1. Problems of counting particles in photoresist

1
Particle Counter KS-41 for photoresist
measurement
1. Problems of counting particles in
photoresist 2. KS-41 Specifications 3. Adjustment
and calibration method 4. Actual measurement
example
2
Principle of the Light scattering particle counter
Interaction between Light and Particle
Reflection
Diffraction
Incident Light (wave length?, IntensityI0 )
Refraction
Absorption
f
Particle (diameterD, refractive indexm1)
Refractive index of mediam0
Scattering
(IntensityIf )
1-1
3
Reyleigh scattering pattern
Direction of electrolytic vibration
Irradiating light
Light scattering intensity pattern
Direction of magnetic vibration
1-2
4
The structure of sensor for Airborne particle
counter
Inlet
Scattering light collection lenses
Scattering light reflection mirror
Photodiode
Beam forming lenses
Outlet
Light source
1-4
5
Pulse signal from PSL particle
Pulse height
Pulse height
Pulse number (frequency)
Time
1-5
6
Cumulative distribution
Frequency distribution
Particle Count (standardization)
Calibration voltage
Pulse voltage
1-6
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Problems of measuring particles in photoresist
Scattering of irradiating light in resist
becomes noise. Refractive index of the resist
(approx. 1.4 to 1.6) affects the precision of
particle diameter determination. Sample flow
rate changes according to its viscosity.
polymer molecule, polymer, etc
1.6 1.5 1.33
Sample
Flow cell
Irradiating light
Photo detector
Particle
Particle
Particle detector
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Scattering by polymer in photoresist (Top view)
Photo Diode
Flow cell
Sample
Lens
Aperture
Laser beam
10
Collection light spot diameter depending on
refractive index (Top View)
Photo Diode
Laser beam
Flow cell
Aperture
Sample
Lens
Laser
Spot diameter in resist
Spot diameter in DI-water
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Noise increase due to photoresist measurement
Scattered light pulses of particles
0.15µm
0.1µm
Scattered light pulses of particles
0.1µm
0.15µm
Noise
Noise
Voltage
Voltage
Time
Time
Scattered light of photo-resist and wall of
flow-cell (DC voltage)
Signal output of photo-detector
Signal output of photo-detector
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KS-41 Specifications

• Outline
• KS-41 is a sensor for measuring particles in
  photoresist.
• By connecting the unit to the controller (KE-40
  or KE-40A), power supply, measurement control and
  data output are carried out.
• As the unit does not incorporate flow control
  circuit, the additional flow rate controller
  should be prepared.

Specifications Optional system 90sideway light
scattering methodLight source Laser
diode (wave length 830nm, rated output 200
mW)Light detector PIN type photodiodesMaterial
s of component parts exposed to sample
fluid Fused silica, PFA
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KS-41 Specifications
Measurement size ranges ³0.15µm, ³0.2µm,
³0.3µm, ³0. 5µm Counting efficiency 5010 (m
easuring PSL particles in the range of 0.3µm,
using count of 0.2µm and above for
comparison with reference unit) Sample fluid
rate 10mL/min Maximum particle
concentration 12,000 particles/mL
(coincidence loss 5 for 0.15 µm
particles) Ambient conditions for
operation 15 to 30ºC, 0 to 85 RH (no
condensation) Allowable sample fluid
pressure 300 kPa or less (gauge pressure)
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Particle detector system for photoresist
measurement
(Side View)
Scattered light ( from fringe of the flow cell)
Photo Diode
Aperture
Scattered light (from center of flow cell)
1 Lenses
Flow Cell
KL-26 Optical System
Laser Beam (Vertical to paper)
Scattered light ( from fringe of the flow cell)
10ch Photo Diode
L Shape Flow Cell
8 Lenses
Scattered light (from center of flow cell)
KS-41 Optical System
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10ch Photo Diode
L Shape Flow Cell
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Photoresist measurement using sensor calibrated
with PSL particles and DI-water
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Standard PSL particlesin DI-water
Standard PSL particlesin photoresist
Adjustment Using a solution of glycerin
(refractive index of 1.4) and PSL
particles. Calibration With PSL particles
(refractive index 1.6) in pure water
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KS-41 Sensor construction drawing
Collection lenses
Photodiode
Scattering light collection lens
Laser diode
Beam forming lenses
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Noise increase when measuring photoresist
Noise increase rate 8.4 times
Noise 64.5mv
Noise 538.6mv
KL-24 Photoresist
KL-24 DI-water
Noise increase rate 1.7 times
Noise 197mv
KS-41 Photoresist
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Example of particle counts in photoresist ( I )
(mV)
0.15lt
0.2lt
0.22lt
0.25lt
0.3lt
Noise
I-line positive
582
1052
97
74
41
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Excimer A
243
740
368
278
173
107
235
620
295
195
83
54
Excimer B
339
236
91
65
33
21
Excimer C
415
256
116
79
45
35
Excimer D
494
584
289
213
118
77
Excimer E
(Number /10mL)
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Example of particle counts in photoresist ( II )
(Number /10mL)
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Particle measurement in DI water
Unit particle/10mL
PSL particle measurement in Ethyllactate
(particle size 0.321 µm)
Reference KS-41 (Counting efficiency 58,
measuring in the range of 0.2 µm, using count of
0.309 µm for comparison with reference unit)
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Viscous resistance of Particle counters

• When sample input pressure is 3 kg/cm2, flow rate
  limitations which depend on viscosity of
  sample are measured.
• Absolute values depend on measurement error of
  sample viscosity and surface exposed to sample
  fluid.
• The difference of the flow path shape varies the
  maximum flow rate widely.

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Measurement of babble and solid particles
1.0E06
KL-26
1.0E04
Relative Intensity
1.0E02
Bubble
PSL
1.0E00
MediaH2O
1.0E-02
0.1
1
10
Diameter(µm)
Light scattering intensity is almost the same
with PSL particles and bubbles in water.
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Particle measurement example in APM cleaning tank

• Particle counts which vary depending on the APM
  temperature are regarded as bubble counts.
• Particle counts are not affected by the
  temperature 60? and below.