In semiconductor manufacturing, a process corner is an example of a design-of-experiments (DoE) technique that refers to a variation of fabrication parameters used in applying an integrated circuit design to a semiconductor wafer . Process corners represent the extremes of these parameter variations within which a circuit that has been etched onto the wafer must function correctly. A circuit running on devices fabricated at these process corners may run slower or faster than specified and at lower or higher temperatures and voltages, but if the circuit does not function at all at any of these process extremes the design is considered to have inadequate design margin.
15-551: OCV may refer to On-chip variation Open-circuit voltage Voltaic Communist Organization (French: Organisation communiste voltaïque ) Offshore Combatant Vessel, a proposed multi-role ship class to be built by the Royal Australian Navy Optical Character Verification (automated verification/inspection of printed text using Machine vision ) Topics referred to by
30-428: A corner designated as FS denotes fast NFETs and slow PFETs. There are therefore five possible corners: typical-typical (TT) (not really a corner of an n vs. p mobility graph, but called a corner, anyway), fast-fast (FF), slow-slow (SS), fast-slow (FS), and slow-fast (SF). The first three corners (TT, FF, SS) are called even corners, because both types of devices are affected evenly, and generally do not adversely affect
45-474: A process called characterization . The results of these tests are plotted using a graphing technique known as a shmoo plot that indicates clearly the boundary limit beyond which a device begins to fail for a given combination of these environmental conditions. Corner-lot analysis is most effective in digital electronics because of the direct effect of process variations on the speed of transistor switching during transitions from one logic state to another, which
60-572: Is an orthogonal set of process parameters that affect back end of line (BEOL) parasitics. One naming convention for process corners is to use two-letter designators, where the first letter refers to the N-channel MOSFET ( NMOS ) corner, and the second letter refers to the P channel ( PMOS ) corner. In this naming convention, three corners exist: typical , fast and slow . Fast and slow corners exhibit carrier mobilities that are higher and lower than normal, respectively. For example,
75-599: Is deposited. The individual devices are connected by alternately stacking oxide layers (for insulation purposes) and metal layers (for the interconnect tracks). The vias between layers and the interconnects on the individual layers are thus formed using a structuring process. Common metals are copper and aluminum . BEOL generally begins when the first layer of metal is deposited on the wafer. BEOL includes contacts, insulating layers ( dielectrics ), metal levels, and bonding sites for chip-to-package connections. For modern IC processes, more than 10 metal layers can be added in
90-570: Is different from Wikidata All article disambiguation pages All disambiguation pages On-chip variation To verify the robustness of an integrated circuit design, semiconductor manufacturers will fabricate corner lots , which are groups of wafers that have had process parameters adjusted according to these extremes, and will then test the devices made from these special wafers at varying increments of environmental conditions, such as voltage, clock frequency, and temperature, applied in combination (two or sometimes all three together) in
105-495: Is not relevant for analog circuits, such as amplifiers. In Very-Large-Scale Integration (VLSI) integrated circuit microprocessor design and semiconductor fabrication , a process corner represents a three or six sigma variation from nominal doping concentrations (and other parameters ) in transistors on a silicon wafer . This variation can cause significant changes in the duty cycle and slew rate of digital signals, and can sometimes result in catastrophic failure of
120-408: Is used. To combat these variation effects, modern technology processes often supply SPICE or BSIM simulation models for all (or, at the least, TT, FS, and SF) process corners, which enables circuit designers to detect corner skew effects before the design is laid out , as well as post-layout (through parasitics extraction ), before it is taped out . Back end of line Back end of
135-409: The entire system. Variation may occur for many reasons, such as minor changes in the humidity or temperature in the clean-room when wafers are transported, or due to the position of the die relative to the center of the wafer. When working in the schematic domain, we usually only work with front end of line (FEOL) process corners as these corners will affect the performance of devices. But there
150-404: The line or back end of line ( BEOL ) is a process in semiconductor device fabrication that consists of depositing metal interconnect layers onto a wafer already patterned with devices. It is the second part of IC fabrication, after front end of line (FEOL) . In BEOL, the individual devices (transistors, capacitors, resistors, etc.) are connected to each other according to how the metal wiring
165-402: The logical correctness of the circuit. The resulting devices can function at slower or faster clock frequencies, and are often binned as such. The last two corners (FS, SF) are called "skewed" corners, and are cause for concern. This is because one type of FET will switch much faster than the other, and this form of imbalanced switching can cause one edge of the output to have much less slew than
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#1732802072221180-430: The nominal cross section of the process target. Then the corners cbest and cworst were created to model the smallest and largest cross sections that are in the allowed process variation. A simple thought experiment shows that the smallest cross section with the largest vertical spacing will produce the smallest coupling capacitance. CMOS Digital circuits were more sensitive to capacitance than resistance so this variation
195-463: The other edge. Latching devices may then record incorrect values in the logic chain. In addition to the FETs themselves, there are more on-chip variation (OCV) effects that manifest themselves at smaller technology nodes . These include process, voltage and temperature (PVT) variation effects on on-chip interconnect, as well as via structures. Extraction tools often have a nominal corner to reflect
210-449: The same term [REDACTED] This disambiguation page lists articles associated with the title OCV . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=OCV&oldid=1255326997 " Category : Disambiguation pages Hidden categories: Articles containing French-language text Short description
225-405: Was initially acceptable. As processes evolved and resistance of wiring became more critical, the additional rcbest and rcworst were created to model the minimum and maximum cross sectional areas for resistance. But the one change is that cross sectional resistance is not dependent on oxide thickness (vertical spacing between wires) so for rcbest the largest is used and for rcworst the smallest
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