IC Knowledge - Glossary B

Glossary of Integrated Circuit Terminology - B

Background Impurity - the concentration of impurity present in a wafer prior to some or all processing. Most wafers as manufactured have a uniform concentration of a dopant already in the wafer. Alternately the background concentration might be set by a relatively deep diffusion or epitaxial deposition step that another dopant was later introduced into.
Bake - a process where wafers are heated above room temperature but below 200^oC.
Ball Bond - when a bond wire is attached to a die or leadframe one technique is to use mechanical and or thermal energy to bond the wire down by forming an intermetallic. Because the end of the wire is heated and or compressed down, a ball forms on the end of the wire at the bond. See also, wire bonder.
Ball Bonding - the process of forming a ball bond.
Ball Grid Array (BGA) - a newer type of package for IC's with very high pin counts. Replaces pin with small solder balls.
Band Gap - a region between the valence band and the conduction band devoid of allowed energy states.
Bandwidth - a range of wavelengths or frequencies. For example, the bandwidth of a light source would be the range of wavelengths produced by the light source. Alternately, the bandwidth of an amplifier would be the range of frequencies the amplifier would amplify.
Barrier Metal - a metal layer designed to stop other layers from interacting. The most common barrier metals is titanium nitride, TiN, titanium tungsten, TiW was widely used at one time, chromium, Cr, has seen some use, tantalum, Ta, and tantalum nitride, TaN, are seeing increased use with copper metalization processes and tungsten nitride ,WN, is a relatively new barrier metal.
Base - chemical definition - a substance that ionizes in water to produce OH- ions. Base solutions have OH- densities >1E^-7 (pH > 7). See also, acid, alkali. Electrical definition - the base is a middle region in a bipolar transistor of one semiconductor type, separating the emitter and collector of the bipolar transistor that are of opposite semiconductor type. For example an NPN transistor would have a P base region separating the N emitter and N collector.
Base Diffusion - the base region of a transistor formed by diffusion.
Batch Process - some semiconductor processes are performed on several wafers simultaneously, multiple wafers processed simultaneously as a group is referred to as batch processing.
Bath Tub Curve - failures rates over time fall into three distinct regions. The first region is referred to as infant mortality, or parts that fail at some relatively higher rate over a short period of time, due to manufacturing defects. Once the infant mortality is removed from the population, the useful life period is reached with a relatively lower failure rate. During the useful life failures are random in time. The final stage is wear out, the parts begin to wear out and fail at some relatively higher rate. If the failure rate of the parts versus time is plotted on a curve, the high failure rates initially and at end of life with relatively low failure rates during the middle period results in a bath tub shaped curve.
Beam Leads - rectangular shaped leads that attach to bond pads on one end and a carrier tape on the other end for tape automated bonding (TAB).
BGA - see Ball Grid Array.
BiCDMOS - a semiconductor technology combining bipolar, CMOS and DMOS devices on one integrated circuit.
BiCMOS - a semiconductor technology combining bipolar and CMOS devices on one integrated circuit.
Binary - the base 2 numbers system. All numbers are represented as a string of ones and zeros. The number system used by digital computers. A one is represented by a voltage and a zero by the absence of a voltage. In 4 bit binary the numbers 0, 1, 2, 3, 4, 5, would be represented by 0000, 0001, 0010, 0011, 0100, 0101 respectively.
Bipolar - a semiconductor device that uses both holes and electrons for conduction simultaneously.
Bipolar Transistor - a transistor that uses both holes and electrons for conduction. A bipolar transistor has an emitter of one semiconductor type that emits carriers into a base region of opposite semiconductor type, and a collector region of same semiconductor type separated from the emitter by the base, the collector collects electrons that transit the base region. Modulating the current injected into the base terminal of a bipolar transistor will modulate the current flowing through the base from the emitter to the collector. Properly biased a signal injected into the base will result in an amplified signal appearing at the collector terminal.
Bit - a single digit of a binary number. A bit is either a one represented by a voltage or a zero represented by no voltage. The number 5 represented in 4 and 8 bit binary would be 0101 and 00000101 respectively.
Boat - a carrier made to hold wafers. Most commonly a boat has 25 slots and is made of quartz, polysilicon or silicon carbide for use in a furnace, polypropylene for general wafer transport or Teflon for use in a wet process. Some furnace boats have 50 slots.
Boat Puller - a mechanical piece of equipment designed to automatically push-in or pull-out boats from a furnace.
BOE - see Buffered Oxide Etch.
Bond Pads - metal pads on semiconductor die where wire bonds can be attached to connect the die to the outside world.
Bonding Wire - tiny gold or less commonly aluminum wires that form connections from bond pads to lead frames. Common gold bond wire is 1 to 3 thousands of an inch in diameter, aluminum bond wire is used for thicker wires such as 5 or 7 thousands of an inch.
Boolean Algebra - a logical calculus named for mathematician George Boole, where alphabetic symbols are used to represent logical variable, 1 and 0 are states, and, AND, OR, and NOT are the basic logical operations. NAND and NOR can be represented by combinations of AND, OR and NOT.
Boron - atomic symbol, B, boron is the 5th element in the periodic table (atomic number 5) with an atomic weight of 10.81. A group III element boron is an acceptor in silicon, i.e., makes silicon P-type. Boron is the most commonly used P-type dopant and has a relatively high diffusivity compared to arsenic and antimony, common N-type dopants, and a diffusivity and similar to phosphorus, another common N-type dopant.
Boron Tribromide - chemical formula BBr₃, boron tribromide is a liquid at room temperature and was at one time widely used as a source of boron during pre deposition processes. During the pre deposition process, Nitrogen gas is bubbled through heated boron tribromide liquid. The nitrogen gas leaves the bubbler carrying vapor of boron tribromide into the per deposition furnace. Boron tribromide's vapor pressure ranges from approximately 15mm of Hg at 0^oC, 63mm of Hg at 25^oC to 170mm of Hg at 50^oC. Boron Trichloride - chemical formula BCl₃, boron trichloride is a corrosive toxic gas with a TLV of 5ppm. Boron trichloride has a pungent irritating odor and is a corrosive. Boron trichloride is most commonly used as an etch gas for aluminum, but may also be used as a Boron Source for Doping.
Boron Trifluoride - chemical formula BF₃, boron trifluoride is a corrosive toxic gas with a TLV of 1ppm. Boron trifluoride is pungent and suffocating. Boron trifluoride is primarily used as a feed gas to create boron species in ion implanters.
Bosch Process - a patented plasma etch process whereby the etcher chemistry is switched every few seconds back and forth between etching and polymerizing chemistries. The Bosch process is commonly used to produce high rate anisotropic trench etching of silicon. During the etch chemistry step, rapid isotropic etching of the silicon occurs. During the polymerizing chemistry portion of the process all exposed surfaces of the substrate are coated with polymer. During the next etch chemistry portion of the process, ion bombardment removes the polymer from the bottom of the trench normal to the direction of ion motion, and a isotropically etched cavity is then created. The Bosch process results in microscopic "scallops" on the trench sidewalls being etched. The degree of sidewall scalloping may be controlled by varying the length of each etch - polymer deposition cycle. See also, inductively coupled plasma.
Boule - in order to grow wafers, a large ingot is drawn from a molten silicon melt. The ingot is also referred to as a boule.
Breakdown - when a critical field is exceeded in an insulator or semiconductor, the material breaks-down electrically allowing current to flow.
Breakdown Voltage - the voltage at which breakdown occurs.
BTAB - see Bumped Tape Automated Bonding.
Bubbler - a Pyrex glass or quartz container with an inlet tube that extends down to near the bottom of the vessel and an outlet tube located near the top of the vessel. When filled with liquid, a gas may be introduced throng the inlet tube and the gas will bubble through the liquid and exit through the outlet tube. Bubblers are used to introduce vapor from a liquid source into a gas.
Buffered Oxide Etch - an etching solution containing hydrofluoric acid, HF, and ammonium fluoride, NH₃F. The hydrofluoric acid etches silicon dioxide and the ammonium fluoride raises the solution pH reducing the attack rate of the solution on photoresist.
Bumped Die - die that have had tiny solder or gold bumps formed on the bond pads.
Bumped Tape Automated Bonding - a process where bumped die are attached to metal leads mounted on a tape carrier. See also, tape automated bonding.
Bumping - the process of forming solder or gold bumps on bond pads of a die. The bumps may be formed by electroplating or evaporation.
Burn-In - the use of elevated temperature and or electrical stress to cause infant mortality failures so they may be removed prior to shipping product to a customer. Burn-In is common on new products until yield enhancement efforts have increased yield and decreased defect density.
Buried Layer - a low resistivity - doped layer underneath the surface of a semiconductor. Buried layers may be formed by pre deposition - diffusion followed by epitaxial growth, ion implantation and diffusion followed by epitaxial growth or by high energy ion implantation.
Butyl Acetate - chemical formula CH₃COO(CH₂)₃CH₃, butyl acetate is a flammable solvent used primarily as a negative photoresist post develop rinse. Butyl acetate is commonly sold as a 100% solution and has a density of 0.88Kg/L. Skin contact and breathing of butyl acetate vapor should be avoided.
Byte - a unit of computer memory, typically 8 bits in length. The smallest addressable unit of memory and most commonly represents a single character such as a letter.