metrics and methods for reducing rinse water consumption

© 2005 FSI International, Inc. All rights reserved. always thinking // better®

Metrics and Methods for Reducing Rinse Water

Consumption in an Immersion System

Steve NelsonFSI International


Outline

• Introduction• Overflow rinse uniformity• Overflow rinse chemical carryover• Dump rinse uniformity• Dump rinse chemical carryover• Conclusions


• 7570 liters UPW per 200mm wafer (SEMI, 2001)

• 80% for wet etching and cleaning (SEMI, 2001)

• 60% is for rinse steps (Micro, May 1995)

• 5-7 liters/cm2 Fab UPW use in 2003 (ITRS 2001)( = 3500-5000 liters per 300mm wafer)

• 0.075 l/cm2 Tool UPW use in 2003 (ITRS 2001)( = 53 liters per 300mm wafer per run, or 2650 liters/50 wafer run)

• ITRS requires significant reductions in future

Water Usage in IC Manufacturing


Cleaning OptimizationMultiple Goal Optimization

• Process Performance– uniformity, defects, surface termination

• Productivity– COO, footprint, cycle time, throughput

• Chemical and DI Water Usage– continuous improvement


Small Footprint, Short Cycle Time• In Batch Immersion Reduced cycle time achieved with:

– Muli-use tanks– Dilute, single-pass chemistry– Chemical injection in final rinse tank

• Challenge: Minimize Chemical and Water Usage


Overflow Rinsing


Plug Flow Rinsing versus High Velocity Water Jet Stir Rinsing

−

= Vqt

oeCC


Overflow Rinse Uniformity200:1 HF thermal oxide etch,

followed by in-situ rinse, 300-mm wafers

Original Rinse Designstdev = 7.8 Årange = 33.6 Å

New Rinse Designstdev = 1.2 Årange = 4.4 Å


Overflow Rinse Carryover

• In-situ resistivity probe installed in overflow catch weir

• Standard practice = rinse to 14 Mohm

• Not representative of water near wafer boundary layer.

– residual chemical in weir

– CO2 dissolution.DI Flow

14 MΩ-cmResistivity

Meter

Mendicino et al., SEMI Technical Symposium, SEMICON West 2001

Traditional “Rinse-to-Resistivity”


Measuring at the Wafer

• Wafer Gap Conductivity CellLindquist et al, p.55, MRS Proc. Vol 386, 1995

• Oxide Trench w/ Buried PolyShadman et al, p.189, Solid State Phenomena Vols. 76-77 (2001) [proceedings of UCPSS 2000]

• Measure pH of Carry Over LayerThis work


Carry Over Layer Method

DI waterwet wafer

Drain

N2 blanket

Measure pH

Orbital Shaker, 10 minutes

Fill tank with diluteHCl solution andsoak wafer.

Place wet wafer intray with DI waterto collect chemicalfor measurement.

Pull Philic waferFrom tank withsome liquid


Carryover Layer Calibration

* R. Spearow, J. Rosato and C. R. Helms, “Studies of Rinse Efficiencies in Wet Cleaning Tools,” Proc. 3rd Intl. Symp. on Cleaning Technology inSemiconductor Device Manufacturing, J. Ruzyllo and R. Novak, Eds., The Electrochemical Society, Pennington, NJ, PV 94-7, 1994, pp. 140-152.

= −

−

k

collected

pH

pH

htan10

107.1414

Surface area of waferand dilution with waterIn collection tray.

300-mm wafer pulled from 0.05 M HCl

Wafer Pull Speed from Bath by Robot (mm/sec)0 5 10 15 20 25 30 35 40 45 50

Liqu

id L

ayer

Thi

ckne

ss (µ

m)

0

5

10

15

20

Liquid drops offwafer bottomreducing collectedamount

* h=1.51 v2/3


Original Rinse Design Results

Rinse Time (minutes)0 1 2 3 4 5 6 7 8 9 10

[H+ ] (

mol

es/li

ter)

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

Overflow liquidTheoretical for CSTRFit (0-6 min and 6-10 min)

Carryover layer

Fit = 4.98x10-2e-0.84t

84% efficiency

Fit = 5.012x10-2e-1.002t

Fit = 1.43x10-2e-0.64t

64 % efficiency

Fit = 5.6x10-2e-0.669t

67% efficiency


New Rinse Design Results

Rinse Time (minutes)0 1 2 3 4 5 6 7 8 9 10

[H+]

(mol

es/li

ter)

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1Overflow liquidCarryover layerFits CSTR model

Fit =7.5x10-2e-0.99t 88.8 % efficient

Fit =5.01x10-2e-1.115t

Fit =5.01x10-2e-1.048t

94.0 % efficient


Etch Uniformity and Particle Results after Rinse Optimization

Rinse Time (seconds)0 60 120 180 240 300C

ross

waf

er u

nifo

rmity

(1 s

igm

a)

0.40.60.81.01.21.41.61.82.0

Rinse Time (seconds)90 120 150 180 210 240 270 300 330

Part

icle

s A

dded

>0.

09 µ

m

0

100

200

300

400

500

600

700

200:1 HF with in-situ overflow rinse using new rinsehardware and settings. 180-second rinse time.Followed by IPA dry.


Benefits for 300-mm Production

120-Liters400-LitersWater Used

180-seconds600-secondsRinse Time

New Rinse MethodOld Rinse Method


Dump Rinsing


Dump Rinse Uniformity

Side spray bars Overhead spray bars

Shadowingfrom tank

Etch Data

Ave. = 20.7 Å

Min. = 17.7 Å

Max. = 36.2 Å

Each color = 1Å

Etch Data

Ave. = 23.8 Å

Min. = 20.6 Å

Max. = 26.0 Å

Each color = 1Å

200:1 HF thermal oxide etchfollowed by chemical dump and spray


Tank Bottom and Wafer Surface Carryover

Tank and waferswith dilute HCl.

Dump tank, wafersand tank coatedwith chemical.

Refill tank with water.Use megasonics to mixchemical with waterto collect and measure.

830-mL chemical remainedin the tank after 15 second dump.


Accounting on Liquid when Tanks Dumps

• Liquid remaining on wafer = πr2h x 2 x # wafers, h = 1.51v2/3 = 170-mL

• Liquid remaining on tank walls = 10-mL

• 600+170+10 = 780-mL

Liquid remaining in bottom of tank,collected with sponge and measured

Quick Dump Time (seconds)0 5 10 15 20 25 30 35

Liqu

id o

n Ta

nk B

otto

m (L

iters

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

15 sec, 600-mL


Dump and Spray Time (seconds)0 15 30 45 60 75 90

[H+]

(mol

es/li

ter)

1e-5

1e-4

1e-3

1e-2

1e-1

Overflow rinseNo inlet flush, with sprayWith inlet flush and spray

Spray Rinse During Dump Step

• Tank inlet flush needed to rinse chemical out of tubing or it ends up in tank in next fill.

• With good coverage spray, chemical is removed faster with dump time up to 60 seconds.


Dump Rinse Recipe Changes

3,000,00040,000Dilution

145-Liters305-LitersTotal Water Used

270-sec425-secTotal Rinse Time

25Number dump cycles

New Dump Rinse Recipe and Hardware

Old Dump Rinse Recipe and Hardware


Conclusions• Oxide etch uniformity and pH measurements can be

effective rinse characterization tools.• Rinsing chemical from the wafer surface behaves

different than rinsing the bulk of the liquid.

• Good spray coverage recommended for dump rinsing.

• Tank inlet flush recommended for dump rinsing.• Longer dump times with fewer dumps save time and

water and rinse better.

metrics and methods for reducing rinse water consumption

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