6.2. thermal oxidation 3 microtech,2013
DESCRIPTION
VLSITRANSCRIPT
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Microelectronic Technology
Thermal Oxidation (III)
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Film Thickness (Å) Colour
500 Tan
700 Brown
1000 Dark violet to red violet
1200 Royal blue
1500 Light blue to metallic blue
2000 Light gold or yellow slight metallic
2700 Red-violet
3100 Blue
3400 Light green
3600 Yellow-green
3900 Yellow
Colour Chart for Thermally Grown SiO2 Films
Dr. G. Eranna Integrated Circuit Fabrication Technology © CEERI Pilani
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Basic Concepts• SiO2 is amorphous even though it grows on a crystalline substrate.
• Four types of defects or charges are associated with Si/SiO2 interface.
++++ +xxxxxx
+++ -
--
K+
TransitionRegion
Na+SiO2
Qm
Qot
Qf
QitSilicon
• Qf - fixed oxide charge• Qit - interface trapped charge• Qm - mobile oxide charge• Qot - oxide trapped charge
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C-V Measurements
• Powerful technique for characterizing semiconductor / insulator structures.
• DC bias + small AC high frequency signal applied.
Accumulation
• Electric field lines pass through the “perfect” insulator and Si/SiO2 interface, into the substrate where they control charge carriers.
• Accumulation, depletion and inversion result.
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C-V Measurements
Depletion
Inversion
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C-V Measurements
Ideal LF
Ideal HF
Deep Depletion
C
Cox
DC Gate VoltageVTH
CMin
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Dr. G. Eranna Integrated Circuit Fabrication Technology © CEERI Pilani
Gate voltage
Capacitance
Co
Capacitance-Voltage curve for MOSFET and shift in V
Metal
Silicon
Oxide +Na+Na
+Na
++ +
+
+Na + + + +X X X X X
Mobile ionic charge (Q )o
Radiation induced charge (N )ot
Fixed oxide charge (Q )s
Interface traps (N )st
otPhysical origin of N , Q and Ns st
Electrical defects in Si-SiO system2
Co
CoCsAccumulation Depletion
CoCs,min
Inversion
0
+VFB
Ideal
FB
Determination of Fixed Oxide Charge Density
VFB=φ ms- Qf /COX
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Determination of Fast Interface States
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C-V Measurements
• HF curve - inversion layer carriers cannot be generated fast enough to follow the AC signal so C is the resultant of Cox and CD. Thus, it remains at minimum value.
• LF curve - inversion layer carriers can be created and recombine at AC signal frequency so C is just Cox and reached at maximum value.
• Deep depletion - “DC” voltage is applied fast enough that inversion layer carriers cannot follow it, so CD must expand to balance the charge on the gate.
• C-V measurements can be used to extract quantitative values for:
tox - oxide thickness NA or ND - the substrate doping profile
Qf, Qit, Qm, Qot - oxide, interface charges
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Advanced Models
• Some advanced models have been developed that include the effect of other parameters such as: pressure, crystal orientation, mixed ambient, substrate doping etc. on growth kinetics.
• An advanced point defect based model for oxidation has been developed which gives results matching very closely with experimental data.
• The model for 2D SiO2 growth kinetics has also been developed.
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Advanced Point Defect Model
Why?• OED ( Oxidation Enhanced Diffusion)• ORD ( Oxidation Retarded Diffusion)
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SUPREM Modeling for Oxidation Processing
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2D Oxidant Diffusion
• Expected oxide thickness: Convex > Planar > Concave• Experimental Result: Planar> Convex > Concave• 2-D Diffusion can,t explain the thinning effects.• It does play some role
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Stress Due to Volume Expansion
• Oxide layers on Si are under compressive stress -- Volume Expansion -- Difference in TCE• On shaped Si surfaces: Stress can be much larger -- Dimensionally confined
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Simulation Result using ATHENA
Recessed LOCOS Isolation Structure
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Oxidation Simulation Results Using ATHENA
Oxidation simulation showing the effects of including stress effects in oxidation .A 20nm SiO2 pad oxide is first grown and a 150nm Si3N4 layer is then deposited. A 90min 100C H2O oxidation was then performed.
Left: No stress dependent parameterRight: With stress dependent parameter
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Dr. G. Eranna Integrated Circuit Fabrication Technology © CEERI Pilani
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High Temperature Furnace Wafer Loading
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Dr. G. Eranna Integrated Circuit Fabrication Technology © CEERI Pilani
OXIDIZING SPECIES ARE CHARGED OR NEUTRAL IS STILL A SUBJECT OF
CONTROVERSY
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