2. A. Rastegar
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
3. A. Rastegar
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)
4. A. Rastegar
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 20144
P. Feeney, SST, Nov. 2010
5. A. Rastegar
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
6. A. Rastegar
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
7. A. Rastegar
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)
8. A. Rastegar
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
9. A. Rastegar
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
10. A. Rastegar
Particle transport in UPW
10
Pipe diameter ( 4 mm)
p
cc
D
D vd
CC
F
F 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
11. A. Rastegar
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
12. A. Rastegar
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)
13. A. Rastegar
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
14. A. Rastegar
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(atoms/cm2)
Courtesy of Mark Bohr- Intel
15. A. Rastegar
Controlling dissolved gas in UPW for megasonic
cleaning
In-situ dissolved gas
chromatography was used to
measure dissolved gas
concentration in UPW
16. A. Rastegar
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
17. A. Rastegar
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
Airinterface
Wall
• Bubble interactions
– Bubble-particle
– Bubble-bubble
– Bubble-surface/interface
18. A. Rastegar
Heat exchangers-UPW temperature and
particles
18
Hot (80C)
Cold (17C)
AddingCO2
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
ParticlespermL
19. A. Rastegar
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 )
SolubilityofSiO2(%)
Handbook of cleaning for semiconductor
Manufacturing - Reinhardt & Reidy
20C 80C
Holms, Parker, Povey, J.O. Physics, Conf. Proc. 2010
20. A. Rastegar
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
21. A. Rastegar
UV radiation and particle formation in UPW
21
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
)(
nm
eVE
hc
E
l
l
185 nm 6.7 ev
Wibowo, Shadman, Blackford, Am. Fluid Technologies
185 nm
254nm
22. A. Rastegar
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
23. A. Rastegar
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
24. A. Rastegar
Summary of particle
interactions
24
vdWF
Particle
DF
ELDF
Flow
p
ScattI .
S
ScattI .
S
refI
p
refI
S
absIp
absI
),(0 lI
Wafer
Particle
),(0
lI p
ScattI .
m
ScattI .
m
refIp
refI
m
absIp
absI
A. Rastegar
Particle
Media
Liquid cellFlow
In solution
On surface
Particle-light
interaction
25. A. Rastegar
Particle detection and sizing in solutions and on a surface?
9 December 201425
Measure particles in solutions Transfer particles to the surface Measure particles on surface
p
ScattI .
S
ScattI .
S
refI
p
refI
S
absIp
absI
),(0 lI
Wafer
Particle
),(0
lI p
ScattI .
m
ScattI .
m
refIp
refI
m
absIp
absI
A. Rastegar
Particle
Media
Liquid cell
Flow
• 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
26. A. Rastegar
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
27. A. Rastegar
Particle detection efficiency on a surface
27
• 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
28. A. Rastegar
Particle detection efficiency in solutions
28
• 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
ConMeasured
h
%3h
29. A. Rastegar
Challenges of monitoring particle defectivity
9 December 201429
Fab Device Defect
monitorFacility
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?
30. A. Rastegar
Particles during rinse and dry processes
9 December 201430
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
Processchemicals
Wafer
31. A. Rastegar
Correlating of particles on surface and on UPW
31
• 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
32. A. Rastegar
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. 2014Native 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
33. A. Rastegar
Detection efficiency in low particle concentrations
33
• All metering pumps adding particles to
UPW
• Alternative technique should be used for
measuring LPC detection efficiency in
low particle concentration
34. A. Rastegar
Particle measurement in low concentrations
34
• 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 LPCDifferent Physics
M. Samayoa-SEMATECH
35. A. Rastegar
Measuring particle trends in UPW
(low particle concentrations)
35Experiments: Matt House
• Comparison of particle count of different LPCs for low particle concentration is challenging
37. A. Rastegar
Current capabilities
Required capabilities
Data extracted from presentation by Don Grant et.al at UPW micro conference 2013
A. Rastegar
Particle filtration challenges
9 December 201437
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
38. A. Rastegar
Particles released from components in UPW
38
• 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
39. A. Rastegar
Sub 10 nm particles in UPW
9 December 201439
Particle Height
0
2
4
6
8
10
12
14
16
18
20
1 2 3 4 5 More
Height (nm)
Count
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
40. A. Rastegar
New particle removal technology for sub 10 nm
HP nodes
9 December 201440
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
41. A. Rastegar
Summary and Conclusions
41
• 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
