NSF Center for Micro and Nanoscale Contamination Control · Measurement of particle adhesion force ... Bare silicon Si-Cap Bare silicon Si-Cap DI-Water DI-Water Dilute SC1 Dilute

NSF Center for Microcontamination Control (NEU, UA)NSF Center for Microcontamination Control (NEU, UA)

NSF Center for Micro and Nanoscale NSF Center for Micro and Nanoscale Contamination ControlContamination Control

Research Focus at the NSF Center for Nano and Microcontamination

ControlAhmed Busnaina

W. L. Smith Professor and DirectorNSF Center for Microcontamination Control,

Northeastern University, Boston, MA 02115-5000Tel: 617 373-2992, Fax: 617 373-2921

Email: [email protected], URL: WWW.CMC.NEU.EDU


Northeastern University

Enrollments (2001-02) 22,599 studentsUndergraduate enrollment: 18,949Graduate enrollment: 3,650Faculty: 1105


Goals and Objectives

Our goal is to provide solutions and state of the art techniques for micro and nanoscale contaminants characterization, control and removal in manufacturing and fabrication processes.


Fundamentals of surface cleaning and preparation.Understanding of physical and chemical cleaning

mechanisms using megasonics, brush and other techniques including damage evaluation and mitigation.

CMP and Post-CMP applications.Cleaning of EUV reticlesMeasurement of particle adhesion forceRemoval of Nanoparticles Laser Shock CleaningHigh Concentration Ozone cleaningSuper Critical CO2 CleaningParticle generation, transport and deposition.Particulate Contamination in low pressure processes (LPCVD, Sputtering, ion implant, etc.)

Contamination during wafer handling.

Research Focus


Research HighlightsMetrology of nanoparticles down to 50 nm

Particle medium has a profound effect on particle deposition and removal

Effective nanoparticle removal down to 28 nmdemonstrated

Effective deep trench cleaning demonstrated

Physical modeling is used to explain the time effect in the cleaning of trenches

Physical modeling is used to show the effect of frequency in the removal of nanoparticles


Membership StatusMemebership from 2003-2006

Seagate, MNEKC Technology (DuPont), CAPCT Systems, CACypress SemiconductorDANanomaterials (Air Products)Ionics pure solutions, Sandia, Climax Engineered MaterialsRidgetop Group Inc.Intel,IBM


The facility includes a 10,000 square foot cleanroom. Our facility includes a complete 6” wafer fabrication facility including bulk micromachining, metal surface micromachining and E-beam lithography. It also include a CMP tool (with end point detection), laser surface scanner, Laser airborne and liquid counter (200 nm resolution), CNC particle counters (10 nm resolution), Zeta potential measurement down to 1 nm particles, several cleaning tools, Atomic Force Microscope in addition to optical and FESEM.

Northeastern’s Kostas Nanomanufacturing Facility

The new George J. Kostas Nanomanufacturing Center at NEU.


10,000 square foot cleanroomFull 6” wafer fabNanolithography System (E-beam, AFM)

capable of making structures down to 20 nmBulk & metal surface micromachining Laser surface scanner (200 nm res.) Laser airborne counter (200 nm res.) TSI CNC particle counters (2 nm res.)PSIA XE150 Atomic Force Microscope Nikkon Fluorscence microscopeKarl Ziess Supra 25 FESEM with EDS Nanoparticle Zeta potential measurementsSurface energy and contact angle

automated measurement Zygo Surface ProfilerCMP tool with end point detectionNanoimprint Lithography

Northeastern’s Kostas Nanomanufacturing Facility


Surface Cleaning Future

65nm poly Si lines

• Nanometer Thin Film

• New Materials

• Nanometer Feature Size

• Single Wafer Cleaning

• CMP Process

• EUVL Process

• Dry Cleaning

Issues

• Clean without Etching

- Non RCA (H2O2 based) Chemistry

• Clean without Pattern Damage

- No Megasonics or Brush clean?

• CMP Induced Defects

• Zero Defect on EUVL Mask

• Cleaning Using SC CO2

• Dry Laser Shock Cleaning

Challenges


1E+3

1E+4

1E+5

1E+6

1 10 100 1000

Microns

PS

I -

Sh

ea

r

Experimental Data

Soda-lime fiber inair (Griffith)

Borosilicate fiber inair (Jerkov)

Bond strength vs. particle diameter ( Experiment data compared with Griffth's tensile strength of glass fiber

and with Jerkov's tensile strength of glass fiber)

Feng, J, Busnaina, A. A., W.P.Ryszytiwskyj, Surface Engineering 2001, Vol.17, No.5.

SEM image of glass chips

Particle Adhesion: Covalent Bonds for glass and Silica Particles

Need to study adhesionvan der Waals and/or

capillary induced deformationCovalent bonds promoted

by moisture

How Does Adhesion Change with Time and Environmental Conditions?

Adhesion Force vs. Aging

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 1 2 3 4 5 6 7

Aging Time(week)

Ad

hes

ion

Fo

rce(

dyn

)

dry 55%RH

wet 55%RH

wet 100%RH

van der Waalsforce(withoutdeformation)

van der Waalsforce(withdeformation)

Covalent bonds for silica particles(Busnaina, NEU, 1994, 2000, 2001)


Particle Contact Area

10-3 10-2 10-1 100 101

Particle Diameter (micron)

0

1

2

3

4

5

Con

tact

rad

ius

/par

ticle

radi

us

PSL particle on SiO2

SiO2 particle on SiO2

a / R = 1

PSL deformation in 95% RHPSL deformation in 40% RHafter 7 daysPSL deformation in 40% RHafter 3 days

1. Krishnan, S., Busnaina, A. A., Rimai, D. S. and DeMejo, L. P., Fundamentals of Adhesion and Interfaces, edited by . Rimai, DeMejo and . Mittal, VSP BV press, The Netherlands, 1995, 2. Krishnan, S., Busnaina, A. A., Rimai, D. S. and DeMejo, D. P., J of Adhesion Science and Technology, vol. 8, No. 11, 1994.3. Feng, J., Busnaina, A., Steel, E. B., and Small, J. A., Proceedings, 24th

Annual Meeting of The Adhesion Society, Williamsburg, VA Feb. 25-28, 2001.


+Electrostatic Force

(Zeta Potential) + Repulsiveor - Attractive

van der Waals Force (Particle’s size )

- Attractive

Total Interaction Force

Total InteractionForce

Electrostatic Force

Van der Waals Force

: Key factorcontrollingdeposition

• In liquid media

Interaction Forces between Wafer and Surface


Removal and Adhesion of Nano Particles

Removal Percentage vs. Moment Ratio Removal Percentage vs. Moment Ratio (Silica Removal Experiment)(Silica Removal Experiment)

The figure shows when RM >1, 80 % of particles are removed.

( )aF

aFR.FRM

momentresistingAdhesion

momentmovalReRM

a

dld

⋅⋅+−=

=

δ3991

U

O1.399R

FAdhesion

Fdrag

δ

a

Rolling removal mechanism

MR

MA

F elec. double layer

Removal Percentage Moment Ratio

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Moment Ratio

Re

mo

val P

erc

en

tag

e


0 5 1 0 1 5 2 0 2 5 3 0In te n s ity ( W /cm 2 )

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

v(cm

/s)

1 M H z8 5 0 k H z7 6 0 k H z3 6 0 k H z

S tre a m in g V e lo c ity v s . A c o u stic P o w e r

Acoustic Streaming

101 102 103 104

Frequency (k Hz)

0

2

4

6

Bo

un

dary

laye

rth

ickn

ess

(mic

ron)

10-3

10-2

10-1

100

101

102

103

Str

eam

ing

Vel

oci

ty(m

/s)

Acoustic, f=360KHzAcoustic, f=760KHzAcoustic, f=850KHzBoundary layer thickness (micron)Streaming Velocity (m/s)

I = 7.75 W/cm2Acoustic Flow Properties

u>0.3c


Silicon Nitride-D.I. Water, Temperature at 38°C

100.0

100.0

94.6

91.6

88.685.582.5

79.576.57 3.470.4

67 .464 .461. 3

Power (%)

Tim

e(S

ec)

30 40 50 60 70 80 90 100

30

40

50

60

70

80

90

100

110

120

efficiency100.094.691.688.685.582.579.576.573.470.467.464.461.358.3

Removal Efficiency For Silicon Nitride Particles Ranging From 0.26 to1.18 um in diameters, Using D.I. Water & Bottom MegasonicTransducer, Temperature at 38°C

Frame 001 ⏐ 20 May 2003 ⏐ .28-1um Si3N4 Removal Power Vs Time @38Frame 001 ⏐ 20 May 2003 ⏐ .28-1um Si3N4 Removal Power Vs Time @38

Complete removal of silicon Nitride particles Complete removal of silicon Nitride particles ((≤≤200nm) Using DI water200nm) Using DI water


2 0 0 30 0 4 0 0 5 0 0 6 0 0P o w e r (W a tts)

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

1 1 0

1 2 0

Tim

e(s

ec)

1 .0 0

1 .0 0

0 .99

0 .9 8

0 .9 8

S in g le M e ga so n ic C le a n in g P ro ce ss, T e m p = 3 5 oCR e m ova l E ffic ie ncy of S ilica P a rtic le s 0 .1≥ µ m

Complete removal of silica or alumina particles down to 100nm by single wafer megasonic cleaning with DI water only.


Visualization of Fluorescent Particles

Nikon G block filter75 W Xenon arc lampHousing for Xenon lampExtra N.D filter

Fluorescent Cube

Xenon Arc lamp

G block fluorescent filter specs. Red Fluorescing particle specs.

5

3

2

14

Particle Inspection Map on Wafer


Images of Fluorescent Particles

Optical MicroscopeBright Field

1K zoom

63 nm Fluorescent ParticlesOptical Microscope

Dark Field1K zoom

63 nm ParticlesFE-SEM

FE-SEM1K zoom


45K

The nano-particle detection has been verified using scanning electron microscopy (SEM). Has proven to be effective for single particle detection down to 50 nm particles.Agglomerated particles can be eliminated from the counting procedure by filtering the count by diameter and aspect ratio values.

Images of Fluorescent Particles


Nanoparticle (63 nm PSL) Removal Using Acoustic Streaming

82.0%

84.0%

86.0%

88.0%

90.0%

92.0%

94.0%

96.0%

98.0%

100.0%

2 3 4 5 6 7 8

Time

rem

ova

l eff

icie

ny

(DI w

ater

)

Bare Silicon wafer+DI water

EUV 4 nm Si_Cap ML wafer+DI water

EUV 11 nm Si_Cap ML wafer+DI water

97%

98%

99%

100%

2 3 4 5 6 7 8

Time

Rem

ova

l eff

icie

ncy

(S

C1)

Bare Silicon wafer+SC1

EUV 4 nm Si_Cap ML wafer+SC1

EUV 11 nm Si_Cap ML wafer+SC1

Dilute SC1 chemistry

DI water

63 nm Before After(Busnaina, NEU, 2004)

PSL 90, 63 and 28 nm nano-particles were removed from bare silicon wafers using the Single wafer megasonic cleaning tank


Nanoparticle (50 nm PSL) Removal Using Acoustic Streaming

1000139837.54.562.52.

1000108237.57871.

Removal Efficiency (%)

AfterBeforeTemperature (OC)

Time (mins)

Power (%)50nm Particle Removal from 11nm Using SC1

97.821938358872.

98.312695357871.

Removal Efficiency (%)

AfterBeforeTemperature (OC)

Time (mins)Power (%)50nm Particle Removal from 11nm Using DI water


Removal Percentage Moment Ratio

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Moment Ratio

Re

mo

val P

erc

en

tag

e

Removal Efficiency of 63nm PSL Particles after 2 minutes

99 98.8

100 99.9

1.2 1.17 1.21

1.37

94

95

96

97

98

99

100

Rem

ova

l Eff

icie

ncy

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

Mo

men

t Rat

io

Experimental Value

Theoretical Value

h

Bare silicon Si-Cap Bare silicon Si-CapDI-Water DI-Water Dilute SC1 Dilute SC1

Nanoparticle RemovalWafers and Masks

Removal efficiency as a Function of Time

98.6

98.8

9999.2

99.4

99.6

99.8100

100.2

0 2 4 6 8

Time (min)

Rem

ova

lef

fici

ency

Bare Silicon / SC1

4 nm Si-Cap / SC1

Bare Silicon / DI-Water

4 nm Si-Cap / DI-water

( )aF

RFMR

momentresistingAdhesion

momentmovalMR

a

D

⋅−=

=

δ74.1

Re


Why does it take time to remove 63 nm particles?

Total time = 0.01 second, Height= 1 cm, width=2 cm


Why does it take time to remove 63 nm particles?


A

10 um

20 um500nm Particles

Experimental & Computational Fluid Dynamics Simulation

A123 456

1 um

2 um63 nm Particles


1

∆t2= 0.63.∆t1

t1= 4.7.t2

10 µ

1

Frequency: 760 KHz

Time Steps: ∆t1

Total Time2896 ∆t1

Total Time976 ∆t2

Frequency: 1.2 MHz

Time Steps: ∆t2

10 µ

Re-deposition

Effect of Frequency on Nanoparticle Removal


0 0.05 0.1 0.15 0.2

Distance Along Wafer Surface (cm) time = 3.9s

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Dis

tan

ceF

rom

Wa

fer

Su

rfac

e(cm

)

Steady Flow

u = 4.3 cm/s

Streamlines and Concentration Contour

0 500 1000 1500 2000

Distance Along Wafer Surface (um) time=1.0s

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

7500

Dis

tanc

eF

rom

Waf

erS

urf

ace(

um)

C-ion #/cm3

1.5E+121.4E+121.2E+121E+128E+116E+114E+112E+111E+111E+101E+091E+081E+071E+06

Steady Rinse Flow:us = 15 cm/s

Geometry:D/W = 5 :1W = 1 mm D = 5 mm

Steady flow induces a vortex inside the cavity. There is no convection between the vortex and the main flow. The transport of contaminant happens by diffusion only, which may take a long time depending on the trench size.

Physical Cleaning Of Submicron Trenches Mixing and Cleaning in Steady and Pulsating Flow

0 0.05 0.1 0.15 0.2

Distance Along Wafer Surface(cm) t/T= 1.50, time= .0579s

0

0.05

0.1

Dis

tanc

eFr

om

Waf

erS

urfa

ce(c

m)

1E+121E+111E+101E+091E+081E+07

OSCILLATING FLOW

f = 25.9 Hzus = 0up = 13.5 cm/suAvg = 4.3 cm/s

W=1mm, D=0.7mm

0 500 1000 1500 2000

Distance Along Wafer Surface (um) time=0.5s

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

7500

Dis

tanc

eF

rom

Waf

erS

urfa

ce(u

m)

C-ion #/cm3

1.5E+121.4E+121.2E+121E+128E+116E+114E+112E+111E+111E+101E+091E+081E+071E+06

Oscillating Rinse Flow:us = 0 cm/sup = 47 cm/suavg = 15 cm/sf = 2000 Hz

Geometry:D/W = 5 :1W = 1 mm D = 5 mm

External oscillating flow stimulates the vortex destruction and regeneration.

Contaminants are dragged out of cavity by the expanded vortex.

The vortex oscillating mechanism significantly enhances the mixing.


Experimental conditions:Time: 1 min, 3 min, 5 min, 8 min and 15 mins.Power: 87 % (max 640 watt.)Temp: 25o DegreeParticle sizes ranging from 0.3 to 0.8 micron are used

The experiments are conducted in a PCT Single Wafer Megasonic Tank (760 kHz). Trenches of 112 micron wide and 508 micron deep are used in the experiments.Particles were imaged before and after cleaning at the wafer surface, 100, 200, 300 micron depths along the sidewalls and at the bottom of the trench.Image pro-plus software is used to count the particles before and after cleaning, Stage Pro is used to zoom into the corresponding locations.

508 µm

112 µm



Trench Cleaning (0.3 micron)

200 micron below surface Bottom of the trench

Beforecleaning


Trench Cleaning (0.3 micron) Megasonics

At the surface of the trench (100 % Removal) 200 micron below surface (100 % Removal)

Bottom of the trench

(50 % Removal)

After cleaning3 minute87 % power25 o C


0%

20%

40%

60%

80%

100%

Eff

icie

ncy

1 2 3 4

Single wafer megasonic cleaning using 300nm PSL particles in DI water at 25 oC

At the surface

100 micron below

200 micron below

Bottom of Trench

Time (minutes)1 min 3 min 5 min 8 min

Particle Removal Experiments

Moment Ratio 300, 800 nm PSL particles

3.5

1.2 1.15 1.18

10.1

3.43 3.29 3.36

0

2

4

6

8

10

12

1 2 3 4

Mo

men

t Rat

io300nm

800nm

At Surface 100mm 200mm Bottom of Trench below below

MR=1


Megasonic Trench Cleaning Summary

100 % removal

100 % removal

90 % removal

100 % removal

50 % removal

80 % removal

30 % removal

50 % removal

Bottom of the trench(0.3 µm)

(0.8 µm)

100 % removal

100 % removal

100 % removal

100 % removal

70 % removal

100 % removal

50 % removal

70 % removal

300 µm below surface(0.3 µm)

(0.8 µm)

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

70 % removal

90 % removal

200 µm below surface(0.3 µm)

(0.8 µm)

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

80 % removal

100 % removal

100 µm below surface(0.3µm)

(0.8 µm)

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

100 % removal

At the Surface (0.3 µm)

(0.8 µm)

8 minutes5 minutes3 minutes1 minutesCleaning for


Particle number chart for Ultrasonic and Megasonic Cleaning for 300 nm Particles

124

138

74

76

84

79

234

268

Before cleaning

0

42

0

63

13

97

61

110

87

124

Bottom of the trench(megasonic)

(Ultrasonic)

0

0

0

24

0

31

0

37

58

54

200 µm below surface(megasonic)

(Ultrasonic)

0

0

0

15

0

22

0

30

65

47


(Ultrasonic)

0

0

0

2

0

52

0

81

1

132

At the surface(megasonic)

(Ultrasonic)

15 minute8 minute5 minute3 minute1 minuteCleaning for


Comparison of Ultrasonic and Megasonic Cleaning for 300 nm Particles

100 % Removal

70 % Removal

100 % Removal

50 % Removal

90 % Removal

30 % Removal

50 % Removal

20 % Removal

30 % Removal

10 % Removal

Bottom of the trench(megasonic)

(Ultrasonic)

100 % Removal

100 % Removal

100 % Removal

70 % Removal

100 % Removal

60 % Removal

100 % Removal

50 % Removal

80 % Removal

30 % Removal


(Ultrasonic)

100 % Removal

100 % Removal

100 % Removal

80 % Removal

100 % Removal

70 % Removal

100 % Removal

60 % Removal

80 % Removal

40 % Removal


(Ultrasonic)

100 % Removal

100 % Removal

100 % Removal

100 % Removal

100 % Removal

80 % Removal

100 % Removal

70 % Removal

100 % Removal

50 % Removal

At the surface(megasonic)

(Ultrasonic)

15 minute8 minute5 minute3 minute1 minuteCleaning for


Why does it take time to remove the particles?



Moment Ratio 300, 800 nm PSL particles

3.5

1.2 1.15 1.18

10.1

3.43 3.29 3.36

0

2

4

6

8

10

12

1 2 3 4

Mo

men

t Rat

io

300nm

800nm

At Surface 100mm 200mm Bottom of Trench below below

MR=1


The simulation shows:

The vortex in the trench is transientThe particle is trapped inside the vortex

The vortex moves the particle inside the trench

The flow is parallel to the trench wallFavorable for particle detachment

The re-deposition slows down the removal process



Particles

Shock Wave Front

WaferWorking Table

Pulsed LaserBeam

Shock Wave Front

Gap

Laser generated plasma induces hypersonic shock waves

Nanoparticle removal is possibleDamage depends on the laser

power and focus point gap

Laser Induced Shock Wave Cleaning

Visualization of laser-induced shock wave generated in the air(Source: Dr. Christian Parigger, UTSI, http://view.utsi.edu/cparigge/osa96/airimages.html)


Laser Induced Shock Wave Cleaning

Laser Shock Wave Cleaning (LSC) is a room

temperature physical cleaning process that has

been shown to be effective in the removal of

particles down to 200 nm from silicon wafers.

Gap

Shock wave front

Sample

PlasmaLaser pulse

Laser Laser irradiationirradiation 1 mm

~ 2.7 µs

Shock Wave Propagation

Side viewTop view


Just 2 laser pulses irradiated

LSC Removal of W Particles from Wafers

Very effective for inorganic particles

Large cleaned areahigh cleaning speedhigh throughput


Schematic illustration (Model: LSC-H200)

LSC Wafer Cleaning System


Cleaning Efficiency of 50 & 60 nm PSL particle on 4 nm Si_cap ML wafer


Brush Cleaning

Brush

u << U=tip Velocity

h ---- Brush Particle distance

F a

F el

1.399R

O'δ a

0 50 100 150 200

BrushRotatingSpeed(RPM)

10-3

10-2

10-1

100

101

102

RM

dl

0.1 umparticle, h=1um0.1 umparticle, h=5um0.1 umparticle, h=10um0.1 umparticle, h=50um0.1 umparticle, h=100um

RM = 1

RM> 1

Removal > Adhesion

Particle will beremoved

RM< 1

Removal < Adhesion

Particle cannotberemoved


Brush CleaningBrush Cleaning

Non - Contact Contact Ideal Contact

brush

brush

brush


RM ( NonRM ( Non--Contact Brush Cleaning)Contact Brush Cleaning)(without double layer force)(without double layer force) (with double layer force) (with double layer force)

0 50 100 150 200

BrushRPM

10-3

10-2

10-1

100

101

102

RM

0.1umparticle,h=1um0.1umparticle,h=5um0.1umparticle,h=10um0.1umparticle,h=50um0.1umparticle,h=100um

RM=1

RM>1

Removal>Adhesion

Particlewillberemoved

RM<1

Removal<Adhesion

Particlecannotberemoved

0.1 micron

0 50 100 150 200


10-3

10-2

10-1

100

101

102

RM

dl


RM=1

RM>1

Removal>Adhesion


RM<1

Removal<Adhesion



0 50 100 150 200

BrushRPM

10-3

10-2

10-1

100

101

102

RM


RM=1

RM>1

Removal>Adhesion


RM<1

Removal<Adhesion


RM ( NonRM ( Non--Contact Brush Cleaning)Contact Brush Cleaning)(without double layer force)(without double layer force) (with double layer force)(with double layer force)

0.5 micron

0 50 100 150 200


10-3

10-2

10-1

100

101

102

RM

dl


RM=1

RM>1

Removal>Adhesion


RM<1

Removal<Adhesion



Contact Brush Cleaning DynamicsContact Brush Cleaning Dynamics

Brush

F a

F el

R

O'δ a

M r

brush brushbrush


Contact Area and Adhesion Force Contact Area and Adhesion Force during the Particle Engulfmentduring the Particle Engulfment

-0.01 -0.005 0 0.005 0.01Angle

10-5

10-4

10-3

10-2

10-1

100

101

102

103

Con

tact

Are

a(

um2

)

0.1 um particle, Contact Area to Wafer0.1 um particle, Contact Area to Brush0.5 um particle, Contact Area to Wafer0.5 um particle, Contact Area to Brush

1 um particle, Contact Area to Wafer1 um particle, Contact Area to Brush

-0.01 -0.005 0 0.005 0.01Angle

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Ad

hesi

on

For

ce(

N)

0.1 um particle, Adhesion Force to Wafer (N)0.1 um particle, Adhesion Force to Brush (N)0.5 um particle, Adhesion Force to Wafer (N)0.5 um particle, Adhesion Force to Brush (N)

1 um particle, Adhesion Force to Wafer (N)1 um particle, Adhesion Force to Brush (N)


RM in Contact Brush CleaningRM in Contact Brush Cleaning

without double layer forcewithout double layer force with double layer forcewith double layer force

0 50 100 150 200

Brush RPM

1014

1015

1016

1017

1018

RM

0.1 um particle0.5 um particle

1 um particle

0 50 100 150 200

Brush RPM

1014

1015

1016

1017

1018

RM

dl

0.1 um particle0.5 um particle

1 um particle


Force-Distance Curve by AFM

Polystyrene particle (2 μm)

Fabricated Colloidal Probe

Possible to attach 0.1 um particles

50 μm

2 μm

Adhesion Force Measurements


Measured Interaction Forces Using AFM

SILK TEOS Cu TaN0.0

-0.5

-1.0

-1.5

-2.0

TaNCuTEOS

Inte

ract

ion

fo

rce

(nN

)

Wafers

pH 11 slurry pH 7 slurry pH 3 slurry

SiLKTM

•Force-Distance Curve Measurements

Park et. al., J. Electrochem. Soc., 150 (5), pp. G327-G322 (2003)


Particle Contamination After Polishing

Cu TaN TEOS SiLK

pH 11

pH 7

pH 3


Zeta Potential of Alumina Particles

Zeta potential

26.2 mV

-26.8 mV

-15 mV

-7.3 mV

Recipes

Oxalic Acid

Citric Acid

No addition

Succinic Acid

• IEP of original alumina was around 9.1• When organic acids were added, IEPs of alumina were changed to acidic pH

Original IEP

2 4 6 8 10 12

-50

-40

-30

-20

-10

0

10

20

30

40

gamma-Alumina

Citric acid added

Succinic acid added

Oxalic acid added

Ze

ta P

ote

nti

al

(mV

)

pH


Adhesion Force of Silica in Cleaning Solutions

The least adhesion force of silica is measured in the citric acid and BTA with NH4OHThe largest adhesion force is measured in the citric acid and BTA with TMAHThe pH and its adjustor selection are very important in cleaning solution design

-11.0

-10.5

-10.0

-9.5

-9.0

-8.5

-8.0

(pH2) (pH6) (pH6)

Adhesion Force

Ad

hesi

on F

orce

( lo

g N

)

D.I Citric acid+BTA Citric acid+BTA+NH4OH Citric acid+BTA+TMAH

Park et. al., J. Electrochem. Soc., 151(10), pp. G327-G322 (2004)


Adhesion Forces of Alumina on Cu in Slurries

1.00E-009

2.00E-009

3.00E-009

4.00E-009

5.00E-009

6.00E-009

AluminaSilicaAluminaSilica

Cu Wafer - Particle Adhesion

DI Water

1.00E-009

2.00E-009

3.00E-009

4.00E-009

5.00E-009

6.00E-009

A

dhes

ion

For

ce (

N )

Citric Acid+NH4OH

Park et. al., MRS 2005 Spring Meeting, San Francisco (2005)


Particle Contamination After Copper CMP

(a) No Addition

(d) Succinic Acid

(b) Citric Acid

(c) Oxalic Acid

Citric acid added slurry (alumina) showed the cleanest surface after Cu polishing

Park et. al., Jpn. J. Appl. Phys., Vol. 41 (2002) pp. 1305-1310

Electrical Double Layer Force

-100

-60

-20

20

60

100

0 2 4 6 8 10 12pH

Zet

a P

oten

tial

(mV

)

Si3N4

Silica

PSL

• Electrical double layer force plays an important role in particle adhesion and removal

• Some approximate expressions for double layer force which are used in colloid science are not suitable for particle adhesion.

• Compression approximation best describes the double layer force for particle adhesion.

1.8E

-08

2.1E

-08

2.5E

-08

-2.E-09

0.E+00

2.E-09

4.E-09

6.E-09

8.E-09

1.E-08

For

ce (

N)

LSA HHF-potential HHF-charge Compression Measurement

Comparison of various expressions with measurement-300 nm PSL particle on thermal oxide wafer

pH=7.8-pH=5

pH=9.3-pH=5

pH=10.2-pH=5

pH=11-pH=5

300nm PSL Particles on Si 3 N 4 Wafer

0

20

40

60

80

100

1E-18 1E-17 1E-16 1E-15

Applied Removal Moment (N m)

Rem

oval

Eff

icie

ncy

(%)

pH=5

pH=7.8

pH=9.3

pH=10.2pH=11

300nm PSL particles on Thermal Oxide Wafer

0

20

40

60

80

100

1E-18 1E-17 1E-16 1E-15


Rem

oval

Eff

icie

ncy

(%)

Comparison of Different Deposition Methods - PSL particles on Si3N4 surface

0

20

40

60

80

100

1E-13 1E-12 1E-11 1E-10


Rem

oval

Eff

icie

ncy

(%)

▲Dry particles are directly deposited on substrate

Particles are suspended in IPA and then deposited on substrate

●Particles are suspended in DI water and then deposited on substrate

• Deposition method has a huge effect on particle adhesion and removal.

• Capillary force caused by the liquid between particle and substrate gives rise to more deformation compared to dry case.

• The liquid with higher surface tension (such as water) gives rise to higher capillary force (compared to IPA).

Effect of Deposition method on Particle Adhesion


Effect of deposition method

Comparison between Different Deposition Methods at Aging Time of 0.1 hour

0

20

40

60

80

100

1E-14 1E-13 1E-12 1E-11 1E-10


Rem

ova

l E

ffic

ien

cy (

%)

Deposition method 1on Thermal Oxide



Deposition method 2on Si3N4




Effect of Cleaning Solution: Aqueous and non-aqueous solution

5 micron PSL particle on thermal oxide Wafer

0

20

40

60

80

100

120

1E-15 1E-14 1E-13 1E-12 1E-11


Rem

ova

l Eff

icie

ncy

(%)

in IPA by DI

in IPA by IPA

in DI by DI

in DI by IPA

Deposition cleaning standard solution deviation

2.0

28.2

0.4

1.5


Effect of Cleaning Solution – Aqueous and non-aqueous solution

5 micron PSL particle on silicon nitride wafer

0

20

40

60

80

100

120

1E-15 1E-14 1E-13 1E-12 1E-11


Rem

ova

l Eff

icie

ncy

(%)

in IPA by DI

in IPA by IPA

in DI by DI

in DI by IPA


2.2

26

0.4

8.6



0.3 micron PSL particle on thermal oxide wafer

0

20

40

60

80

100

120

1E-19 1E-18 1E-17 1E-16 1E-15


Rem

ova

l Eff

icie

ncy

(%) in IPA by DI

in IPA by IPA

In DI by DI

in DI by IPA


8.5

14.0

2.0

18.0



0.3 micron PSL particle on silicon nitride wafer

0

20

40

60

80

100

120

1E-19 1E-18 1E-17 1E-16 1E-15


Rem

ova

l Eff

icie

ncy

(%) in IPA by DI

in IPA by IPA

in DI by DI

in DI by IPA


13.5

22.6

2.0

29.5



0.5 micron silica particle on thermal oxide wafer

0

10

20

30

40

50

60

70

80

90

100

1E-17 1E-16 1E-15 1E-14


Rem

ova

l Eff

icie

ncy

(%)

in IPA by DI

in IPA by IPA

in DI by DI

in DI by IPA


5.0

3.2

10.5

2.3



0.5 micron silica particle on silicon nitride wafer

0

10

20

30

40

50

60

70

80

90

100

1E-17 1E-16 1E-15 1E-14


Rem

ova

l Eff

icie

ncy

(%) in IPA by DI

in IPA by IPA

in DI by DI

in DI by IPA


5.2

6.6

2.3

2.6


-100

-60

-20

20

60

100

0 3 6 9 12

pH

Zet

a P

ote

ntia

l (m

V) Si3N4

Silica

PSL

Accurate Calculation of Electrical Double Layer Force


Accurate Calculation of Electrical Double Layer Force

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07F

orc

e D

iffe

ren

ce (

N)

LSA HHF-charge Compression Measurement

Comparison of various approximate expressions with measurement- 300 nm PSL on silicon nitride wafer

pH=10.2-pH-9.3

pH=11-pH=9.3

The measurement results show that “compression” approximation under constant charge boundary condition accurately describes the electrical double layer force, while the Hogg-Healy-Fuerstenau (HHF) expression under constant potential boundary condition which is widely used in colloidal science is inaccurate in magnitude as well as the sign of the force.


Conclusions

The removal of nanoscale particles (63 nm) using megasonic and laser shock cleaning is investigated experimentally in this study.

The laser cleaning results for the EUV 11 nm and 4 nm Si_cap ML wafers show that the measured removal efficiency obtained for both substrates were in the high nineties.

Heating due to LSC seems to have minimal effect on possible substrate damage. Damage will only occur when the plasma is very close the surface.

The moment ratio model is consistent with the experimental results for nano-scale particles

The simulation shows that 63nm particle are detached and redepositedmany times before final removal. Complete removal of 63nm particles was achieved using 760 KHz and higher frequencies, but 1.2MHz showed 4 times faster removal compared to 760K.

Complete removal of PSL particles from 500 micron deep trenches was achieved.


Advantage

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Reduced University OverheadLess than 15%

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www.cmc.neu.eduwww.cmc.neu.edu

Documents

NSF Center for Micro and Nanoscale Contamination Control · Measurement of particle adhesion force ... Bare silicon Si-Cap Bare silicon Si-Cap DI-Water DI-Water Dilute SC1 Dilute