Welcome to the SQI Glossary!
These definitions work as a beneficial resource to helping our customers better understand our products and services.
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Acceptor: an impurity, such as boron, in the silicon monocrystalline structure that creates a “hole” which will cause electrons from neighboring silicon atoms to jump, thus changes the electrical properties of the material. This creates an extrinsic semiconductor that is p-type.
Acid: a substance with a pH of less than 7.0. Acids may be used in cleaning, stripping oxide, or wet etching of silicon wafers.
Angstrom (Å): a measure of length equal to 1/10,000,000,000 of a meter. There are 10,000 angstroms in a micron. A silicon atom measures approximately 3-6 angstroms in length. Film thickness is typically expressed in angstroms.
Annealing: a heat-treating process. In wafering process it is used to annihilate oxygen induced donors.
Atomic Force Microscope (AFM): a tool used to measure the surface micro-roughness of a wafer on the near-atomic level (see application notes for AFM example on SQI-processed wafers).
Autodoping: doping of an epitaxial layer from sources other than the intended dopant, such as the present surfaces of the substrate.
Backside: the surface of a wafer that is not to be polished. While there is no clear definition of the backside specification, SQI uses its own grading system (refer to the application note.)
Boat: a quartz carrier for holding wafers while thermal oxide is grown.
Bow: A concave deformation of a wafer in a free, unclamped condition. Bow is independent of thickness variation.
BOX: Buried oxide layer on an SOI wafer.
Cassette: a container for holding wafers and keeping them separate.
Chip: a defect at the edge of a wafer that may lead to breakage
Cleanroom: an area that is controlled to maintain a certain level of particles in the air. This environment is maintained through the use of air filters, physical barriers and special garments and procedures for everyone inside the Cleanroom. Cleanrooms are designated by the level of airborne particles greater than 0.5 µm in a cubic meter of air. SQI’s Cleanroom is Class 100, indicating that there are 100 or less particles of this size in a cubic meter.
Cleavage plane: the plane along which a wafer will tend to break in straight lines, due to the crystallographic orientation. For a <100> wafer this is at right angles to the flat or notch and for a <111> wafer it is at 45°.
CMP: chemical-mechanical polishing. This a process that uses mechanical means, such as a polishing pad, and chemical means, such as polishing slurry, to bring the surface of a wafer to a mirror-like condition.
Collimated light: light, such as that from a laser, which has a low rate of angular dispersal (spreading) as it travels away from its source. This type of light is used to inspect the surface of wafers.
Contamination: can be surface contamination, such as particles or haze or can be crystal contamination, which affects the structure of the crystal lattice.
Crow’s feet: a defect in a wafer that resembles a crow’s foot
Crystal: a pattern in the atomic structure of a substance that repeats itself in all three dimensions. A monocrystalline wafer is one where the crystal pattern is repeated uniformly throughout the wafer. This is the opposite of amorphous material, which has no crystal structure at all.
CVD: chemical vapor deposition. This is a means of depositing a substance on a wafer’s surface using gaseous reactants, or precursors. An example is silicon nitride, which is formed by reacting nitrogen gas with a silicon wafer at high temperature.
Czochralski Process (CZ): the most common method for growing silicon ingots, named for its inventor, Jan Czochralski.
Dielectric: a material that does not conduct electrical current when applied. Silicon dioxide and silicon nitride are two examples of dielectric materials.
Donor: an impurity, such as phosphorus, in the silicon monocrystalline structure that creates essentially an extra electron that will move throughout the crystal structure, thus changing the electrical properties of the material. This creates an extrinsic semiconductor that is n-type.
Dopant: a substance added to a semiconductor material to change its resistivity. In silicon, the common dopants are phosphorus, arsenic, antimony (which produce n-type wafers) and boron (which produce p-type wafers).
Edge Grinding: a process by which the edge of a wafer is shaped. The new shape, which is a symmetrical bevel, gives the wafer additional strength at the edges. The process is sometimes called edge rounding.
Ellipsometer: a device that measures film thickness by using laser light and reflection. It can also measure the index of refraction.
Epi: an epitaxial layer deposited on the surface of a wafer. The epi layer will have the same orientation as the substrate, but it may have other properties that are different, such as type or dopant levels.
Etch: a chemical process to alter the surface condition of a wafer. Mirror etching creates a shiny surface for visual or electrical inspection. Preferential etching dissolves material at different rates depending on the orientation plane.
Extrinsic semiconductor: a semiconductor material that has been doped to change the resistivity level.
Flat: a portion or portions of the wafer’s circumference that is a straight line instead of an arc. The flat shows where the <110> plane is oriented. Also, the combination of primary and secondary flats will show the type and orientation of the wafer.
Float-zone silicon: a method for growing silicon ingots that results in higher purity silicon than the CZ method.
Gettering: a process that attracts contaminants and traps defects when wafers are heated
Global flatness: the concept of flatness applied to the entire surface of a wafer.
GOI: Gate oxide integrity.
Grinding: a process that abrades material, reducing it to dust and conveying it away from the work piece. An ingot is ground about the circumference to bring it to the proper diameter. Wafers are ground at the surface as part of the thinning and back grinding processes.
Haze: Defects that scatter light, caused by microscopic defects at the surface of a polished wafer.
Hillocks: microscopic mounds in the wafer’s surface.
Ingot: a grown cylinder of semiconductor material. Typically, ingots are in the raw stage, without having been ground on the diameter or sliced into wafers.
Integrated circuits (ICs): tiny electrical components produced on the surface of a wafer.
Interstitial: the spaces between the crystal structure, where some ions or non-metal substances can reside.
Intrinsic semiconductor: a semiconductor material that is undoped, thus making the resistivity a function purely of the material’s properties, rather than the amount of dopant used.
Lapping: a process that uses a chemical compound to remove saw-marks from a wafer’s surface.
Laser cutdown: using a laser cutting tool to cut out smaller diameter wafers. The yield may be one-for-one, as in the case of 150mm to 125mm. The yield may also be more, as in the case of producing 4 2” wafers from a single 200mm wafer. Cutdown is a cost-effective way to convert unusable low-cost wafers into wafers that can be useful.
Laser mark: a mark scribed into a wafer’s surface with a laser for identification purposes. Wafers may be manufactured with a laser mark in place or they may have a laser mark added after manufacture (see application notes for details about SQI process).
Lifetime: the amount of time, measured in seconds, that a free electron or hole can exist in a crystal structure.
Lot: a group of wafers with comparable properties and the same processing steps to be processed together.
LPD: light particle defect. LPD specs are given in terms of the size of the particle and the count per wafer.
Melt: a pool of molten silicon to be turned into an ingot in the CZ process.
MEMS: micro-electromechanical systems; tiny mechanical components produced on the surface of a wafer.
Micron (µm): a measure of length equal to 1/1,000,000 of a meter, 1/1000 of a millimeter, 10,000 angstroms and 1,000 nanometers. Microns are sometimes called micrometers or micro-meters. Wafer thickness is most often expressed in microns.
Mil: a measure of length equal to 1/1000 of an inch; sometimes called a thousandth. A mil is equivalent to 25.4 microns.
MOS: Metal oxide semiconductor. This is a process for device fabrication.
Nanometer (nm): a measure of length equal to 1/1,000,000,000 of a meter. There are 10 angstroms in a nanometer. Nanometers may be used to express film thickness, but they more frequently are seen in discussions of spectroscopic measures.
Nanotopology: variations in a small portion of the surface of a wafer.
Notch: a small cutout in the circumference of a wafer. The notch gives information about the crystal orientation and is typically seen in wafers 150mm or larger. Notches are in lieu of flats
N-type: Silicon wafers that are doped with substances having more than 4 valence electrons, such as arsenic or phosphorus. This gives the crystal structure donors.
Ohm-centimeter (Ω-cm): the measure of the resistivity of a semiconductor.
Orange peel: A surface defect in a wafer that resembles orange peel.
Orientation: the direction in which the crystal structure is turned in relation to the outside edges of an ingot and by extension, a wafer. A <100> wafer is like a box sitting flat on the floor and pushed into the corner of a room. A <110> wafer is like a box that is flat on the floor, but angled at 45° so that only an edge is touching each wall. A <111> wafer is like a box that has one corner on the floor and one on each wall.
OSF: Oxygen stacking fault.
Polished surface: the surface of the wafer that is processed to a mirror-like finish, making it ready for device fabrication or bonding.
Poly coating: a fine grain polycrystalline silicon coating that is deposited on the back side of wafer. This is used to enhance the properties of the substrate wafer as per a user’s requirements.
Polycrystalline silicon: silicon with many different crystal orientations.
Preferential etching: a technique to affect the shape of a wafer by taking advantage of different etching rates along different orientation planes.
P-type: Silicon wafers that are doped with substances with fewer than 4 valence electrons, such as boron. This gives the crystal structure acceptors.
Resistivity: a measure of a given amount of a material’s ability to oppose electrical current. It is equivalent to the overall resistance multiplied by the ratio of the cross-sectional area to the length of the conductor.
ROG: Radial oxygen gradient. The variation in oxygen content from the center of the wafer to the edge.
RRG: Radial resistivity gradient. The variation in resistivity from the center of the wafer to the edge.
SEMI: Semiconductor Equipment and Materials Institute. The body that oversees and sets standards for the semiconductor industry.
Silicon: an elemental metalloid that makes up roughly one quarter of the earth’s crust by mass. Its abundance and versatility for semiconductor applications make it a natural choice for many industries.
Site flatness: the concept of flatness applied to individual sites. The size and arrangement of these sites must be defined in order to measure site flatness effectively.
Slip: a defect caused when a wafer moves along the crystallographic plane in a shearing motion. The crystal structure is maintained, and the wafer typically remains intact.
Slurry: a solid suspended in a liquid used in the CMP process.
SOI: silicon-on-insulator. Typically refers to two wafers that are bonded together with an oxide layer between them.
Stacking faults: pyramid-shaped imperfections in the crystal structure of a wafer.
Substrate: a surface on which material adheres. A silicon substrate may have oxide, nitride, poly coating, or metals deposited.
Thermal oxidation: a method for growing an oxide layer on the surface of a wafer. Dry oxide is performed in a furnace with high temperature in an oxygen atmosphere. Wet oxidation is performed in a tube with high temperature in a water vapor and oxygen atmosphere.
Thickness: the distance between the front and back surfaces of a wafer.
TIR: Total indicator reading. This is a measure of how much vertical distance there is between the highest and lowest point on a wafer’s surface.
TTV: Total thickness variation. This is a measure of the difference between the thickest and thinnest points on a wafer.
Type: a measure of the conductivity of an extrinsic semiconductor.
Wafer: a slice of semiconductor material.
Warp: A deformation in a wafer that is both concave and convex.