Pds 67 Eight

An Introduction of Etch ProcessAn Introduction of Etch ProcessAn Introduction of Etch Process

Gumi Process Team3Gumi Process Team3

Kang, Ho YoungKang, Ho Young

IntroductionContentsContents

Basic of Etch ProcessBasic of Etch Process

Inside the Plasma Inside the Plasma

Plasma Etch Equipment Plasma Etch Equipment

Etch Process Roadmap Etch Process Roadmap

Terminology in Etching Terminology in Etching

2SQRA - 021125 - 2 -- - 22 - -Hynix SemiconductorHynix Semiconductor


Pattern Transfer Method 1Pattern Transfer Method 1


Film Deposition

Photo Etching

PR Ashing & clean

Subtractive

Lithography


Pattern Transfer Method 2Pattern Transfer Method 2


Substrate

PR Masking Film Deposition

PR Ashing & clean

Additive


Directionality of Etching ProcessDirectionality of Etching Process


Isotropic Etch Directional Etch Vertical Etch

AnisotropicEtch


Two Kinds of Etching MethodTwo Kinds of Etching Method

Wet Etching - by Wet chemical solution - Isotropic etching

Dry Etching - by Plasma - Anisotropic etching

Vertical E/R Horizontal E/RPure Chemical Reaction

High SelectivityCD Loss or Gain

Vertical E/R >> Horizontal E/RIon assisted

Relatively low SelectivityNo CD bias



Wet ProcessWet ProcessAdvantage- Low Cost- Reliability- High Throughput- Excellent Selectivity

Disadvantage- Very hard to control Critical feature Dimension- Difficult to control the degree of overetching due to undercut- Decrease in Etch rate as Reagent solutions are consumed- Hazardous and Difficult to handle- Toxic Fume



Applications of Wet ProcessApplications of Wet Process

- Wet Cleaning for Polymer & PR removal- Pre-cleaning before Deposition & Oxidation

Wet EtchingWet Etching

CleaningCleaning


- Silicon Oxide EtchSiO2 + 6HF H2SiF6 + 2H2OHF : Etchant, NH4F : Buffering Agent

- Poly-Si EtchSi + HNO3 + 6HF H2SiF6 + HNO2 + H2 + H2OHNO3 : Oxidant, HF : Etchant, CH3COOH : Buffering Agent

- Al EtchHNO3 : Oxidant, H3PO4 : Etchant

- Silicon Nitiride EtchHot (>150C) H3PO4 : Etchant


Wet Cleaning ProcessWet Cleaning Process

PreventRe-adsorption

Particles:

Cleaning solution should take electrons awayfrom adhering metals and d isso lve t he minto solution as positive ions.

Cleaning using high redox potential valueto decompose them to sm al ler molec ulessuch as CO2, H2O and etc.

Organic impurities:

SC-1 (NH4OH/H2O2/H2O = 1/4/20 at 80 C) cleaning

. Si + 2H2O2 = SiO2 + H2O (on Si surface)

. SiO2 + 2NH4OH = ( NH4)2 SiO3 + H2O

. Alkaline solutions like SC-1 or

. Surfactant containing acidic solutions

Prevent re-adhesionSame polarity of zeta potential between particle and substrate

Lift-offSlight etch orMegasonic vibration

Lift off

SC-2 (HCl/H2O2/H2O= 1/1/6 at 85 C) cleaning

M0 (metallic state) in UPW M0 ---> M+ + e- (ionic state in SC-2)

cf: CLN_B, CLN_R, HF/H2O2, HNO3, HNO3/HF, O3-UPW and etc

Metals:

SPM (H2SO4/H2O2 = 3/1 ~ 4/1 at 90 C ~ 130 C ) cleaning

H2SO4 + H2O2 = H2SO5 + H2O

H2SO5 + Carbon compound = CO2 + H2SO4 + H2Ocf: O3-UPW and etc



Particle Removal MechanismParticle Removal Mechanism


Lift off . Slight Etch ( Substrate and/or Particle) or/and . Megasonic Irradiation

Prevent re-adhesion. Same Polarity of Zeta Potential between Particle and Substrate

Prevent re-adhesion

Lift off

1cm 1mm 100m 10m 1m 100nm 10nm

PollenMoldTick

Bacteria Virus

1nm

Smoke (Cigarette)Carbon Mist (Exhaust)

Dry Milk

Dust

Raindrop Mist

Flying Ash

Hair


Prevention of Particle Re-depositionPrevention of Particle Re-deposition


Same polarity of zeta potential between particles and substrate

Zeta potential value vs. pHvalue

In acidic solution containingsurfactant

+

Hydrophobic

+ ++

Hydrophilic++

Hydrophobic

++ ++++

Hydrophilic

Hydrophobic________

__ ++ __

___ __

__

_

_Anion surfactant : + H+Hydrophobic

_Anion surfactant : + H+Hydrophobic

in low pH value:

M-OH + H+ + OH-

M-OH2+ + OH-

in high pH value

M-OH + H+ + OH-

M-O- + H2O + OH-

Ref: T. Kezuka, SWPCC, p.337,1999

Ref: M. Itano, IEEE, (5)p.114,1992

2 4 6 8 10 12-80

-60

-40

-20

0

20

40

60

80

pH

Zeta

Pote

ntial (m

V) Si SiO

2PSL Si

3N

4 a-Al 2O3

Si

SiO2

PSL

Si3N4

a-Al2O3

In case of silicon oxide surface

In case of silicon surface

0 1 10 100- 150

- 100

- 50

0

50

Si

SiO2

Si3 N4

PSL

Al2 O3

No surfactant

Anionic surfactant in 0.5% HF (ppm)

Zeta

pot

entia

l val

ue (m

V)

partic

les

partic

les

= x X me

o r

Electrostatic Double - Layer Interactions

Diffusion Layer

0 : Surface Potential : Stern Potential : Zeta Potential (mV)

++

++

++

++

++

++

++

Distance

Elec

tric

Pot

entia

l

Stern LayerSurface

Slipping Plane(Shear plane)

0



Dry Method of Wet ProcessDry Method of Wet Process

N2 + IPA Mixture1) Diffusion of IPA into Wafer Surface - Formation of IPA Layer at Wafer surface

2) IPA Concentration ; A > B - Meniscus Geometry

3) IPA Decreases Surface Tension

4) Surface Tension ; A < B5) Liquid Flow from A to B

- Marangoni force

6) Withdraw wafer out of water

Wafer

Water

AB

Marangoni Force

Marangoni Dry


Some kinds of ContaminantSome kinds of Contaminant

Contaminant ParticleInorganic material

Native oxide

Adsorbed molecule

AnionCation metal

Organicmaterial

Si surface



SolutionsSolutions for Removing Polymerfor Removing Polymer


Low Temp. 23~35

Middle Temp. 50~75High Temp. 70~90

High Temp. 70~90

Semi-Aqueous Fluoride-Based Chemistry

Semi-AqueousAmine-Based Chemistry

AqueousAmine-Based Chemistry

NE-14/28/87/89

EKC-640/650

EG/HF, ST-200

ACT-935

EKC-265/800/830

PRX-170/180

1. Polymer dissolution

2. Polymer lift-off by under-layer slight etch


Some aftereffects of Wet CleaningSome aftereffects of Wet Cleaning


Dependence of Al2O3 growth on surfaces

0

5

10

15

20

25

30

35

40

45

50

0 20 40 50

number of cycles

SPM clean HF last HF vapor

arbi

trar

y un

its (t

hick

ness

)

Deposition time (min)

HF only on c-Si

HF -> SC-1Deposition at 650

70

60

50

40

30

20

10

00 5 10 15 20 25 30 35 40

Nitr

ide

Film

Thi

ckne

ss (

)

4.3 min

4.1

on c-Si surface

Incubation time with surface termination

Ref: IMEC Bi-weekly report


Plasma Etching Plasma Etching A + B A + B C C

ee

AA

BB

CC

Vacuum Vacuum PumpPump

Atmosphere

Highly Selective EtchHighly Selective Etch - PEC Test for New Gas Chemistries

ESH: PFC emission reductionESH: PFC emission reduction - PFC Alternative Gas Evaluation - Abatement Test

Plasma DiagnosticsPlasma Diagnostics - Electrostatic probe - Mass Spectrometer - Optical emission Spec.

AbatementAbatementor Recycleor Recycle

Definition of Plasma EtchingDefinition of Plasma Etching


Low Damage EtchLow Damage Etch - Pulsed Plasma Etch & New Source Evaluation - Damage Characterization

ChillerChiller& Heater& Heater



Generation of Etchant Species(Discharge)

e + Cl2 2Cl + e

SiClx(ads) SiClx(gas)

SiO2

Cl / Cl2 Sisurf - nCl

Adsorption Desorption(Pumping Out)

Si - nCl SiClx(ads) Reaction

Plasma(ex. Cl2 Poly Etch)

Sequential Steps in Plasma EtchingSequential Steps in Plasma Etching


Classification of Plasma Etching ProcessClassification of Plasma Etching Process(Refer to the Etching Materials)(Refer to the Etching Materials)


Silicon Etching(Si, Doped Poly..) - Process : ISO, WL, BL, Capacitor (SN, CP), Poly E/B etc - Chemistry : Cl2, HBr, NF3, CF4, SF6, etc

Metal Etching(Al,W,Ti,TiN,Pt, ) - Process : WL, BL, Cap, MLM: Al, W, Pt, Ru, Ta, etc - Chemistry : Cl2, BCl3, CCl4, etc

Dielectric (SiO2, Si3N4, Low-k Oxide,PSG, ) Etching - Process : ISO, Contact (Poly C/T, Metal C/T, Via), Spacer Planar Etch Back, Pad & Repair - Chemistry : fluoro-compounds(CF4, CHF4, C4F8, .etc)


Basic Method of Plasma EtchingBasic Method of Plasma Etching

1.Chemical Etching


2.Sputtering Etching

3.Energetic Ion Enhanced Etching

4.Protective Ion Enhanced Etching



1.Chemical

Neutral Radical Volatile by-Product

Chemical Reaction

Thermalized neutral radicals chemically combine withsubstrate material forming volatile products

- Isotropic- Purely Chemical Reaction- High Pressure- Batch Wafer Type- Less Electrical Damage




2.Sputtering

IonSputtered Atom (Molecule)

Physical bombardment

The ion energy mechanically ejects substrate material

- Anisotropic- by Purely Physical Process- High Directionality- Low Pressure : long mean free path- Single Wafer Type- Low Etch rate




3.Energetic Ion EnhancedIon bombardment enhances or promotes the reactionbetween an active species and the substrate material

- Damage Enhanced Chemical Reactivity- Chemical Sputtering- Chemically Enhanced Physical Sputtering- Removal of Polymer as a By-product- Ion Reaction

Neutral RadicalVolatile by-Product

Chemical Reaction

Ion



Example of Ion Enhanced EtchingExample of Ion Enhanced Etching

Ar/ XeF2 Chemistry



4.Protective Ion EnhancedAn inhibitor film coats the surface forming a protective barrier

which excludes the neutral etchant

- Sidewall Passivation- Stopping lateral attack by neutral radical- Ion directionality- Involatile polymer film- Additive film former (N2 , HBr, BCl3, CH3F ..)

SidewallPassivation

Film

Remove Involatile polymer film

Ion




Examples of Protective EtchingExamples of Protective Etching

SF6/ CFCl3 ChemistryHCl/O2/BCl3 Chemistry



Etching Gas & By-ProductsEtching Gas & By-Products



Difficult Etching Materials in PlasmaDifficult Etching Materials in Plasma

Fe, Ni, Co Halides are not volatile, Carbonyls do not form readily

Cu Chloride is volatile above 200

Al2O3 Volatile products can be formed but the reaction is uphill thermodynamically(2Al2O3 + 12Cl => 2Al2Cl6 + 3O2)

Alkali Metals and Alkaline Earths (Groups I and II) tend to form involatile Halides LiNbO3, Pyrex (contains Na)



Partially ionized gas containing about equal concentrations of positive and negative particles and chemically activated radicalsDegree of ionization (fi) = No. of charged ions / original atoms and/or molecules Normally, fi = 10-2 ~ 10-5

Processing plasmas are described by the term Glow Discharge Electrically neutral density of electrons + negative ions = density of positive ions

+

-

+

+

+

+

+

+

+

+

++

-

-

-

--

--

-

--

m = 6.6 x 10-23 gT = 20 = 293K 1/40eVc = 4.0 x 104 cm/sec

mi = 6.6 x 10-23 gTi = 500K 0.04eVci = 5.2 x 104 cm/sec

me = 9.1 x 10-28 gTe = 23000K 2eVce = 9.5 x 107 cm/sec

Neutrals

Ions

Electrons

Typical parameter values for a glow discharge plasma

What is Plasma ?What is Plasma ?Neutral ParticlesNegative Ions

Negative Electrons

Positive Ions

-+

-

Inside the PlasmaInside the Plasma


A Variety of PlasmasA Variety of Plasmas

10 -2 10 2 10 410 0

10 18

10 14

10 10

10 6

10 2

10 -210 6

10 22

Ele

ctro

n D

ensi

ty (c

m-3

)

Electron Temperature (eV)

InterstellarSpace

Ionosphere

Flames

Solid State

High PressrueArcs

Low PressrueArcs

ProcessPlasmas

High DensityGlow Discharges

SolarCorona

ProposedThermonuclear

Fusion



Electron Reactions in PlasmaElectron Reactions in Plasma


Positive IonizationA + e A+ + 2e

DissociationM + e 2A* + e

Recombination

PhotoemissionhvA

A

A

A

ExcitationA + e A* + e

Electron ReactionElectron Reaction

e + A A+ + 2e Ionizatione + A A* + e e + A + hn Excitation & Relaxatione + A* 2e + A+ Penning ionizatione + AB e + A + B Dissociation (Radicals)Dissociation (Radicals)e + AB 2e + A+ + B Dissociative ionizatione + AB A- + B Dissociative attachment


Ignition of PlasmasIgnition of Plasmas

Ve-

e-

e-Ar Ar+

e-

d

Paschen curve (plasma turn on voltage)

V

VB

Pd (Torr cm)

Ar

H2

Ignition of plasma

Acceleration of e-

by E-field

Ionization

(ion and e-)

Acceleration of ion

to the electrode

Production of

secondary e-


Ignition Condition Sufficient Electron Energy + Sufficient Collisions - Electron Energy depends on E-Field(Applied Voltage)

- Collision depends on Pressure and Electrode Gap


Sustaining of PlasmasSustaining of Plasmas

E field

Powersupply

e-

Limited area(sheath,skin depth,ECR layer)

collisions

Bulkplasma

diffuse out

Sheath

ionization dissociation excitationelastic collision recombination

Collisional energy loss

ions and electrons to the wall

Diffusional energy loss

Capacitively coupled plasma Inductively coupled plasma Wave heated plasma

Energy absorbed by e- = +

Charges created in the plasma = charges lost to the wall + charges lost by recombination



Classification of PlasmasClassification of Plasmas CCP (Capacitively Coupled Plasma)

powered electrode is directly coupled to the plasmahigh electic field is formed near the powered electrodepower transfer efficiency is relatively low but very uniform plasma can be generatede.g.) DC, RF(13.56MHz), VHF(>30MHz), UHF(~100MHz), MF(~100KHz)

ICP (Inductively Coupled Plasma)power is transferred to the plasma by the induction, like transformerno electrode exists inside the plasmapower transfer efficiency is highsubstrate bias can be controlled independently

WHP(Wave Heated Plasmas)power is transferred from the propagating EM wavepower transfer efficiency is very highe.g.) Microwave plasma, ECR (microwave + B-Field), Helicon and helical plasma(RF + B-Field),

Surface Wave (10MHz ~ 10GHz)

- by the energy transfer mechanism



Principles of DC PlasmaPrinciples of DC Plasma


Plasma : conducting gas constant potential Plasma potential (Vp) : maximum potential Sheath formation : both on anode and on cathode Anode sheath voltage drop = Vp Cathode sheath voltage drop = Vp + Vsupplied Typical Values in a Glow Discharge - Ionization : ~1018 electron-ion pairs per second - Degree of Ionization : 10-3~10-5

- Relative Concentration of Radicals : 10-1~10-3

- Current Density : the order of 1mA/cm2

Ionization collision between an Argon and anelectron in DC glow dischargeIonization collision between an Argon and anelectron in DC glow discharge

+

+e-

e-

e-

e-

+Are-

e-

e-

e-

Cathode(Electrode)

Anode(Chamber Wall)

High Energy Secondary Electron

X (Distance)

AnodeDark Space

CathodeDark Space

Vp

V

-Vc

Vc

e-

Plasma

Radical : an atom or collection of atoms with incomplete chemical bonding (electrically neutral)

eg) F, Cl, O, H, OH, CF, CF2, etc.

~10%


Generation of DC Self-bias VoltageGeneration of DC Self-bias Voltage

Blocking Capacitor

RF Power

Bottom ElectrodeWafer

va

vb



Directional Etching by DC Self-biasDirectional Etching by DC Self-bias

E field is formedby DC Self-bias


DarkSpaceSheath

E


Etch rate, profile, selectivity

Machine Type, Etch Scheme

Etcher / Plasmas

Wafer

Ar + CF4 + e

CFx+ ions

e- electrons

CxFy radicals

CF4, Ar molecules

Kinetic energy(IED)Density (ni)Angular distribution (IAD)

Energy(EEDF), density (ne)

Density

Density(residence time)

Resistance, Leakage, Cap, etc.

Powers, Gas, Pressure, Temp., etc.

Needs for Plasma DiagnosticsNeeds for Plasma DiagnosticsInside the PlasmaInside the Plasma


Coolant

He

Langmuir Probe

13.56 MHz RF

Pump

13.56 MHz RF

TMP

Mass filter

Electrostatic energy analyzer

9 Process gases (PG)Ar

OES

Mass spectrometer

Interferrometer

Optical EmissionSpectrometer

Langmuir Probe

Inte

nsity

(arb

. uni

ts)

0 2 4 6 8 10 12 14 16 18 20 22 24 260

20

40

60

80

100

120

140

6 mTorr

5 mTorr

3.5 mTorr

8 mTorr

10 20 30 40 50 60 70 80 90103

104

105

Inte

nsity

(cou

nt/s

)

Mass (m/e)

CF3+

CF3H+CF2+

CF+

C+

O+CFH+

Ar+CFO+

CF2O+CF3O+

CO+

Ion energy = 11 eV9.1% Ar gas ratio

200 250 300 350 400 450 500 550 600 650 700 750 8000

100200300400500600700800900

100011001200

H 48

6.1

nm

H 65

6.3

nmBr

635

.7 n

mBr

614

.9 n

mBr 4

47.7

nm

Br 4

44.7

nm

Si 2

43.5

nm

Ar 7

72.4

nm

Ar 7

63.5

nm

Ar 7

50.5

nm

F 73

8.7

nm

Ar 7

06.7

nm

F 69

6.5

nmAr 4

15.8

nm Ar 4

20.7

nm

Si 2

88.2

nm

Si 2

52.8

nm

HBr/Ar

Inte

nsity

(a.u

)

Wavelength (nm)

Plasma Diagnostics ToolsPlasma Diagnostics Tools



Trend of Plasma Etch EquipmentTrend of Plasma Etch Equipment

Wet EtchingBipolar Tech.Wet Etching

Bipolar Tech.

Anisotropy

Plasma EtchingMOS Tech.

Plasma EtchingMOS Tech.

Parallel Plate Plasma Etching64kb 256kb DRAM

Parallel Plate Plasma Etching64kb 256kb DRAM

Reactive Ion Etching1Mb,4Mb DRAM

Reactive Ion Etching1Mb,4Mb DRAM

Magnetically Enhanced RIE16Mb, 64Mb DRAM

Magnetically Enhanced RIE16Mb, 64Mb DRAM

ECR, Helical, TCP,DPS, Helicon, HRe-

> 128Mb DRAM

ECR, Helical, TCP,DPS, Helicon, HRe-

> 128Mb DRAM

Plasma Potential DC Self-bias

Plasma Density

Plasma Etch EquipmentPlasma Etch Equipment

High Density Plasma 10E11/cm3


Trend of Etching Tools DevelopmentTrend of Etching Tools Development

Wet Etching

High Density Plasma(Low Pressure)

Pulsed Plasma

Neutral Beam Etch (Hyper-Thermal)

Neutral Beam Etch (CT)

Low & Medium Density Plasma (High Pressure)

NBE (CT)

NBE (HT)

Pla

sm

a d

ensity

Electron temperature



Dry Etching Equipment of Major MakerDry Etching Equipment of Major MakerDry Etching Equipment of Major Maker


19971995 1998 1999 20001994 199619901988 1991 1992 19931987 1989

Hitachi ECR M206 / M216 / M300 / M500 / M600Hitachi ECR M206 / M216 / M300 / M500 / M600

Centura DPS / IPS / Super-eAME8000 / P5000 MxP Series AMAT

Excel / Excelan / Excelan HPLRC

Hitachi

Sumitomo ECR OZ Series SWPSumitomo

IEM / Advance IEMDRM

TEL

LAM PlasmaEtcher

Anelva / DryTek / PMT(Trikon) / Tegal HRe- / Ulvac / etc

0.130.15

Rainbow RIE SeriesRainbow RIE Series

Centura HDP ICP

TCP / PTX9000 SeriesTCP / PTX9000 Series Definium / 2300 Series

0.10

M700M700Advanced ECRAdvanced ECR

2001


Low Density Plasma ReactorsLow Density Plasma Reactors

Barrel Etcher- No Temp Control- Non Uniformity- Undercutting

- Isotropic Etching- Batch Wafer Type - Dielectric Vessel (Quartz, Floating)- PR Ashing

- High Throughput- Inexpensive- Low Electrical Damage (Etch Tunnel - Cyl. Mesh)



Low Density Plasma ReactorsLow Density Plasma Reactors

Plasma Etcher- Plasma Etching Mode in Parallel Plate or Planar Reactor- Wafer placed on the Grounded Electrode- Capacitively Coupled Plasma

- Isotropic by Radical- Plasma Potential (Low Ion Energy)- High Pressure- Single Wafer Type- Less Electrical Damage- Reinberg Reactor



Medium Density Plasma ReactorsMedium Density Plasma Reactors

RIE Etcher- Reactive Ion Etching (RIE) = Plasma Etching + Energetic Ion Bombardment- Reactive Ion Etching (RIE) Reactive Sputter Etching (RSE)- Wafer placed on the RF-driven Electrode- Capacitively Coupled Plasma

- Anisotropic by Ion- DC Self-bias (High Ion Energy)- Middle Pressure- Single Wafer Type- Electrical Damage




MERIE Etcher- Magnetic field is above and Parallel to the cathode surface- Keep the Secondary Electron by Cycloidal Motion in ExB Field- Probability for electron-neutral collisions can be increased- Ionization efficiency in Dark Sheath Region is increased

- B field is rotated electrically- Anisotropic by Ion- Low Pressure- Single Wafer Type- Lower Electrical Damage



Ex)MERIE DRM (Tokyo Electron Lab.)

Medium Pressure Control 10mT

RIE Base

Confined Plasma by Dipole Ring Magnet

- Medium Density Plasma ~ 10 11

Highly Uniform Plasma Density

Lower Etch Damage

Magnet

Top ElectrodeBottomElectrode




- Planar, Cylindrical, Dome Type- Capacitively Initiation & Inductively Breakdown (r) Dim mode, Bright mode- Lenz Law, Faradays Induction Law

ICP (Inductively Coupled Plasma)

High Density Plasma ReactorsHigh Density Plasma Reactors



Ex)TCP : Lam ResearchRF(TCP Power)

Plasma

RF(Bias power)

TCP coil

Chiller

Wafer

Vacuumpump

Low Pressure Control 5mT Independent Power Control - Plasma Source = TCP power - High Density Plasma ~ 10 12

- Ion DC Bias = Bias Power Low Temperature Etching : -50C ~ +50C Improved Plasma Uniformity




Ex)HDP : Applied Materials

Low Pressure Control 5mT

Power Transfer by ICP Coil

- High Density Plasma ~ 10 12

- Ion DC Bias = Bias Power

Polymer Control by Roof-Si

Improved Plasma Uniformity

WaferElectrode

High Density Plasma~1012 /cm3 Ion Density




Cyclotron Resonance = Maximum Electron EnergyAngular Frequency in B field (875G) = Microwave Frequency (2.45GHz)

ECR (Electron Cyclotron Resonance)




- Helicon Wave : Power Transfer >1000 than Collision Process- Landau Damping : Collisionless Mechanism

Helicon (M0RI)




Ex)M RI Helicon (Trikon)

Wafer

RF BiasBackside Helium

Coolant

Gas Inlet Hole 4 Places

Coil

MagneticBucket

Quartz Belljar RF Source

Low Pressure Control 3mT

Independent Power Control

- Plasma Source = MRI Coil

- High Density Plasma ~ 10 12~13

Low Temperature Etching

: -50C ~ +50C

Highly Uniform Plasma Density

Lower Etch Damage




Trends of HDP Reactors- Low Temperature Process : Low Activity of Radical Anisotropic, Less Polymer Clean Process

- Low Pressure Process : Long Mean Free Path, Fine Patterning

- In-situ Process : Single Wafer : Multi-chamber

- High Density Plasma : High Etch Rate


Introduction Basic of Etch ProcessesBasic of Etch Processes

Inside the Plasma

Plasma Etch Equipment

Etch Process Roadmap

Terminology in EtchingTerminology in Etching

ContentsContents



1.1.Etch RateEtch Rate

- Etched Thickness per Unit time- nm/min, /min, /sec

Etch Rate - RF Power Source Power Bias Power - Gas Flow Rate - Pressure- B Field (Gauss)- Electrode Temp - Pattern Density

Etch Time = t

txRE =)/(Etch Rate

x



2.2.Etching SelectivityEtching Selectivity

- The Ratio of the Etch Rates of two Materials etched Simultaneously such as etched Layer and PR mask

BAS /B

ABA E

ES =/ AE

BE

In same Plasma Condition = Etch Rate of Layer A = Etch Rate of Layer B : Selectivity of A to B

- Selectivity to PR mask and Under-layer is needed in the most of Etch Process for the Over Etch- by Gas Chemistry Control



3.3.Etching UniformityEtching Uniformity

- or Non-uniformity- Point to Point Within a Wafer, Wafer to Wafer, Lot to Lot

100/2

][%)( minmax

-=

NEEEUniformityi

Ei : Etch Rate at Several PointsEmax : Maximum Etch RateEmin : Minimum Etch Rate

- Chamber Configuration : Pumping Position, Gas Inlet Position- B-field, Etch Mode, Power, Pressure ..



4.4.EPD(End Point Detection)EPD(End Point Detection)

-Pressure Change-Impedence Change-Mass Spectrometry-Optical Emission Spectroscopy-Laser Interferometry & Reflectance

- Etchant Signal, by-product Signal, Underlying by-product- End-point, Just Etching & Over Etching



EPD Signal Sample (Lam Research TCP9460)


Back He Pressure

Chamber Pressure

EPD Channel A

EPD Channel B

( = 405 )

( = 550 )

Example of Optical Emission Spectroscopy


5.5.Loading Effect 1Loading Effect 1

1.Macro-Loading- In the Constant supply of Reactants, Etch rate goes down with increase the Surface Area

The Difference of EtchantConcentration per Unit Area

Sufficient supply of Ethant- High Pressure- High Source Power- Low Bias Power (Slope)



5.5.Loading EffectLoading Effect

2.m-Loading (and Reverse m-Loading)

- Sputtered materials and redeposition (Polymer) slow down Etch rate at Tight Spaces

The Difference of Pump out Rate

Shorter Residence Time- Low Pressure- High Total Flow Rate



Some Example of Some Example of mm--LoadingLoading

0.2um 0.3um 0.6um Open Area

6mT

3mT

9mT

Bottom Rounding: 20mT



2. Ion reflection from sidewall

Oxide

Photoresist

++

sheath+ +

+

Parameters: Ion angular distribution & sidewall slope, etc.

reflectionprobability

direct ion flux

reflected ion flux

1. Mask charging by electrons

----

---

----

---

+ + +

+ e-sheath

Parameters: sheath potential, electron density, negative ion density, etc

6. 6. mm - -TrenchTrench



Some Examples of Some Examples of m-Trench-Trench

0.25 um 0.30 um 0.40 um 0.50 um Open area (>300 um)

85.5 86.5 87.0 87.5 86.0

8 mTorr 10 mTorr4 mTorr 100 W0 W

Pressure Dependency Bias Power Dependency

Pattern Dependency



7.7.Abnormal Plasma EtchingAbnormal Plasma Etching


These Defects are caused by Insufficient Etching Target(depends on Topology)Abnormal EOP, Non-Uniform Pattern Layout and Plasma Unstable(ChamberPara.:Power,Pressure,Gas Flow..) etc.

UnderEtch

Residue, Stringer Over Etch



9.9.ESC(ElectroStatic Chuck)ESC(ElectroStatic Chuck)

Plasma

Ion Sheath

Wafer

Insulator

Electrode

Vdc

Applied V

Vpp

It is impossible to be operated vacuum chuck at vacuum chamber. So the mechanicalchuck(Clamp) is adopted, but there were many disadvantages. On the contrary, ESCproposed by Wardly in 1973 has several advantages. In recent semiconductorindustry, ESC is the general clamping system of vacuum chamber.



10. 10. After Treatment in EtchingAfter Treatment in Etching

Light Etch - Si surface Damage removal. - After treatment of Contact, LDD, etc - Chemical Downstream Etch

Al Passivation - Prevent the corrosion of pure Al - O3 Plasma Treatment cf) Al2O3 Formation

IMD adhesion Treatment - Prevent the IMD Peel-Off cf)O2 Plasma Treatment after SOG E/B

Documents

Pds 67 Eight