Rastegar SST webcast v8

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Surface Cleaning Challenges in

the Advanced Technology Nodes

(Solid State Technology Webcast)

Abbas Rastegar

Fellow

SEMATECH

Albany, August 2014

A. Rastegar Solid State Technology Webcast

Outline

• Device size, structure and integration schemes

• Device size and surface cleaning

• Contamination by wet cleaning

• Challenges of wetting and drying of surfaces

• Physical techniques for particle removal

• Update on Gigasonic cleaning technology

23 January 2015 2


Device Size and Surface Cleaning

• As device sizes reduce, new device structures, integration schemes and materials are introduced

• As device sizes reduce, new challenges for wafer cleaning, inspection, and characterization are introduced

• Minimum defect size determines the requirements for cleaning, defect inspection and characterization

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14 nm / 10 nm 7 nm / 5 nm / 3 nm 45 nm / 32 nm / 22 nm

• 2D • Spin

• SiGe Stressors • High-/Metal Gate • Bulk FinFETs / FD-SOI

• SiGe Channels • Ge Channels • ET-SOI

MoS2: EPFL SiGe Channel: SEMATECH

TFET: SEMATECH Bulk FinFETs: INTEL

SiGe Stressors: INTEL High-/Metal Gate: TSMC

Ge FinFET: TSMC

III-V FET: SEMATECH

FD-SOI: GLOBALFOUNDRIES Spintronics: IBM

• Ge/III-V FinFETs • Vertical NW • TFET

• Lateral device dimension reduces smaller chip area

• Vertical device dimension increases 3D structures

Source :Chris Hobbs- SEMATECH

New Device Structures (Logic technology roadmap)

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Shrinking of the 3D structures

22 nm FinFET-Intel

• Fins shrink laterally and grow vertically Fin aspect ratio increases

• Fin pitch reduces and sidewalls become more vertical

• Fins become structurally weaker

Images: Courtesy of Mark Bohr- Intel

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http://www.eetimes.com/document.asp?_mc=RSS_EET_EDT&page_number=2&doc_id=1323476&image_number=3

http://www.eetimes.com/document.asp?print=yes&doc_id=1323476&image_number=4

A. Rastegar Solid State Technology Webcast 6

Integration Schemes – (III-V Fin Formation)

• Cleaning depends on the integration scheme

• Simultaneous cleaning of materials with different compositions (Si, Ge, III-V) are required

Source :Richard Hill -SEMATECH

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New Materials in Gate Structures

Cs 55

Ba 56

La 57

Hf 72

Ta 73

W 74

Re 75

Os 76

Ir 77

Pt 78

Au 79

Hg 80

Tl 81

Pb 82

Bi 83

Po 84

At 85

Rn 86

K 19

Ca 20

Sc 21

Ti 22

V 23

Cr 24

Mn 25

Fe 26

Co 27

Ni 28

Cu 29

Zn 30

Ga 31

Ge 32

As 33

Se 34

Br 35

Kr 36

Rb 37

Sr 38

Y 39

Zr 40

Nb 41

Mo 42

Tc 43

Ru 44

Rh 45

Pd 46

Ag 47

Cd 48

In 49

Sn 50

Sb 51

Te 52

I 53

Xe 54

Na 11

Mg 12

Al 13

Si 14

P 15

S 16

Cl 17

Ar 18

Li 3

Be 4

B 5

C 6

N 7

O 8

F 9

Ne 10

H 1

He 2

Ho 67

Er 68

Tm 69

Yb 70

Lu 71

Ce 58

Pr 59

Nd 60

Pm 61

Sm 62

Eu 63

Gd 64

Tb 65

Dy 66

Lanthanides

Metal gate electrode

Metal Oxide gate electrode

Metal + MO gate electrode

Other semiconductor applications

• Many new materials come into contact with cleaning chemistries Source :David Gilmer-SEMATECH

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Ultra Thin Films and Monolayers in Gate Structures

Breakdown

• New integration schemes use ultra-thin layers which are only a few monolayers thick

• Layer integrity and quality strongly depends on the interface quality

• Surface cleaning and preparation strongly influences the interface quality

• Molecular surface contamination becomes important

• Under layer properties contribute to the surface energy

• Monolayers can not be etched to loosen the particles

Breakdown image: Dmitry Veksler

Courtesy of Mark Bohr- Intel

SEMATECH

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Myths and Realities of the Surface Cleaning Expected

Reality

• Critical defect size determines the challenges of the surface cleaning

• Progress in cleaning is possible only if metrology and defect characterization are available for a certain technology node

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Particle adders by wet cleaning

Drying and evaporation

Particle dynamics in the flow Particle –surface interaction

Fluid dynamic

Fluid properties

Nozzle parameters

Surface energy Contact angle Surface roughness Surface composition Underlayers Surface charge

surfactant

• Many parameters contribute to particle adders on the surface

• Particles in UPW and chemicals should be controlled to achieve low adder cleaning processes

Pro

cess

ch

em

ical

s

Wafer

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Particle Contamination by UPW Organic particles

• UPW brings organic and colloidal silica particles to the surface

SiO2 shell

Si Mo

Ru

Colloidal silica particles

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Making Cleaning Processes Cleaner!

• Particle/light interaction in solutions

• Particle /flow interactions

• Particle /flow interactions

• Particle/surface interactions

• Particle/light interaction on a surface

Major particle interactions

• Understanding particle detection and transport in solutions and on the surface is necessary to improve the cleanliness of the cleaning processes

• SEMATECH has done extensive research on improving particle defectivity

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Particle Metrology Gaps

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Wet Cleaning

Wetting Residue removal

Particle removal

Ions/ molecule removal

Drying Function

Cleaning Steps

• Physics governing different steps of the surface cleaning is size-dependent

• In the sub-10 nm domain, the surface interaction will change the physical properties of materials as we know it!

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Wetting of a Surface

• Why should we wet the surface? – Carry active species to the surface (Etch,

Clean, rinse)

– Improved fluid dynamics

• How to wet the surface? – Lower the contact angle by modifying

molecules on the surface

• Wetting of high aspect ratio contacts – Water penetrates inside a hydrophilic

contact hole under capillary forces driven by Laplace pressure

– In closed-end contact holes gas get trapped and liquid penetration is very lengthy or never is complete

)cos( LVSLSV

)cos( LVLVSLW

)cos(

4 2

r

lt

23 January 2015 15


Wetting of Surface in sub-10 nm Dimension

• Surface energy and surface tension will change in sub-20 nm – Surface wetting and particle adhesion will be modified – No data exist for surface of interest! – Water molecules are more ordered (less liquid) in very confined

geometries

Surface tension Contact angle

Nanoparticle Technology Handbook Edited by M. Hosokawa, K. Nogi, M. Naito, T. Yokoyama

• Filling time of 10 nm contact holes is very long

• Contribution of the surface

forces should be included in the filling time calculation

)cos(

4 2

r

lt

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Surface Drying

• Drying is one of the most critical steps in surface cleaning – Surface charging

– Particles remaining on surface

– Residues remaining on surface

– Ions remain on surface

– Pattern collapse

• Drying of high sub-10 nm structures – Surface tension should be reduced to

prevent pattern collapse ( surfactant)

– Surfactants will leave residues

– Dehydration steps (vacuum, heating) need to be used

100 nm

Defect grown from remaining sulfate ions on surface

Hattori , ECS 3(1) N3054 (2014)

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Nonvolatile Residues After Drying

• Non-volatile residues (NVR) form nanoparticles on the surface

• Depending on the surface energy, NVR droplet can have circular symmetry with shrinkage morphology

Residue Pinned line

Contamination line

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SiO2 30 nm

7 nm

~4 nm

A B

A B

Dissolved Silica Is Major Nonvolatile Residue in UPW

• Non-volatile residues from nanodroplets are very flat with a thickness of about 4 nm

• These nanoparticles are coming from dissolved silica in UPW

30 nm

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Can Nonvolatile Residues in UPW Become a Yield Issue?

30 nm

50 nm

h=1

8400 ppm

NVR

30 nm

50 nm

10 micron droplet

3 ppb

NVR

h=1

• Combination of wafer drying process and non-volatile residues in UPW can lead to severe yield issues!

• Nonvolatile residues in UPW should be minimized

SEMATECH

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How Particles Impact Yield?

• Electrical blocking

– Non-conductive particles in contact holes

Particle

Contact

holes

Particle Lines • Electrical short

– Conductive particles between lines

In film particle Light

Resist

• Optical obscuration

– Absorb or scatter light

Ions

Resist Metal

Blocked etch

• Block etch in RIE

– Different selectivity

Selective

Etchant Particle -

+ Nodule • Nodule formation on selective etch

– Spike structures under particle

Selective

precursor Particle

• Film discontinuity in ALD

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Are sub-10 nm Particles Conductive?

• Physical properties of particles depend on their size in sub-20 nm dimensions

• Nanoparticle interaction with surface and light strongly affected by their size ( i.e., particle adhesion, removal, scattering)

• No electrical conductivity data of individual nanoparticles is available for particles of interest in semiconductors

Nanoparticle Technology Handbook Edited by M. Hosokawa, K. Nogi, M. Naito, T. Yokoyama

Melting point O Ni

Fe Cr Si

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Particle Removal From The Surface

Particle on surface Detaching Breaking vdW forces

Lift-Off Repulsive forces

Transport away Hydrodynamic forces

Physical forces

Momentum transfer • Hydrodynamic flow

• Megasonic

• Shockwave

• Radiation

• Gigasonic

Chemical Forces

Dissolving • Delivery of active spices to particle

• Depends on particle composition

• Selectivity to substrate

• Radiation

• Contamination

Mechanisms of particle removal

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SEMATCH Strategies for Removal of sub-50 nm Particles

Generate active species Generate fast flow close to surface Activate chemical interaction at interface

UV

Laser Nozzle Cleaning Technology Gigasonic Cleaning Technology In-situ UV Cleaning Technology

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Challenges of Particle Removal by Cavitation

• Cavitation is the main mechanism used frequently for particle removal efficiency (PRE)

– High PRE can be achieved by cavitation collapse

– Transient cavitation collapse can result in damage

• Cavitation is a chaotic phenomenon

– Onset of cavitation bubble and its collapse is affected by many physical parameters which can not be controlled precisely

30 nm Sensitivity 50 nm Sensitivity

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Acoustic Streaming in GHz region

• Boundary layers will approach the particle sizes

• Streaming velocities in GHz regions are 5 orders of magnitudes higher than that of MHz region

• Above 10 GHz streaming velocities are in supersonic region (Sound speed in water 1484 m/s)

• GHz acoustic waves attenuate rapidly in distances above few 10s of microns

)/(102.2100022.0)1( 36 cmdBxxGHzw

1GHZ

10 MHZ

Absorption in the water

Am

plit

ud

e (

I/Io

)

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Damage Free nanoparticle removal with gigasonic cleaning

Patterned wafer surface after gigasonic cleaning

Patterned wafer surface covered with particles

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New particle removal technology for sub 10 nm HP nodes

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Pattern : 65 nm SiO2 Particles: 50 nm PSL Process: Particle dep rinse dry

• Gigasonic cleaning is a new technology for particle removal for sub10 nm HP nodes that is under development in SEMATECH


Summary and Conclusions

• In advanced technology nodes – lateral dimensions of devices shrink while vertical dimensions

increase • Fragile structures, hard to reach ( wetting, flow)

• Hard to detect particle defects

– Ultra-thin film of a few monolayers is introduced • Very selective chemistries are required

• Very sensitive to the interface quality (molecular contamination)

– Contamination control and surface cleaning will be one of the most critical steps in semiconductor manufacturing

• SEMATECH continues efforts to enable required infrastructure and build fundamental understanding required to tackle surface contamination challenges in sub-10 nm dimension

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Rastegar SST webcast v8

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