Design and Implementation of VLSI Systems

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Design and Implementation of VLSI Systems (EN0160)
Sherief Reda Division of Engineering, Brown
University Spring 2007
sources Sedra/Prentice Hall, Saint/McGrawHill,
Weste/Addison Wesley
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Lecture 03 CMOS fabrications

• Last time

• How do transistors make up different CMOS gates?

• Today

• Fabrication of CMOS gates

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What needs to be fabricated?
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Top view
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Fabrication Target Inverter
GND
VDD
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Gate layouts is decomposed into primitives
layouts that would be printed in sequence
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Wafer preparation
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Photolithography is used to print desired
patterns on the wafer
masks
The feature size directly depends on the
wavelength of your lithographic system
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P Type start wafer
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Grow P-epitaxial layer
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Spin Resist Coating
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Expose N Well Mask
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Develop resist (remove resist exposed to light)
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Implant N Well
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Remove Resist
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Main 5-6 Steps SEDAR

• (possible pre-spin action, e.g., deposit)
• Spin resist
• Expose (using mask)
• Develop resist
• ACTION (e.g., implant, etch, oxidize)
• Remove Resist

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Anneal wafer to grow new oxide layer and diffuses
N well
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Remove oxide from anneal
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Spin Resist
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Develop resist
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Expose resist with active diffusion mask
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Grow oxide on exposed surface
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Remove resist
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Grown thin oxide over silicon surfaces
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Deposit poly using Chemical Vapor Deposition (CVD)
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Spin resist expose resist using the GATE mask
develop resist etch poly
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Remove thin oxide layer where exposed
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Spin resist expose with P implant mask
develop resist implant P
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Spin resist expose with N implant mask
develop resist implant N
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Remove resist anneal wafer oxide etch
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Deposit oxide using CVD spin resist expose
Contact mask develop resist - etch contact hole
remove resist
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Deposit metal 1 spin resist - expose metal 1
mask develop resist - etch metal remove resist
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Fabrication Summary
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Spin polyimide spin resist expose via 1 mask
etch via remove resist
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Deposit metal 2 spin resist expose metal 2
etch metal remove resist
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Spin polymide spin resist expose via 2 mask
etch via remove resist
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Deposit metal 3 spin resist expose metal 3
mask develop resist etch metal remove resist
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Spin polyimide spin resist expose passivation
mask develop resist - etch poly remove resist
deposit nitride spin resist expose
passivation mask etch nitride remove resist
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More metal layers?
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The printer
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Summary

• Today
• Reviewed fabrication process
• Next time
• How to print different gates?