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