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Circuits and CMOS Technology
Hooman NabovatiSadjad Institute for Higher Education
Mashhad, Iran
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19th Century - Solid-State Rectifiers 1907 - Application of Crystal Detector in Radio
1947 - BJT Constructed by Bardeen and Brattain andschockly
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Invention: 1947,at Bell Laboratories.
John Bardeen, WalterBrattain, andWilliam Schockly developed the firstmodel of transistor (a Three Pointstransistor, made with Germanium)
They received Nobel Prize in Physics.
12/21/20093
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- TM Device characteristics
# of transistors 42 000 000 Line width: 0.18 m=>( 0.13 m)
P4 die size: 224 mm
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12/21/20095
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Evolution in Complexity
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u yMPU Gate Length (nm)
30
35
20
25
10
15
0
5
7
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ec no ogy oa map as emor esbits/cm2
.
. +
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1.00E+10
2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
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em con uc or anu ac ur ng ar e
Systemspecification
Design PackagingFabrication TestIC
$200 billion
Tools: designsimulationemulation
Equipment Material Equipment Equipment
$3.4 billion $16.8 billion $2.0 billion $5.2 billion
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- Typically use p-type substrate for nMOS transistors
Requires n-well for body of pMOS transistors
A
n+ +
YDD
n+ +
SiO2
n+ diffusion
p+ diffusion
p substraten well polysilicon
metal1
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Substrate must be tied to GND and n-well to VDD Metal to lightly-doped semiconductor forms poor
connection called Shottky Diode
A
Y DD
n+
p substrate
p+
n well
n+p+ n+ p+
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substrate tap well tap
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Transistors and wires are defined by masks
Cross-section taken along dashed line
A
Y
GND VDD
substrate tap well tapnMOS transistor pMOS transistor
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Six masks
n-well
Polysilicon
n well
p+ diffusion
Contactn+ Diffusion
MetalContact
p+ Diffusion
Metal
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Start with blank wafer
Build inverter from the bottom up
First step will be to form the n-well 2
Remove layer where n-well should be built
Implant or diffuse n dopants into exposed wafer Strip off SiO2
p substrate
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Grow SiO2 on top of Si wafer 900 1200 C with H2O or O2 in oxidation furnace
p substrate
SiO2
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Spin on photoresist Photoresist is a light-sensitive organic polymer
Softens where exposed to light
SiO2
Photoresist
p substrate
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Expose photoresist through n-well mask
Strip off exposed photoresist
Photoresist
p substrate
SiO2
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Etch oxide with hydrofluoric acid (HF)
Only attacks oxide where resist has been exposed
SiO2
Photoresist
p substrate
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Strip off remaining photoresist
Use mixture of acids called piranah etch
Necessary so resist doesnt melt in next step
p substrate
SiO2
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- n-well is formed with diffusion or ion mplantation
Diffusion Place wafer in furnace with arsenic gas
Ion Implanatation
Blast wafer with beam of As ions Ions blocked by SiO2, only enter exposed Si
n well
SiO2
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Strip off the remaining oxide using HF
Back to bare wafer with n-well
Subsequent steps involve similar series of steps
n well
p substrate
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Deposit very thin layer of gate oxide < 20 (6-7 atomic layers)
Chemical Vapor Deposition (CVD) of silicon layer
Forms many small crystals called polysilicon
Heavily doped to be good conductor
Polysiliconn ga e ox e
p substraten well
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Use same lithography process to pattern polysilicon
Polysilicon
p substrate
Thin gate oxide
o ys con
n well
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- Use oxide and masking to expose where n+ dopants
s ou e use or mp an e
N-diffusion forms nMOS source, drain, and n-well
p substraten well
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- Pattern oxide and form n+ regions
e -a gne processw ere ga e oc s us on
Polysilicon is better than metal for self-aligned gates because itdoesnt melt during later processing
n+ Diffusion
n well
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p substrate
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- . Historically dopants were diffused
Usually ion implantation today
But regions are still called diffusion
n well
n+n+ n+
p substrate
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- Strip off oxide to complete patterning step
n wellsubstrate
n+n+ n+
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- Similar set of steps form p+ diffusion regions for
p source an ra n an su s ra e con ac
p+ Diffusion
p substraten well
n+n+ n+p+p+p+
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Now we need to wire together the devices
Cover chip with thick field oxide
Etch oxide where contact cuts are needed
Contact
p substrate
Thick field oxide
n well
n+n+ n+p+p+p+
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Sputter on aluminum over whole wafer
Pattern to remove excess metal, leaving wires
Metal
Metal
Thick field oxide
n well
n+n+ n+p+p+p+
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p substrate
