Transcript Plasma Immersion Ion Implantation

Modulator Design for
Plasma Ion Implantation
Professor Michael Bradley
Dale Heggie, Joel Leslie, Curtis Olson
March 24th, 2004
Objective
Convert an existing vacuum chamber into a
plasma ion source for Ion Implantation
Applications in Materials Processing
1.
Electronics Industry
•
•
2.
Semiconductor doping
IC Fabrication
Mechanical Treatment
•
•
Surface hardness
Frictional Properties
3. Biomedical Implants
•
Biocompatible materials
Applications in Materials Processing
1.
Electronics Industry
•
•
2.
Semiconductor doping
IC Fabrication
Mechanical Treatment
•
•
Surface hardness
Frictional Properties
3. Biomedical Implants
•
Biocompatible materials
What’s a plasma??
Four States of Matter
1. Solid
2. Liquid
3. Gas
4. Plasma
Plasma Examples




Neon lights
Lightning
Sun
Aurora
Borealis
Plasma Examples



Neon lights
Lightning
Aurora
Borealis
PII Material Processing
1.
Insert sample into
chamber
2. Strike a plasma
3. Apply high
negative voltage
4. Ions hit the
sample and are
implanted
+ + + + + + +
Silicon
-5 kV
PII Material Processing

+
+
+
+
Characterize the effects
of implant depth and
dose
Sample Material
Sample Holder
-20
-5
-10kV
kV
Implant Implications
 Kinetic energy is
transferred into heat
 Sample overheating
from continuous
implant
 Requires pulsed
voltage
+
+ + + +
+ +
Voltage Pulsing
+ + + + + + + + +
 Energy
contamination
from rising and
falling edges
Voltage
Implanting
Cooling
Time
Final System
Vacuum Chamber
Modulator
High Voltage Source
+ -
Modulator Design
 Solid state
transistor
modules
 One master timer
 Expandable
Master Timer
Time
Start
Optical Fiber
High Voltage Source
+ -
To Vacuum
Final System
Circuit Performance
 5 switching
modules
 Excellent rise and
fall times
 Expandable
without affecting
performance
Timer
High Voltage
Successful Implant




5 switching modules
1600 V negative bias
2” Silicon Wafer
Short Nitrogen implant
Special Thanks
Dr. Michael Bradley
 Dave McColl, P. Eng.
 Dr. Ajay Singh
 Dr. Akira Hirose
 Perry Balon
 Vic Meyer, Electrical Shops

Questions???
Master Controller

Circuit Description



Monostable 555 for
implant duration
Astable 555 for pulse
frequency
Features



Duty cycle variation
Implant Time (5, 10, 30
seconds)
Start Control
Circuit Development

High Voltage Switching Units


PC Board layout in Traxmaker
Fabricated by Electrical Engineering Shops
Vacuum Chamber Results
• 2 x 10-7 Torr base pressure
• 0.01% impurities from background gas
Vacuum Chamber Pump Down Curve
1.00E-04
Pressure (Torr)
0
0.5
1
1.5
1.00E-05
1.00E-06
1.00E-07
Time (days)
2
2.5
Sample Holder


Secure silicon wafer
inside chamber
Thermal conductivity

Aluminum
Plasma Generation


Raise to 2
mTorr
pressure with
Nitrogen
Filament
generation
Testing
By the Numbers…
Vacuum Chamber
• Goal - Base pressure < 1 µTorr
Result – 2 x 10-7 Torr
High Voltage Switching
• Goal - < 10 microsecond rise and fall
Result – 300 ns rise, 700 ns fall
Switching Problems
• Less than 1% energy contamination
Overall Circuit Performance
• 5 modules at 1600 Volts
• Expandable without
affecting performance
Vacuum Chamber


Base pressure
1 in 10 000
contamination
Langmuir Probe
Langmuir Probe Curve

Characterize our plasma
for accurate implant doses
Ion saturation current of
12 mA
400
300
Current (mA)

200
100
0
-100 -40
Current (mA)
Langmuir Probe Curve
4
2
0
-2
-4
-6
-8
-10
-12
-14


Isat
-30
-20
Voltage (V)
-30
-20
-10
Vf loat (-5v)
0
Voltage (V)
Vf loat (-5v)
-40
Isat
-10
0
Ion Density of Plasma
(~2 x 109 ions/cm3)
0.57% ionization
10
Modulator Design
• Modules
• Insulated gate bipolar
junction transistor
(IGBT)
• Internal battery power
• Optical Isolation
• Synchronization
Future Design Projects
1. High Voltage Isolation
1. Metal boxes
2. Fast Zener clamping for each module
2. Increase Plasma density
1. Shorter implant times
2. Increase saturation current via RF source
3. Better Power Supply