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Plasma Assisted Surface Modification:
Low Temperature Bonding
SFR Workshop
November 8, 2000
Yonah Cho, Adam Wengrow, Chang-Han Yun Nathan Cheung
Berkeley, CA
2001 GOAL: to establish plasma recipes and adhesion data
for Si, oxide and metal surfaces by 9/30/2001.
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Motivation
LEDs on Si
Silicon-On-Insulators
Si
Si
200 mm
<Si> Micro Cavities
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SOI SOI
Dual Gate MOS
SiO2
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Bonding Methods &
Temperature Dependence
• Anodic Bonding
• Direct Bonding
• Metal Bonding
• Adhesive Bonding
Bonding Energy (mJ/m2)
Bonding Energy vs. Temperature
3000
2500
2000
1500
Hydrophilic Si
1000
500
0
Hydrophobic Si
100 200 300 400 500 600 700 800 900
Annealing Temperature (oC)
Choice of bonding method
depends on thermal budget & materials systems
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Bonding Schematics
Gases Used:
O2, He, N2, Ar
Plasma Treatment
+
Room Temp Bonding
Pressure
200mTorr
Power
50W-300W
Time
15-30 seconds
O2
-
Chemical Cleaning:
Piranha + RCA
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Thermal Annealing
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Bonding Kinetics
o
200
Temperature ( C)
100
50
O2 Plasma-treated
Si-Si
Ea > 0. 7 eV
2
Bonding Energy (mJ/m )
Si-Si
1000
Ea ~ 0.2 eV
100
10
2.0
O2 Plasma-treated
Si-SiO2
Chemically cleaned
Si-Si
Ea ~ 0.07 eV
Chemically cleaned
SiO2-SiO2
2.5
3.0
1000/Temperature (K)
3.5
Plasma treated Si surfaces achieve covalent bonding as low as 105oC
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Surface Chemistry: XPS
Si
Si
SiO2
SiO2
Intenasity (A.U.)
600
500
Hydrophilic
Si
Hydrophobic
Si
400
300
200
100
90
95
100
105
Intenasity (A.U.)
600
110
115
90
95
O2
plasma
treated
Si
500
400
100
105
110
115
Thermal
SiO2
300
200
100
90
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95
100
105
Binding energy (eV)
110
115
90
95
100
105
Binding energy (eV)
110
115
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Surface Morphology
Chemically cleaned Si
O2 plasma
150W-300W
30 seconds
RMS < 0.5 nm
RMS < 0.5 nm
No Change in Surface Roughness
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Surface Modification by Concomitant/Sequential
Plasma Treatment
• Mechanical and chemical
properties of surface can
be effected.
Surface Layer
Si Substrate • Modified surface layer can
be from substrate or grown
/ deposited / transferred
Plasma
layer.
Treatment
• Physical and/or chemical
Modified
Surface
changes of surface
possible by altering
chemical composition of
plasma and ion energies.
*By simply varying the potential of the PIII reactor,
it can serve as surface modifier to implanter.
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2002 and 2003 Goals
Demonstrate concomitant plasma treated deposition layer as
effective diffusion layer by 9/30/2002.
Demonstrate polymer surface modification with plasma
implantation by 9/30/2003.
Project summaries & publications are available at
http://plasmalab.berkeley.edu
11/8/2000