Effect of Pumping Method on Wafer Cleaning

6th LEVITRONIX CMP and Ultrapure ConferenceThe Westin Park Central, Dallas, Texas

May 11-12, 2011

Effect of Pumping Method on Effect of Pumping Method on Wafer Cleaning

R Prasanna Venkatesh Jung Soo Lim and Jin Goo ParkR. Prasanna Venkatesh, Jung-Soo Lim and Jin Goo Park

May 12, 2011

Department of Materials Engineering, Hanyang University,Ansan, 426-791, Korea

Semiconductor Cleaning

Particle

Organic contaminant

M l

Interaction Force

MetalNative oxide Attached Particle

W t Cl i

Si Wafer

• Wet Cleaning

• Dry Cleaning

ex) SC1, SC2, Piranha, HF etc…

2 Nano-Bio Electronic Materials and Processing Lab.

• Dry Cleaningex) Laser shock cleaning, Plasma, Anhydrous HF, Jet Fluid, Cryogenic etc…

ITRS Roadmap for DRAM


41 36 32 29 25 Mask defect size, nm

ITRS Roadmap for DRAM


Semiconductor cleaning

22nm22nm

167nm

High Aspect ratio (>8 : 1)

※ Generic Logic Flow 200711Metal Layers• 11Metal Layers

• 556 Total Steps• Cu Dual Damascene Tech. Multi layer （65nm, 2006）Leaning

• No pattern damages• No pattern damages• Film loss freeN t i l

5 Nano-Bio Electronic Materials and Processing Lab.Delamination

• New materials

Issues for the next Generation

6 Nano-Bio Electronic Materials and Processing Lab.S. Nadahara, “Wet Cleaning Technology Innovation”, SPCC (2011)

Cleaning target

7 Nano-Bio Electronic Materials and Processing Lab.S. Nadahara, “Wet Cleaning Technology Innovation”, SPCC (2011)

EUVL mask contamination sources & cleaning issues& c ea g ssues

13 5 nm

Contamination sourcesA pellicle cannot be used in EUVL due to itst d ti it h ld b l d

HO i

13.5 nm EUV Light

strong adsorption, it should be cleaned morefrequently

Haze

Ru C-L(2.5nm)

TaN A-L(80nm)

Oxidation

OrganicParticle

Surface roughness

Substrate(Quartz)

Mo-Si M-L(280nm)

Defect

(Quartz)Cond. Film

(CrN, 70nm)

Zero printable defect on a finished mask• Zero printable defect on a finished mask• No pellicle adders might be formed during handling and use• To clean new material surface, development of new cleaning solution and process


- ruthenium, TaOx (Quartz and Si included)• To prevent reflectivity loss, control of particle, roughness, carbon-contamination, pattern damage

Semiconductor cleaning methods

High effective & Low COO

Chemical Cleaning • Megasonic

But, physical damages & High initial cost

Chemical Cleaning

• RCA

• Droplet / Jet spray

• Gas aerosol

• Gas dissolved water

• Solvent / Chelating

• Gas / Vapor phase

• Dry ice cleaning

• Laser shock cleaning

• Cluster cleaning

Physical Cleaning

Gas / Vapor phase

• Plasma

• UV light

• Cluster cleaning

• ScCO2

Cheap & High Throughput


But, chemical etching & residues

Gas dissolved DI water cleaning

Definition of gas dissolved DI

water cleaning1. DI water based solutions

2. it contains a small amount specific ESH

Low CoO

2. it contains a small amount specific

gas and chemicals in ppm level

3. W/ or W/O Application of physical

h M i Specific

ESHenvironmentenvironmentSafetySafetyHealthHealth

energy such as Megasonic

H2, O3….with

Specific gases

High Cleaning Efficiency

Megasonic

Room temp.Room temp.PPProcessProcess

LowchemicalLow

material


residuesmaterialloss

Gas dissolved DI water generationand cleaning systemg y

Out-Gas Out-Gas

Pump Gas

LiquidH2-DIW Contactor(Phaser II, Engetris)

H2-DIW Sensor(TOA-DKK, Japan)

Hydrogen

Extra gas

H2-DIW

Buffer Tank H2-DIWPump(Levitronix)

Single Tool+ Megasonic

• Dissolved Hydrogen sensor : DHDI-1 (TOA-DKK, Japan)

• Gas contactor : pHasorⅡ (Entegris, USA)

• Circulation Pump : BPS-3 (Levitronix, USA)

• Single tool (Aaron, Korea)

• Megasonic /1 MHz (Durasonic, Korea)

Cone & twin type Cone & twin type Evaluation of H2-DIW


Cone & twin type Cone & twin type /1MHz (/1MHz (DurasonicDurasonic, Korea), Korea) Characteristics, PRE, Analysis of Si wafer surface….

PRE of H2-DIW w/ or w/o megasonic

DIW + NH4OH100

DI water+NH4OH

PRE of w/ MS @ 1MHz PRE of w/o MS

90

1004

H2-DIW (2.0 ppm) + NH4OHMS power : 1 W80

DI water+NH4OH H2-DI water(2.0 ppm)+NH4OH

Cavitation effect

0

80

40

60

PRE

(%)

10

7020

Change of electrostatic force by zeta potential value

0

W/ 32.0 ppm NH4OHW/ 1.4 ppm NH4OHW/O NH4OHpH 10pH 9pH 6.5

0pH 10pH 9pH 6.5

W/ 32.0 ppm NH4OHW/ 1.4 ppm NH4OHW/O NH4OH

• PRE was improved as gas concentration and pH increased

• H2-DIW(2.0ppm) w/ NH4OH has Higher PRE than DIW-NH4OH

High pH and H2 concentration result in Higher PRE (cavitation effect and Zeta potential)

• Cavitation effect is highly improved by adding H2 gas in DI water


• Cavitation effect is highly improved by adding H2 gas in DI water

• Cavitation effect by megasonic is more dominant factor than change of zeta potential value

PRE comparison with conventional method

100

MS power : 1 W

As deposited : 5000 ea

Surface scanner

90H 9 0H 9 0pH 10 5 H 10 5

scannerimages

80 +NH4OHH2-DIW pH 9.0

DIW pH 9.0

SC-1/25oCpH 10.5 pH 10.5

RE

(%) SC-1/50oC

+NH4OHH2-DIW(2.0ppm) + MS (1W)106 ea

SC-1/50℃ + MS (1W) : 322 ea

Scan range : 0.18 ~ 1.6 μm

10

70PR

106 ea

0

10

PRE : 98%PRE : 96%

• Conventional SC-1 has over 96% of PRE in single type cleaning with MS.

2ppm of H2-DIW (pH9) has the highest PRE over 98%


• H2-DIW can be proposed as an alternative cleaning solution

Hanyang University

Wafer cleaning in DI Water using pumps with and without pulsationWafer cleaning in DI Water using pumps with and without pulsationpumps with and without pulsation

1 I t d ti

pumps with and without pulsation

1 I t d ti1. Introduction- MLC (without Pulsation) vs. Positive displacement pumps

( ith l ti )

1. Introduction- MLC (without Pulsation) vs. Positive displacement pumps

( ith l ti )(with pulsation)- Magnetic levitation centrifugal vs. Positive displacement pumps (with pulsation)

- Magnetic levitation centrifugal vs. Positive displacement pumps

2. Results & Discussion- Wafer cleaning using DI water in wet bath

2. Results & Discussion- Wafer cleaning using DI water in wet bath - Wafer cleaning using DI water in single processor tool

3. Summary- Wafer cleaning using DI water in single processor tool

3. Summary

14 Nano-Bio Electronic Materials and Processing Lab.Electronic Materials and Processing Lab.

INTRODUCTION-Applications of Pumps in Wafer Cleaningpp p g

• For delivering and circulating chemicals for various processes in semiconductor industries such as wafer cleaning, CMP etc.

P F P F

Tank

Regulator

Tank

Regulator

HeaterHeater

Bubble CutterBubble Cutter

Dampner

FilterFilter

Dampner

Conventional (Diaphragm) Pump

Pump Check V/V Pump Check V/V

Centrifugal Pump (SC-1)


(SC-1)

INTRODUCTION- Centrifugal vs. Positive Displacement Pumps

Merits of Centrifugal Pumps• Flow is continuous in centrifugal whereas pulsatile in positive • Flow is continuous in centrifugal whereas pulsatile in positive

displacement (PD) pumps.

Demerits of Centrifugal PumpsDemerits of Centrifugal PumpsThe process require continuous and stable flow. However PD pumps are generally used because of the following issues associated with centrifugal pumps pumps

• It accepted as high shear devices due to high speed of operation• Delivery of ultra clean and delicate fluid is a major issue due to the y j

mechanical failure of shaft seal.• Bearings in centrifugal pump get destroyed if the pumping fluid

contain abrasive particles which is common in CMP application

What is the solution?– Bearingless, sealingless centrifugal Pump :


g , g g pMagnetic Levitation centrifugal (MLC)Pump

INTRODUCTION- MLC vs. Positive Displacement Pumps

Particle agglomeration : Higher in positive displacement pumps due to high Particle agglomeration : Higher in positive displacement pumps due to high shear force exerts on the liquid being pumped1

CMP: MLC pumps leaves less scratches on wafer surface due to lower particle p p pagglomeration2

Particle shedding: MLC pumps shed lower number of particles during Particle shedding: MLC pumps shed lower number of particles during processing when compared to positive displacement pumps3

Foaming effect: positive displacement pump generates lot of bubbles when Foaming effect: positive displacement pump generates lot of bubbles when surfactant triton X is used4

These reports confirm that MLC pump overcome the major issues associated i h i l if l d i i di lwith conventional centrifugal and positive displacement pumps

What is the influence of pumps on surface preparation?


OBJECTIVES AND METHODOLOGIES

Objectives:

To study the effect of pumping methods (with and without pulsation) on cleaning process performance in

1. Conventional wet bath2. Single wafer processor

Methodologies:

Estimation of number of particles added onto the silicon waferduring cleaning in DI water at different flow rates when pumpswith and without pulsation were applied

Estimation of random yield loss from particle count data usingvarious correlations.


WAFER CLEANING EXPERIMENTS

Single Processor Wet Station

SC-1

Drain

Diaphragm PumpSingle tool Supply

Bath Circulation


Schematic diagram of Experimental set up

WAFER CLEANING EXPERIMENTS IN WET BATH

Schematic diagram and Photograph of wet bath


Schematic diagram and Photograph of wet bath

EXPERIMENTAL FLOW CHART- WET BATH

Connecting Pump to the circulation line

DI water circulation for 24 hours

Flushing and Refilling Tank with DI water

To remove particles generated during initial pumping

Flushing and Refilling Tank with DI water

Pre -circulation for 30 min

For stable flow

Wafer pre-Cleaning : SC-1

D i Si l Aki t lTo ensure the surface is hydrophillic

-For stable flow

Drying : Single Akiron tool

Wafer immersion in circulation bath for 10 min10 min

Wafer inspection before and after immersion

End of every 4 hr

(0,4,8,12,16,20 and 24th hr)

21 Nano-Bio Electronic Materials and Processing Lab.End

EXPERIMENTAL CONDITIONS

Experimental Test Conditions in Wet Bath

Pump Flow rate (LPM) Pressure (PSI)Pump Flow rate (LPM) Pressure (PSI)

BPS-600 (MLC) 10 and 15 30

Diaphragm (D1) 10 and 15 30±3

Wafer Inspection using surface scanner (ST6600, KLA Tencor, USA)

Diaphragm (D2) 10 and 15 30±6


EFFECT OF PUMPING METHODS ON WAFER CLEANING IN WET BATH

25000

30000

35000

Particles (ea)

Out of inspection range

25000

30000

35000

articles (ea)


25000

30000

35000

Particles (ea)


5000

10000

15000

20000

Num

ber of Add

ed P

5000

10000

15000

20000

Num

ber of Add

ed Pa

5000

10000

15000

20000

Num

ber of Add

ed P

0

0 4 8 12 16 20 24

N

Pump Circulation Time (hours)

0

0 4 8 12 16 20 24

N


(MLC) (D1) (D2)

0

0 4 8 12 16 20 24Pump Circulation Time (hours)

No. of particles added on to the wafer during circulation is very muchlower in BPS -600 pump (< 5000) at all the flow rates

In diaphragm pumps, number of particles added onto the wafer goesbeyond the inspection range of the Instrument (>30,000).

In diaphragm pumps, increase in flow rate increases the number ofparticles. However in MLC pump, the trend is different.


RANDOM YIELD LOSS OF DEVICES

Particle size distribution analysis shows that most number of particles in the range of 0.178 -0.326 μm which is in the critical regime for making defects5

Yield loss is simulated from this particle count data using various correlations.

Correlation for no. of particles in UPW to defect density6 Correlation for no. of particles in UPW to defect density

DO = NBSKRPD [1]where Nb : No. of particles in DI waterS : Amount of DI water that contacts wafer during fabrication stepKR : Fraction of killing particlesPD : Probability of particles deposited onto critical areas

Linear correlation exists b/w no. of particles in the bath and on the wafer7

NB = ANW [2]NB ANW [2]whereNW : No. of particles on the waferA : Constant . The value of A is same for all the pumps if the particles composition generated by

all the three pumps are same


all the three pumps are same

RANDOM YIELD LOSS OF DEVICESContd...

Ratio of defect density of two pumps (Using Equations [1] and [2] )

O,M LC B,M LC

O,D B,D

D N =

D N

Negative binomial yield model is used to estimate the yield as a function of critical area8function of critical area

CC 0

1Y = A D

1

where

C 0A D1+

C

Y : YieldAc : Critical area of the chipC : Clustering factor


RANDOM YIELD LOSS OF DEVICES IN WET BATH

1

MLC

Assumption: Clustering factor (C)=2; DO,MLC

= 10.6

0.8

Yield

MLCD1D2

Note: Flow rate: 15 LPM and recirculation time : 24 hrs 0.2

0.4Chip Y

0

0 2 4 6 8 10

Critical Area cm‐2

• The chip yield is higher for MLC pump

Critical Area, cm‐


WAFER CLEANING EXPERIMENTS IN SINGLEWAFER PROCESSOR

Schematic diagram of single wafer processor

Experimental Test conditionExperimental Test condition

Flow rate: Maximum value of each pump i.e. 20 LPM for MLC pumps and 15 LPM for both the diaphragm


pumps and 15 LPM for both the diaphragm

EXPERIMENTAL FLOW CHART- SINGLE WAFER PROCESSOR

Connecting pump to the circulation line

Line flushing with DI water *Process Recipe

1. DIW rinse (Pump circulation and supply)

pre- circulation : 30 min

Drain and refilling Tank with DI waterTime : 60 sFlow rate : 0.5 LPM

W f Cl i SC 1

pre circulation : 30 min

- For flow stableSpin speed : 500 RPM

2. Spin Dry Wafer pre-Cleaning : SC-1

Wafer cleaning* at the end of every 4th

h (0 4 8 12 16 20 d 24th h )

Time : 60 sSpin speed : 1,500 RPM

hour (0,4,8,12,16,20,and 24th hour)

Wafer inspection

28 Nano-Bio Electronic Materials and Processing Lab.End

EFFECT OF PUMPING METHODS ON WAFER CLEANING IN SINGLE WAFER PROCESSOR

3500

4000

4500

cles (e

a)

1500

2000

2500

3000

er of A

dded

Partic

MLC

D1

D2

0

500

1000

0 4 8 12 16 20 24Num

bePump Circulation Time (hours)

In BPS-600, number of particles on the wafer is around 300 and inD2, only the lower number of particles on the wafer (500) isobserved


observed.

The number of particles in D1is relatively higher and increases withcirculation timecirculation time.

The reason for observed lower number of particles on wafer inSingle wafer tool might be due to low process time


Single wafer tool might be due to low process time

RANDOM YIELD LOSS OF DEVICESIN SINGLE WAFER PROCESSOR

0.8

1

MLCD1

Assumption:

Clustering factor (C)=2; D 1

0.4

0.6

0.8

Chip Yield

D1D2

DO,MLC = 1

0

0.2

C

0 2 4 6 8 10

Critical Area, cm‐2

• The chip yield is higher for MLC pump


EFFECT OF PUMPING METHODS ON TEMPERATURE RISE OF THE SOLUTION

20

25

10

15

Δ T (℃

)0

5

0 4 8 12 16 20 24

In general, there is a power loss within the pump due to the difference in thebrake horsepower and water horsepower developed. These power losses are


p p p pconverted in to heat and results in a temperature rise of the liquid beingpumped.

The tempe at e ise of the DI ate d ing ci c lation is highe in BPS 600 The temperature rise of the DI water during circulation is higher in BPS -600pump than Magnum 620r and Futur 50 pumps.

The influence of flow rate on ΔT is more significant in BPS -600 than the other


gtwo pumps

SUMMARY

1. Number of particles added onto the wafer is lower in the case of MLC pump than the other diaphragm pumps in both wet bath and single wafer processor.

2. Simulated yield as a function of critical area shows that there is a significant difference between MLC pump and Diaphragm pumpsdifference between MLC pump and Diaphragm pumps

3. The temperature rise of DI water during circulation is higher in MLC pumps than both the diaphragm pumps.

Thus, choosing the right pump is critical in wafer i tprocessing steps


Effect of Pumping Method on Wafer Cleaning

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