Aixtron - Glossary

German Version

Glossary of Terms

ALD	Atomic Layer Deposition is a method for producing ultra thin films for semiconductor devices and new, emerging non-semiconductor applications. ALD is a technology that is capable of meeting scaling production requirements of next-generation geometries (0.13 micron and below). ALD process uses pulse and purge of two reactants to deposit films, where the purge is done using inert gases like Argon or nitrogen.
AVD	Atomic Vapor Deposition. A liquid delivery and evaporation technology. Liquid precursors or precursor solutions are sprayed in the form of discrete pulses directly into the flash vaporizer via injectors. Up to four injectors, one for each precursor source, can be used.
Back-end manufacturing	The testing and assembly of chip manufacturing, which occurs after the wafer has left the clean room. This term is also used in wafer Fabs to indicate all the processing related to interconnect to Front-end transistor.
Bond	A compound semiconductor chip is not a fully completed device. In order to construct a device, e.g. an LED a connection must be completed to an electrical source via an ultra-thin gold wire. This is the bond.
Capacitors	A circuit element formed by placing an insulating layer between two conducting layers; its function is to store a measure of electrical charge until needed. It is a very important component of memory chips.
Carrier gas	In the process for the production of compound semiconductor layers or silicon devices, the raw materials are converted into gases and are then transported into the reactor with a carrier gas. Principally used carrier gases are hydrogen and nitrogen. Very pure hydrogen can be produced easily and nitrogen is not highly reactive.
Characterization	Each layer of a compound or silicon semiconductor is quality tested by complex physical measurements.
Chip	A very small part of a semiconductor wafer which is turned into a complete device.
Clean Room	The place where semiconductor manufacturers do all their wafer processing. Dust and particles which might fall on the wafers during processing and result in the circuits not working are kept out of the clean room by filtering the air and managing the air flow. Humans are required to wear specially designed clean room bunny suits (overalls) and booties over their street clothes, and must put on gloves and face masks (humans tend to shed skin and hair). Normal paper is not allowed in clean rooms - only clean room low particulate paper may be taken in.
Cluster tool	A machine which contains more than one process module. This is particularly useful if there are a number of processes which have to happen in sequence. An example of this is the deposition of a multi-layer metal film with each layer being deposited in a different module (chamber). Cluster tools nevertheless represent savings in cost and space even if all the process modules are identical.
CMOS	Complementary Metal Oxide Semiconductor is a major class of integrated circuits. CMOS technology is used in chips such as microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits such as image sensors, data converters, and highly integrated transceivers for many types of communication.
Compound semiconductors	These consist of several elements. They can be subdivided into three categories according to the groups in the periodic system to which they belong. Group II/VI consists of compounds like zinc selenide; group IV-IV of silicon germanium compounds or silicon carbide; and group III/V, widely preferred because of their numerous uses, consists of gallium arsenide, indium phosphide, gallium nitride or compounds of three or four different elements. Compound semiconductors have several advantages over simple, single element semiconductors. These components are very fast and some can also operate under very high temperatures. They also possess good opto-electronic characteristics. They convert energy into light and lasers, or they detect light and produce energy. At the same performance level, they require less energy than silicon chips.
Conductor	A material that allows electrical current to pass through it.
CVD	Chemical Vapor Deposition, Deposition of thin films (usually dielectrics/insulators) on silicon wafers by placing the wafers in a mixture of gases which react at the surface of the wafers. CVD can be done at medium to high temperature in a furnace, or in a CVD reactor in which the wafers are heated but the walls of the reactor are not. Plasma enhanced CVD avoids the need for a high temperature by exciting the reactant gases into a plasma.
Deposit/Growth	Semiconductor devices comprise several layers. A deposit is the correct term for the laying down of these layers on a wafer as the layers grow.
Devices	These are the completed products which are manufactured with the compound or silicon semiconductor chips at their core. For example LEDs and lasers, transistors, memory and logic chips, and solar cells.
Detector	A compound semiconductor which is able to convert incoming light of any wavelength into electrical energy. Detectors are required for optical communication systems.
Die	The term for a single semiconductor chip, plural dice.
Dielectric	see insulator
Diodes	A two-terminal electronic device which permits significant current flow in only one direction. Diodes typically function as a rectifier, i.e., converting alternating current into direct current.
Display	A display device, also known as an information display is a device for visual presentation of images (including text) acquired, stored, or transmitted in various forms. Most common displays are designed to present information dynamically in a visual medium.
DRAM	Dynamic Random Access Memory is a type of semiconductor memory. DRAMs account for a significant percent of the total semiconductor market (between 15 and 30%) and so DRAM manufacturers are big equipment buyers. DRAM manufacturing is concentrated in Japan and Korea.
Epitaxy	The deposition of thin single crystalline layers on a suited substrate in the form of crystal growth.
FeRAM	Ferro-electric Random Access Memory* is a type of non-volatile computer memory. It is similar in construction to DRAM, which is currently used in the majority of a computer's main memory, but uses a ferroelectric layer to achieve non-volatility. Although the market for non-volatile memory is currently dominated by Flash RAM, FeRAM offers a number of advantages, notably lower power usage, faster write speed and a much greater maximum number (exceeding 1016 for 3.3V devices) of write-erase cycles.
Flash	Is a form of non-volatile computer memory that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards.
Footprint	The area a machine takes up in the clean room. This is important because clean room space is expensive, and so minimizing the footprint of a machine is a good thing to do. There are two numbers that semiconductor manufacturers are interested in - the footprint and the linear frontage number (length of the front of the machine). The linear frontage number affects how many machines will fit into a bay since the machines are all lined up side-by-side.
Gas foil rotation	The wafer holders in AIXTRON MOCVD equipment turn friction-free on gas cushions. This movement is powered by a directed gas flow.
Gate	An element of a transistor to which voltage may be applied in order to turn a circuit on or off. A gate structure requires the use of insulating materials to allow the buildup of an electrical field.
Glovebox	The hermetically sealed cabinet with arm-length gloves in which the operator can slide his hands in order to carry out internal work from outside the cabinet. These cabinets are at the core of the equipment which produce compound semiconductors. They are filled with extremely pure gas, for example, with nitrogen, and house the MOCVD reactor.
Heating	During the MOCVD process for the production of compound semiconductor layers, the raw materials, gases, are dispersed inside the reactor across the wafers. To obtain crystal growth deposits, the wafers must be heated. Usually, this is achieved with lamps or with high-frequency induction heating systems.
High k dielectric	An insulator which will not conduct electricity but which, when sandwiched between metal plates, will easily allow these plates to talk to each other via electric fields (this is called a capacitor structure). Silicon dioxide and silicon nitride is popular insulator. However, to increase the capacitance, hence the storing power, silicon dioxide and nitrides will be replaced by insulators which has higher dielectric constant (k). Increasing dielectric constant increases the capacitance. AIXTRON offers Aluminium oxide (k = 9), Hafnium oxide (k = 25) etc as high k dielectric films.
Hydrogen	Can be produced to high levels of purity and is often used as a carrier gas in MOCVD technology.
Insulator	A material which will not allow an electric current to flow through it. In semiconductor chips, commonly used insulators are silicon dioxide (glass) and silicon nitride (silicon + nitrogen). Also commonly referred to as a dielectric in the semiconductor industry.
Integrated circuit	A complete electronic circuit with transistors and wires connecting these transistors (metal interconnects) on a semiconductor chip.
LED	Light Emitting Diode * The main use for compound semiconductors. Compound semiconductors can emit very bright light and are energy efficient. On average, an LED has a life of more than 100,000 hours, while a normal electric lightbulb lasts for just about 8,000 hours.
Light emitter	Light emitters, for example a laser or LED, convert electrical energy into light. The opposite of a light emitter is a detector, as used at the end of a glas fiber, or a solar cell.
Logic chip	A chip which does computations, makes decisions, or makes things happen. For example, the main chip in a computer is a microprocessor and does mathematical computations, amongst other things.
LPE	A relatively simple production method for compound semiconductors. The compounds to be deposited are liquified under normal pressure and the wafer is then bathed in the fluid. The advantage is that thick layers can be produced very quickly. The disadvantage is that such layers cannot be finely dosed. For this reason, the process is generally only used for weaker LEDs.
MBE	This method for compound semiconductors was for many years the first choice in basic research for scientists wishing to make very thin layers. The raw materials sit in vessels inside the equipment or reactor and evaporate under extremely low pressure, around one millionth of normal atmospheric pressure. The advantage is that, contrary to LPE, the low pressure allows for greater semiconductor purity. The disadvantage is that the creation of a vacuum makes the process the most expensive and production is limited to small volumes. In addition, not all materials can be produced with the MBE method.
Memory chip	A chip which retains information for logic chips to use. For example, in a computer, the memory chips will store the word processing program while it is being used, and the letters of the word processing documents which are being worked on. DRAM is the type of memory used most in computers, and is by far the most important type of memory from a total worldwide revenue standpoint.
Micron	One thousand microns make one millimeter. A human hair is about 100 microns thick. A transistor in an advanced semiconductor process might have an area of about 4 microns by 1.5 microns (though of course transistors vary greatly in size depending on their purpose). In general, the micron number assigned to a technology (e.g. 0.25 micron technology) refers to the width of the smallest patterned feature of a transistor which is the polysilicon transistor gate.
MIM	A Metal-Insulator-Metal diode is formed by sandwiching two metal layers around a thin insulator. When a voltage is applied between the two metal layers, electrons are induced to quantum mechanically tunnel from one metal to the other through the thin insulator. For this to occur at low voltages (1 volt and below), the insulator must be very thin, typically less than 50 angstroms.
MOCVD	With this compound semiconductor production method, the raw material “metallo-organic compounds” are transformed into gases and then, bound to a carrier gas, are fed into the reactor. This transformation also occurs under reduced pressure, around one-tenth of normal atmospheric pressure. The advantage is that the gases introduced are clean as with the MBE method and can be finely dosed. MOCVD equipment allows the processing of quite large surface areas and is therefore first choice for the production of compound semiconductors. MOCVD is also the cheapest method. AIXTRON is the global market leader in this technology.
Non-volatile memory	Semiconductor memory which will not forget its data once the power is switched off. This is in contrast to volatile memory (e.g. DRAMs), which lose their information when there is no power supplied to the chip.
OVPD	Organic Vapor Phase Deposition is a technology for the thin film deposition of small molecular organic materials. It utilizes the advantages of gas phase deposition, where the materials are transported to the substrate by an inert carrier gas.
OLED	Organic Light Emitting Diode* An OLED is a monolithic, solid-state device that typically consists of a series of organic thin films sandwiched between two thin-film conductive electrodes. The choice of organic materials and the layer structure determine the device’s performance features: emitted color, operating lifetime and power efficiency.
Periodic System	All natural elements are ordered according to their atomic number. Hydrogen is the first element with an atomic number of one.
Planetary rotation	A production process which is constituent of the MOCVD reactor, whereby a number of small discs in a large plate orbit like planets in space. The large plate also turns. This method achieves a homogeneous, even deposit of compound semiconductor layers on the wafer. AIXTRON uses this process as part of its MOCVD technology.
Run	A single production run for the manufacture of compound semiconductor layers.
Semiconductor	A material such as silicon whose conductivity is between that of a conductor and an insulator. Its conductivity can be modulated by adding impurities such as boron or phosphorus. Shunt (or, to shunt)
Silicon	An element on the periodic table with the symbol Si. Silicon is a semiconductor used to fabricate most transistors and integrated circuits.
Substrate	The base material on which the gas mixture is deposited. The substrate is a very thin crystalline disc, also called the wafer, and consists of gallium arsenide. Sapphire or silicon.
Susceptor	This serves as the holder for the wafer, the substrate. Normally it consists of graphite so that even temperatures can be achieved.
Transistors	Transistors are miniature electronic switches. They are the building blocks of the microprocessor which is the brain of the computer. Transisitors have no moving parts and are turned on and off by electrical signals. The on/off (binary) switching of transistors facilitates the work performed by microprocessors.
Tungsten	A metal commonly used to make the plugs used for connecting metal wires to one another or to the devices in integrated circuits.
Two-inch wafers	Wafers of this size are most often used as a basis for compound semiconductors. They are large enough to produce 15,000 chips.
VPE	This is an older, established process for the production of compound semiconductors. In contrast to MOCVD, this gas phase process uses inorganic substances as starting materials. The method allows for clean deposits of very thick and pure layers. However, not all materials can be produced by this method. AIXTRON produces such equipment for niche applications. Recently, this method (also referred to as HVPE – Hydride VPE) has gained much attention as a way to produce high quality gallium nitride substrates or templates.
Wafer	The technical term for the round substrate material, a thin disc, on which the gas mixtures are deposited in the reactor. Wafers are typically 2, 4, 6, 8, 12 inch in diameter.