chapter 7. cleaning solution & cleaner
TRANSCRIPT
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
-----
---- --
++
+ +
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+++
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Zeta potential
Stern Layer
Diffused Layer
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- - - -- - -- -
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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.