Semiconductor device fabrication

Last updated
NASA's Glenn Research Center clean room Clean room.jpg
NASA's Glenn Research Center clean room

Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications.

Integrated circuit electronic circuit manufactured by lithography; set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are orders of magnitude smaller, cheaper, and faster than those constructed of discrete electronic components. The IC's mass production capability, reliability and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.

Electronics physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter

Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. The identification of the electron in 1897, along with the invention of the vacuum tube, which could amplify and rectify small electrical signals, inaugurated the field of electronics and the electron age.

Photolithography, also termed optical lithography or UV lithography, is a process used in microfabrication to pattern parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate. A series of chemical treatments then either engraves the exposure pattern into the material or enables deposition of a new material in the desired pattern upon the material underneath the photo resist. For example, in complex integrated circuits, a modern CMOS wafer will go through the photolithographic cycle up to 50 times.

Contents

The entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as foundries or fabs. [1] In more advanced semiconductor devices, such as modern 14/10/7 nm nodes, fabrication can take up to 15 weeks with 11–13 weeks being the industry average. [2]

In the microelectronics industry a semiconductor fabrication plant is a factory where devices such as integrated circuits are manufactured.

The 14 nanometer technology node is the successor to the 22 nm/(20 nm) node. The 14 nm was so named by the International Technology Roadmap for Semiconductors (ITRS). One nanometer (nm) is one billionth of a meter. Until about 2011, the node following 22 nm was expected to be 16 nm. The first 14 nm scale devices were shipped to consumers by Intel in 2014.

In semiconductor fabrication, the International Technology Roadmap for Semiconductors (ITRS) defines the 10 nanometer (10 nm) node as the technology node following the 14 nm node. "10 nm class" denotes chips made using process technologies between 10 and 20 nanometers.

By industry standard, each generation of the semiconductor manufacturing process, also known as "technology node", is designated by the process’s minimum feature size. Technology nodes, also known as "process technologies" or simply "nodes", are typically indicated by the size in nanometers (or historically micrometers) of the process's gate length.[ clarification needed ]

Micrometre one millionth of a metre

The micrometre or micrometer, also commonly known by the previous name micron, is an SI derived unit of length equalling 1×10−6 metre ; that is, one millionth of a metre.

As of 2019, 14 nanometer and 10 nanometer process chips are commonly in mass production, with 7 nanometer process chips in mass production by TSMC, although their node definition is similar to Intel's 10 nanometer process.

In semiconductor manufacturing, the International Technology Roadmap for Semiconductors defines the 7 nanometer (7 nm) node as the technology node following the 10 nm node. Single transistor 7 nm scale devices were first produced in the early 2000s. While some claim that the node designation of "7 nm" has no physical meaning beyond marketing purposes, others point to transistor density as the real important number that is represented by these designations.

TSMC Dedicated independent (pure-play) semiconductor foundry

Taiwan Semiconductor Manufacturing Company, Limited, also known as Taiwan Semiconductor, is the world's largest dedicated independent (pure-play) semiconductor foundry, with its headquarters and main operations located in the Hsinchu Science and Industrial Park in Hsinchu, Taiwan.

Intel American semiconductor company

Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, in the Silicon Valley. It is the world's second largest and second highest valued semiconductor chip manufacturer based on revenue after being overtaken by Samsung, and is the inventor of the x86 series of microprocessors, the processors found in most personal computers (PCs). Intel ranked No. 46 in the 2018 Fortune 500 list of the largest United States corporations by total revenue.

History

Semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, including Europe, the Middle East, and Asia. It is a global business today. 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. Samsung, Qualcomm, and Broadcom, among the biggest semiconductor manufacturers, [3] also have facilities spread in different countries.

Texas State of the United States of America

Texas is the second largest state in the United States by both area and population. Geographically located in the South Central region of the country, Texas shares borders with the U.S. states of Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the west, and the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas to the southwest, while the Gulf of Mexico is to the southeast.

California State of the United States of America

California is a state in the Pacific Region of the United States. With 39.6 million residents, California is the most populous U.S. state and the third-largest by area. The state capital is Sacramento. The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second and fifth most populous urban regions, with 18.7 million and 8.8 million residents respectively. Los Angeles is California's most populous city, and the country's second most populous, after New York City. California also has the nation's most populous county, Los Angeles County, and its largest county by area, San Bernardino County. The City and County of San Francisco is both the country's second-most densely populated major city after New York and the fifth-most densely populated county, behind only four of the five New York City boroughs.

Europe Continent in the Northern Hemisphere and mostly in the Eastern Hemisphere

Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west and the Mediterranean Sea to the south. It comprises the westernmost part of Eurasia.

Progress of miniaturisation, and comparison of sizes of semiconductor manufacturing process nodes with some microscopic objects and visible light wavelengths. Comparison semiconductor process nodes.svg
Progress of miniaturisation, and comparison of sizes of semiconductor manufacturing process nodes with some microscopic objects and visible light wavelengths.

Prevention of contamination and defects

When feature widths were far greater than about 10 micrometres, semiconductor purity was not as big an issue as it is today in device manufacturing. As devices became more integrated, cleanrooms became even cleaner. Today, fabrication plants 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.

Cleanroom facility designed to maintain extremely low levels of particulates, such as dust, airborne organisms, or vaporized particles

A cleanroom or clean room is a facility ordinarily utilized as a part of specialized industrial production or scientific research, including the manufacture of pharmaceutical items and microprocessors. Cleanrooms are designed to maintain extremely low levels of particulates, such as dust, airborne organisms, or vaporized particles. Cleanrooms typically have an cleanliness level quantified by the number of particles per cubic meter at a predetermined molecule measure. The ambient outdoor air in a typical urban area contains 35,000,000 particles for each cubic meter in the size range 0.5 μm and bigger in measurement, equivalent to an ISO 9 cleanroom, while by comparison an ISO 1 cleanroom permits no particles in that size range and just 12 particles for each cubic meter of 0.3 μm and smaller.

Pressurization or pressurisation is the application of pressure in a given situation or environment.

Crystallographic defect disruption of the periodicity of a crystal lattice

Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, determined by the unit cell parameters. However, the arrangement of atoms or molecules in most crystalline materials is not perfect. The regular patterns are interrupted by crystallographic defects.

Wafers

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.

Processing

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

Modern chips have up to eleven metal levels produced in over 300 sequenced processing steps.

Front-end-of-line (FEOL) processing

FEOL processing refers to the formation of the transistors directly in 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), 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 dynamic random-access memory (DRAM) devices, storage capacitors are also fabricated at this time, typically stacked above the access transistor (the now defunct DRAM manufacturer Qimonda implemented these capacitors with trenches etched deep into the silicon surface).

Back-end-of-line (BEOL) processing

Metal layers

Once the various semiconductor devices have been created, they must be interconnected to form the desired electrical circuits. This occurs in a series of wafer processing steps collectively referred to as BEOL (not to be confused with back end of chip fabrication, which refers to the packaging and testing stages). BEOL processing involves creating metal interconnecting wires that are isolated by dielectric layers. The insulating material has traditionally been a form of SiO2 or a silicate glass, but recently new low dielectric constant materials are being used (such as silicon oxycarbide), typically providing dielectric constants around 2.7 (compared to 3.82 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). Siliconchip by shapeshifter.png
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 have been composed of aluminum . In this approach to wiring (often called subtractive aluminum), blanket films of aluminum 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 then 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), because 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 so significant as to prompt a change in wiring material (from aluminum to copper interconnect layer) and a change in dielectric material (from silicon dioxides to newer low-K insulators). This performance enhancement also comes at a reduced cost via damascene processing, which eliminates processing steps. 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, extending outside the depth of focus of available lithography, and thus 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 when 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. For example, thin film metrology based on ellipsometry or reflectometry is used to tightly control the thickness of gate oxide, as well as the thickness, refractive index and extinction coefficient of photoresist and other coatings. Wafer test metrology equipment is used to verify that the wafers haven't been damaged by previous processing steps up until testing; if too many dies on one wafer have failed, the entire wafer is scrapped to avoid the costs of further processing. Virtual metrology has been used to predict wafer properties based on statistical methods without performing the physical measurement itself. [1]

Device test

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. Manufacturers are typically secretive about their yields, but it can be as low as 30%. Process variation is one among many reasons for low yield. [4]

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. Currently, electronic dye marking is possible if wafer test data is logged into a central computer database and chips are "binned" (i.e. sorted into virtual bins) according to the predetermined test limits. The resulting binning data can be graphed, or logged, on a wafer map to trace manufacturing defects and mark bad chips. This map can also be used during wafer assembly and packaging.

Chips are also tested again after packaging, as the bond wires may be missing, or analog performance may be altered by the package. This is referred to as the "final test".

Usually, the fab charges for testing time, with prices in the order of cents per second. Testing times vary from a few milliseconds to a couple of seconds, and the test software is optimized for reduced testing time. Multiple chip (multi-site) testing is also possible, because many testers have the resources to perform most or all of the tests in parallel.

Chips are often designed with "testability features" such as scan chains or a "built-in self-test" to speed testing, and reduce testing costs. In certain designs that use specialized analog fab processes, wafers are also laser-trimmed during the testing, in order to achieve tightly-distributed resistance values as specified by the design.

Good designs try to test and statistically manage corners (extremes of silicon behavior caused by a high operating temperature combined with the extremes of fab processing steps). Most designs cope with at least 64 corners.

Die preparation

Once tested, a wafer is typically reduced in thickness in a process also known as "backlap" [5] , "backfinish" or "wafer thinning" [6] before the wafer is scored and then broken into individual dice, a process known as wafer dicing. Only the good, unmarked chips are packaged.

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 the pads to the pins. In the old days[ when? ], wires were attached by hand, but now specialized machines perform the task. Traditionally, these wires have been composed of gold, leading to a lead frame (pronounced "leed frame") of solder-plated copper; lead is poisonous, so lead-free "lead 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; a 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 then etches the chip's name and numbers on the package.

List of steps

This is a list of processing techniques that are employed numerous times throughout the construction of a modern electronic device; this list does not necessarily imply a specific order.

Hazardous materials

Many toxic materials are used in the fabrication process. [7] These include:

It is vital that workers should 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. Most fabrication facilities employ exhaust management systems, such as wet scrubbers, combustors, heated absorber cartridges, etc., to control the risk to workers and to the environment.

See also

Related Research Articles

Microelectromechanical systems technology of very small devices

Microelectromechanical systems is the technology of microscopic devices, particularly those with moving parts. It merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines in Japan, or micro systems technology (MST) in Europe.

Very Large Scale Integration process of creating an integrated circuit by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed

Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining hundreds of thousands of transistors or devices into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. Before the introduction of VLSI technology most ICs had a limited set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM and other glue logic. VLSI lets IC designers add all of these into one chip.

Thin-film transistor

A thin-film transistor (TFT) is a special kind of field-effect transistor made by depositing thin films of an active semiconductor layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, because the primary application of TFTs is in liquid-crystal displays (LCDs). This differs from the conventional transistor, where the semiconductor material typically is the substrate, such as a silicon wafer.

In semiconductor manufacturing, a low-κ is a material with a small relative dielectric constant relative to silicon dioxide. Although the proper symbol for the relative dielectric constant is the Greek letter κ (kappa), in conversation such materials are referred to as being "low-k" (low-kay) rather than "low-κ" (low-kappa). Low-κ dielectric material implementation is one of several strategies used to allow continued scaling of microelectronic devices, colloquially referred to as extending Moore's law. In digital circuits, insulating dielectrics separate the conducting parts from one another. As components have scaled and transistors have gotten closer together, the insulating dielectrics have thinned to the point where charge build up and crosstalk adversely affect the performance of the device. Replacing the silicon dioxide with a low-κ dielectric of the same thickness reduces parasitic capacitance, enabling faster switching speeds and lower heat dissipation.

In semiconductor fabrication, a resist is a thin layer used to transfer a circuit pattern to the semiconductor substrate which it is deposited upon. A resist can be patterned via lithography to form a (sub)micrometer-scale, temporary mask that protects selected areas of the underlying substrate during subsequent processing steps. The material used to prepare said thin layer is typically a viscous solution. Resists are generally proprietary mixtures of a polymer or its precursor and other small molecules that have been specially formulated for a given lithography technology. Resists used during photolithography are called photoresists.

The term high-κ dielectric refers to a material with a high dielectric constant κ. High-κ dielectrics are used in semiconductor manufacturing processes where they are usually used to replace a silicon dioxide gate dielectric or another dielectric layer of a device. The implementation of high-κ gate dielectrics is one of several strategies developed to allow further miniaturization of microelectronic components, colloquially referred to as extending Moore's Law.

Front end of line

The front-end-of-line (FEOL) is the first portion of IC fabrication where the individual devices are patterned in the semiconductor. FEOL generally covers everything up to the deposition of metal interconnect layers.

Back end of line

The back end of line (BEOL) is the second portion of IC fabrication where the individual devices get interconnected with wiring on the wafer, the metalization layer. Common metals are copper and aluminum. BEOL generally begins when the first layer of metal is deposited on the wafer. BEOL includes contacts, insulating layers (dielectrics), metal levels, and bonding sites for chip-to-package connections.

Microfabrication processes of fabrication of miniature structures

Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" or "semiconductor device fabrication". In the last two decades microelectromechanical systems (MEMS), microsystems, micromachines and their subfields, microfluidics/lab-on-a-chip, optical MEMS, RF MEMS, PowerMEMS, BioMEMS and their extension into nanoscale have re-used, adapted or extended microfabrication methods. Flat-panel displays and solar cells are also using similar techniques.

Lam Research company

Lam Research Corporation is an American corporation that engages in the design, manufacture, marketing, and service of semiconductor processing equipment used in the fabrication of integrated circuits. Its products are used primarily in front-end wafer processing, which involves the steps that create the active components of semiconductor devices and their wiring (interconnects). The company also builds equipment for back-end wafer-level packaging (WLP), and for related manufacturing markets such as for microelectromechanical systems (MEMS).

Shallow trench isolation

Shallow trench isolation (STI), also known as box isolation technique, is an integrated circuit feature which prevents electric current leakage between adjacent semiconductor device components. STI is generally used on CMOS process technology nodes of 250 nanometers and smaller. Older CMOS technologies and non-MOS technologies commonly use isolation based on LOCOS.

The term salicide refers to a technology used in the microelectronics industry used to form electrical contacts between the semiconductor device and the supporting interconnect structure. The salicide process involves the reaction of a thin metal film with silicon in the active regions of the device, ultimately forming a metal silicide contact through a series of annealing and/or etch processes. The term "salicide" is a compaction of the phrase self-aligned silicide. The description "self-aligned" suggests that the contact formation does not require lithographic patterning processes, as opposed to a non-aligned technology such as polycide. The term salicide is also used to refer to the metal silicide formed by the contact formation process, such as "titanium salicide", although this usage is inconsistent with accepted naming conventions in chemistry. In chemistry, the term refers instead to compounds of salicin e.g. potassium salicide.

Metal gate

A metal gate, in the context of a lateral Metal-Oxide-Semiconductor MOS stack, is just that—the gate material is made from a metal.

Through-silicon via

In electronic engineering, a through-silicon via (TSV) or through-chip via is a vertical electrical connection (via) that passes completely through a silicon wafer or die. TSVs are high performance interconnect techniques used as an alternative to wire-bond and flip chips to create 3D packages and 3D integrated circuits. Compared to alternatives such as package-on-package, the interconnect and device density is substantially higher, and the length of the connections becomes shorter.

In microelectronics, a three-dimensional integrated circuit is an integrated circuit manufactured by stacking silicon wafers or dies and interconnecting them vertically using, for instance, through-silicon vias (TSVs) or Cu-Cu connections, so that they behave as a single device to achieve performance improvements at reduced power and smaller footprint than conventional two dimensional processes. 3D IC is just one of a host of 3D integration schemes that exploit the z-direction to achieve electrical performance benefits.

A substrate is a solid substance onto which a layer of another substance is applied, and to which that second substance adheres. In solid-state electronics, this term refers to a thin slice of material such as silicon, silicon dioxide, aluminum oxide, sapphire, germanium, gallium arsenide (GaAs), an alloy of silicon and germanium, or indium phosphide (InP). These serve as the foundation upon which electronic devices such as transistors, diodes, and especially integrated circuits (ICs) are deposited.

Tokyo Electron Japanese company

Tokyo Electron Limited, or TEL, is a Japanese electronics and semiconductor company headquartered in Akasaka, Minato-ku, Tokyo, Japan.

Atomic layer etching is an emerging technique in semiconductor manufacture, in which a sequence alternating between self-limiting chemical modification steps which affect only the top atomic layers of the wafer, and etching steps which remove only the chemically-modified areas, allows the removal of individual atomic layers. The standard example is etching of silicon by alternating reaction with chlorine and etching with argon ions.

In integrated circuits (ICs), interconnects are structures that connect two or more circuit elements together electrically. The design and layout of interconnects on an IC is vital to its proper function, performance, power efficiency, reliability, and fabrication yield. The material interconnects are made from depends on many factors. Chemical and mechanical compatibility with the semiconductor substrate, and the dielectric in between the levels of interconnect is necessary, otherwise barrier layers are needed. Suitability for fabrication is also required; some chemistries and processes prevent integration of materials and unit processes into a larger technology (recipe) for IC fabrication. In fabrication, interconnects are formed during the back-end-of-line after the fabrication of the transistors on the substrate.

References

  1. 1 2 Neurotechnology Group, Berlin Institute of Technology, IEEE Xplore Digital Library. “Regression Methods for Virtual Metrology of Layer Thickness in Chemical Vapor Deposition.” January 17, 2014. Retrieved November 9, 2015.
  2. "8 Things You Should Know About Water & Semiconductors | China Water Risk". chinawaterrisk.org. Retrieved 2017-09-10.
  3. "Top 10 Worldwide Semiconductor Sales Leaders - Q1 2017 - AnySilicon". AnySilicon. 2017-05-09. Retrieved 2017-11-19.
  4. "A Survey Of Architectural Techniques for Managing Process Variation", ACM Computing Surveys, 2015
  5. "Introduction to Semiconductor Technology" (PDF). p. 6.|first1= missing |last1= in Authors list (help)
  6. "Wafer Backgrind".
  7. CNET. “Why tech pollution's going global.” April 25, 2002. Retrieved November 9, 2015.

Further reading