Magnetron-sputtering.pdf

8/10/2019 Magnetron-sputtering.pdf

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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?



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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Sputtering targets

A used target

Sputter sources

Chimneys

Shutter


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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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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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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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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?



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?



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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Software interface (without active functions)


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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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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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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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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

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