resulting chip can be put into a thin device like a smartcard or PCMCIA card.)

Die preparation

Wafer mounting

Die cutting

IC packaging

Die attachment

IC Bonding

Wire bonding

Thermosonic Bonding

Flip chip

Tab bonding

IC encapsulation

Baking

Plating

Lasermarking

Trim and form

IC testing

Hazardous materials

Many toxic materials are used in the fabrication process. These include:

poisonous elemental dopants such as arsenic, antimony and phosphorus

poisonous compounds like arsine, phosphine and silane

highly reactive liquids, such as hydrogen peroxide, fuming nitric acid, sulfuric acid and hydrofluoric acid

It is vital that workers not be directly exposed to these dangerous substances. The high degree of automation common in the IC fabrication industry helps to reduce the risks of exposure of this sort. Most fabrication facilities employ exhaust management systems, such as wet scrubbers, combustors, heated absorber cartridges etc, to control the risk to workers and also the environment if these toxic materials are released into the atmosphere.

See also

Atomic layer deposition

Electronic design automation

Foundry (electronics)

GDS II

Health hazards in semiconductor manufacturing occupations

International Technology Roadmap for Semiconductors

Microfabrication

OASIS (Open Artwork System Interchange Standard)

Semiconductor Equipment and Materials International (SEMI) the semiconductor industry trade association

References

^ Zeno Gaburro (2004). "Optical Interconnect". in Lorenzo Pavesi and David J. Lockwood. Silicon Photonics. Springer. ISBN 3540210229. 

^ http://www.uic.com/wcms/WCMS2.nsf/index/Resources_26.html

External links

Semiconductor glossary

BYU Cleanroom - semiconductor properties, calculators, processes, etc.

Categories: Semiconductor device fabricationHidden categories: Articles needing additional references from September 2008 | All articles needing additional references