Introduction to Layout
Jack Ou, Ph.D.CES 522 V
VLSI DesignSonoma State University
Flow Chart
Cross Sectional of an Inverter
Mask SetD D
S S
Basic Ingriedents
• n-well (N_WELL)• Polysilicon (POLY)• n+ diffusion• p+ diffusion• contact• metal
Manufacturing the n-well• Grow a protectiveLayer of oxide.• Remove oxidein selected region• Ion Implantation
• Poly silicon(doped to makegood conductor,Block n+ diffusion)• n-diffusion
p-diffusion, contacts and metal
Thick metal oxide provides insulationp+ diffusion is made selectively using silicon dioxide and photo resist
λ
• λ is half of the smallest feature size– In 0.18 um, λ is 0.09 um
• λ based design rules makes it easy to migrate from one process to process.
• Industrial design rules are usually specified in microns, which makes it difficult to migrate to a more advanced process.
Simplified λ based design rules
Example from tsmc 0.18 um process
POLY has a width of 2 λContacts are 2 λ x 2 λ
Design Rules
Schematic/Layout of an Inverter
p+ diffision
n+ diffision
Ground
VDD
Schematic/Layout of a NAND2
p+ diffision
n+ diffision
Ground
VDD
Substrate Contact
P_WELL
P_WELL+P_PLUS_SELECT
P_WELL+P_PLUS_SELECT+Active(43)
P_WELL+P_PLUS_SELECT+Active(43)+Contact to Active
P_WELL+P_PLUS_SELECT+Active(43)+Contact to Active+Metal1
Nwell Contact
NWELL
NWELL+N_Plus_Select+
NWELL+N_Plus_Select+Active Layer
NWELL+N_Plus_Select+Active Layer+Contact to Active Layer
NWELL+N_Plus_Select+Active Layer+Contact to Active Layer+Metal 1
DRC
DRC
Check: to run DRCFirst: to see the first DRC violationNext: to step through the DRC errors
DRC Results
DRC violation
Use the Rule Deck to Repair the Layout
Repaired Layout
Enlarged N Plus Select
Reduced Result Count