Process Engineering in Microelectronic Fabrication Siddhartha Panda Department of Chemical Engineering IIT Kanpur
Process Engineeringin Microelectronic Fabrication
Siddhartha PandaDepartment of Chemical Engineering
IIT Kanpur
Miniturization
Enhanced capabilities
Electronic chips
Logic
Memory
Drivers Trends
Trends
BS, CHE, 1960PhD, CHE, 1963
Andy Grove
Sequence of unit processes
Enabled by process engineers
Evolution
Developments of the semiconductor industry
Structure developments Process developments
Process EngineeringChip/Circuit/System design
* Process development * Equipment design/fab. * Integration
Unit Processes and role of chemical technology
• Layering film growth vapor depositions (plasma enhanced, chemical, physical etc.)epitaxy
• Patterning( wet and dry) etching – dielectrics, semiconductors (silicon), metalsresist development
•Dopingchemical, ion implantation
•HeatingHot plates, IR
•Planarizationchemical and mechanical polishing (slurry)
Mass, momentum, energy, species balanceElectromagnetic field (Poisson’s eqn)
oxidation kinetics
2 phase flow
polymer processing
diffusion
heat transfer
Not just processesbut also equipment designs
Some unit processes
* Crystal Growth and Wafer Fabrication * Oxidation (thermal)* Dopant Diffusion * Ion Implantation * Rapid Thermal Processing* Chemical Mechanical Planarization * Physical Vapor Deposition* Chemical Vapor Deposition * Lithography * Wet Etching* Plasma Deposition
and Plasma Etching16 Mbit (~1991) 64 Mbit (~1996)
An example DRAM chips
(Courtesy – Siemens)
Non-planar Advent of CMP (early 1990s) enabled*denser packing* more metallization layers
Quartz Tube
Rotating Chuck
Seed Crystal
Growing Crystal(boule)
RF or ResistanceHeating Coils
Molten Silicon(Melt)
Crucible
* How to control the diameter of the boule?
* What is the maximum velocity of pulling the crystal from the melt?
Crystal Growth
Analysis at the melt interface
Heat transfer
Mass transfer
Dopants - segregationCz
Need to formulate a model describing incorporation of dopants into growing crystals
L
So C
Ck =
Concentration profiles
Moving molten zones(boundaries)
bulk gasflow
stagnantgas layer
oxide silicon
Cg
Cs
Co Ci
F1 F2
F3
Oxidation
Mass transportReactions
xCv
xCD
tC
∂∂
−∂∂
=∂∂
2
2
∂∂
∂∂
=∂∂
xCD
xtC eff
+= **
*
V
VV
I
II
eff
CCf
CCfDD
∫∫∫ ∫ +=
+===
0
21
0
0
0
000)()(/ EE en
R
EP EfEf
dESS
dEdxdE
dEdxRP
Dopant diffusion
Drift diffusion
Concentration dependence of D Defect dependence
RTP
Ion stopping distance
Material properties Transport phenomena
substratesource materialheat heat
substrate
Surface chemistry surface reaction direct reaction between incoming species and surface site
Eley-Rideal mechanismreaction between surface species
Langmuir-Hinselwood mechanism
ζ
νν
δδi
RTEE
r
di
rd
ir J
eJ
kkJR
sdr
=
+=
+=
−− /)(
0
01/1 Ed – Er
Physical Vapor Deposition
RTEE
c
s scea /)(
0
0 −=Λνν 2RT
Thermodynamics(statistical mech)
TransportReactions
Parameters –Transport, Kinetic, …. Macroscale Atomic phenomena
Surface diffusion
Chemical Vapor Deposition
Equipment design
Wet etching
PLASMARF heating electron generation
Electron impact with atoms more electrons + ions + fragments
Cascading reactions species generation
2/1
20
=
enkT
e
eD
ελ
Plasma processing – deposition and etching
time
etch stop
(Panda et al., MicroelectronicEngineering, 2004)
Knudsen diffusionSurface reactions
* TransportMomentum, Mass, Energy, Charge
* Reactions
Tunable gas distribution
Dual zone chuck
Specialized gases
Multiple frequency configuration
AMAT – Mariana
Etch - Sub 70 nm Si trenches
Advances in equipment design
AMAT
RTP
Heat transferFilamant design/configuration
Uniform heat flux
Thoughts
• Process engineering
• PE in Microelectronic fabrication -- India perspective
* Demand for electronic goods* Domestic manufacturing* Need for trained manpower