Download Chemical Unit Operations

Chemical Engineering Tools for
Semiconductor Fabrication
David Cohen, PhD
AIChE Norcal Symposium
April 12, 2005
1
Integrated Circuit
Courtesy of Integrated Circuit Engineering (ICE)
Novellus Confidential
DGC-4/05 2
Moore’s Law
Number of Transistors per Integrated Circuit
Courtesy of Intel
Novellus Confidential
DGC-4/05 3
Feature Size Evolution
Novellus Confidential
DGC-4/05 4
Chemical Unit Operations
METALS
DIELECTRICS
PASSIVATION
INTERCONNECT
VECTOR
INOVA xT
SEQUEL
SABRE xT
IMD
VIA
ILD/PMD
CONTACT
SPEED
BARRIER/ARL
ALTUS
STI
FEATURE SIZE
Novellus Confidential
DGC-4/05 5
Example of Chemical Process - Electroplating
Electrofill
Cu+2(aq) + 2e- = Cu0 (solid)
Cathode (Wafer)
CuSO4 Electrolyte
Cu Anode
Cu0 (solid) = Cu+2(aq) + 2e-
Novellus Sabre
Novellus Confidential
DGC-4/05 6
Example of Chemical Process - CVD
RF
Power
PECVD
Shower Head
SiH4, NH3 and N2
RF Plasma
SiN
Heater Block
Optional RF Bias
Novellus Vector
Novellus Confidential
DGC-4/05 7
Plasmas Today
Plasmas have played vital role in:
 Physical Vapor Deposition
PECVD
 Plasma Enhanced Chemical
Vapor Deposition (right)
 Etching
 Cleaning
 Passivation
 Plasma sources of UV
radiation for lithography
Novellus Confidential
DGC-4/05 8
Future Limitations of Plasmas
 Extreme selectivity required for
advanced applications.
• Need to produce desired plasma chemical
reactions and prevent undesirable ones.
• The ability to tailor the energy distributions
of plasma particles is key to this selectivity.
 As feature sizes get smaller, plasma
energy requirements get larger.
 Need to enhance models to fully couple
reactor scale to feature scale.
Novellus Confidential
DGC-4/05 9
Atomic Layer Deposition
 Surface controlled, layer by layer deposition
method
ALD Group, Univ of Colorado
Novellus Confidential
DGC-4/05 10
Quantum Chemistry Modeling
 Predict surface reactions to understand ALD
 Challenge coupling reactor scale flow behavior with surface
chemistry
 Ability to model is limited by computational power because of
extreme complexity of film growth chemistry
Collin Mui, Novellus Systems
Novellus Confidential
DGC-4/05 11
Moving to Low-k
 As features become
smaller, reduced
capacitance is necessary
to increase IC clock
speed
 Reduction in dielectric
constant (k)
 SiO2 is primary insulator –
k=4.0
 Need to get down to k<2.0
Material
Dielectric Deposition
Constant Method
FSG (Fluorinated Silicate Glass)
Polyimides
DLC (Diamond-Like Carbon)
SOG (Spin-On Glass)
3.4-3.8
3.0-3.5
2.8-3.0
2.7-3.1
CVD
Spin-on
CVD
Spin-on
Siloxanes
Poly(arylene ethers)
Fluorinated Polyimides
C-doped Oxide
2.7-2.9
2.6-2.9
2.5-3.3
2.5-2.9
Spin-on
Spin-on
Spin-on
CVD
PTFE
Nanoporous Silica
Nanoporous Organic
? 2.0
? 2.0
? 2.0
Spin-on
Spin-on
Spin-on
Mesoporous Silica
Silica Xerogels
Silica Aerogels
1.9-2.2
1.5-2.2
1.1-2.2
Supercritical CO2
Spin-on
Spin-on
Air Gap
1.0
TBD
Novellus Confidential
DGC-4/05 12
Challenges of Low-k
Porosity increases with decreasing dielectric constant
(k)
9
 Mechanical Strength
(CMP, bonding, packaging)
 Pore Size
• killer pore (< 10% CD)
• need for CVD barrier
• CVD barrier increases
effective k
Dielectric Constant
 Thermal Conductivity
8
SiO2
7
SiN
6
5
4
3
2
1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Porosity
Novellus Confidential
DGC-4/05 13
Chemical Mechanical Planarization
 Removes surface textures and allows multiple
interconnect layers to be used
 Removes excess material
Novellus Xceda
Courtesy of Alpsitec
Novellus Confidential
DGC-4/05 14
CMP Challenges
 Pressure of CMP Pad results in dishing of soft
materials or damage of low-k films
 Need to provide better polishing control
• Chemistry of CMP slurries will drive more uniform
polish
• Chemical polish can replace mechanical force
 Uniformity prediction relies on development of
model that takes into account pad motion, fluidstructure interaction, and removal rate
Novellus Confidential
DGC-4/05 15
Electroplating Modeling
 Need to include:
•
•
•
•
•
turbulent/rotating flow
mass transfer
electrical current flow
terminal effect (electrical current flow in the seed layer)
Chemistry – not well understood
Novellus Confidential
DGC-4/05 16
Use of Electroplating Models
Larry Gochberg, Novellus Systems
 Model can be used to test various additive
chemistries for Cu electroplating
Novellus Confidential
DGC-4/05 17
Effluent Management
 On-site abatement necessary to minimize
environmental impact of IC manufacturing
 Gas phase emissions
• Hazardous Air Pollutants (HAPs)
• Volatile Organic Compounds (VOCs)
• Ozone Depleting Substances (ODSs)
• Perfluorinated Compounds (PFCs)
 Liquid phase emissions
• Suspended solids
• Phosphates, Nitrates
• Organics
• Transition Metals
• pH, Temperature, etc.
Novellus Confidential
DGC-4/05 18
Summary
 There are a number of chemical unit operations
involved in IC manufacture.
 Feature size has evolved to below 100 nm.
 New technologies will be required to keep
reducing IC feature size.
 Modeling enhancements are needed to better
understand plasma, electroplating, CMP, ALD.
 Advances in semiconductor manufacture need to
include emission control and energy reduction.
Novellus Confidential
DGC-4/05 19