Chapter 6.14
Edwards EB3 Electron Beam
Evaporator
(edwardseb3)
1.0
Title
edwardseb3 ¡V
electron beam (e-beam) evaporation process
2.0
Purpose
This document has specific
information about the Edwards EB3 e-beam evaporator in 432A to help operators understand
its safe and correct operation.
3.0
Scope
The Edwards e-beam evaporator is a high vacuum e-beam evaporation
system. One mechanical pump is installed for rough pumping and one turbo pump
for fine pumping. A liquid Nitrogen trap is fitted to
the Auto 306 vacuum coaters. The LN2 trap can be filled with 1.4 litres of LN2;
this is sufficient for up to approximately eight hours of operation. The
purpose of the LN trap is to increase the pumping speed for water vapor, a
significant residual gas in a vacuum systme. The e-gun can accommodate four crucibles at a time to allow multiple and
sequential evaporations. There are three 6-inch wafer holders. If you are going
to evaporate other sizes of wafers or small pieces, you could use the Kapton
tape to tape your samples on a 6-inch wafer. A crystal monitor enables direct
read-out in Å/sec resolution for deposition rate and in nm for thickness. The
edwardseb3 may be used to evaporate metals and dielectrics.
4.0
Applicable Documents
Description of a basic vacuum system:
http://microlab.berkeley.edu/labmanual/chap6/vacuum.pdf
Vendor
manual: AUTO 306 Vacuum Chamber & EB3 Multihearth Electron Beam Source.
5.0
Definitions & Process Terminology
5.1 AUTO 306 vacuum
chamber: contains e-gun, hearth liner, wafer holder, crystal monitor and heat
lamp. The door has a magnetic bearing and users should gently close the door
without adding forces on it to assure good seal of the chamber.
5.2
Vacuum control
panel: allow you to vent and pump the chamber.
5.3
EB3 power
supply unit: sitting on the floor at bottom left of the vacuum chamber. Always ON.
5.4
EB3 source
control: switch on/off of high voltage control of e-gun as well as analog
control of e-gun current.
5.5
Yogogawa
function generator for ebeam sweep control: provides sinusoidal, square wave
and other waveforms to the Edwards beam sweep circuits for sweeping the ebeam
in the X and/or Y directions.
5.6
EB3 turret
control: control the rotation of the crucibles.
5.7
Hearth/crucible:
4 crucibles are the maximum capacity. You may use intermetallic or graphite
crucibles depending on the metals you are going to evaporate.
5.8
Crystal
Note: It
is the labmember¡¦s responsibility to replace the crystals in the thickness
monitor.
5.9
Evaporation
materials: Al, Ti, Au, Ni, Ge, Cr, Cu, Pd, and Pt. For other metals and
dielectrics, e-mail edwardseb3@silicon to propose your material for evaporation.
6.0 Safety
6.1 Read
all relevant instructions before you operate any accessories.
6.2 Surfaces
within the AUTO 306 may be very hot or very cold. Do not touch hot or cold
surfaces such as the pump body, source holders, vacuum chamber and components
of the e-beam source.
6.3 Intense
light will be emitted from the evaporation materials. Always use dark safety
glasses when you look in the chamber.
6.4 Observe
all safety precautions when you come into contact with dangerous substances,
which have been used with the evaporation materials.
6.5 Wear
clean lint-free gloves when you handle components in the chamber to prevent
contamination of the evaporation materials and its accessories.
6.6 Do not
operate the e-beam source when there is magnetic interference.
6.7 Do not
overfill the hearth/crucible with evaporation materials. If you do, molten
materials can spill out of the crucible and contaminate the e-beam source and
evaporation materials in other hearths.
6.8 Ensure
the correct crucible is fitted to the hearth.
6.9 Ensure
the sources inside the crucible are not higher than the crucible edge. It will
hinder the rotary drive for switching between crucibles.
6.10 Do not add extra
forces when you close the chamber door. It will damage the magnetic bearing.
7.0 Statistical/Process
Data
Au: 5.5 Å/sec evaporation rate at 130 mA gun current.
Ti: 2.5 Å/sec evaporation rate at 120 mA gun current.
8.0
Available Processes, Gases, Process Notes
8.1 Pumping speed: 4.5 hours to reach 9e-7 torr.
8.2 Pumping
speed with heat lamp (70ºC chamber temperature): 2.5 hours to reach 9e-7
torr.
8.3 Available metal data in
FTM7 crystal monitor control:
Layer# |
Metal Name |
Acoustic Impedance (105 g/cm2-sec) |
Density (g/cm3) |
Tooling Factor |
|
1 |
Ti |
14.05 |
4.50 |
0.30 |
|
2 |
Au |
23.17 |
19.30 |
0.30 |
|
3 |
Ni |
26.66 |
8.91 |
0.30 |
|
4 |
Ge |
17.10 |
5.35 |
0.30 |
|
5 |
Cu |
20.20 |
8.93 |
0.30 |
|
6 |
Pd |
24.72 |
12.00 |
0.30 |
|
7 |
Pt |
36.06 |
21.40 |
0.30 |
|
8 |
Cr |
28.94 |
7.20 |
0.30 |
8.4 Inspect the door seal before closing the chamber. If you see particulates
or any contamination, wipe gently with a fresh clean wipe and a small amount of
isopropyl alcohol. The door seal is a contiguous viton o-ring and requires no
vacuum grease for sealing. Many vacuum greases have relatively high vapor
pressure and adding any to the door seal will make it more difficult for the
system to achieve best base pressure.
9.0
Equipment Operation
9.1
Enable
edwardseb3 on WAND.
9.2
Check
the vacuum. The display on the vacuum control panel (Figure 1)
should read FINE PUMPING. If not, refer to Section 10 (Troubleshooting) of this manual. If
problem persists report the FAULT and do not operate the machine.
9.3
Make
sure the high voltage control switch is OFF.
9.4
Make
sure the gun control switch is OFF.
9.5
Press
Seal on the vacuum control panel. This will close the valve to turbo
pump to prevent contamination from venting.
9.6
Press
Vent on the vacuum control panel. This will vent the chamber.
9.7
Do
not try to open the door until the display on the vacuum control panel reads
7.6+2 torr (room atmosphere).
9.8
Open
the door gently by pulling the door lever upward first and then outward.
9.9
Load
the crucibles. Make sure your sources inside the crucible did not exceed the
crucible height. This will hinder the rotation of the hearth liner.
9.10
Make
a note of your crucibles with the corresponding number on the turret control
panel (Figure 2). You will use the turret control panel to
switch to different crucibles for multiplayer evaporation; therefore, it is
important to know where your crucibles sit in the hearth liner.
9.11
Load
the wafer. Make sure the 6¡¨ wafer sits tightly on the holder.
9.12
Press
SS1 on the shutter control panel (Figure 3). A green
LED will be lit. This will close the shutter and the shutter should sit at the
proximity above the crucible.
9.13
Close
the door gently.
9.14
Do
not use any vacuum grease on the door seal.
9.15
Press
Process on the vacuum control panel. It will activate the mechanical
pump to do rough pumping.
9.16
Fill
the LN trap before
you use the vacuum coater to reduce the pump-down
time.
9.17
Select
the metal to be deposited on the crystal control monitor panel to match the
crucible by pressing Data button (FTM-7, Figure 4)
until the light adjacent to layer is lit.
Note: It is the labmember¡¦s
responsibility to replace the crystals in the thickness monitor.
9.18
Use
the arrow keys to select layer numbers (refer to Section 8.2
for the corresponding metals).
9.19
Consult
Section 8.1 for pumping time vs. chamber pressure.
Evaporation is better to be done at pressure at or lower than 1e-6 torr.
9.20
When
the pressure goes down to the wanted pressure, turn on the high voltage control
by pressing the button (Figure 5).
9.21
After
the LED labeled power is lit, turn on the gun control by pressing the
button (Figure 5).
9.22
After
the LED labeled gun is lit, slowly turn the gun current knob clockwise
until the gun current meter reads 30 mA. Stay under this current for two
minutes. This will degas the e-gun.
9.23
At
the mean time, see through the observation window on the chamber door to see if
the e-gun is hitting around the center of the source. If not, report a FAULT so
that the technician could make adjustment.
9.24
Slowly
increase the current to 60 mA and you will see the source glow.
9.25
Wait
for 2 minutes for the source to outgas.
9.26
Open
the shutter by pressing SS1 on the shutter control panel. The green LED
will be off.
9.27
Slowly
increase the gun current and read the evaporation rate on the FTM-7 panel
simultaneously. Refer to process data section to general evaporation rate vs.
gun current for different metals.
9.28
The
Yogogawa function generator is powered ON by pressing the Blue power button on
the lower left-hand front side of the unit. Wait 10 seconds for unit to complete
self-checks. Channel 1 controls X
and Channel 2 controls Y sweep.
Channel selection is made by pressing either the ¡§CH1¡¨ or the CH2¡¨
buttons on the upper left-hand side front of the unit. Once a channel is selected use the
touchpad/monitor to select voltage, waveform, frequency, dc offset
parameters. Use the rotary knob on
the upper right-hand front to adjust selected parameters. Typical set up; both
channels on, running a sine wave at 12 volts p-p, 5 ¡V 15hz with 0 dc
offset. This provides a uniform
sweep, prevents spitting and provides uniform melt of the source material. Adjust the DC offset if most of the
material is more in one quadrant than another.
9.29
After
the evaporation, close the shutter and let the machine cools for 15 minutes.
9.30
Press
Seal to close valve to turbo pump.
9.31
Press
Vent and wait until the pressure reads 7.6+2 torr.
9.32
Open
the door gently.
9.33
Unload
the sample and crucibles.
9.34
Close
the door gently.
9.35
Press
Process to pump the machine down to base pressure.
9.36
Disable
edwardseb3 on WAND.
10.0
Troubleshooting Guidelines
10.1
Rectification
of interlock problem
10.2
Safety
interlock
10.3
Vacuum
level interlock
10.3.1
Hi-Vac
Error recovery
►
Hit
reset then cycle on Vacuum Controller. If problem persists, enter
into Faults.
10.4
Water
interlock
10.5
Rotary
drive interlock
10.6
Source
control overload
10.7
Power
supply unit circuit breaker trip
10.8
Motorized
turret drive motor overload
10.9
Crystal
Monitor Problems
10.9.1
x1
and x2 crystal
indicators blinking
►
Replace
crystal
10.9.2
No
response from monitor
►
Enter
into Faults
10.10
Gun
Control Panel
10.10.1 No display
►
Check
interlocks are made on controller. Enter into Faults.
10.11
Crucibles
The following
recommendations (from Poco Graphite, a specialty material supplier)
address several common crucible problems.
10.11.1
Melt Levels
The
most common cause of crucible failures is overfilling. Overfilling can cause
the melt to spill over the edge of the crucible. When a spillover occurs, a
thermal hort is created between the crucible and the hearth. The resultant
thermal stress causes the crucible to crack. For this reason a maximum melt
level of 80% of the crucible capacity and a minimum melt level of 30% of the
crucible capacity are recommended.
10.11.2
Crucible Contact
Another
significant cause of crucible failures is cracking due to the improper seating
of the crucible in the hearth. Out of round or chiseled hearths often create nonuniform
mechanical stresses on the crucible walls. For the longest crucible life and
for the most reproducible evaporation results, contact between the graphite
crucible and the copper hearth should be restricted to the bottom of the
crucible and the bottom on the hearth cavity. A circular graphite or copper
shim is frequently used to achieve proper contact.
10.11.3
Handling
Improper crucible handling and storage also can be the
source of crucible life problems. Crucibles should be handled with tongs,
gloves or finger cots; never with bare hands or fingers. Used crucibles
available for reuse should be stored in a dry, oxygen-free environment.
10.11.4
Aluminum Melts
Aluminum carbide formation affects the life of crucibles
used for aluminum evaporation. The aluminum carbide forms a transparent,
yellowish film on the surface of the aluminum. When the film covers the entire
surface of the aluminum, the evaporation rate is reduced to near zero. The
presence of this phenomenon is indicative of excessive crucible temperature. The
beam power should be reduced to minimize the formation of aluminum carbide.
11.0 Figures & Schematics
Figure 1
Figure 2
Figure 3
Figure 4
11.5
Crystal Monitor Control Panel
Figure 5
11.6
Temperature Control Panel
Figure 6