Process corners

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 properly at any of these process extremes the design is considered to have inadequate design margin. 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 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.…

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 properly at any of these process extremes the design is considered to have inadequate design margin. 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 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 is not relevant for analog circuits, such as amplifiers. ==Significance to digital electronics== 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 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. ==Types of corners== 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 is an orthogonal set of process parameters that affect back end of line (BEOL) parasitics. ==Accounting for corners== 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. ==References== ==External links== US Patent# 6606729 - Corner simulation methodology

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