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U-chart
an attributes chart used to track the number of nonconformities with varying sample size, for example, to track the particle density per wafer.
UHF
Ultra High Frequency. (1) A bonded-wafer process technology used in Melbourne, Fla. for fabrication of enhanced bipolar products, particularly linear and high-frequency operational amplifiers and other linear products. (2) Also, the portion of the radio spectrum between 300 and 3000 megahertz (MHz). This includes television channels 14 through 83, as well as most radar use.
Ultrapure water (UPW)
deionized and filtered water.
Ultrashallow junction
dopant junction in silicon in which the junction is less than 100 nm deep.
Ultrasonic bonding
a packaging process that involves high-frequency waves and pressure techniques to join two materials.
Uncontrolled work area
any area outside of a secondary containment system where people are likely to be present.
Undercut
in the leadframe of a dual inline semiconductor package produced by etching, a beveled edge caused by the etchant attacking the metal laterally as well as vertically. Also see etch factor.
Undercutting
the lateral etching into a substrate under a resistant coating, as at the edge of a resist image.
Unencapsulated thermal test chip
an unpackaged, specially designed silicon die with standard test junctions that, after mounting into a package, may be used to thermally characterize that package. This technique is useful in determining the difference between various vendors' packages and package designs.
Uniformity
It is important that any given process affects all areas of the wafer equally. The measure of this is called the uniformity of the process. A common (though undesirable) occurrence is that center to edge non-uniformities occur. For example, the center of the wafer might get etched more rapidly than the edge, or the edge of a wafer might polish down more quickly than the center.
Unit
any wafer, die, packaged device, or piece part thereof; includes product and nonproduct units.
Unix
An operating system developed at AT&T Bell Labs by Ken Thompson and Dennis Ritchie, and further extended at the University of California, Berkeley, by a number of students, including Bill Joy, one of the founders of Sun Computers. The key feature of Unix is that while all versions of Unix are not the same, it is an open architecture and not proprietary to any hardware vendor. This means that application programs are more easily ported between different versions of Unix than between any other proprietary operating systems. See open architecture.
Unload
to remove a cassette from the cassette stage of the equipment. Contrast load.
Unscheduled downtime
the total time during which equipment is not in a condition to perform its intended function because of unplanned downtime events. Also see unscheduled downtime state.
Unscheduled downtime state
one of the six equipment states or conditions; a period during which equipment is not in a condition to perform its intended function because of unplanned downtime events.
Unstable
1 adj: ending toward decomposition or other unwanted chemical change during normal handling or storage. 2 n : a chemical that, in the pure state, or as produced or transported, will vigorously polymerize, decompose, condense, or will become self-reactive under conditions of shock, pressure, or temperature.
Upper range input value
in mass flow devices, the highest value of input at which the instrument is specified to operate. In mass flow controllers, this is full scale or the highest set point at which the instrument is specified. In mass flow meters, this is full scale or the highest actual flow value at which the instrument is specified.
Uptime, equipment
the amount of time during which the equipment is in a condition to perform its intended function; includes productive, standby, and engineering time; does not include any portion of nonscheduled time.
UPW
see ultrapure water.
Usable resolution
the smallest image that can be produced and subsequently processed in a given thickness of resist coating.
User
in communications and control of semiconductor manufacturing equipment, a human or humans who represent the factory and enforce the factory operation model. A user is considered to be responsible for many setup and configuration activities that cause the equipment to best conform to factory operations practices.
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