Monitoring Air Supply in Spin Coating Photolithography Process · 2018-08-14 · Monitoring Air...

ADVANCED MATERIALS HANDLING | APPLICATION NOTE

Monitoring Air Supply in Spin Coating Photolithography ProcessAuthor: Kanjanawadee Shiraishi, Entegris

Photoresist film uniformity is one important factor among many

when spin coating photoresist. To control the uniformity of the

photoresist film, fluid flow at the dispense point plays an import-

ant role. To ensure uniform topography, fluid must form a

straight, solid stream at the nozzle tip, and it must flow at a

constant flow rate. Controlling fluid flow at the nozzle tip can

be achieved by adjusting the open and close timing of a stop

suckback valve that is usually installed between the dispense

pump and nozzle. After the dispense pump dispenses the fluid,

the stop suckback valve needs to open at the right time to enable

the fluid to form a straight, solid stream. If the valve opens too

early, there is not enough pressure to form a solid fluid stream

and the fluid will drip out of the nozzle tip. If the valve opens too

late, the flow rate will be compromised and too much fluid will

flow at the beginning, and too little will flow at the end.

Equally important to opening at the right time, the valve needs

to close at the right time as well. If the valve closes too early,

there will be an insufficient amount of fluid to cover the whole

wafer. If the valve closes too late, there may be a drop of fluid

that dispenses after the main fluid stream stops flowing because

the valve is not yet closed. To prevent these undesirable events,

the open and close timing of the stop suckback valve must be

precisely controlled.

Though most stop suckback valves are digitally controlled,

some are pneumatically controlled and require air to open and

close them. Air-operated valves need very consistent air pressure

to control the valve actuation and avoid fluctuations between

dispense cycles. Supplying consistent air pressure to lithography

production processes is vital but not easy to achieve. Air pressure

fluctuation is often inevitable, particularly when too many devices

require air at the same time. In those instances, it is likely the

stop suckback valve could receive insufficient air supply than

is necessary to actuate it. This consequently leads to a delay in

opening and closing the valve, which will eventually cause

poor uniformity of photoresist film on wafers during the

coating process.

To monitor photoresist dispense uniformity, Entegris offers a

dispense pump with an integrated monitoring “confirmation tool”.

The confirmation tool confirms whether the last dispense has the

same characteristic as the reference dispense that is recorded

prior as a good dispense. If the stop suckback valve open and

close timing varies due to fluctuating air pressure, the confirma-

tion tool can detect the change in the fluid flow rate and alert the

operator before wafers are compromised.

This application note introduces four of the nineteen tools in

Entegris’ confirmation tool that are responsive when air supplied

to the external stop suckback valve is weakened.

FOUR RESPONSIVE TOOLS AND THEIR PRINCIPLES—

Pressure Profile Compare (%)

Compares the pressure profile of the last cycle to the reference.

The matching percentage enables user to identify if they can

achieve the same quality of dispense in the last cycle as in the

reference.

Maximum Dispense Pressure (psi)

Measures the maximum level of pressure in the dispense cham-

ber. Observing a maximum pressure difference between the

reference cycle and the last cycle enables user to control

dispense quality.

Average Pressure (psi)

Monitors the average level of pressure in the dispense chamber

during dispense. Observing the average pressure difference

between the reference and the last cycle enables user to control

the dispense quality and be aware when an abnormal event

occurs.

Maximum Pressure Time (ms)

Monitors the timing of the peak pressure in the dispense chamber

during dispense. Observing the timing difference between the

reference and the last cycle enables user to be aware when an

abnormal event occurs.

2

EXPERIMENT

—Testing was performed in the Entegris laboratory using

an IntelliGen® LV pump with firmware “V1005_987”

installed with Impact® 2 OF UPE 3 nm filter. Isopropyl

Alcohol (IPA) and 193 nm BARC were used as the

process fluids.

The event of weak air supplied to the external stop

suckback valve was created by installing a needle

valve to the pneumatic line, and then incrementally

closing the needle valve to decrease the amount

of air going to the valve. The detailed test setup is

shown in Figure 1.

Original air pressure supply to the external stop

suckback valve was set at 350 kPa (50.76 psi),

300 kPa (43.51 psi) and 250 kPa (36.26 psi) using a

pressure regulator. The needle valve was adjusted

to the following four conditions at each pressure

level: 1) Fully open, 2) ¼ closed, 3) ½ closed, and

4) ¾ closed. The actual air pressure was monitored by

a Keyence pressure sensor and the test values of the

four confirmation tools of the IntelliGen IG-ULV were

observed and recorded.

Tubing configuration

Location ID × length

Bottle to pump inlet 1/4" 70 cm

Pump outlet to flow sensor 1/4" 50 cm

Flow sensor to air operating valve 1/4" 70 cm

Air operating valve to nozzle 2 mm × 100 cm

Vent line 2 mm × 50 cm

RESULT AND DISCUSSION

—Test results are divided into two parts, 1) Confirmation

whether air supplied to the external stop suckback

valve is weakened when the needle valve is closed,

and 2) Results of the four confirmation tools: Pressure

Profile Compare, Maximum Dispense Pressure,

Average Pressure, and Maximum Pressure Time.

1. Confirmation whether air supplied to the external

stop suckback valve is weakened when needle valve

is closed:

350 kPa (50.76 psi) is the pressure specification.

Normally, users are required to provide this level of

pressure to the stop suckback valve. 300 kPa (43.51)

and 250 kPa (36.26 psi) are the test cases when air

supply is lower than the requirement.

The confirmation shows that air supplied to the

outlet valve starts to become weak when the needle

valve (installed at the air line between the pressure

regulator and pneumatic valve) is half closed.

Figures 2 through 4 demonstrate the pressure

monitored by Keyence pressure sensor.

Figure 1. Test setup.

IPA 1 L Impact 2 V2 3 nm UPC UC

Flow sensor

Vent

Pump outlet

IG-ULV

Inlet

Air operating valve

Needle valve1⁄4, 1⁄2, 3⁄4 close

3

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350 kPa Air Supply with Fully Opened Needle Valve

PressureValve signal

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350 kPa Air Supply with 1⁄4 Closed Needle Valve


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Figure 2. Actual pressure (blue) and valve signal (red) monitored by Keyence at air supply of 350 kPa.

Pre

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al300 kPa Air Supply with 3⁄4 Closed Needle Valve


12:1

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3


2. Test results of four confirmation tools: Pressure

Profile Compare, Maximum Dispense Pressure,

Average Pressure, and Maximum Pressure Time.

Results show that the four confirmation tools give a

reliable response to the situation when air supplied

to the external stop suckback valve is weaker than

the reference situation. Figures 5 through 8 show

the test results of Pressure Profile Compare, Maxi-

mum Dispense Pressure, Average Pressure, and

Maximum Pressure Time at the air supply of 350

kPa, 300 kPa, and 250 kPa, respectively. Figures 9

through 11 show the pressure profile when the

needle valve is fully opened, ¼ closed, ½ closed,

and ¾ closed, respectively.

5

Dis

pen

se P

ress

ure

(%)

350 kPa Dispense Pressure Profile Compare

120

100

80

60

40

20

0

Dis

pen

se P

ress

ure

(%)

120

100

80

60

40

20

0

Dis

pen

se P

ress

ure

(%)

120

100

80

60

40

20

0



0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number

Top: Original air supply is at 350 kPa

Bottom: Original air supply is at 300 kPa


Figure 5. Test results of Pressure Profile Compare Confirmation tool; Running No. 1 to 100: needle valve is fully opened, Running No. 101 to 200: needle valve is ¼ closed, Running No. 201 to 300: needle valve is ½ closed, Running No. 301 to 400: needle valve is ¾ closed and Running No. 401 to 500: needle valve is fully opened again.

Dis

pen

se P

ress

ure

(psi

)

350 kPa Dispense Maximum Pressure

17

16

15

14

13

12

11

Dis

pen

se P

ress

ure

(psi

)

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16

15

14

13

12

11

Dis

pen

se P

ress

ure

(psi

)

17

16

15

14

13

12

11



0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number




Figure 6. Test results of Maximum Confirmation tool; Running No. 1 to 100: needle valve is fully opened, Running No. 101 to 200: Needle valve is ¼ closed, Running No. 201 to 300: Needle valve is ½ closed, Running No. 301 to 400: needle valve is ¾ closed and Running No. 401 to 500: needle valve is fully opened again.

6

Dis

pen

se P

ress

ure

(psi

)

350 kPa Dispense Average Pressure

5.5

5.0

4.5

4.0

3.5

3.0

7.0

6.5

6.0

5.5

5.0

4.5

4.0

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3.0

Dis

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se P

ress

ure

(psi

)

Dis

pen

se P

ress

ure

(psi

)



0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number




Figure 7. Test results of Average Pressure Confirmation tool; Running No. 1 to 100: Needle valve is fully opened, Running No. 101 to 200: needle valve is ¼ closed, Running No. 201 to 300: Needle valve is ½ closed, Running No. 301 to 400: needle valve is ¾ closed and Running No. 401 to 500: needle valve is fully opened again.

Dis

pen

se P

ress

ure

Tim

e (s

ec)

350 kPa Dispense Maximum Pressure Time

1100

1050

1000

950

900

850

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700

Dis

pen

se P

ress

ure

Tim

e (s

ec)

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1050

1000

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Dis

pen

se P

ress

ure

Tim

e (s

ec)

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1050

1000

950

900

850

800

750

700



0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number

0 100 200 300 400 500

Running Number




Figure 8. Test results of Maximum Pressure Time Confirmation tool; Running No. 1 to 100: needle valve is fully opened, Running No. 101 to 200: needle valve is ¼ closed, Running No. 201 to 300: needle valve is ½ closed, Running No. 301 to 400: needle valve is ¾ closed and Running No. 401 to 500: needle valve is fully opened again.

7

Pre

ssu

re (p

si)

350 KPa Reference Pressure Profile when Needle Valve is Fully Open

350 KPa Compare Reference Pressure Profile when Needle Valve is 1⁄4 Closed

16

14

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8

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4

2

0

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ReferenceNeedle valve

-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

Pre

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Pre

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Reference


-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

Figure 9. Pressure profile when original air supply is at 350 kPa.

Pre

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Pre

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re (p

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-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

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Pre

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Reference


-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)


8

SUMMARY—Among the four pressure sensor based tools, the

Pressure Profile Compare showed the most sensi-

tive response when air supplied to the stop suckback

valve is weakened. The percentage of Pressure

Profile Compare test results drop to 80% from

100% of reference level when air supplied is half of

the original level, and 20% – 40% when air supply is

one quarter of the original level. Though the setting

limit for alarm activation depends upon the user,

in general the warning limit is usually set between

80% – 90% and the error limit is between 70% – 80%.

The 80% test result is sufficient to activate the alarm,

and the 20% – 40% test result is definitely able to

activate the alarm.

One can confidently use the Pressure Profile Com-

pare confirmation tool to accurately monitor air

supply fluctuations. Figure 12 shows the overall

dispense system setup.

Even though they are not the most responsive, the

Maximum Pressure, Average Pressure, and Maximum

Pressure Time pressure sensor based tools showed a

reliable response to this abnormal event. Test results

show an obvious and stable change when air supplied

to the stop suckback valve is weakened. These three

tools could also be used to monitor air supply

fluctuations.

Pre

ssu

re (p

si)



16

14

12

10

8

6

4

2

0

Pre

ssu

re (p

si)

16

14

12

10

8

6

4

2

0


-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

Pre

ssu

re (p

si)



16

14

12

10

8

6

4

2

0

Pre

ssu

re (p

si)

18

16

14

12

10

8

6

4

2

0


Reference


-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)

-1.0 -0.5 0 0.5 1.0 1.5 2.0

Time (sec)


9

SYSTEM LAYOUT—

CONCLUSION—Consistent air pressure is critical in maintaining high

quality control over chip manufacturing processes.

However, it is not easy to establish. Adding an air

pressure confirmation tool can help manufacturers

better control the wafer coating process. When the

ability to monitor and control air pressure increases,

wafer yield also increases.

Entegris has an innovative photochemical dispense

pump with an integrated pressure sensor. User-

friendly MMI software with robust confirmation tools

simplifies recipe programming and provides real-time

status. The integrated Pressure Profile Compare

confirmation tool is featured in the IG-Mini and new

pumps IG-ULV, IG-LV and IG-MV, and enables reliable

monitoring and control in numerous applications.

Implementing a dispense pump with a pressure

sensor confirmation tool can help minimize costly

wafer defects.

ACKNOWLEDGEMENT—The author would like to thank Entegris colleagues

Mitsutoshi Ogawa, application engineer, for engineer-

ing the test setup, Tomohiro Wagatsuma, field service

engineer, for participating in useful discussion, and

Keigo Yamamoto, product manager, for guiding the

experiment to completion.

Figure 12. Dispense system setup.

Drain

Inlet

OutletVent

Wafer

Nozzle

N₂ pressure

Bottle

L/E

Pump cable

Multi interface module

I/O signal

24V power

IntelliGen ULV/LV/MV

Outlet valve

Solenoid

IntelliGen NCS Factory database

Computer

Fluid

Utility

Electricity

N₂ pressureand vacuum

LAN

RS-422

Trackinterface

FOR MORE INFORMATION

Please call your Regional Customer Service Center today to learn what Entegris can do for you. Visit entegris.com and select the Contact Us link to find the customer service center nearest you.

TERMS AND CONDITIONS OF SALE

All purchases are subject to Entegris’ Terms and Conditions of Sale. To view and print this information, visit entegris.com and select the Terms & Conditions link in the footer.

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Tel +1 952 556 4181Fax +1 952 556 8022Toll Free 800 394 4083

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Entegris®, the Entegris Rings Design®, and other product names are trademarks of Entegris, Inc. as listed on entegris.com/trademarks. All third-party product names, logos, and company names are trademarks or registered trademarks of their respective owners. Use of them does not imply any affiliation, sponsorship, or endorsement by the trademark owner.

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