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Process variation is the naturally occurring variation in the attributes of transistors (length, widths, oxide thickness) when integrated circuits are fabricated. It becomes particularly important at smaller process nodes (<65 nm) as the variation becomes a larger percentage of the full length or width of the device and as feature sizes approach the fundamental dimensions such as the size of atoms and the wavelength of usable light for patterning lithography masks. Process variation causes measurable and predictable variance in the output performance of all circuits but particularly analog circuits due to mismatch.〔Patrick Drennan, "Understanding MOSFET Mismatch for Analog Design" ''IEEE Journal of Solid-State Circuits, Vol 38, No 3'', March 2003 http://www.solidodesign.com/uploads/drennan-mismatch.pdf〕 If the variance causes the measured or simulated performance of a particular output metric (bandwidth, gain, rise time, etc.) to fall below or rise above the specification for the particular circuit or device it reduces the overall yield for that set of devices. == History == The first mention of variation in semiconductors was by William Shockley, the co-inventor of the transistor, in his 1961 analysis of junction breakdown.〔W. Shockley, “Problems related to p-n junctions in silicon.” ''Solid-State Electronics, Volume 2'', January 1961, pp. 35–67.〕 An analysis of systematic variation was performed by Schemmert and Zimmer in 1974 with their paper on threshold-voltage sensitivity.〔W. Schemmert, G. Zimmer, "Threshold-voltage sensitivity of ion-implanted m.o.s.transistors due to process variations." ''Electronics Letters, Volume 10, Issue 9'', May 2, 1974, pp. 151-152〕 This research looked into the effect that the oxide thickness and implantation energy had on the threshold voltage of MOS devices. sources of variations 1) gate oxide thickness 2) random dopant fluctuations 3) Device Geometry, Lithography in nanometer region 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Process variation (semiconductor)」の詳細全文を読む スポンサード リンク
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