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Understanding UPW-induced particle

defectivity in sub10 nm technology

nodes

Abbas Rastegar

Matt House, Martin Samyoa

SEMATECH

Albany- New York

December 2014

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Outline

2

• Particle defectivity in advanced technology nodes

• Particles in UPW systems

• Particle interactions and behavior

• Correlation between particles in solutions and on the surface

• Challenges of measuring low concentration of particles in UPW

• Particle removal in sub 10 nm HP technology nodes

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Yield challenges in 14 nm HP node

3

• Yield improvement for 14 nm HP node is much slower than that of 22 nm HP node

• Particle defectivity is one of the key challenges of yield at 14 nm HP node

Intel.com ( 2014 November)

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More particles in 3D gate structures

22 nm FinFET-Intel

• Replacement gate structures require more CMP steps ( 4X) more particles

• Fins aspect ratio increases particle traps, more difficult to inspect

• Fins become structurally weaker difficult to clean

Images: Courtesy of Mark Bohr- Intel

9 December 2014 4

P. Feeney, SST, Nov. 2010

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CMP for the gate-last FinFET processes

5

• Multiple CMP processes are required during a replacement gate process

• Particles generated during CMP have many different compositions

Integration sketch: Tat Ngai

Last CMP step in (Gate last or Replacement Gate) integration

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New Materials in Semiconductors

• Many new materials are introduced in the semiconductor manufacturing which result in particles with many different compositions

• Particle interaction with surface depends on their compositions

Source :David Gilmer-SEMATECH

6

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Particles in UPW systems

7

Pretreatment System

Reverse Osmosis

Vacuum Degasifier

Ion Exchanger

UPW Tank

I.E or MB polisher

Ultra- Filtration

Heat Exchanger

• UPW system for semiconductor applications are using multiple modules with different functionalities

• Each module and component contribute to particle defectivity • Particles can be generated from components in contact with UPW

– Tubing, Pumps, Valves, Regulators, Flow meters, Heater, Sensors, Tanks, Fittings, UV, Filters, Ion exchange resins

• Focus of today’s talk is on understanding nanoparticle behavior in UPW system

UV (185 nm)

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Particle behavior and interactions in UPW

8

Particle behavior Particle interactions

• Particle behavior in the UPW can be explained by particle interactions with surface, flow and light and their subsequent interactions

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Particle generation in UPW

9

• How particles are generated in UPW? – Transport from outside by incoming water – Release from a surface

• Vibration • Heat • Shear stress by flow variation • Contact

– Generated from a surface • Contact • Cavitation • Mechanical stress (cracks)

– Form in UPW • Agglomeration • Precipitation • Flocculation

Source: internet

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Particle transport in UPW

10

Pipe diameter ( 4 mm)

p

cc

DD vd

CC

FF 3

1

Drag force is effective

Brownian diffusion

• Particles in the boundary layer will not be affected by bulk flow and eventually will reach the surface

• Even in very fast flows hydrodynamic boundary layers are of orders of 10’s of microns

Parabolic flow in a tube

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UPW tubing: Particle retention and release

11

• Nanoparticles in solution eventually will pass the boundary layer and come into contact with surface

• When particles are in contact with surface they cannot be removed by flow

Boundary layer

Bulk flow(advection)

Time

Surface (wafer, pipe, filter,…)

Controlled release of particles

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Particle retention and release in UPW tubing

12

• Particles in UPW are continuously deposited on the surface of tubing and other components.

• High density of particles can be released from surfaces

• No tubing stay clean for long time!

½ inch PFA tube Length 20 mm

Random burst of particles detected @ 25 nm channel during night time (no cleanroom activity)

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Open

0.5 L/min

20 mL/min

Simulations: Huseyin Kurtuldu

Particle trajectory

500 mL/min

20 mL/min

Open (480 mL/min)

10 m pore -100 m space T fitting Single membrane filter

• Particles distribution in the flow is not uniform

• In slow flows, particle diffusion dominates and particles reach to the surface by Brownian motion

Particle-flow interactions

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Degasifiers: Why dissolved gas should be removed from UPW?

14

• UPW is degassed to remove dissolved oxygen and prevent unwanted Si oxidation

• Dissolved gases also impact megasonic cleaning

• Dissolved gas in UPW is important in bubble formation

• Gas bubbles strongly interact with particles and flow

Yagi et. al. IEEE Trans. On Semi, Man. Vol 5, No.2.1992

Si (

ato

ms/

cm2)

Courtesy of Mark Bohr- Intel

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Controlling dissolved gas in UPW for megasonic cleaning

In-situ dissolved gas chromatography was used to measure dissolved gas concentration in UPW

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Megasonic damage by dissolved oxygen in UPW

• Dissolved gas in UPW is extracted in cavitation bubble by acoustic waves

• The higher the gas content the higher is cavitation which means more damage

• Sonication of UPW with dissolved oxygen creates OH radicals that are very active and damage the surface

Damage on EUV mask blanks

OH radical formation in UPW by megasonic

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Bubble-Particle interactions Dissolved gas in UPW

• Bubbles are formed when the concentration of dissolved gas in UPW is more than its saturated solubility limit

• Saturated solubility depends on gas pressure, type and temperature

Effects of Temperature on Quantity of Dissolved CO2, O2, N2, and He in UPW (at partial pressures of 1 atm).

Fig. 3 Effects of Pressure (Partial Pressure) on Solubility of O2 in 1 mL Water (at 25 °C)

Bubble

Particle

Bubble Bubble

Bubble UPW

Air interface

Wal

l

• Bubble interactions

– Bubble-particle

– Bubble-bubble

– Bubble-surface/interface

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Heat exchangers-UPW temperature and particles

18

Hot (80C)

Cold (17C)

Ad

din

g C

O2

PMS –CLS 1000

• Increasing temperature results in bubble

• Nonvolatile residues (NVR) and particles are attracted to the water-bubble interface

• Bubbles attach to the surface and leave residues

Particles in UPW

Uwe Dietze- Suss Microtec- nanoparticle workshop 2013

Particles on surface

Part

icle

s p

er

mL

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UPW heaters and particle generation

19

• The surface of quartz heaters reach to the temperature of about ~ 350C

• Silica will be dissolved from heater wall into the UPW by heat and appear as nonvolatile residue

• High shear stress by flow on very hot surface of quartz tubing release particles from the surface

• Temperature change also affect particle dynamics – Both bulk and shear viscosity reduces – Particles move from hot surface toward cold

(Thermophoretic force )

Temperature (C )

Solu

bili

ty o

f Si

O2 (

%)

Handbook of cleaning for semiconductor Manufacturing - Reinhardt & Reidy

20C 80C

Holms, Parker, Povey, J.O. Physics, Conf. Proc. 2010

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Nanoparticles formed from dissolved silica in UPW

• Nonvolatile residues from nanodroplets are very flat with thickness about 4 nm

• These nanoparticles are coming form dissolved silica in UPW

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UV radiation and particle formation in UPW

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172 nm@ 7.2 ev

Discharge O3 generator 3 nm gas filter No filter for ozonated UPW

• UV light (l< 200 nm) is able to breakdown many organic molecules

• Fitting and tubing exposed to UV become brittle and form cracks and eventually under stress release particles

• UV will oxidize metallic ions and they will precipitate as particles

• UV generate ozone and ozone react with tubing and metallic surfaces and generate particles

• UV react with quartz surface and increase Si dissolution

)(

1240)(

nmeVE

hcE

l

l

185 nm 6.7 ev

Wibowo, Shadman, Blackford, Am. Fluid Technologies

185 nm

254nm

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Particle-surface interactions in UPW in nano-scale

22

Hydrodynamic boundary layer

Bulk flow(advection) Order of micrometer and reduces by increasing flow velocity

Electrostatic double layer

Diffusion layer

Order of nanometer and reduces by increasing ionic strength

• A particle may deposit or repel from surface depending on zeta potential of surface and particle and pH of solution

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Particle deposition in UPW– electrostatic interactions

23

During UPW rinse Al2O3, Fe2O3 particles will not be deposited on RuO2 surface ( Same sign of z potential) but will be deposited on the quartz surface ( different sign of z potential)

colloidal silica particles will be deposited on RuO2 surface but will Not be deposited on the quartz surface during UPW

• Depending on the pH of the solution, zeta potential of the surface and particles, some particles may or may not be deposited on a surface

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Summary of particle interactions

24

vdWF

Particle DF

ELDFFlow

p

ScattI .

S

ScattI .

S

refIp

refI

S

absIp

absI

),(0 lI

Wafer

Particle

),(0

lI p

ScattI .

m

ScattI .

m

refIp

refI

m

absIp

absI

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Particle

Media

Liquid cell Fl

ow

In solution On surface

Particle-light interaction

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Particle detection and sizing in solutions and on a surface?

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Measure particles in solutions Transfer particles to the surface Measure particles on surface

p

ScattI .

S

ScattI .

S

refIp

refI

S

absIp

absI

),(0 lI

Wafer

Particle

),(0

lI p

ScattI .

m

ScattI .

m

refIp

refI

m

absIp

absI

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Particle

Media

Liquid cell

Flo

w

• Incident light ( l,)

• Particle properties • Shape, size, composition

• Media properties ( UPW, Chemicals) • molecular scattering,

absorption

• Incident light ( l,)

• Particle properties • Shape, size, composition

• Surface properties (Roughness) • Scattering , reflection and

absorption

Intensity of the scattered light

Particle size

Particle detection in solutions Particle detection on surface

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Particle size and composition

26

x1,000

x1,000,000

x10

K. Kondo et.al., JSAP(2013)

• Scattered light is proportional to

• (1/ wavelength4) shorter wavelengths lead to higher sensitivity

• (particle diameter)6 Sensitivity drastically reduces for small particles

• Type of calibration particles determine pixel size of LPC and inspection tools

Rayleigh approximation

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Particle detection efficiency on a surface

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• Optical properties of particles and surface determine particle detectability on a surface

• As the calibration particles are fixed on the surface, multiple inspections results in reliable measurement of the particle detection efficiency

• High detection efficiency ( 95% to 99%) at the tool sensitivity is achievable

• Due to high capture efficiency very low defect concentration on surface are detectable ( ~10 defects)

Inspection wavelength =266 nm, SiO2 particles, Inspection wavelength =485 nm on quartz surface

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Particle detection efficiency in solutions

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• Multiple detections of the same particles in solution is not feasible

• Detections of known particles with known concentration is used to measure detection efficiency

• Preparation of nanoparticles with known concentration is very challenging

• In practice, h is measured by diluting a known concentrated of known particles.

• This technique works for higher particle concentration.

K. Kondo , Bunseki, Vol.9 P499 (2012)

Ideal LPC

Real LPC

%100100.

ConKnown

ConMeasuredh

%3h

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Challenges of monitoring particle defectivity

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Fab Device Defect

monitor Facility

Device

Suppliers UPW

Chemicals

Gases

Litho

Etch

Clean

CMP

Deposition

Implant

Tool

Suppliers

Process Defect

Monitor

Bare

wafer

Correlation Liquid

Gas

Defect

Monitor

How to correlate particles in UPW and process chemicals to the particles on the wafer?

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Particles during rinse and dry processes

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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 surface

• Standard processes ( rinse, dry, surface, particle type) should be developed to get reproducible number of particles on surface

Pro

cess

ch

em

ical

s

Wafer

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Correlating of particles on surface and on UPW

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• Particle release experiment

• LPC

• Surface Ru capped mask blank

• Standard rinse /dry

• Two different inspection tools was used

• Results

• Released particles have different size, shape and compositions (i.e. native particles)

• Only qualitative correlation can be seen with tool with higher sensitivity

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Correlation of particles in UPW and on surface

32

( mostly Al2O3)

ITRS-WG experiment 90 nm SiO2 particles KLA -SP1 ( 90 nm sensitivity)

S. Libman – UPW conf. 2014 Native particles (mostly metal oxide) >40 nm ,Lasertec M7360 ( 30 nm PSL sensitivity)

• Real (native) particles have different sizes, shapes and composition

• Particle counts on surface and in solution are linearly correlated, however, the linear slope depends on particle and surface parameters as well as inspection tools

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Detection efficiency in low particle concentrations

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• All metering pumps adding particles to UPW

• Alternative technique should be used for measuring LPC detection efficiency in low particle concentration

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Particle measurement in low concentrations

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• In low particle concentrations , particle dynamics should be considered. ( particles do not behave like molecules, i.e. dilution)

• Other sources of noise in LPC ( electrical, optical, detection, Gama,..) become significant

Calibration particles size 3X of LPC sensitivity

particles size 30% > LPC sensitivity

%5h

%100h

Working range of this LPC Different Physics

M. Samayoa-SEMATECH

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Measuring particle trends in UPW (low particle concentrations)

35 Experiments: Matt House

• Comparison of particle count of different LPCs for low particle concentration is challenging

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Gaps in Particle Metrology-modified

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UPW

Chemicals

Slurries LPC

100 nm

50 LPC

20 nm 25

SPM (SEM,AFM)on surface

Inspection tool

50 nm

PIV -200 nm

22 30

108

107

106

105

104

103

102

10

0

2 5 10 20 30 50 100 200 300 500 1000

Size (nm)

Part

icle

count (

per

mL)

A. Rastegar SEMATECH

Aerosol metrology(DMA+CPC)

DLS

LIBS

in situ -OPC in situ -other

On surface

DMA: Differential Mobility Analyzer

CPC: Condensation Particle Counter

DLS: Dynamic Light Scattering

SPM: Scanning Probe Microscopy

LPC: Liquid Particle Counter

PIV : Particle Imaging Velocimetry

LlBS: Laser Induced Breakdown Spectroscopy

1

30

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Current capabilities

Required capabilities

Data extracted from presentation by Don Grant et.al at UPW micro conference 2013

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Particle filtration challenges

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12 nm SiO2 particles, face velocity 4 cm/ min, 0.2 monolayer coverage

• No detection tool exists for developing filters with high retention for low particle concentration (~10 particle/mL) at sub 10 nm sizes

• Existing infrastructures can study filter retentions in very high particle concentrations

Micron scale pores in a 10 nm class filter

10 m

10 nm - filter

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Particles released from components in UPW

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• During manufacturing of valves, pumps, filters, fittings, tubes surfaces of fluorinated polymers (PFA,, PTFE) com into contact with other materials ( Al2O3, Stainless steel)

• Nanoparticles generated during part manufacturing can not be removed and will be released in UPW

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Sub 10 nm particles in UPW

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Particle Height

0

2

4

6

8

10

12

14

16

18

20

1 2 3 4 5 More

Height (nm)

Co

un

t

Random burst of very small particles (>2.5 nm) in UPW

Small organic particles are agglomerated

• There are many sub 10 nm particles in UPW that will end up on surface and can not be detected

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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

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Summary and Conclusions

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• Advanced technology nodes are using surfaces with higher topography which are prone to particles

• Many components in UPW systems are contributing to particle defectivity – Degasification, heating and UV exposure impact particle

defectivity in UPW

• Interaction of particles with surface and flow determines particle deposition and release in UPW

• Correlation particles in UPW and on surface is challenging and depends on many parameters

• There are increasing evidence of sub 10 nm particles in UPW, but current particle metrology can not sufficiently detect these particles