A New Nonvolatile Residue Monitor for the Semiconductor Industry

By

David Blackford Ph.D.

Fluid Measurement Technologies

• What exactly is nonvolatile residue?• Why do I need to measure it?• What good is it if you can’t tell me what the

residue consists of?• And so far I have managed perfectly well

without measuring NVR, so why should I start now?

Questions about Nonvolatile Residue

What exactly is nonvolatile residue?

Nonvolatile residue is dissolved inorganic material. • Primarily silica, both dissolved and colloidal.• Also ions and trace metals.

Nonvolatile residue is not.• Particles.

Why do I need to measure NVR?

Nonvolatile Residue is increasingly being used as a measure of overall water quality. It is frequently the first on-line measurement to indicate a problem in a UPW system.

Nonvolatile residue can now be monitored at ppt levels in almost real-time.

What good is NVR if you can’t tell me what the residue consists of?

On-line TOC monitors and particle counters cannot identify the specific TOC compound or particle composition.

BUT, speed is everything. The true value of on-line monitors comes from a fast indication of a problem. Then, you can collect and analyze a sample to identify the source of the contamination.

And so far I have managed perfectly well without measuring NVR, so why should I start now?

As semiconductor line-widths become smaller, semiconductor manufacturing becomes more susceptible to contamination.

As the ITRS Roadmap committee looks to the future, it is working to find parameters to measure at the required detection limits. So the day is coming when maybe you should consider monitoring NVR.

How the NRM was “born”

• 20 years ago, Bob MacIntosh asked me if there was a way to get some response to the presence of colloidal silica in UPW.

• In 1992 the original NRM was introduced.

• The basic concept was not new. In 1964 two Australian professors had proposed using a nebulizer, a drying column and a particle counter to measure nonvolatile residue in solvents.

The original NVR nephelometer system (Salkowski and Werle, 1964)

Schematic for the new Nonvolatile Residue Monitor

The NRM technique

“Drip-counter” for measuring very low flow rates

Improvements over the original NRM• Expanded measurement range, 1ppt to 60 ppb.• No more n-butyl alcohol.• 10x faster response time.• 1/3rd the weight and 2/3rd the volume.• Innovative water inlet flow monitor.• Able to measure water up to 80 degrees centigrade.• Universal power supply.• Pressure actuated water regulator (no more water

leaks).

NRM Model 8000

Time (minutes)

0 50 100 150 200

Ra

w N

RM

co

un

t d

ata

0

2000

4000

6000

8000

10000

12000

14000

1 ppb

2 ppb 3 ppb

KCl challenges

9.8 ppt challenge of KClData averaged every 60 seconds

Time (seconds)

0 500 1000 1500 2000 2500 3000 3500

Raw

NR

M c

ou

nt

dat

a

900

1000

1100

1200

1300

1400

1500

US Semiconductor FacilitySimultaneous data collected for the NRM and a Hach

Silica Monitor

Non

vola

tile

Res

idue

(pp

t)

Time

Dissolved S

ilica (ppb)

0

1

2

3

4

NVR

SiO2

4pm 5pm 6pm 7pm 8pm 9pm 10pm 11pm 12pm 1am 2am 3am 4am 5am 6am

0

100

200

300

400

Low level (<10 ppb) 22nm colloidal silica challenge20 nm pore size filter

Time (minutes)

Filter removal efficiency 72%

0 10 20 30 40 50 60 70

Raw

NR

M c

ou

nt

dat

a

0

200

400

600

800

1000

1200

1400

1600

1800

2000

400 meshdiffusion screen

thro

ugh

filte

r

filte

r by

pass

ed

2007 ITRS “Round Robin”Data collected at Point of Entry (POE)

Parameters monitored were particles by SEM, TOCAn/Cat and TM, DO and DN and NVR.

Average NVR data for UPW collected over 3 days

Site A 245 ppt

Site B 243 ppt

Site C 199 ppt

Site D 156 ppt

Site E 102 ppt

Site F 96 ppt

Conclusions

The new Nonvolatile Residue Monitor offers improved contamination measurement of UPW:

• Expanded measurement range.

• Smaller, lighter, faster.

• Knocking at the door of ppq.