magnetron-sputtering.pdf
TRANSCRIPT
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Ngo Duc TheAdvanced Memory Laboratory
Magnetron sputtering
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Content
Why sputtering?
Physics of sputtering deposition DC and RF Sputtering
Standard procedures in BESTEC Chimera
System at the AML
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Why sputtering?
We are working in thin film world a technique to
produce high quality thin film materials is really
needed!
Sputter belongs to physical approaches of thin film
deposition;
Thermal evaporation has been widely used as a
cheap and fast technique but the quality of the filmis not good enough (definitely, it was grown in
medium-high or less vacuum);
MBE allows fabricating thin film with excellentquality (single crystal film) but it is very expensive
(too vacuum, very high purity raw material);
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Why sputtering?
Sputtering does not require too high vacuum;
The raw materials must not be high purity;
Able to grow the films with very slow rates;
High quality of the film can be reliable;
Easy for large-scale production.
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Content
Why sputtering?
Physics of sputtering deposition DC and RF Sputtering
Standard procedures in BESTEC Chimera
System at the AML
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Physics of sputtering deposition
Sputtering is a process whereby atoms are ejected
from a solid target material due to bombardment of the
target by energetic particles;
Sputtering is a deposition process by transferring kinetic
energy. Physical sputtering is driven by momentum
exchange between the ions and atoms in the materials,
due to collisions; No evaporation in sputtering process.
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Concepts in sputtering
Target: Source material to fabricate the film on the
substrate. Target is mounted at the sputter source and
connected to the cathode of the power supply. During
sputter process, target is heated and must be cooled by a
cooling water.
Manipulator: A part of the sputtering where the substrate is
placed on. Manipulator is linked to the anode of the powersupply and is able to rotate, to heat the substrate and is able
to lift up and down for transferring.
Chimney: A part at the sputter source, which surrounds thetarget. Chimney has a same electric potential to the anode,
so that the gas only bombards the target. Chimney is used
to concentrate the materials to the anode.
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Concepts in sputtering
Sputtering targets
A used target
Sputter sources
Chimneys
Shutter
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Concepts in sputtering
Base pressure: the pressure in the SP chamber before
it is filled by the gas for sputtering process. The better
vacuum (less pressure), more quality of the sputteringfilm is possible.
Gas pressure: Pressure of the gas filling in the SP
chamber for sputtering. If the pressure is too low, thesputter is weak and difficult to occur, but if the gas
pressure is too high, sputter becomes over, deposition is
too quick and quality of the film will be less.
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Physics of sputtering deposition Sputtering gas should be an inert one; otherwise,
compound will be created if the active gas is used;
For efficient momentum transfer, the atomic weight of the
sputtering gas should be close to the atomic weight of thetarget;
Ar, Kr or Xe are preferred for heavy elements whereas Ne
or He are used for light elements;
Ion/electron mixture at low pressure causes negative
plasma that can be visually observed.
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Physics of sputtering deposition
The higher base vacuum in the chamber, mean free path
of the ion is longer, the better sputtering process is
expectable;
Sputtering is sometimes employed for milling or etching sputter etching;
Of other approaches, a controlled ion beam is used to
bombard the target
ion beam sputtering.
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Physics of sputtering deposition
To enhance the efficiency of the sputtering, magnets are
placed under the target to trap the charges from the plasma;
The electrons are not free to bombard the substrate to the
same extent as with diode sputtering;
Circuitous path carved by these same electrons when trapped
in the magnetic field, enhances their probability of ionizing a
neutral gas molecule. This increase in available ions
significantly increases the rate at which target material is
eroded and subsequently deposited onto the substrate.
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Physics of sputtering deposition
Sputter deposition is a complex function of gas pressure,
sputtering power, distance from the target to thesubstrate, rotation of manipulator
These take a long time for calibrating the sputter.
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Content
Why sputtering?
Physics of sputtering deposition DC and RF Sputtering
Standard procedures in BESTEC Chimera
System at the AML
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DC Magnetron Sputtering
If the target is conductive (metallic materials), a DC
voltage applied to the substrate and the target can make
a closed circuit;
Current in this case only flows from substrate (anode) to
the target (cathode);
DC sputtering is only possible for conductive targets;
Sometimes, power is pulsed Pulsed DC sputtering.
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RF Magnetron Sputtering
As target is insulator, DC power is not suitable, anode
cathode acts like a capacitor an alternating current
(AC) is able to flow through a capacitor used for
sputtering of insulator target;
Power supplies a high-frequency (radio frequency)
current we have a RF sputtering process;
In order to maximise the power in the target, animpedance matching network must be used.
MgO target for RF sputtering
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Content
Why sputtering?
Physics of sputtering deposition DC and RF Sputtering
Standard procedures in BESTEC Chimera
System at the AML
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BESTEC Chimera deposition system
Loadlock
Sputter
Preparation
MBEElectronic cabinet
(MBE)Electronic cabinet
(SP)
Turbo pump
Transfer arm 2
Transfer arm 1
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BESTEC Chimera deposition system
Software interface (without active functions)
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BESTEC Chimera deposition system
Loadlock (LL): first chamber for loading the substrates
before transferring to deposition. The best vacuum in the LL
is about 210-8 Torr.
Preparation chamber (PR): the second stage for pre-
cleaning the substrates and transferring to MBE chamber.
The best vacuum in the PR is about 3.510-9 Torr.
Sputter chamber (SP): sputtering deposition chamber with8 2-inch sources and 1 4-inch source. The SP chamber can
reach the best vacuum of ~7.010-10 Torr.
MBE chamber: a chamber for epitaxial deposition with 6
effusion cells and 4 cells for e-beam evaporator. The bestvacuum in the MBE chamber can be 3.510-11 Torr
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Loadlock chamber (LL)
The best vacuum ~210-8 Torr;
Can load maximum 6 samples;
Lamps system to heat the chamber(~200oC) for degassing;
Positioning of sample during
transferring by counters in transferarms.
Loadlock chamber
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Sputter chamber (SP)
SP chamber view from the top
Sputter sources
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Sputter chamber (SP)
The best vacuum ~7.010-10 Torr;
Eight 2-inch sources for DC/PDC sputtering;
One 4-inch source for DC/PDC/RF sputtering
Two gas lines (Ar, Kr) with separated gas
pipes to each source, flow rate controlled by
MFC;
Heating substrate to maximum 700o
C; Active gas nozzle (N2, O2) to substrate for
active sputtering;
PDC: 1000 W (maximum);
DC: 500 W (maximum);
RF: 600 W (maximum).
SP manipulator
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Sputter chamber (SP)
Minimum distance from the substrate to the 4 target: 56.4 mm
Maximum distance: 336.4 mm
SP guns cross section
min. distance
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Sputter chamber (SP)
The change in the vertical position of themanipulator may caused different uniformity of
the film;
The height in the software is different from theposition on the ruler (0: the highest pos.,
280mm: the lowest pos.);
Optimum position for sputtering of 2 sources
is 130 mm (in software) the best uniformity
of the film)
The height for 4 source depends on the
target.
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Standard procedures for sputtering
Transferring samples from LL to SP chamber; Preparing the gas
Preparing manipulator position and rotation;
Setting sputter condition and macro (ifneeded);
Do sputtering
Finish and transfer back to LL unload
samples
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Load samples to LL
Load the samples to the LL;
Evacuate the LL;
Wait for the vacuum (should be ~10-7 Torr range);
Degas the chamber (200oC 30 min.) if required; Transfer to PR chamber for cleaning or to SP
chamber for deposition;
Do not forget wearing clean suits to avoid the
contamination to the LL.
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Transferring routes
Loadlock
Preparation(Plasma, hydrogen
cleaning)
Sputter(Sputtering deposition)
MBE(Epitaxial deposition)
mple
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Transferring from LL to SP
After manipulators are ready, open V2 and
V3 for transferring;
Carefully transport of samples by transfer
arms;
Transfer to SP only when the PR manipulator
is at Process position.
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Preparation of SP stage
Make sure SP manipulator shutter is closed and atvalid position before deposition;
Move SP stage to deposition height position (e.g.
130 mm);
Set rotation speed (e.g. 45 rpm);
Open SP manipulator shutter when deposit or
move SP state near the 4 target.
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Preparation of gas ambient
Make sure V3 closed;
Close V53 and V32 to protect TMP
P10;
Close V31 and open V37 to clean
the gas lines before sputtering; Close V37 as the gas lines are
clean enough (pressure at G14