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Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-1
CMOS Analog Circuit Design © P.E. Allen - 2016
LECTURE 04 - ULTRA-DEEP SUBMICRON AND BiCMOS
TECHNOLOGIES
LECTURE ORGANIZATION
Outline
• Ultra-deep submicron CMOS technology
- Features
- Advantages
- Problems
• BiCMOS technology process flow
- CMOS is typical submicron (0.5 µm)
• Summary
CMOS Analog Circuit Design, 3rd Edition Reference
New material
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-2
CMOS Analog Circuit Design © P.E. Allen - 2016
ULTRA-DEEP SUBMICRON (UDSM) CMOS TECHNOLOGY
USDM Technology
• Lmin ≤ 0.1 microns
• Minimum feature size less than 100 nanometers
• Today’s state of the art:
- 22 nm drawn length
- 5 nm lateral diffusion (12 nm gate length)
- 1 nm transistor gate oxide
- 8 layers of copper interconnect
• Specialized processing is used to increase drive capability and maintain low off
currents
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-3
CMOS Analog Circuit Design © P.E. Allen - 2016
65 Nanometer CMOS Technology
TEM cross-section of a 35 nm NMOS and PMOS transistors.†
NMOS: PMOS:
These transistors utilize enhanced channel strains to
increase drive capability and to reduce off currents.
† P. Bai, et. Al., “A 65nm Lobic Technology Featuring 35nm Gate Lengths, Enhanced Channel Strain, 8 Cu Interconnect Layers, Low-k ILD and
0.57 µm2 SRAM Cell, IEEE Inter. Electron Device Meeting, Dec. 12-15, 2005.
220 nm pitch
NMOS
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-4
CMOS Analog Circuit Design © P.E. Allen - 2016
UDSM Metal and Interconnects
Physical aspects:
Layer Pitch
(nm)
Thickness
(nm)
Aspect
Ratio
Isolation 220 230 -
Polysilicon 220 90 -
Contacted Gate Pitch 220 - -
Metal 1 210 170 1.6
Metal 2 210 190 1.8
Metal 3 220 200 1.8
Metal 4 280 250 1.8
Metal 5 330 300 1.8
Metal 6 480 430 1.8
Metal 7 720 650 1.8
Metal 8 1080 975 1.8
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-5
CMOS Analog Circuit Design © P.E. Allen - 2016
What are the Advantages of UDSM CMOS Technology?
Digital Viewpoint:
• Improved Ion/Ioff 70 Mbit SRAM chip:
• Reduced gate capacitance
• Higher drive current capability
• Reduced interconnect density
• Reduction of active power
Analog Viewpoint:
• More levels of metal
• Higher fT
• Higher capacitance density
• Reduced junction capacitance per gm
• More speed
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-6
CMOS Analog Circuit Design © P.E. Allen - 2016
What are the Disadvantages of UDSM CMOS Technology (for Analog)?
• Reduction in power supply resulting in reduced headroom
• Gate leakage currents
• Reduced small-signal intrinsic gains
• Increased nonlinearity (IIP3)
• Increased noise and poorer matching (smaller area)
Intrinsic gain and IP3 as a function of the gate overdrive for decreasing VDS:†
† Anne-Johan Annema, et. Al., “Analog Circuits in Ultra-Deep-Submicron CMOS,” IEEE J. of Solid-State Circuits, Vol. 40, No. 1, Jan. 2005, pp.
132-143.
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-7
CMOS Analog Circuit Design © P.E. Allen - 2016
What is the Gate Leakage Problem?
Gate current occurs in thin oxide devices due to direct tunneling through the thin oxide.
Gate current depends on:
1.) The gate-source voltage (and the drain-gate voltage)
iGS = K1vGS exp(K2vGS) and iGD = K3vGD exp(K4vGD)
2.) Gate area – NMOS leakage ≈ 6nA/µm2 and PMOS leakage ≈ 3nA/µm2
Unfortunately, the gate leakage current is nonlinear with respect to the gate-source and
gate-drain voltages. A possible model is:
Base current cancellation schemes used for BJTs are difficult to apply to the MOSFET.
051205-03
f(vGS)
f(vGD)+
-
vGD
+
-
vGS f(vDG)
f(vSG)
+
-
vSG
+
-
vDG
NMOS PMOS
Large Signal Models
ggd
ggs
NMOS
gsg
gdg
PMOS
Small Signal Models
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-8
CMOS Analog Circuit Design © P.E. Allen - 2016
UDSM CMOS Technology Summary
• Increased transconductance and frequency capability
• Low power supply voltages
• Reduced parasitics
• Gate leakage causes challenges for analog applications of UDSM technology
- Can no longer use the MOSFET for capacitance
- Conflict between matching and gate leakage
• Other issues
- Noise
- Zero temperature coefficient behavior
- Etc.
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-9
CMOS Analog Circuit Design © P.E. Allen - 2016
BiCMOS TECHNOLOGY
Typical 0.5µm BiCMOS Technology
Masking Sequence:
1. Buried n+ layer 9. Base oxide/implant 17. Contacts
2. Buried p+ layer 10. Emitter implant 18. Metal 1
3. Collector tub 11. Poly 1 19. Via 1
4. Active area 12. NMOS lightly doped drain 20. Metal 2
5. Collector sinker 13. PMOS lightly doped drain 21. Via 2
6. n-well 14. n+ source/drain 22. Metal 3
7. p-well 15. p+ source/drain 23. Nitride passivation
8. Emitter window 16. Silicide protection
Notation used in the following slides:
BSPG = Boron and Phosphorus doped Silicate Glass (oxide)
Kooi Nitride = A thin layer of silicon nitride on the silicon surface as a result of the
reaction of silicon with the HN3 generated, during the field oxidation.
TEOS = Tetro-Ethyl-Ortho-Silicate. A chemical compound used to deposit conformal
oxide films.
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-10
CMOS Analog Circuit Design © P.E. Allen - 2016
n+ and p+ Buried Layers
Starting Substrate:
n+ and p+ Buried Layers:
p-substrate 1mm
5mmBiCMOS-01
p-substrate
n+ buried layer p+ buried
layer
n+ buried layer p+ buried layer
1mm
5mm
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-02
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-11
CMOS Analog Circuit Design © P.E. Allen - 2016
Epitaxial Growth
Comment:
• As the epi layer grows vertically, it assumes the doping level of the substrate beneath
it.
• In addition, the high temperature of the epitaxial process causes the buried layers to
diffuse upward and downward.
p-substrate
n+ buried layer p+ buried
layer
n+ buried layerp+ buried layer
p-type
Epitaxial
Silicon
p-well n-well p-well
1mm
5mm
NMOS TransistorPMOS TransistorNPN Transistor
n-well
BiCMOS-03
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-12
CMOS Analog Circuit Design © P.E. Allen - 2016
Collector Tub
Comment:
• The collector area is developed by an initial implant followed by a drive-in diffusion to
form the collector tub.
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-welln-well
p-well
1mm
5mm
Collector Tub
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-04
Original Area of
CollectorTub Implant
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-13
CMOS Analog Circuit Design © P.E. Allen - 2016
Active Area Definition
Comment:
• The silicon nitride is use to impede the growth of the thick oxide which allows contact
to the substrate
• -silicon is used for stress relief and to minimize the bird’s beak encroachment
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-14
CMOS Analog Circuit Design © P.E. Allen - 2016
Field Oxide
Comments:
• The field oxide is used to isolate surface structures (i.e. metal) from the substrate
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
FO
X
p-welln-well
p-well
1mm
5mm
Collector Tub
Field Oxide Field Oxide
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-06
FOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-15
CMOS Analog Circuit Design © P.E. Allen - 2016
Collector Sink and n-Well and p-Well Definitions
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mm
Collector Tub
Field Oxide
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-07
FO
X
Field Oxide
Collector Sink Anti-Punch ThroughThreshold Adjust
Anti-Punch ThroughThreshold Adjust
n-well
FOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-16
CMOS Analog Circuit Design © P.E. Allen - 2016
Base Definition
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
FO
X
p-well p-well
1mm
5mm
Collector Tub
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-08
Field Oxide Field Oxide
n-well
FOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-17
CMOS Analog Circuit Design © P.E. Allen - 2016
Definition of the Emitter Window and Sub-Collector Implant
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mm
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-09
Field Oxide
n-well
Sub-Collector
FO
X
Field Oxide
Sacrifical Oxide
FOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-18
CMOS Analog Circuit Design © P.E. Allen - 2016
Emitter Implant
Comments:
• The polysilicon above the base is implanted with n-type carriers
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mm
Collector Tub
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-10
Field Oxide
n-well
Sub-Collector
FO
X
Field Oxide
Emitter Implant
FOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-19
CMOS Analog Circuit Design © P.E. Allen - 2016
Emitter Diffusion
Comments:
• The polysilicon not over the emitter window is removed and the n-type carriers diffuse
toward the base forming the emitter
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mm
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-11
Field Oxide
n-well
FO
X
Field Oxide
Emitter
FOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-20
CMOS Analog Circuit Design © P.E. Allen - 2016
Formation of the MOS Gates and LD Drains/Sources
Comments:
• The surface of the region where the MOSFETs are to be built is cleared and a thin gate
oxide is deposited with a polysilicon layer on top of the thin oxide
• The polysilicon is removed over the source and drain areas
• A light source/drain diffusion is done for the NMOS and PMOS (separately)
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mm
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-12
Field Oxide
n-well
FO
X
Field OxideFOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-21
CMOS Analog Circuit Design © P.E. Allen - 2016
Heavily Doped Source/Drain
Comments:
• The sidewall spacers prevent the heavy source/drain doping from being near the
channel of the MOSFET
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mm
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-13
Field Oxide
n-well
FO
X
Field OxideFOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-22
CMOS Analog Circuit Design © P.E. Allen - 2016
Siliciding
Comments:
• Siliciding is used to reduce the resistance of the polysilicon and to provide ohmic
contacts to the base, emitter, collector, sources and drains
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mm
NMOS TransistorPMOS TransistorNPN Transistor
BiCMOS-14
Field Oxide
n-well
FO
X
Field Oxide
Silicide TiSi2 Silicide TiSi2 Silicide TiSi2
FOX Field Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-23
CMOS Analog Circuit Design © P.E. Allen - 2016
Contacts
Comments:
• A dielectric is deposited over the entire wafer
• One of the purposes of the dielectric is to smooth out the surface
• Tungsten plugs are used to make electrical contact between the transistors and metal1
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mmBiCMOS-15
Field Oxide Field Oxide
n-well
FO
X
Field Oxide Field Oxide
Tungsten Plugs Tungsten PlugsTungsten PlugsTEOS/BPSG/SOG TEOS/BPSG/SOG TEOS/BPSG/SOG
FOX
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-24
CMOS Analog Circuit Design © P.E. Allen - 2016
Metal1
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mmBiCMOS-16
Field Oxide Field Oxide
n-well
FO
X
Field Oxide Field Oxide
TEOS/BPSG/SOG TEOS/BPSG/SOG TEOS/BPSG/SOG
Metal1 Metal1Metal1
FOX
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-25
CMOS Analog Circuit Design © P.E. Allen - 2016
Metal1-Metal2 Vias
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mmBiCMOS-17
Field Oxide Field Oxide
n-well
FO
X
Field Oxide Field Oxide
TEOS/BPSG/SOG TEOS/BPSG/SOG TEOS/BPSG/SOG
Tungsten Plugs Oxide/
SOG/
Oxide
FOX
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-26
CMOS Analog Circuit Design © P.E. Allen - 2016
Metal2
p-substrate
n+ buried layer p+ buried
layern+ buried layer p+ buried layer
p-type
Epitaxial
Silicon
p-well p-well
1mm
5mmBiCMOS-18
Field Oxide Field Oxide
n-well
FO
X
Field Oxide Field Oxide
TEOS/BPSG/SOG TEOS/BPSG/SOG TEOS/BPSG/SOG
Metal 2
FOX
Oxide/
SOG/
Oxide
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-27
CMOS Analog Circuit Design © P.E. Allen - 2016
Metal2-Metal3 Vias
Comments:
• The metal2-metal3 vias will be filled with metal3 as opposed to tungsten plugs
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-28
CMOS Analog Circuit Design © P.E. Allen - 2016
Completed Wafer
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-29
CMOS Analog Circuit Design © P.E. Allen - 2016
Silicon-Germanium
Physical Perspective (130nm):
Electrical:
Max. voltage = 2V
≈ 300
fT ≈ 100 GHz
Lecture 04 – UDSM and BiCMOS Technologies (3/10/14) Page 04-30
CMOS Analog Circuit Design © P.E. Allen - 2016
SUMMARY
• UDSM technology typically has a minimum channel length less than 0.1µm
• UDSM transistors utilize enhanced channel strains to increase drive capability and
reduce off currents
• Advantages of UDSM technology include:
- Smaller devices
- Higher speeds and transconductances
- Improved Ion/Ioff
• Disadvantages of UDSM technology include:
- Gate leakage currents
- Reduced small signal gains
- Increased nonlinearity
• BiCMOS technology
- Offers both CMOS transistors and a high performance vertical BJT
- CMOS is typically a generation behind
- Silicon germanium can be used to enhance the BJT performance