WIKI
Adapter
A mechanical device for the precise alignment of fiber-optic connectors, consisting of a splice sleeve (connection sleeve) that secures the two ferrules together.
Adapter Sleeve
A mechanical receptacle integrated into the adapter housing that precisely positions and securely holds two pre-terminated fiber optic connectors. The adapter sleeve is typically made of phosphor bronze, ceramic, or plastic.
Absorption
The absorption of light energy within an optical fiber due to natural impurities in the glass. Together with scattering, absorption is one of the main causes of attenuation (signal loss) in optical fibers.
Angle of Incidence
The angle at which light enters the core of the fiber.
Add/Drop multiplexer
A device that inserts one or more optical channels into a continuous signal or extracts them from it.
Attenuation
The decrease in signal strength (optical power) during transmission between two points. It describes the total loss of an optical system and is specified in decibels per kilometer (dB/km) at specific wavelengths; this glossary distinguishes between “intrinsic” and “extrinsic” attenuation.
BOW
The deviation of the center of the center plane of a free, unsupported wafer from a reference center plane defined by three points equally spaced on a circle with a diameter that is a specific value smaller than the wafer’s nominal diameter.
Carrier Concentration
Unlike metallic conductors such as aluminum or copper, semiconductors have two independent charge carriers: electrons and holes. The behavior of diodes, transistors, and other semiconductor devices often depends on the relative concentrations of holes (p) and electrons (n), expressed in cm³. In pure silicon, they are generated thermally in pairs.
In this intrinsic state, n and p remain equal. Their product is np = n² ≈ 10E10/cm³ at room temperature. In a p-type substrate, however, the doping of the silicon lattice with acceptor atoms (such as boron) leads to an excess of holes. Then pp >> np, indicating an excess of majority charge carriers (holes) relative to minority charge carriers (electrons). The product np = ni² remains constant under thermal equilibrium (without an applied bias or other disturbances).
Conductivity Type
An n-type (negative-type) extrinsic silicon semiconductor is a semiconductor material produced by doping silicon with an n-type Group V A element, such as P, As, or Sb. Consequently, electrons are the primary charge carriers in the material.
Effect of impurities
The effect of certain atoms as impurities in semiconductors can be understood based on their position in the periodic table. Across a period, the number of electrons in the outermost shell increases from left to right: elements such as copper have one valence electron, zinc has two, gallium has three, and so on, up to fully filled shells, such as krypton with eight electrons.
When foreign atoms with a higher valence group than the host material are introduced, they possess an extra electron that is not incorporated into the regular bonds of the crystal lattice. Such materials therefore exhibit an excess of free electrons and are referred to as n-doped or n-type.
Conversely, atoms with fewer valence electrons than the host material result in missing bonding electrons, known as “holes.” These act as positively charged carriers, so the material is referred to as p-doped or P-type.
One example is arsenic in germanium: The arsenic atom contributes five valence electrons, four of which are used for bonds in the germanium lattice. One electron remains and is only weakly bound. This electron can easily break free and is available as a free charge carrier. As a result, additional free electrons are created in an arsenic-doped germanium crystal, but no corresponding additional holes, since the original bonds remain locally confined. The crystal remains electrically neutral overall, since each released electron leaves behind a fixed positive charge at the donor atom. Such impurity atoms are referred to as donors, and the free electrons constitute the majority charge carriers, while holes are minority carriers.
Flatness Measurements
Describes the deviation of the front wafer surface, expressed as TIR or maximum FPD, relative to a specified reference plane, assuming the back of the wafer is ideally flat—for example, when it is drawn by a vacuum onto an ideally clean, flat clamping ring.
FDP - Focal Plane Deviation
The distance parallel to the optical axis from a point on the wafer surface to the focal plane of the optical system.
The greatest positive or negative deviation from a reference plane which approximates the focal plane, when the wafer is mounted on a flat vacuum chuck.
The focal plane deviation is the greatest distance above or below the chosen focal plane.
Focal Plane
The distance, parallel to the optical axis, from a point on the wafer surface to the focal plane of the optical system.
GTIR – Global Total Indicated Reading
Maximum peak to valley deviation of a wafer from a given reference plane.
HBSD - Hard Back Side Damage
Hard Back Side Damage (HBSD) is a process used to enhance the performance of silicon wafers. In this process, the back side of the wafer is treated with a humid stream of fine quartz particles and then cleaned with high-purity wafers. This step is performed early in the wafer manufacturing process.
The mechanically damaged layer formed on the back side is later removed in subsequent processing steps. The intentionally introduced defects serve as getter sites that attract impurities such as residues from the Czochralski (CZ) crystal growth process. As a result, exposed zones form within the wafer, leading to improved material purity—particularly on the front side.
HBSD is widely used by leading wafer manufacturers. It is generally assumed that most highly doped wafers from top suppliers undergo HBSD treatment or comparable processes such as brushing, even though this is not typically specified in certification documents. The induced damage is not visible to the naked eye and can only be identified using specialized volume analysis techniques.
Due to their benefits for material quality, HBSD-treated wafers are considered suitable and are recommended for a wide range of applications.
Haze Free
A silicon wafer with the best possible surface finish and a micro-roughness of less than 10A.
Local Thickness Variation
The local thickness variation at each point is the vector sum of the height differences between any two immediately adjacent points.
LPD - Light Point Defects
Light Point Defects (LPDs), also known as Localized Light Scatterers (LLS), are tiny surface defects on semiconductor wafers. They are identified using laser scanning techniques, in which they appear as bright spots caused by scattered light. Such defects can be caused by particles, surface depressions, or crystal-related imperfections such as crystal-origin particles (COPs) and can negatively impact the yield in the manufacture of integrated circuits (ICs).
Non-Linear Thickness Variation
Thickness variation on a wafer, defined by the thickness at the center and four thickness values at the edges, measured at a distance of ⅛″ from the edge of the wafer.
Orientation
The growth plane of crystalline silicon is characterized by so-called Miller indices such as (100), (111), or (110). Depending on their orientation, these planes—when viewed from a specific perspective—exhibit different arrangements of atoms or crystal lattice structures.
P/V - Peak-to-Valley Flatness
The total magnitude of the maximum positive and negative deviations from a reference plane, which corresponds to the average surface of the wafer, while it is secured to a flat vacuum chuck (ADE).
Prime Grade
The highest quality grade of a silicon wafer. The SEMI organization defines the requirements for volume, surface area, and physical properties that must be met for a wafer to be classified as a “Prime Wafer.”
Primary flat
The longest flattened edge at the perimeter of the wafer. The so-called primary flat has a defined crystal orientation relative to the wafer surface and is also referred to as the main flat side.
Quality Area
The percentage of the wafer that meets the specified requirements is determined.
Reclaim Grade
A lower-quality wafer that was already used in the production process, subsequently processed—for example, through reclamation, etching, or polishing—and then reused in manufacturing.
Resistivity
Volume resistivity describes the resistance a material offers to an electric current per unit volume when the current flows perpendicular to two parallel surfaces. More generally, it is the ratio of the potential gradient in the direction of the current to the current density within the material.
Secondary Flat
Indicates both the crystal orientation and the doping type of the wafer.
SEMI
SEMI is a global trade association representing the electronics manufacturing and development industry. It connects more than 3,000 member companies and approximately 1.5 million professionals worldwide (as of April 2026).
SEMI members drive innovation in areas such as materials, design, equipment, software, devices, and services, thereby contributing to the development of more powerful, faster, and more cost-effective electronic products.
Since 1970, SEMI has been fostering connections within the industry, supporting its members in gaining market access, and helping to address common industry challenges.
Slice Orientation
The crystallographic orientation of the wafer surface. The most important and most commonly used slice orientations include (100), (111), and (110).
Striations (dopant rings)
According to SEMI, striations are described as spiral-shaped structures on silicon wafers that arise from periodic fluctuations in dopant uptake during crystal growth at the rotating solid-liquid interface.
After a selective etching process, these structures are visible to the naked eye. Experienced and trained personnel can sometimes detect them on heavily doped wafers even without prior etching. These striations are not a defect in the wafer, but rather a characteristic remnant of the dopant distribution from the crystal growth process. They have no effect on the electrical properties of the wafer.
Taper
Taper describes the deviation from parallelism between the back side of the wafer and a defined focal plane. The value specified as the criterion corresponds to the maximum difference between these two planes and not to the surface slope. Therefore, it is specified in micrometers across the entire wafer diameter and not in micrometers per millimeter.
Test Grade
A silicon wafer made of high-purity material whose quality level is below that of “Prime” wafers and which is used primarily for testing and inspection processes. SEMI defines the requirements for volume, surface, and physical properties that must be met for a wafer to be classified as a “test wafer.”
Thickness
The perpendicular distance through a disc or wafer in the direction of the surface normal at a defined point.
TIR
The difference in height between the highest and lowest points on the wafer surface, expressed as an absolute value.
The minimum perpendicular distance between two planes parallel to the reference plane that enclose all points on the wafer’s front side within the defined flatness quality range or specified location.
TTV – Total Thickness Variation
The absolute difference in thickness between the thickest and thinnest points of the wafer.
Warp
The difference between the largest and smallest deviations of the median surface from the 3-point reference plane on the back side and from the best-fit median surface reference plane, respectively.
XRD
A crystal is characterized by a periodically repeating arrangement of atoms. From the perspective of an electron or photon penetrating the crystal, this structure appears differently depending on the viewing or incident angle. Depending on the orientation, for example, continuous crystal channels may be visible, or only the topmost atomic layers. As a result, the material properties also vary depending on the crystal orientation. Precise control of crystal orientation is therefore crucial to ensure reproducible and well-defined material properties.
Determining crystal orientation plays a central role in processes such as ion implantation, lithography, and epitaxy, as well as in the manufacture of laser and other optical components. The basis for this is the so-called azimuth scan—an intelligent measurement method for the precise geometric determination of crystal orientation.
Using this technology, both the tilt of the main crystal axis and all directions of the crystal planes can be measured in just about ten seconds. XRD systems enable the measurement of virtually all single-crystal geometries, including wafers, ingots, columns, pucks, and other single-crystal shapes.