Well and Substrate Taps Substrate must be tied to GND and n-well to VDD Metal to lightly-doped semiconductor forms poor connection called Shottky Diode Use heavily doped well and substrate contacts taps GND n+ n+ p+ p+ n+ n well p substrate substrate tap well tap Digital IC 6
Digital IC Well and Substrate Taps • Substrate must be tied to GND and n-well to VDD • Metal to lightly-doped semiconductor forms poor connection called Shottky Diode • Use heavily doped well and substrate contacts / taps n+ p substrate p+ n well A Y GND VDD p+ n+ substrate tap well tap n+ p+ 6
Latchup External voltages can ring below GND or above VDD GND Dx ns n+ DA n+ p-substrate n-wel R (a) Substrate Tap Well Tap n well R n+ R (b) ut GND p substrate n+guard ring p+guard ring 7 (a) (b)
Digital IC Latchup External voltages can ring below GND or above VDD 7
Inverter Mask Set Transistors and wires are defined by masks Cross-section taken along dashed line GND nMOS transistor pMOS transistor substrate tap well tap Digital IC 8
Digital IC Inverter Mask Set • Transistors and wires are defined by masks • Cross-section taken along dashed line GND VDD Y A substrate tap well tap nMOS transistor pMOS transistor 8
Detailed Mask Views(Six masks) o n-well n well ·Polysilicon 图 Polysilicon 。n+diffusion n+Diffusion p+diffusion p+Diffusion Contact Contact 。Metal ☑ Metal Digital IC 9
Digital IC Detailed Mask Views(Six masks) • n-well • Polysilicon • n+ diffusion • p+ diffusion • Contact • Metal Metal Polysilicon Contact n+ Diffusion p+ Diffusion n well 9
Devices and Layers from a Silicon Chip Top protective layer Conductive layer Metal layer Insulation layers Recessed conductive layer Silicon substrate Silicon substrate Semiconductor Manufacturing Technology by Michael Quirk and Julian Serda Digital IC 10
Digital IC Devices and Layers from a Silicon Chip Silicon substrate drain Silicon substrate Top protective layer Metal layer Insulation layers Recessed conductive layer Conductive layer Semiconductor Manufacturing Technology by Michael Quirk and Julian Serda 10