Characteristics of Neutral Beam Generated by a Low
Angle Reflection and Its Etch Characteristics by
Halogen-Based Gases
Geun-Young Yeom
SungKyunKwan University
Problems of Current Etch Technology
ƒ
-
Scaling down of the device to nano-scale : increased volunability to processing
damage
Physical damage
Electrical damage (Charging damage)
DRAM Half Pitch
Gate Length
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Charging Effects
3/32
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Trend of Etching Tools Development
4/32
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Researtch Status of Neutral Beam Etching Technologies
1) Gas dynamics or hyperthermal atomic beam (Heating of gas)
- Caltech by Giapis in 2000 (laser), PSI Inc. in 2000 (laser),
NEC by Nishiyama in 1995 (thermal heating), etc.
Oklahoma Univ. in 2000 (hyperthermal)
2) Ion-neutral scattering (charge exchange process)
- Hitach by Mizutani in 1995 (ion removal by retarding grid),
NTT by Matuso in 1995 (ion removal by magnetic field), etc.
3) Ion-electron recombination (surface neutralization)
- IBM by Chen in 1997 (sheath recombination by ion and electron)
- Tohoku University in 2002
- Ebara Research Co. in 1995 (capillary hole)
- Tokyo Univ. in 2000 (focused fast atom beam)
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Neutral Beam Etching using Gas Dynamics
PSI Inc. in 2000 (laser)
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Researtch Status of Neutral Beam Etching Technologies
1) Gas dynamics or hyperthermal atomic beam (Heating of gas)
- Caltech by Giapis in 2000 (laser), PSI Inc. in 2000 (laser),
- NEC by Nishiyama in 1995 (thermal heating), etc.
- Oklahoma Univ. in 2000 (hyperthermal)
2) Ion-neutral scattering (charge exchange process)
- Hitach by Mizutani in 1995 (ion removal by retarding grid),
- NTT by Matuso in 1995 (ion removal by magnetic field), etc.
3) Ion-electron recombination (surface neutralization)
- IBM by Chen in 1997 (sheath recombination by ion and electron)
- Tohoku University in 2002
- Ebara Research Co. in 1995 (capillary hole)
- Tokyo Univ. in 2000 (focused fast atom beam)
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Neutral Beam Etching by Ion - Neutral Scattering
(Tatsumi Mizutani et. al, hitachi, 1995)
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Researtch Status of Neutral Beam Etching Technologies
1) Gas dynamics or hyperthermal atomic beam (Heating of gas)
- Caltech by Giapis in 2000 (laser), PSI Inc. in 2000 (laser),
NEC by Nishiyama in 1995 (thermal heating), etc.
Oklahoma Univ. in 2000 (hyperthermal)
2) Ion-neutral scattering (charge exchange process)
- Hitach by Mizutani in 1995 (ion removal by retarding grid),
NTT by Matuso in 1995 (ion removal by magnetic field), etc.
3) Ion-electron recombination (surface neutralization)
- IBM by Chen in 1997 (sheath recombination by ion and electron)
- Tohoku University in 2002
- Ebara Research Co. in 1995 (capillary hole)
- Tokyo Univ. in 2000 (focused fast atom beam)
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Neutral beam etching by Ion-Electron Recombination (I)
(Demetre J. Economou et.al, Houston Univ., 2000)
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Generation of Directional Neutral Beam
by Low Angle Reflection
Recombination by low angle forward scattering
retarding grid
reflection plate
˚
10~30
90
˚
Neutral beam
˚
5~15
˚
Ion beam
5~15
Reflection plate : Si
neutral beam
ion beam
Ion gun
O 2,
SF6
faraday cup or sample
rf coil
• When the ion beam was reflected by a reflector at the angles lower than 15˚,
most of the ions reflected were neutralized and the lower reflector angle showed
the higher degree of neutralization.
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Experimental Low Angle Reflected Neutral Beam System
Quartz
Plasma
Electromagnet
RF Coil
Φ4
Acceleration Grid
Focusing Grid
Deceleration Grid
6 inch
Ion Beam Flux
PlatePlate-type Reflector
25 mm
5o Reflection Angle
Neutral Beam Flux
Substrate
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Ion current density (uA/cm2)
Ion Flux and Neutral Flux
as a function of Acceleration Voltage
400
300
o
SF6
SF6 5 reflection
NF3
NF3 5 reflection
CF4
CF4 5 reflection
Ar
Ar 5 reflection
retarding grid
reflection plate
o
o
neutral beam
o
ion beam
200
100
Grid hole size:Ø2
faraday cup or sample
rf coil
0
0
100
200
300
400
500
600
700
Acceleration voltage (volts)
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SiO2 Etch Rate as Functions of Acceleration Voltage and
Gas Flow Rates for SF6, NF3, CF4, and Ar
Condition :
Condition :
reflector angle: 5˚ , rf power: 500W
Va : 700V
8
4
SF6
NF3
CF4
Ar
3
SiO2 etch rate (nm/min.)
SiO2 etch rate ( nm/min. )
reflector angle: 5˚ , rf power: 500W
SF6 gas flow rate: 7 sccm
2
1
0
SF6
NF3
CF4
Ar
7
6
5
4
3
2
1
0
100
200
300
400
500
600
Acceleration voltage (Volts)
700
2
4
6
8
10
12
14
16
Flow rate (sccm)
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SiO2 and Si Etch Rate as a Function of SF6 Gas Flow Rate
Condition :
reflector angle: 5˚ , rf power: 400W, distance between
reflector and sample : 4 cm, pure SF6, Va: 400 V, Ve: -100 V
1300
200
1100
Etch rate (A/min)
Etch rate (A/min)
180
160
140
120
100
Si
1200
SiO2
Va: 400 V
Ve: -100 V
8
10
12
14
16
18
20
Flow rate (seem)
22
24
26
1000
900
800
700
Va: 400 V
Ve: -100 V
600
500
8
10
12
14
16
18
20
22
24
26
Flow rate (sccm)
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Etch Rate and Etch Selectivity as a Function of Gas Flow
Rate Using the Neutral Beam Etching System
Condition :
rf power: 300W , acceleration voltage: 400V, reflector angle: 5o
reflector material: Si
0.70
500
Si
SiO2
PR
Si/PR
SiO2/PR
0.60
0.55
300
Selectivity
Etch rate(A/min)
400
0.65
200
0.50
0.45
0.40
0.35
100
0
0.30
0.25
4
6
8
10
12
14
CF4 flow rate (sccm)
16
18
20
4
6
8
10
12
14
16
18
20
CF4 flow rate (sccm)
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Etch Rate and Etch Selectivity as a Function of H2 to CF4
Using Neutral Beam Etching System
Condition :
rf power: 300W , CF4+H2: 15sccm, acceleration voltage: 400V,
reflector material: metal, reflector angle: 5o
450
3.0
400
2.5
Si
SiO2
PR
300
Etch selectivity
Etch rate(A/min)
350
250
200
150
100
2.0
1.5
1.0
0.5
50
0
Si/PR
SiO2/PR
0
10
20
30
40
H2/(H2+CF4)%
50
60
70
0.0
0
10
20
30
40
H2/(H2+CF4)%
50
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60
70
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SEM Micrograph of SiO2 Etch Profiles
(Neutral Beam Etching)
Condition : SF6 2.5 sccm, rf power: 400 W , acceleration voltage: 400V, reflector angle: 5o
etch mask : Cr
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SEM Micrograph of Si Etch Profiles
Condition : CF4 15sccm, rf power: 300W , acceleration voltage: 400V, reflector material: metal,
reflector angle: 5o
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Effect of Reflector Angle on Reflected Angle and Flux
of the Neutrals
Condition :
SF6 10 sccm(0.6 mTorr), rf power: 400W , acceleration voltage: 400V
reflector material: Si
500
400
300
SiO2 etch depth(A)
5
o
10
o
15
o
20
o
5
o
10
o
15
o
20
80
120
60
500
o
SiO2 etch depth(A)
100
600
600
200
140
400
40
300
200
160
20
100
0
180
0
0
o
Reflected polar angle θr ( )
100
200
100
300
400
0
500
0
20
40
60
80
600
100
o
Reflected polar angle θr ( )
500
Incident ion energy: 400V
10
o
5
400
500
60
o
10
o
5
400
o
300
30
150
200
SiO2 etch depth(A)
SiO2 etch depth(A)
Incident ion energy: 400V
90
120
300
200
100
100
0
0
100
200
300
400
0
500
-100 -80 -60 -40 -20 0
20 40 60 80 100
o
Reflected azimuthal angle φr ( )
0
180
330
210
Incident beam direction
240
300
270
o
Reflected azimuthal angle φr ( )
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Effect of Reflector Materials on Reflected Angle and
Flux
Condition :
SF6 10 sccm(0.6 mTorr), rf power: 400W , acceleration voltage: 400V
reflector angle: 5o
100
700
700
Incident angle θi: 5
SiO2 etch depth(A)
600
o
400
80
SiO2
DLC
Si
Metal
60
600
500
140
40
400
DLC
Si
Metal
SiO2
500
120
300
200
160
100
20
+
SF6
0
180
300
0
100
200
200
100
400
0
600
0
o
Reflected polar angle θr ( )
300
500
700
0
20
40
60
80
100
o
Reflected polar angle θr ( )
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C-V Characteristics
Before and After Neutral Beam & ICP Etch
1.20E-010
5.00E-011
Capacitance (F)
8.00E-011
6.00E-011
4.00E-011
2.00E-011
0.00E+000
reference
neutral 30 min
ICP 2 min
4.00E-011
Capacitance (F)
reference
neutral 30 min
ICP 2 min
1.00E-010
3.00E-011
2.00E-011
1.00E-011
-6
-5
-4
-3
-2
-1
-6
0
-5
Voltage (V)
-4
-3
-2
-1
0
Voltage (V)
<Big dot: 300um x 300 um >
<middle dot: 200um x200um>
Al(5000A)
Si3N4(50nm)
SiO2(2nm)
Si p-type, (100)10Ωcm
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I-V Characteristics
Before and After Neutral Beam & ICP Etch
Treatment
Current (A)
- ICP plasma
power: 500 W, bias voltage: -100 V,
gas: O2, time: 2 min
- Neutral beam
power: 500 W, acceleration voltage: 400V,
extraction voltage: -100V
gas: O2 , time: 30 min, distance: 5 cm
5.0x10
-7
4.0x10
-7
3.0x10
-7
2.0x10
-7
1.0x10
-7
0.0
reference
neutral beam etching
ICP etching
0
-2
-4
-6
-8
-10
Voltage (V)
5.0x10
-7
4.0x10
-7
3.0x10
-7
2.0x10
-7
1.0x10
-7
0.0
-7
reference
neutral beam etching
ICP etching
5.0x10
reference
neutral beam etching
ICP etching
-7
4.0x10
Current (A)
Current (A)
<small dot: 100um x 100um>
-7
3.0x10
-7
2.0x10
-7
1.0x10
0
-2
-4
-6
Voltage (V)
-8
-10
<middle dot: 200um x200um>
0.0
0
-2
-4
-6
-8
-10
Voltage (V)
<Big dot: 300um x 300 um >
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SEM Micrograph of Poly-Si and Poly-Si/SiO2 Etch Profiles (ICP
Etching)
condition : rf power: 700W,
(Poly-Si)
Bias voltage: -75V pure SF6 5 mTorr,
(Poly-Si/SiO2)
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SEM Micrograph of Poly-Si and Poly-Si/SiO2 Etch Profiles (Ion
Beam Etching)
condition : SF6
2.5 sccm(0.3 mTorr),
rf power: 400W ,
Ve: -100V,
Va: 400V, etch mask: Cr
(Poly-Si)
(Poly-Si/SiO2)
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SEM Micrograph of poly-Si and SiO2 Etch Profiles
(Neutral Beam Etching)
condition : reflector angle: 5˚, SF6
(Poly-Si)
2.5 sccm(0.3 mTorr), rf power: 400W , Ve: -100V, Va: 400V
(Poly-Si/SiO2)
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GaN and GaAs Etching
as a Function of Flow rate, Additive Gas
Process conditions
35
45
30
40
25
20
15
GaAs
GaN
10
0
5
10
15
Cl2 flow rate (sccm)
<Cl2 Flow rate>
20
Etch rate (Angstrom)
Etch rate (Angstrom)
Fixed power : 400W, Fixed acceleration voltage : 400V
GaAs
GaN
35
30
25
20
0
5
10
15
Ar flow rate (sccm)
<Cl2+Ar Flow rate>
Total flow rate : 15sccm
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Damage Analysis Etched n-GaN, GaAs
Process conditions
Fixed acceleration voltage : 400V, pure Cl2, Gas flow rate : 3sccm,
GaN Photoluminescence
GaAs PhotoReflectrance
As-received
ICP treatment
Neutral treatment
PL Intensity (a.u.)
100
10
1
350
400
450
500
550
600
650
∆R/R (arb. units)
Room Temp.
1.30
Reference
ICP ethcing
Neutral etching
1.35
1.40
1.45
1.50
Wavelength (nm)
Photon energy (eV)
<GaN PL>
<GaAs PRS>
1.55
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1.60
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I-V Characteristics of GaN LEDs after Neutral
Beam Etching of p-GaN
9 Condition
- Neutral beam etching : Power 400W / Bias +400V / CF4 15sccm / 40min / thickness 600-650Å
- ICP etching : Power 400W / Bias -400V / CF4 15sccm / 15sec / thickness 750-800Å
100
100
Reference
ICP etching
Neutral beam etching
80
10
1
Reference
ICP etching
Neutral beam etching
LogA (mA)
Current (mA)
0.1
60
40
0.01
1E-3
1E-4
1E-5
20
1E-6
1E-7
0
1E-8
-15
-10
9 Device Structure
-5
0
-10
5
p - contact : Cr/Au
-5
0
5
Voltage (V)
Voltage (V)
Hole size : 2μm
p - contact : ITO
Reference
p - GaN
P-GaN surface
Multi quantum well
Neutral beam etch
n - contact : Ti/Al
n - GaN
ICP etch
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GaN Device Efficiency
after Neutral Beam Etching of p-GaN
Hole patterns
<Reference (No pattern)>
Emission intensity (A.U)
1200
<Neutral beam etch (patterned)>
Reference
Neutral beam textured
1000
800
600
400
9 Emission at 20mA
200
0
9 Emission intensities were increased about 22%
in neutral beam textured GaN LED (OES analysis)
420
440
460
480
500
520
Wave length (nm)
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Commercialization
Alpha Version – for 12inch Dia. Silicon Nano Processing
Item
Ion source
RF Matcher
사양
- Source type : ICP
- Power 3000W
- Density : 5.5E+11(4mTorr, 2500W)
Grid
Plasma source
Reflector
Grid & Reflector
+ Plas+ma
+
+
+
+ bias
Chuck
Grid
&
Process Chamber
Control voltage
Ground
Wafer
Reflector
- Grid에 DC Bias 인가
- Grid hole size; 2, 3, 4mm
- Grid gap; 2, 4, 6mm
- Reflector angle; 3, 5, 7°
- Chuck & reflector gap; 50, 100, 150mm
- Grid material : Graphite
Pump
- Tilting(Manual, 45°) & Rotating(Automatic, 15RPM)
Chuck
- Lift pin & Mechanical clamp
- No Cooling & heating
Control box
Chamber
&
Vacuum system
Gas
<설비 구성>
- Vertical type
- Chamber pressure : 0.3mTorr with Ar 40sccm
- TMP 4200ℓ/s
- Gate valve : ø400, Step motor Operation(Pressure control)
- Gas box type : IGS(1.25)
- Gas line : 14 line
<설비 사양>
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Summary
ƒ Using a low energy reflection of reactive ion beam, directional
reactive neutral beam for chargeless etching was successfully
fabricated.
ƒ By using the neutral beam, nanoscale etching of silicon and silicon
oxide could be achieved.
ƒ No charging damage was detected by the use of the neutral beam
while the conventional ICP etching showed a significant damage
such as leakage of gate oxide, RIE-lag, etc.
ƒ It is believed that, neutral beam etching technique is benificial for
the nanodevice processing not only for the top-down devices but
also for the bottom-up devices
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