chapter 7. cleaning solution & cleaner

Chapter 7.

Cleaning Solution & Cleaner

Contents

1. What is Cleaning

2. Importance of Cleaning

3. Classification of Cleaning

4. Cleaning Solution

5. Selecting the cleaning solution

6. Development of Cleaning

7. Summary

8. Paper Review

1. What is Cleaning ?

DefinitionDefinition

To reduce the surface contamination to a minimum level during semiconductor manufacturing processes in order to achieve higher yield.

Contamination

Pre-Cleaning

Post-Cleaning

Cleaning process for subsequent process. Ex) surface preparing, cleaning before CVD and furnace

To remove the contamination induced in previous process. Ex) post-CMP cleaning, Post PECVD

RCA 세정법을기본으로한전통적인반도체습식세정법

세정액 세정목적 부작용

H2SO4/H2O2 (SPM) 유기물,금속 미립자

NH4OH/H2O2/H2O(APM) 미립자,유기물 금속

HCl/H2O2/H2O(HPM) 금속(표면위) 미립자

HF/H20(DHF) 산화막,금속(산화막내부) 귀금속(Cu등),미립자

(1) 세정 공정수가 많다.(2) 화학액 및 초순수의 사용량이 많다.(3) 장치가 매우 크다.(4) 오염 재부착으로 인해 고청정화가 곤란하다.(5) 부식으로 인해 금속재료가 노출해 있는 표면 세정에는 사용할 수 없다.

RCA 세정의문제점

- 전체 공정의 약 25%, 100개 이상의 공정에서 세정이 이루어짐- 습식세정은 100도 이하의 온도에서 모든 물질을 용해 혹은 액중 분산시키고, 웨이퍼 표면에 손상을

주지 않는 등의 뛰어난 특징을 가지고도 그 중요성을 확보하고 있다.

- 요구사항 (1) 아주 청정한 표면을, (2) 부작용 없이, (3) 단시간 내에, (4) 높은 재현성을 가지고, (5) 낮은 원가로 실현.

1. What is Cleaning ?

2. Importance of Cleaning• Cleaning process must be added after each process in semiconductor processes

• Decrease of device dimensions

• Reduction of electrical characteristics

• Yield

Cleaning Mechanism

기능 1오염의이탈

-파티클오염 (불용성/난용성의경우) →물리력-금속오염및유기물오염→용해및분해기능

기능 2오염의재부착방지

-파티클오염→제타전위제어,젖음성제어등-금속오염→ pH산화환원전위제어 /킬레이트제활용

기능 3하부막의식각

-막표면과강고하게화학결합해있는오염,막내부에존재하는오염

3. Classification of Cleaning

< Mechanical Type >

< Chemical solution >

Scrubber Megasonic Single-wafer spin

NoncontactContact

APM (SC-1)

HPM (SC-2)

DHF BOE Ozonated / waterSPM

Metal

Particle

Metal Heavy organic

Metal

Oxide Film

Metal

Oxide Film

Oxide Film

Metal

Aerosol SCF

DryWet

4. Cleaning Solution4 -1 RCA

Au, Ag, Cu, Ni, Cd, Zn, Co, Cr

Etching the particles

Prevention of readhesion

< SC-1 ; APM> Lift off

< SC-2 ; HPM> Dissolution

HCl : H2O2 : DIW = 1:1:5 at 75~85℃

Heavy metal, Alkali ions, Metal hydroxides

Hydrophilic after the cleaning

Repulsive Force

Wafer- ---

- ---

Attractive Force

---

+++

Particle

-

Netnegativecharge

-----

---- --

++

+ +

++

+

+

+

+

++

+++

++

Zeta potential

Stern Layer

Diffused Layer

+

-

+

+

+

+

+

+

++

+

+

+ +

++

+

+

- - - -- - -- -

--

-

- -

-

-

-

- -

-+

+

+

+

+

+

+

+

+

-+

+

+

+

+

+

+

+

+

+

+

+

+

+

+-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

--

--

-

-

-

-

-

Zeta Potential

4-2. HF & BOE

• Oxide film

• Metal except noble metal as Cu, Au

• Impurity in oxide film

< HF >

< BOE > ; Buffered Oxide Echant

NH4F + HF

Stable etch rate by buffer

High chemical wettability with surfactant

4-3. O3 / HF(SCROD)

DHF

Si + O3 SiO2 +O

Ozonated water

SiO2 + HF H2O + SiF4

Oxide

By oxide film removal

Oxide removal

Particles removal

Particle removal

Metal removal

5. Selecting the cleaning solution

Goal

Particle

Metal

Noble metal

Material of wafer

Si

Copper

APM + ScrubberSCROD

APM + Megasonic

Scrubber + DHF or HPM

Scrubber + HPMSCROD

DHFExcept

Noble metal

6. Development of Cleaning

< IMEC >

Reduction of process time

Little light Chemistry

Eco-friendly

3 - 1. Scrubber Mechanism

van der Waals Energy + Electrostatic Energy

((Zeta Potential) Zeta Potential)

- Repulsive/Attractive

((HamakerHamaker constantconstant+Particle+Particle s size )size )

- Attractive

Total Interaction

Energy=

Noncontact : Hydrodynamic drag force

Contact : Rotation torque of brush

Brush force > Total interaction force

Remove !

BrushBrush

Brush

Noncontact Partial Contact

Full Contact

Removal force

Adhesion force

Removal force with DIW

Removal force with SC-1N

Brush rpm< 0.1㎛, Noncontact >

∴ Physical Force > Total Energy

Force Scratch Defects

Added chemical solution

Surfactant

Brush

+

+Brush Brush + Brush

+

Brush

+

BrushBrush out

+

< Readhesion >

Physical force

Zeta potential

< with surfactant >

Physical force Brush

-

-Brush Brush - Brush

-

Brush

-

BrushBrush out

-

))/2exp(1ln()()/exp(1)/exp(1ln2)( 0

22

21

0

0210 xH

xHxHRHV

1. Physisorption(Van Der Waals Forces) : E= - AR / 6D

2. Electrostatic Attraction– Surface charge : Zeta-Potential– E

3. Chemisorption : Chemical reaction between particles and surfaces

4. Capillary Condensation : Fc = 4πRγL

Particle Deposition Mechanism Particle Deposition Mechanism

3 - 2. Megasonic

CavitationAcoustic streamingRadiation forceMegasonic energy(1000-15500kHz)

< Application of Megasonic >

3 - 3. Single wafer spin

< SEZ Spin Etcher > < Single wafer spin >

• Lower chemical and water

• High efficiency and short process time

• Lower scratch by particles

• With O3 / DHF / N2

3 - 4. Cryogenic Aerosol-based Cleaning Technology

• Physical force of Aerosol

• No surface tension

N2 Gas is more light than CO2, Ar

Conventional gas : CO2, Ar

Damage of pattern in semiconductor

3 - 5. SCF (Super Critical Fluid) cleaning

Damage of pattern in Wet cleaningby surface tension

Environment problem

Dry process

SCF Cleaning

CO2 (31℃, 7.3MPa)

Super critical fluid

:Surface tension is zero

3-6. 기능수 세정

전해 환원수에 의한 CMP후 세정효과

전해 환원수와 수소용해수의세정능력 비교

7. Summary

• Cleaning solution is selected by slurry, wafer and kind of removed material.

• Cleaning station must be composed of machine and chemical solution.

• Reduction of damage by surface tension.

• Goal of cleaning solution is little light chemistry in the future.

• Recently, many researches are progressing Cu CMP cleaning

• As development of new materials and size reduction of device, cleaning solution and cleaner will be important.

Paper review

A Study on Particle Removal of PVA Brush

Cleaning based on Contact Mode

2006 2008 2010 2012

Maximum Substrates Diameter (mm) 300 300 300 450

DRAM 1/2 Pitch (nm) 70 57 45 36

Particle size (nm) at front > 90 > 90 > 65 > 45

Particle (ea/㎠) at front > 0.17 > 0.17 > 0.17 > 0.17

Particle (ea/wafer) at front < 116 < 120 < 115 < 265

Particle size (nm) at back > 160 > 160 > 140 > 140

Particle (ea/wafer) at back < 400 < 200 < 200 < 200

2006 ITRS Road Map

• Cleaning process occupies more than 35% of semiconductor fabrication.• As pattern size decrease, effect of defect is becoming large.• Cleaning process performance affect directly device yield and cost.• Eco-friendly process

Production rate = 4 times

Post-Cu CMP Cleaning

Electroplating Cu

Metal Trench

Damascene Patterning

Substrate

Via

Metal Dep. & Anneal

CMP Process

Post-Cu CMP Cleaning

Conventional Chemical Cleaning

Wet Station RCA cleaning process (SC-1, SC-2) Chemical

ComponentChemical

Ratio Time Target Contamination

SC-1 NH4OH:H2O2:H2O(50~90 ℃) 1:1:5~0.05:1:5 10

min~

Particle, Organic and

Metal

SC-2 HCl: H2O2:H2O(80~90 ℃) 1:1:6~1:2:8 10

min~Noble Metal,Alkaline ions

Yearly chemical use / wet station

Yearly DI water use / wet station 64,821,120 Gallon

19,235 Gallon

Yearly chemical cost / wet station $ 1,136,300

• Based on 8” wafer, 96 run/day• Data from Semiconductor International 2000

• Waste huge chemistry and DIW• Environment Problem• Cross contamination• Chemical attack (corrosion, etching)• Non-uniform cleaning performance

Disadvantage

Brush Cleaning

Porosity (%) 85-95

Average pore size (㎛) 110-150

Apparent density (g/㎤) 0.7-0.11

30 % compressive stress (g/㎠) 10-110

Tensile strength (kg/㎠) 2-6

Tensile elongation (%) 200-400

Water absorption (wt%) 700-1500

Maximum allowable temperature (℃) 80 dry, 60 wet

Decomposition point (℃) 170

Typical physical properties of the PVA brush

• Does not make dusts• Good chemical stability• Strong cleaning force• Double side cleaning

Advantage

• Pattern damage due to contact process• Contamination stuck• Inducing scratch

Disadvantage

Background

J. Taylor, “Yield Enhancement through Understanding the Particle Adhesion and Removal Mechanisms in CMP and Post CMP Cleaning processes”, IEEE Advanced Semiconductor Manufacturing Conference, pp. 14-17, 2000

A. A. Busnaina, “Particle Adhesion and Removal Mechanisms in Post-CMP Cleaning Processes”, IEEE Transaction on Semiconductor Manufacturing, Vol. 15, No. 4, pp. 374-382, 2002

• The boundary of partial and ideal contact is vague.

• Difficult realization of partial and ideal contact.

• While brush cleaning has been widely used, little theoretical workhas been done in the fields.

Monitoring System

Contact condition

Monitoring Sys’

Non-contact condition

Full contact condition

Velocity

Gap between brush and wafer

Friction force

Re-adhesion of particle

Monitoring Sys’

Particle removal efficiency

Scratch

DefectivityAFM

lithography

Objective

Cu PETEOS

Cu

PETEOS180 nm

Cu PETEOS

- - -- - - Repulsive

forceAttractive force+ + + + + + + - - - - - - -

After CMP Process

Many particles remain selectively on Cu surface, rather than on PETEOS.

We focus on the particle removal from the Cu surface after Cu CMP process.

Particle Adhesion on Different Surface

Applicable Wafer Size : 8inch and 12 inch

Configuration : Stand alone with 4 cleaning stations- 1 Pre Cleaning with DIW Spray- 2 Double-side Roll Brush Cleaning- 1 Spin Rinse Dry with N2 Blow

Size- 1700W 960D 1300H- Brush size : Ø70(OD) Ø32(ID) Ø320(L)

Ø38(OD) Ø22(ID) Ø310(L)Chemical : NH4OH ~1wt% available

Brush type : PVA brush, Both side of wafer cleaning

Brush rotation speed : Max 300rpm

Spin speed : Max 2500rpm

- DI rinse / N2 blow

Control Module- PC Monitor Interface- Programmable Sequence- Sequence Control: PC

Experimental Setup: GnP Cleaner systemGnP Cleaner812L

Pre-cleaning Brush scrubbing

Spin rinse dry Megasonic

Definition of Terms

3. Brush overlap: Brush overlap is the amount of overlap between wafer and brush.

Brush

Brush

2. Friction force : Friction force is defined as a force generated between brushes and wafer

Brushes

Brushes

1. Contact force: Contact force is defined as a force to pressurize a wafer.

Brush Module

wafer

Data Acquisition Program- CleanEYE

Contact force Friction force

Contactforce

Contactforce

Frictionforce

Frictionforce

Experimental Condition

Parameter Conditions

Wafer 4 inch blanket wafer (CVD Cu deposition 1㎛)8 inch PETEOS for re-adhesion test

SlurryTST-D2 (Techno Semichem Co.), Mean diameter of abrasive : 60nmpH : 10

Cleaning solution Citric acid (0.5 wt%), BTA (0.03 wt%)NH4OH (1 wt%)

Pre-cleaning time (s) 10

Brush scrubbing time (s) 60

Spin dry speed (rpm) 3000

Spin dry time (s) 60

Brush velocity (rpm) 240

Brush gap (㎛) Under 10

od AulCF2

2

D

22D8

uldCF pd

6Re

1Re24

3/2p

pDC

Ref : Busnaina et al, “Particle adhesion and removal mechanisms in post-CMP cleaning process”, 2002

Contact condition

Non-contact Condition

Non-Contact Condition

60 rpm 120 rpm

240 rpm

Results of Non-Contact Condition: Brush Velocity

Gap< 10 ㎛

10 ㎛ < Gap< 20 ㎛

20 ㎛ < Gap< 30 ㎛

40 ㎛ < Gap< 50 ㎛

Results of Non-Contact Condition: Brush Gap

}])3(6[3{ 2/123 WRWRPWRPKRa

Johnson-Kendall-Roberts (JKR) equation.

)1(20

2

RzrWRF A

Ref : Fan Zhang et al, Journal of Electrochemical Society,1999

P : Load R : Radius a : Contact area W : Interaction Force

FA : Adhesion force between two material

r : Contact Radius W : Thermodynamic work of adhesion

Contact Area Small Middle Large

Adhesion Force Small Middle Large

Theoretical Mechanism of Full Contact Condition

Friction Force Monitoring Sys

PC

ChargeAmp.

A/D conv.

F2

F1

Monitoring System for Friction Force

0.117kgf 0.195kgf

0.601kgf

Scratch length

0.406kgf

Results of Full Contact Condition: Friction Force

Typical Value

Specified Values

Thickness (㎛) 4 3.0-5.0

Mean width (㎛) 30 22.5-37.5

Length (㎛) 125 115-135

Force constant (N/m) 42 10-130

Resonance frequency (kHz) 330 204-497

Guaranteed tip radius of curvature (nm) < 10

Scratch Test on Cu surface: Experiment

PPP-NCHPt non-contact probe

Properties of PPP-NCHPt non-contact probe

• AFM lithography mode

• Probe single crystal silicon

• 1000 nN ~ 6000 nN

XE-100

4000 nN

5000 nN

6000 nN

Scratch Test on Cu surface: Results

A

B

A B

5000 nN

6000 nN

A

B

A B

Scratch Test on Cu surface: before and after

Before After

Conclusion

10-6 ~10-7 N10-10 ~10-11 N

Conclusion

Contact condition was classified into two broad categories (non-contact and full contact) using monitoring system.

In non-contact condition, removal efficiency was dominated by velocity and gap between brush and wafer, which matched well theoretical mechanism.

High friction force have strong removal force, but it is poor to defectivity.

Through AFM scratch test, force that induced scratch could be estimated.

Full contact condition had re-adhesion problem by contaminating brush.