ADVANCED MATERIALS HANDLING | APPLICATION NOTE

Novel Bubble Sensing Systems for Advanced LithographyAuthor: Kanjanawadee Shiraishi, Entegris

Bubbles, which can translate to wafer defects, are critical in

the lithography process. While bubbles smaller than 100 µm

can be completely dissolved into the resist, larger diameter

bubbles (typically >300 µm diameter), cannot be fully adsorbed

by the resist and the bubbles can remain even after one hour.1

Sensing bubbles of this size has become a critical challenge

within lithography processes.

To address this challenge, Entegris has developed an integrated

flowmeter and dispense system with robust air-monitoring

software. The software utilizes the principle of heat conduction

in different media combined with an exact copy theory to detect

the existence of air bubbles. This software is called “Flow Profile

Compare.”

In-house testing has proven that the Flow Profile Compare moni-

toring software is sensitive to air bubbles as small as ~ 800 µm in

diameter. Combining the flowmeter with this software into your

production line would prevent the adversities caused from air

bubbles in photochemicals.

PRINCIPLE OF FLOWMETER AND FLOW PROFILE COMPARE—The flowmeter has a sensor that measures the temperature

gradient at two points. Due to a correspondence of liquid

flow and temperature gradient, the flowmeter can convert

the observed temperature gradient into liquid flow rate. When

bubbles pass through the temperature sensor during a measuring

time, the sensor can sense the distorted temperature gradient

and output the flow rate profile signal that is different from one

where there are no bubbles. Afterwards, the dispense system

compares the difference in the two flow rate profiles. If the

difference exceeds the alarm setting limit, the dispense system

will alert the alarm.

There are two types of alarms, a warning alarm and an error

alarm. A warning alarm is alerted when the measured value

exceeds the set warning limit, and an error alarm alerts when

the measured value exceeds the set error limit. A warning alarm

tells users that the measured value is close to an unacceptable

level, while the error alarm tells that the measured value has

reached the unacceptable level. Both warning and error alarms

can send the signal to the coater developer and halt the process

and prevent defective wafers. Users can select what type of alarm

they want to use to halt the process. For details please see

Entegris application note Confirmation tools – Advanced

Monitoring of Photolithography Dispense Operation (IG-LV,

IG-ULV and IG-MV).

2

Figure 1 shows how Flow Profile Compare

works in case the error alarm is selected to

halt the production process.

Figure 1. Diagram demonstrating how flowmeter works as a confirmation tool.

EXPERIMENT—Testing was performed in the Entegris facility using

an IntelliGen® LV pump with firmware “Released

V1005_987” installed with Impact® 2 OF UPE 3 nm

filter. Isopropyl Alcohol (IPA) and 193 nm BARC were

used as the process fluids.

Air bubble events were created in order to evaluate

the sensitivity of the flowmeter and its software.

A flow profile was compared for both IPA and

193 nm BARC.

Figure 2. Testing rig.

Air bubbles of the following sizes, 0.001 mL to

0.009 mL in 0.001 mL incremental, 0.01 mL to

0.09 mL in 0.01 mL incremental and 0.1 mL were

injected into the outlet tubing via the injection port

made of a T-Connector. The bubble is controlled

to flow through the flow sensor at the same time

the sensor measures the liquid flow rate. Flow Profile

compare value is observed and recorded.

Tubing configuration

Location ID × length

Bottle to pump inlet 1/4" 500 mm

Pump outlet to air injection port 1/4" 50 mm

Pump outlet to flow sensor 1/4" 500 mm

Flow sensor to air operating valve 1/4" 700 mm

Air operating valve to nozzle 2 mm × 1000 cm

Vent line 2 mm × 50 cm

Sensor measures temperature gradient of point A and point B

Output signal of flowmeter

Input signal of dispense system

Flow rate profile of the last dispense is the same as the reference

Use copyexact theory

≥80% copy,dispensesystem does not alert alarm

Alarm signal is sent to coaterdeveloper

≤79% copy,dispensesystem alerts alarm

Flow rate profile of the last dispense is di�erent from the reference

Dispense system compares the flow rate profile of the dispense without air (reference) and the dispense with air

Flow sensor Dispense system

Flow rate profile

A B

0.001 mL Air, 193 nm BARC, 62% Dispense Volume = 1.7 mL Dispense Rate = 0.35 mL/s

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Reference of 0.001 mL, 193 nm BARC Dispense Volume = 1.7 mL Dispense Rate = 0.35 mL/s

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Reference of 0.001 mL, 193 nm BARC Dispense Volume = 1.7 mL Dispense Rate = 0.35 mL/s

Coater developer

Dispense is halted

Use copyexact theory

IPA 1 L Impact® 2 V2 3 nm UPC UC

Flow sensor

Air injection port

Vent

Pump outlet

IG-ULV

Inlet

Air operating valve

3

RESULT AND RESULT DISCUSSION—Table 1 summarizes the Flow Profile Compare data

percentages. The lower the percentage, the more

sensitive it is to air bubbles. Table 1 shows that

with an appropriate setting of dispense volume and

dispense rate, the flow profile compare can give a

percentage value lower than 70%. In general, the

alarm limit is set at 80% for Warning and at 70% for

Error. The test results prove that a dispense pump can

alert an Error alarm in the presence of the smallest

bubble, 0.001 mL or diameter of 0.8 mm (800 µm)

in size. This data confirms that adding a flowmeter

into the production line helps prevent air bubbles

from being dispensed onto wafers.

Table 1. Summary of percentage of flow profile compare

Bubble size

193 NM IRF BARC IPA

Flow compare

Dispense volume (DV) and dispense rate (DR)

Flow compare

Dispense volume (DV) and dispense rate (DR)

0.001 mL 62% DV 1 .7 mL DR 0.35 mL/sec 96% DV 0.7 mL DR 0.15 mL/sec

0.002 mL 31% DV 0.5 mL DR 0.15 mL/sec 32% DV 0.5 mL DR 0.15 mL/sec

0.003 mL 14% DV 0.3 mL DR 0.15 mL/sec 26% DV 0.3 mL DR 0.15 mL/sec

0.004 mL 27% DV 0.3 mL DR 0.15 mL/sec 53% DV 0.3 mL DR 0.15 mL/sec

0.005 mL 27% DV 0.3 mL DR 0.15 mL/sec 38% DV 0.3 mL DR 0.15 mL/sec

0.006 mL 58% DV 0.3 mL DR 0.15 mL/sec 17% DV 0.3 mL DR 0.15 mL/sec

0.007 mL 34% DV 0.3 mL DR 0.15 mL/sec 35% DV 0.3 mL DR 0.15 mL/sec

0.008 mL 38% DV 0.3 mL DR 0.15 mL/sec 33% DV 0.3 mL DR 0.15 mL/sec

0.009 mL 52% DV 0.3 mL DR 0.15 mL/sec 33% DV 0.3 mL DR 0.15 mL/sec

0.01 mL 55% DV 0.3 mL DR 0.15 mL/sec 33% DV 0.3 mL DR 0.15 mL/sec

0.02 mL 34% DV 0.3 mL DR 0.15 mL/sec 36% DV 0.3 mL DR 0.15 mL/sec

0.03 mL 34% DV 0.3 mL DR 0.15 mL/sec 42% DV 0.3 mL DR 0.15 mL/sec

0.04 mL 38% DV 0.3 mL DR 0.15 mL/sec 41% DV 0.3 mL DR 0.15 mL/sec

0.05 mL 39% DV 0.3 mL DR 0.15 mL/sec 44% DV 0.3 mL DR 0.15 mL/sec

0.06 mL 44% DV 0.3 mL DR 0.15 mL/sec 37% DV 0.3 mL DR 0.15 mL/sec

0.07 mL 37% DV 0.3 mL DR 0.15 mL/sec 38% DV 0.3 mL DR 0.15 mL/sec

0.08 mL 44% DV 0.3 mL DR 0.15 mL/sec 46% DV 0.3 mL DR 0.15 mL/sec

0.09 mL 42% DV 0.3 mL DR 0.15 mL/sec 44% DV 0.3 mL DR 0.15 mL/sec

0.1 mL 44% DV 0.3 mL DR 0.15 mL/sec 43% DV 0.3 mL DR 0.15 mL/sec

Note: The lower the percentage, the more sensitive to air bubbles.

4

Figures 3 through 21 summarize the differences

between reference flow rate profile (dispense without

air bubble) and the flow rate profile of the dispense

with air.

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0.001 mL Air, IPA, 96% Dispense Volume = 0.7 mL Dispense Rate = 0.15 mL/s

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Reference of 0.001 mL, IPADispense Volume = 0.7 mL Dispense Rate = 0.15 mL/s

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0.001 mL Air, 193 nm BARC, 62% Dispense Volume = 1.7 mL Dispense Rate = 0.35 mL/s

Fig 3 Table 1 Fig 3 Table 2

Fig 3 Table 3 Fig 3 Table 4

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Reference of 0.001 mL, 193 nm BARC Dispense Volume = 1.7 mL Dispense Rate = 0.35 mL/s

Top: Reference flow rate profile for 0.001 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.001 mL air in IPA

Figure 3.

Top: Flow rate profile of the dispense with 0.001 mL air in 193 nm BARC resulting in 62% flow profile compare

Bottom: Flow rate profile of the dispense with 0.001 mL air in IPA resulting in 96% flow profile compare

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0.002 mL Air, IPA, 32% Dispense Volume = 0.5 mL Dispense Rate = 0.15 mL/s

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0.002 mL Air, 193 nm BARC, 31% Dispense Volume = 0.5 mL Dispense Rate = 0.15 mL/s

Fig 4 Table 1 Fig 4 Table 2

Fig 4 Table 3 Fig 4 Table 4

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Reference of 0.002 mL, 193 nm BARC Dispense Volume = 0.5 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.002 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.002 mL air in IPA

Figure 4.

Top: Flow rate profile of the dispense with 0.002 mL air in 193 nm BARC resulting in 31% flow profile compare

Bottom: Flow rate profile of the dispense with 0.002 mL air in IPA resulting in 32% flow profile compare

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0.003 mL Air, IPA, 26% Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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Reference of 0.003 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.003 mL Air, 193 nm BARC, 14% Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 5 Table 1 Fig 5 Table 2

Fig 5 Table 3 Fig 5 Table 4

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Reference of 0.003 mL, 193 nm BARC Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.003 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.003 mL air in IPA

Figure 5.

Top: Flow rate profile of the dispense with 0.003 mL air in 193 nm BARC resulting in 14% flow profile compare

Bottom: Flow rate profile of the dispense with 0.003 mL air in IPA resulting in 26% flow profile compare

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0.004 mL Air, IPA, 53% Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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Reference of 0.004 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.004 mL, 193 nm BARC, 27% Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 6 Table 1 Fig 6 Table 2

Fig 6 Table 3 Fig 6 Table 4

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Reference of 0.004 mL, 193 nm BARC Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.004 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.004 mL air in IPA

Figure 6.

Top: Flow rate profile of the dispense with 0.004 mL air in 193 nm BARC resulting in 27% flow profile compare

Bottom: Flow rate profile of the dispense with 0.004 mL air in IPA resulting in 53% flow profile compare

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0.005 mL Air, IPA, 38% Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.005 mL Air, 193 nm BARC, 27% Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 7 Table 1 Fig 7 Table 2

Fig 7 Table 3 Fig 7 Table 4

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Reference of 0.005 mL, 193 nm BARC Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.005 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.005 mL air in IPA

Figure 7.

Top: Flow rate profile of the dispense with 0.005 mL air in 193 nm BARC resulting in 27% flow profile compare

Bottom: Flow rate profile of the dispense with 0.005 mL air in IPA resulting in 38% flow profile compare

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0.006 mL Air, IPA, 17%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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Reference of 0.006 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.006 mL Air, 193 nm BARC, 58%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 8 Table 1 Fig 8 Table 2

Fig 8 Table 3 Fig 8 Table 4

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Reference of 0.006 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.006 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.006 mL air in IPA

Figure 8.

Top: Flow rate profile of the dispense with 0.006 mL air in 193 nm BARC resulting in 58% flow profile compare

Bottom: Flow rate profile of the dispense with 0.006 mL air in IPA resulting in 17% flow profile compare

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0.007 mL Air, IPA, 35%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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Reference of 0.007 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.007 mL Air, 193 nm BARC, 34%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 9 Table 1 Fig 9 Table 2

Fig 9 Table 3 Fig 9 Table 4

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Reference of 0.007 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.007 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.007 mL air in IPA

Figure 9.

Top: Flow rate profile of the dispense with 0.007 mL air in 193 nm BARC resulting in 34% flow profile compare

Bottom: Flow rate profile of the dispense with 0.007 mL air in IPA resulting in 35% flow profile compare

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0.008 mL Air, IPA, 33%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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Reference of 0.008 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.008 mL Air, 193 nm BARC, 38%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 10 Table 1 Fig 10 Table 2

Fig 10 Table 3 Fig 10 Table 4

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Reference of 0.008 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.008 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.008 mL air in IPA

Figure 10.

Top: Flow rate profile of the dispense with 0.008 mL air in 193 nm BARC resulting in 38% flow profile compare

Bottom: Flow rate profile of the dispense with 0.008 mL air in IPA resulting in 33% flow profile compare

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0.009 mL Air, IPA, 33%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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Reference of 0.009 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.009 mL Air, 193 nm BARC, 52%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 11 Table 1 Fig 11 Table 2

Fig 11 Table 3 Fig 11 Table 4

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Reference of 0.009 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.009 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.009 mL air in IPA

Figure 11.

Top: Flow rate profile of the dispense with 0.009 mL air in 193 nm BARC resulting in 52% flow profile compare

Bottom: Flow rate profile of the dispense with 0.009 mL air in IPA resulting in 33% flow profile compare

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0.01 mL Air, IPA, 33%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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Reference of 0.01 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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0.01 mL Air, 193 nm BARC, 55%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 12 Table 1 Fig 12 Table 2

Fig 12 Table 3 Fig 12 Table 4

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Reference of 0.01 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.01 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.01 mL air in IPA

Figure 12.

Top: Flow rate profile of the dispense with 0.01 mL air in 193 nm BARC resulting in 55% flow profile compare

Bottom: Flow rate profile of the dispense with 0.01 mL air in IPA resulting in 33% flow profile compare

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0.02 mL Air, IPA, 36%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

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1500

1000

500

0

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Time (sec)

Flo

w R

ate

Rea

d b

y Fl

ow

Sen

sor

(mL/

s)

Reference of 0.02 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

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(mL/

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0.02 mL Air, 193 nm BARC, 34%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 13 Table 1 Fig 13 Table 2

Fig 13 Table 3 Fig 13 Table 4

15 201050-5

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Time (sec)

Flo

w R

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d b

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Sen

sor

(mL/

s)

Reference of 0.02 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.02 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.02 mL air in IPA

Figure 13.

Top: Flow rate profile of the dispense with 0.02 mL air in 193 nm BARC resulting in 34% flow profile compare

Bottom: Flow rate profile of the dispense with 0.02 mL air in IPA resulting in 36% flow profile compare

10

15 201050-5

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Time (sec)

Flo

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(mL/

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0.03 mL Air, IPA, 42%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

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Rea

d b

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Sen

sor

(mL/

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Reference of 0.03 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

w R

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Rea

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(mL/

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0.03 mL Air, 193 nm BARC, 34%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 14 Table 1 Fig 14 Table 2

Fig 14 Table 3 Fig 14 Table 4

15 201050-5

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Time (sec)

Flo

w R

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Rea

d b

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Sen

sor

(mL/

s)

Reference of 0.03 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.03 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.03 mL air in IPA

Figure 14.

Top: Flow rate profile of the dispense with 0.03 mL air in 193 nm BARC resulting in 34% flow profile compare

Bottom: Flow rate profile of the dispense with 0.03 mL air in IPA resulting in 42% flow profile compare

15 201050-5

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Time (sec)

Flo

w R

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(mL/

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0.04 mL Air, IPA, 41%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

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Rea

d b

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Sen

sor

(mL/

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Reference of 0.04 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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2000

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1000

500

0

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Time (sec)

Flo

w R

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Rea

d b

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Sen

sor

(mL/

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0.04 mL Air, 193 nm BARC, 38%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 15 Table 1 Fig 15 Table 2

Fig 15 Table 3 Fig 15 Table 4

15 201050-5

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0

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Time (sec)

Flo

w R

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Rea

d b

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ow

Sen

sor

(mL/

s)

Reference of 0.04 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.04 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.04 mL air in IPA

Figure 15.

Top: Flow rate profile of the dispense with 0.04 mL air in 193 nm BARC resulting in 38% flow profile compare

Bottom: Flow rate profile of the dispense with 0.04 mL air in IPA resulting in 41% flow profile compare

11

15 201050-5

2500

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Time (sec)

Flo

w R

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sor

(mL/

s)

0.05 mL Air, IPA, 44%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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2000

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1000

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0

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Time (sec)

Flo

w R

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Rea

d b

y Fl

ow

Sen

sor

(mL/

s)

Reference of 0.05 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

2500

2000

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1000

500

0

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Time (sec)

Flo

w R

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Rea

d b

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Sen

sor

(mL/

s)

0.05 mL Air, 193 nm BARC, 38%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 16 Table 1 Fig 16 Table 2

Fig 16 Table 3 Fig 16 Table 4

15 201050-5

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0

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Time (sec)

Flo

w R

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Rea

d b

y Fl

ow

Sen

sor

(mL/

s)

Reference of 0.05 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.05 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.05 mL air in IPA

Figure 16.

Top: Flow rate profile of the dispense with 0.05 mL air in 193 nm BARC resulting in 38% flow profile compare

Bottom: Flow rate profile of the dispense with 0.05 mL air in IPA resulting in 44% flow profile compare

15 201050-5

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Time (sec)

Flo

w R

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(mL/

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0.06 mL Air, IPA, 37%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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2000

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0

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Time (sec)

Flo

w R

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Rea

d b

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Sen

sor

(mL/

s)

Reference of 0.06 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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2000

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Time (sec)

Flo

w R

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d b

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sor

(mL/

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0.06 mL Air, 193 nm BARC, 44%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 17 Table 1 Fig 17 Table 2

Fig 17 Table 3 Fig 17 Table 4

15 201050-5

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Time (sec)

Flo

w R

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Sen

sor

(mL/

s)

Reference of 0.06 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.06 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.06 mL air in IPA

Figure 17.

Top: Flow rate profile of the dispense with 0.06 mL air in 193 nm BARC resulting in 44% flow profile compare

Bottom: Flow rate profile of the dispense with 0.06 mL air in IPA resulting in 37% flow profile compare

12

15 201050-5

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Time (sec)

Flo

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(mL/

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0.07 mL Air, IPA, 38%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

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Rea

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(mL/

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Reference of 0.07 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

w R

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Rea

d b

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(mL/

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0.07 mL Air, 193 nm BARC, 37%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 18 Table 1 Fig 18 Table 2

Fig 18 Table 3 Fig 18 Table 4

15 201050-5

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0

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Time (sec)

Flo

w R

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Sen

sor

(mL/

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Reference of 0.07 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.07 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.07 mL air in IPA

Figure 18.

Top: Flow rate profile of the dispense with 0.07 mL air in 193 nm BARC resulting in 38% flow profile compare

Bottom: Flow rate profile of the dispense with 0.07 mL air in IPA resulting in 38% flow profile compare

15 201050-5

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Time (sec)

Flo

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0.08 mL Air, IPA, 46%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Flo

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(mL/

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Reference of 0.08 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

w R

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(mL/

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0.08 mL Air, 193 nm BARC, 44%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 19 Table 1 Fig 19 Table 2

Fig 19 Table 3 Fig 19 Table 4

15 201050-5

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Time (sec)

Flo

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(mL/

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Reference of 0.08 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.08 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.08 mL air in IPA

Figure 19.

Top: Flow rate profile of the dispense with 0.08 mL air in 193 nm BARC resulting in 44% flow profile compare

Bottom: Flow rate profile of the dispense with 0.08 mL air in IPA resulting in 46% flow profile compare

13

15 201050-5

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Time (sec)

Flo

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(mL/

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0.09 mL Air, IPA, 44%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

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(mL/

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Reference of 0.09 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Time (sec)

Flo

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0.09 mL Air, 193 nm BARC, 42%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 20 Table 1 Fig 20 Table 2

Fig 20 Table 3 Fig 20 Table 4

15 201050-5

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0

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Time (sec)

Flo

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(mL/

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Reference of 0.09 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.09 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.09 mL air in IPA

Figure 20.

Top: Flow rate profile of the dispense with 0.09 mL air in 193 nm BARC resulting in 42% flow profile compare

Bottom: Flow rate profile of the dispense with 0.09 mL air in IPA resulting in 43% flow profile compare

15 201050-5

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0.10 mL Air, IPA, 43%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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(mL/

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Reference of 0.10 mL, IPADispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

15 201050-5

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Flo

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0.10 mL Air, 193 nm AR50, 44%Dispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Fig 21 Table 1 Fig 21 Table 2

Fig 21 Table 3 Fig 21 Table 4

15 201050-5

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Time (sec)

Flo

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(mL/

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Reference of 0.10 mL, 193 nm BARCDispense Volume = 0.3 mL Dispense Rate = 0.15 mL/s

Top: Reference flow rate profile for 0.10 mL in 193 nm BARC

Bottom: Reference flow rate profile for 0.10 mL air in IPA

Figure 21.

Top: Flow rate profile of the dispense with 0.10 mL air in 193 nm BARC resulting in 44% flow profile compare

Bottom: Flow rate profile of the dispense with 0.10 mL air in IPA resulting in 43% flow profile compare

14

CHART COMPARING SIZE OF DETECTABLE BUBBLE BY THREE DETECTORS—Figure 22 compares the sizes of bubbles that can be

detected by a liquid particle counter (left), Flow Profile

Compare Confirmation tool (middle), and Maximum

Pressure Confirmation tool (right). It was confirmed

in an Entegris laboratory that with the integration of

flowmeter technology, bubble detection improves

20 times compared to pressure sensor based tech-

nology. We can see that the smallest bubble detected

by Flow Profile Compare is 0.001 mL in volume, while

the smallest bubble detected by Maximum Pressure

is 0.02 mL. However, users must be aware that the

air bubble must pass through the flowmeter to be

detected by Flow Profile Compare. On the other

hand, the air bubble does not need to pass through

the pressure sensor to be detected by Maximum

Pressure, it just needs to exist in the outlet line. This

functionality differentiates the Flow Profile Compare

Confirmation tool from the Maximum Pressure

Confirmation tool.

Figure 22. Diagram comparing size of bubbles that are detected by a liquid particle counter (left); Flow Profile Compare Confirmation tool (middle); Maximum Pressure Confirmation tool (right).

Size of Detectable Bubble by Various Confirmation Tools

Minimum detectable bubble size

Volume <0.001 Ø<0.8 mm (0.03")

Volume = <0.001 Ø ≈ 0.8 mm (0.03")

Metrology

0.99 mm (0.04")

Ø3.96 mm(0.16")

Confidence range of

detection

Volume = <0.02 mL Ø ≈ 2.5 mm (0.1")

Volume = 0.04 mL Ø ≈ 3 mm (0.12")

Volume = 0.005 mL Ø ≈ 1.8 mm (0.07")

Flow profile compare• Drop to ≈ 60 % or below

Need to pass through flow sensor at the same timing as dispense starts

Liquid particle counterhigh-speed camera

Maximum pressure• Decrease 1 psi

Average pressure• Decrease 0.5 psi

Air detect volume• Increase 0.018 mL

Need to stay close to pressure sensors in dispense chamber. Signal is weaker

as bubble moves further away

15

WINDOWS OF OPERATION—To successfully detect bubbles using the flowmeter,

correctly setting up the dispense volume and dispense

rate are critical. An improper setting will lead to failed

bubble detection. Based on in-house testing, the

optimal setting for detecting an air bubble with a

diameter of 1.3 mm or larger has a dispense volume =

0.3 mL and a dispense rate of 0.15 mL/sec. Success-

fully detecting an air bubble with a diameter of

1.2 mm has a dispense volume = 0.5 mL and a dis-

pense rate of 0.15 mL/sec. Successfully detecting an

air bubble with a diameter of 0.8 mm has a dispense

volume = 1.7 mL and a dispense rate of 0.35 mL/sec.

The smaller the air bubble is, a higher dispense

volume and dispense rate are needed to increase

the time necessary for the flowmeter to detect the

existence of air. It is necessary that the bubble pass

through the sensor inside the flowmeter at the

same time the flow sensor measures the liquid flow

rate. If the timing is off, bubble detection cannot

be successful.

SETUP FOR A SUCCESSFUL BUBBLE DETECTION BY FLOW SENSOR—Besides using proper dispense volume and

dispense rate, the dispense line should be set

up properly. Follow these four tips to achieve

successful bubble detection.

1. When building the dispense line, do not use a fitting

for the tubing connection, especially between the

pump outlet port and the flowmeter. If there is a

fitting, bubbles coming from the dispense pump

will get stuck inside the fitting and cannot pass

through the flowmeter.

2. About 50 cm before the flowmeter location, incline

the tubing at a 10 – 15 degree angle. Too steep an

angle makes air bubbles move too quickly and they

cannot be detected by the flowmeter. Conversely,

too flat an angle causes bubbles to move too slowly

to reach the flowmeter and be detected.

3. About 5 cm before the flowmeter location, ensure

the tubing is perfectly horizontal. To achieve suc-

cessful air detection, the air bubble needs to pass

through the sensor installed inside the flowmeter at

the exact same time the flow sensor measures the

liquid flow rate. Perfectly horizontal tubing ensures

that air bubbles move slowly enough to be detected

by the flowmeter.

4. When building the dispense line, make sure that

the air bubble stops right before the flowmeter

before the next dispense starts. If the air bubble

stops in front of the flowmeter, it is more likely

to be detected than if it does not stop and pass

through the flow sensor before the next dispense

begins.

Dis

pen

se R

ate

(mL/

sec)

0.8 1.0 1.2 1.4 1.81.60.60.40.2

Bubble size

0.003 mL, Ø1.3 mm – Ø0.1 mL, Ø4 mm

0.002 mL, Ø1.2 mm

0.001 mL, Ø0.8 mm

0.35

0.30

0.25

0.20

0.15

Dispense Volume (mL)

Figure 23. Bubble diagram of dispense volume and dispense rate for a successful bubble detection.

Pump and filter

2. Tubing about 50 cm before flowmeter should be inclined at an angle of 10–15°

3. Tubing about 5 cm before flow sensor should be horizontal

4. Bubble should stop right before flowmeter and flow through the sensor inside flowmeter at the same time the sensor measures flow rate during dispense segment

To nozzle

Flow sensor1. Do not use a fitting for tubing connection

Figure 24. Setup of production line for successful bubble detection.

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CONCLUSION—With an appropriate window of operation and dis-

pense line, the experiment on both 193 nm BARC and

IPA showed successful bubble detection. This means

that Flow Profile Compare can be applied to various

photochemicals without any serious concerns.

Because this bubble-sensing software

uses copy exact theory for the confirmation, the

last dispense is the same as the reference. As long

as the liquid measured for the reference and for the

last cycle are the same, this bubble sensing system,

Flow Profile Compare, can be applied to all types of

chemicals in lithography process to detect bubbles

and prevent their translation to costly wafer defects.

REFERENCES—1. ”Air Bubble Formation and Dissolution in Dispens-

ing Nanoimprint Technology,” Xiaogan Liang, Hua

Tan, Zengli Fu, and Stephen Y. Chou, Nanostructure

Laboratory, Department of Electrical Engineering,

Princeton University, Princeton, NJ 08544, USA,

Nanonex Corporation, Monmouth Junction, NJ

08552, USA

ACKNOWLEDGEMENT—The author would like to thank Entegris colleagues

Mitsutoshi Ogawa, Entegris application engineer, for

engineering the test setup, Tomohiro Wagatsuma,

field service engineer, for participating in useful

discussion, and Keigo Yamamoto, product manager,

for guiding the experiment to completion.