04_Diffusion=) - Diffusion Introduction Fick's Law...

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(Gan 2010/11) Diffusion Introduction Fick’s Law Pre-deposition & Drive-in Electric field effects Concentration dependent diffusivity Diffusion mechanisms Readings: Plummer sections 7.1 – 7.3, 7.5
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(Gan 2010/11) Silicon Microelectronics Today A thick web of interconnects, many levels deep. High density of very small transistors. Take the cover off a microprocessor. What do you see? Intel’s Pentium II
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(Gan 2010/11) Interconnects and Transistors Bird’s eye SEM view of a 7-level Interconnect network Cross-sectional view of 7-level interconnect: 1-level of W “local interconnect”, and 6-level Cu “global interconnect A MOSFET cross- section enlarged! 0.2 μ m MOSFET gate
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(Gan 2010/11) Particles move in response to a potential gradient Drift - Charged particles (electrons, holes, ions) moving in a electric field (electrical potential gradient), characterized by mobility μ , measurable as conductivity Diffusion - Neutral particles (atoms, molecules) moving in a concentration gradient (chemical potential gradient), characterized by diffusivity D , measurable as a change in concentration profile Atoms may also migrate under stress gradients – stress migration In all cases, the particle motion is a simple consequence of the minimization of free energy Particle motion may consist of multiple components, corresponding to different driving forces (gradients) Introduction
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(Gan 2010/11) In addition to gradients, particles may also move under momentum exchange, eg. electron impact induced atomic motion – electromigration All these mechanisms for motion can occur in all phases of matter For MS3002, focus on Diffusion of Dopants (As, P, B) in crystalline Semiconductors (Si) Introduction
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(Gan 2010/11) Primary use of diffusion as a process in microelectronics manufacturing is in doping Usages of doping: formation of source, drain, pn junctions in transistors Doping profiles determine many short-channel characteristics Two main diffusion processes: 1. Predeposition – low T, short time To introduce dose (total number of dopant atoms) on a thin surface layer Doping 2. Drive-in – high T, long time To drive dopants into the desired depth
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(Gan 2010/11) Junction depth P-N Junction Form by diffusing in a different species of dopants (e.g. acceptors) into Si that has a different background dopant type (e.g. donors) Junction forms at where the 2 concentrations are the same or net impurity concentration is zero
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(Gan 2010/11) • Resistance impacts drive current R contact R source R ext R chan R poly Silicide V G V S V D Sidewall Spacers x J x W Year of Production 1998 2000 2002 2004 2007 2010 2013 2016 2018 Technology N ode (half pitch) 250 nm 180 nm 130 nm 90 nm 65 nm 45 nm 32 nm 22 nm 18 nm MPU Printed Gate Length 100 nm 70 nm 53 nm 35 nm 25 nm 18 nm 13 nm 10 nm Contact Resi stivity r C (ž cm 2 ) 2x10 -7 1.6x10 -7 1x10 -7 6x10 -8 1.7x10 -8 8.7x10 -9 5x10 -9 S/D Extens ion Abruptness (nm/decdade) 4.1 2.8 TBD TBD TBD TBD S/D Extens ion Sheet Resistance (PMOS) (ž /sq) 660 890 1875 510 550 580 S/D Extens ion x J (nm) 50-100 42-70 25-43 20 14 7.2 10 7.2 5.1 Min Supply Voltage (volts) 1.8-2.5 1.5-1.8 1.2-1.5 0.9-1.2 0.8-1.1
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04_Diffusion=) - Diffusion Introduction Fick's Law...

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