Nanoclus

OXFORD APPLIED RESEARCH

NC200U-B RF/DC Nanocluster source

RF/DC Nanocluster Source NC200U-B

OXFORD APPLIED RESEARCH

NC200U-B Operation and Maintenance

 Oxford Applied Research Nanotech House, Nursery Rd North Leigh Business Park Witney Oxfordshire OX29 6SN United Kingdom Telephone: (0)1993 880005 Fax: (0)1993 880060

http://www.oaresearch.co.uk Sales: [email protected]

Table of Contents Safety

1

System Description

3

Principle of Operation Installation and Maintenance

3 5

Magnetron Sputter Target Loading

5

Target Removal

6

Target replacement

7

Connections

9

Water cooling

9

Gas inlets

9

Electrical

9

Aggregation tube cooling

10

Aggregation Tube, Differential Pumping TPiece and Apertures 11 Vacuum Gauge & Differential Pump

13

Bake-out

13

Operation

14

Start-Up (DC Mode)

14

Start-Up (RF Mode)

15

Shut Down (RF and DC mode)

16

Maintenance Cleaning the isolator

18 18

Options

20

Specifications

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B

Section

Version: 4.00

1 Safety

U

sers of this equipment must be made aware of the hazards associated with its use. Throughout this manual attention is drawn to the safety hazards as follows;

!WARNING! Failure to observe a warning could lead to injury or death to personnel.

!CAUTION! Failure to observe a caution could lead to damage to the equipment. Failure to observe these cautions will invalidate the warranty

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

(i.)

Become familiar with the principle of operation of the equipment and be aware of the function and operating voltage of each part of it.

(ii.)

Disconnect the power supply from the mains before adjusting any of the cables.

(iii.)

Disconnect the electrical feedthrough leads before handling the equipment.

(iv.)

Do not probe the power supply or the connector leads. There are no user serviceable components within them.

(v.)

Ensure that all electrical, water and gas connections are properly made.

(vi.)

Ensure that all of the equipment is properly earthed (grounded).

(vii.)

Ensure that there is sufficient ventilation for the electronics unit. The air intakes are in the base of the box with the outlet at the rear.

!WARNING! Failure to earth the equipment could lead to high voltages appearing on exposed surfaces.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U

Section

Version: 4.00

2

System Description This section introduces the principles of operation of the NC200U-B cluster source.

Principle of Operation

T

he NC200U-B is a nanocluster source designed for use in an ultra high

vacuum environment. A DC or RF magnetron discharge is used to generate the clusters, DC for targets of conducting materials and RF where the material to be sputtered is an electrical insulator. Inside the liquid nitrogen-cooled aggregation tube, a rare gas, typically argon or helium, cools and sweeps the atoms and clusters from the aggregation region towards an aperture. The cluster size can be varied by adjusting several parameters such as the power supplied to the magnetron, the aperture size, the rate of rare gas flow, type of rare gas(es) being used, temperature of the aggregation region and distance between the magnetron and the aperture. The following gives a general description of the instrument and its application:

•

A 2” magnetron designed specifically for high pressure operation is used to provide the sputtered species†. The magnetron has been designed specifically for high operating pressure in the aggregation region and for a high sputter rate. Rare earth magnets are positioned at the back of the

•

magnetron behind the target and the assembly is water cooled. Standard 2” targets can be used for most metals (for magnetic materials it is necessary to use thin targets – see section 3). The separation between the magnetron and the aperture can be adjusted using a linear motion-drive. This allows the user to vary the residence time of the clusters in the aggregation region, and hence the cluster size.

Design concept licensed from Prof. Hellmut Haberland of the University of Freiburg.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

• • •

Three gas inlets to the magnetron are provided: two for a combination of gases such as argon and helium and a third for a vacuum gauge to monitor the pressure in the aggregation region. Liquid nitrogen or water can be used to cool the aggregation tube. A T-piece is provided for differential pumping. A number of apertures of different sizes are provided to suit the customer's deposition system.

Connections for water cooling and gas inlets

Magnet assembly

Magnetron

Pressure gauge flange Apertures

Aggregation gas feed

To system Linear drive to move magnetron

Liquid Nitrogen

Ar gas feed to magnetron

Differential pumping port

Aggregation region

Figure 1: Schematic showing the NC200U-B nanocluster source.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U

Section

Version: 4.00

3

Installation and Maintenance Standard UHV practice should be adopted in installing the NC200U-B nanocluster source.

Magnetron Sputter Target Loading The magnetron uses targets of 50.8mm (or 2”) diameter with a maximum thickness of 6mm and a minimum thickness of 1mm. A thin molybdenum back-plate is supplied to prevent sputtering of the magnetron head once the target is worn through.

NOTE Magnetic Materials The magnetic field created to confine the electrons in the magnetron plasma can be adsorbed by ferromagnetic target materials. For these materials it is therefore necessary to use thinner standard targets. For Element Fe Co Ni

Target thickness (mm) 1 mm 2-3mm 2-4mm

NOTE Fe Gencoa Loop Targets For Fe the Gencoa Loop targets can be used on the source. This target design allow thicker Fe to be sputtered giving a longer target lifetime (see section 5 for ordering details).

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

Target Removal (i)

Undo the 150mm / 6 inch flange and remove the magnetron from the aggregation tube and T-piece assembly (fig. 2). The flange between the aggregation tube and differential pumping T-piece may be left in place.

Figure 2: NC200U-B components

(ii)

Remove the three nuts (a spanner is provided with the source for these) from the base of the magnetron cover and gently ease the cover away from the main body and gas line (fig. 3). Remove any flaky deposits that may have accumulated during the previous operation. Nut

Nut

Remove

Magnetron cover

Figure 3: Removal of the magnetron cover

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

Target Magnetron

Back plate

Target

Target holder

Target holder

Figure 4: Removing the target

(iii)

Rotate the target holder anti-clockwise and remove it from the main body (fig.4). The target and Mo back-plate can now be removed.

Target replacement (i)

Ensure that the molybdenum back-plate is inserted behind the target to prevent sputtering of the head after extended use. The target and back plate must be inserted so that they sit in the recess in the magnetron head. The recess will centralise the target. !WARNING! If inserting a ferro-magnetic material take extra care as the magnetic field of the magnetron is very strong!

(ii)

Replace the target holder and tighten gently while holding the target in position. DO NOT OVERTIGHTEN! Ensure that the target is still central and that no gaps can be seen between the target and the target holder.

(iii)

Replace the magnetron cover, aligning the gas feed pipe with the gas feed holes, and the three threaded studs with the holes in the support ring.

(iv)

Insert a thickness gauge (supplied with the source) between the magnetron cover and the target holder. Adjust the nuts on the reverse of the magnetron cover so that the magnetron cover- target 7

Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

separation is either 0.3 or 0.2mm (fig. 6). The separation should be the same all the way round the circumference of the target to ensure even gas flow. (v)

Ensure that there is high resistance between the target and the magnetron cover using a resistance meter. A low resistance may indicate that the cover is touching the target holder, that there are flakes of sputtered material between the cover and the holder, or that the main isolator for the source requires cleaning. See the next section for information on how to access the isolator.

Figure 6: Setting magnetron cover-target holder separation

(vi)

Re-insert magnetron into the aggregation tube.

NOTE For non-magnetic materials, the separation between the magnetron cover and the target holder should be about 0.3mm. For magnetic materials, the separation should be reduced to 0.2mm.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U Version: 4.00

Connections Water cooling Connect the water cooling pipes to the magnetron. Either connection can be used as the inlet/outlet. It is advisable to use de-ionised water with a flow rate that exceeds 1l/min. Source mounting flange RF or DC Power Input (N-Type) Sputter gas (VCR)

Water (1/4” Swagelok)

Water (1/4” Swagelok)

Aggregation gases (VCR)

Figure 7: Connections at the back of the magnetron.

Gas inlets There are three VCR fittings for the gas inlets. The inlet in the centre is for argon and is used for the magnetron discharge. The other two VCR inlets to the left and right can be used for introducing gases into the aggregation tube. A vacuum gauge can also be attached to one of these two inlets for monitoring the aggregation region pressure. If any of these gas inlets are not used, they must be sealed with a blank VCR fitting. Each time a VCR fitting is removed, a new mini VCR gasket must be used for refitting in order to maintain the vacuum seal. Electrical Connect the magnetron power supply to the N-type connector. The central pin of the connector should be biased negative when using the source in DC mode. Ensure that the positive connection is also connected to ground on the power supply. For operation in RF mode, the short RF cable from the matching unit must be connected to the N-type connector, and a further RF connection made between the RF power supply and the matching unit. All

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

power supplies provided with the NC200 have their own product manual which should be read in conjunction with this manual. !WARNING! Ensure that the power supply is turned off before connecting and disconnecting the magnetron connector.

Aggregation tube cooling Connect the water or liquid nitrogen supply to one of the connections via a Swagelok coupling. If using liquid nitrogen the other connection should be coupled via a Swagelok fitting to an exhaust, which should be ducted to outside the building.

Figure 8: Nitrogen cooling connections.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

Aggregation Tube, Differential Pumping T-Piece and Apertures There are a number of standard aggregation tube aperture plates that are supplied with the source (plates with 3 screw holes). (i)

Load the nozzle into the aperture plate, and fit the desired aperture plate to the end of the dome using the screws provided (fig.9 and 10)

Figure 9: Dome, nozzle, and aperture plate.

Figure 10: Fixing the dome with nozzle and aperture plate to the end of the aggregation tube.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

(ii)

Fit one of the flat aperture plates to the double -sided flange (fig.11)

Figure 11: Fitting the aperture to the double-sided flange.

(iii)

Fit the double-sided flange to the end of the T-piece. Position the two flanges, as shown in fig. 12, so that the holes for the five M5 fixing bolts are aligned. Fix the flange using the M5 bolts. Use a copper gasket between the flange and the T-piece. T-piece Double-sided flange

M5 bolt holes

Figure 12: Fitting the double-sided flange to the T-piece.

(iv)

Fit the T-piece, with the double-sided flange attached, to the deposition system and then fit the aggregation tube into the Tpiece assembly (fig. 2)

(v)

Fit the magnetron inside the aggregation tube.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

Vacuum Gauge & Differential Pump A vacuum gauge can be attached to the NW35CF conflat flange on the Tpiece for monitoring the pressure inside the T piece. A vacuum gauge may also be connected to one of the auxiliary VCR gas connections to measure the pressure inside the aggregation zone. A pump can be connected to the differential pumping port to reduce the gas load in the deposition chamber. A 500l/s or 1000l/s turbo pump is most suitable.

Bake-out The nanocluster source can be baked to 250°C. Before commencing bake-out ensure that all water connections are disconnected and the water blown out from the system using compressed air. The electrical connections should also be disconnected. !CAUTION! Ensure that the cooling water has been purged from the water jacket and that the water lines are open to atmosphere. A build up of steam within the water jacket may damage the instrument

!CAUTION! The maximum bake-out temperature of the instrument with the water, liquid nitrogen and electrical connections removed is 250ºC.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U Version: 4.00

Section

4

Operation

B

efore operation ensure that the pressure of the system is less than 1x10-4 mbar and that there is sufficient coolant flow through the magnetron.

Start-Up (DC Mode) (i)

Ensure that the required DC mode power supply is connected to the N-Type connector on the NC200. Ensure that you have read the separate product manual for the DC power supply before starting. For operation in DC mode the magnetron target must be made from an electrically conducting material.

(ii)

Set the aggregation length by rotating the hand-wheel. This may also be adjusted during operation of the source.

(iii)

Introduce water or liquid nitrogen into the aggregation tube and allow the tube to reach an equilibrium temperature.

(iv)

Ensure that the cooling water for the NC200 source is switched on.

(v)

Increase the voltage from the power supply to about 4-500V. At this time the power supply will be in voltage control mode. The current limit should also be increased above zero, otherwise it will not be possible to strike a plasma.

(vi)

Introduce argon into the magnetron until a discharge is struck. This is indicated by a current reading on the power supply (>0.02A), and the power supply switching from voltage to current control mode.

(vii)

Adjust the current limit (and if necessary also the voltage limit) to give the required power and introduce the aggregation gas(es) if required.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

(viii)

A quartz crystal monitor can be used to measure the deposition rate. A quadrupole mass filter, or other device, can be used to measure the cluster size.

!CAUTION! Throughout the operation, make sure water is constantly flowing through the magnetron so that it will not freeze and damage the cluster source. Failure to ensure constant water flow throughout the operation and shutdown procedures will damage the cluster source and invalidate the warranty.

The lifetime of a 5mm thick Cu target, using Ar as the sputtering gas, is about ~2kW hours. Targets made of other materials will have a different lifetime due varying sputter rates. The thickness of the target material is obviously an important factor for the lifetime.

!CAUTION! Ensure that the power and running time during each experiment are noted so that the target wear can be estimated. The magnetron is supplied with a Mo backplate which should be used to prevent the sputtering of the instrument head. After extended use if the conditions change dramatically, possibly with jumps in the current on the power supply, the magnetron should be removed and the target inspected.

Start-Up (RF Mode) (i)

Ensure that the RF matching unit is connected to the NC200 source and the RF power supply is connected to the matching unit. Ensure that you have read the separate product manuals for these units before starting.

(ii)

Set the aggregation length by rotating the hand-wheel. This may also be adjusted during operation of the source.

(iii)

Introduce water or liquid nitrogen into the aggregation tube and allow the tube to reach an equilibrium temperature.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

(iv)

Ensure that the cooling water through the NC200 source is switched on.

(v)

Introduce argon into the magnetron up to a gas flow of ~20 sccm.

(vi)

Turn on the RF power supply and set a forward power in the range 50-100W. Turn the RF power on. Do not turn on the RF power if there is no gas flowing through the source!

(vii)

The reflected power should stay below 5W at all times during operation and will be tuned automatically by the auto-tune unit. If the reflected power is above this level or is fluctuating it is likely that there is an RF short in the source. This can usually be cured by cleaning the insulator or cleaning any flakes of sputtered material from the inside surface of the magnetron cover. Do not run the source for more than a few seconds if the reflected power is above 5 W as this will cause damage to the source. The cause of the high reflected power must be investigated before proceeding.

(viii)

Adjust the RF power and gas flow as required. The auto- tune unit should automatically compensate for any changes in the operating conditions and reduce the reflected power. When using RF powers greater than 200 W, it is wise to check the outlet temperature of the water at regular intervals. If this rises significantly above ambient temperature, then a higher water flow should be used.

(ix)

A quartz crystal monitor can be used to measure the deposition rate. A quadrupole mass filter, or other device, can be used to measure the cluster size.

Shut Down (RF and DC mode) (i)

Switch off the magnetron DC or RF power supply.

(ii)

Turn off the gas valves.

(iii)

If liquid nitrogen is used turn off the control valve. Due to the subzero temperature in the aggregation region, make sure water is constantly flowing through the magnetron for at least one hour after the liquid nitrogen control valve is turned off. This will ensure the cooling water will not freeze. If water is used for the aggregation zone cooling, it is still necessary to keep the water running for 30 minutes after source shut down to remove the residual heat from the source. 16

Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

(iv)

Allow the aggregation tube to reach room temperature before venting the vacuum chamber. This will minimise atmospheric water condensation on the cluster source.

!WARNING! On venting the vacuum system, cluster-particles may emanate as a fine dust which may be hazardous if inhaled. A suitable respiratory mask should be worn.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U

Section

Version: 4.00

5

Maintenance Cleaning the isolator The main isolator for the NC200 is shielded inside a metal casing to protect it from any sputtered materials, however because it must electrically isolate the head of the source, it cannot be completely enclosed. Over time it is likely that there will be a build-up of material on the isolator from the sputter target, and if this material is electrically conducting then it will eventually short out the source. If no other reason can be found for a short, then this is the most likely explanation. For access to the isolator for inspection and cleaning, the isolator shield must be removed. This section describes how to do this. i) Remove the magnetron cover, target holder and target from the source as described in section 3. ii) Remove the magnetron cover securing ring from the source. This is secured to three support legs by three cap-head screws (marked by white arrows in fig 13) which must first be removed. The ring may then be withdrawn from the source by pulling it carefully and evenly in the direction away from the source flange (direction of red arrows, fig 13). Note for re-installation that the cut-out section in this ring fits over the Ar gas pipe. Isolator shield Gas feed pipe

Magnetron cover securing ring

Plus one more screw underneath

Figure 13: Removing the cover securing ring

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

iii) Remove the two recessed securing screws from the isolator shield marked by red arrows in figure 14. The two halves of the shield may now be removed separately through the gaps between the support legs for the magnetron cover securing ring. The covers are asymmetric and the position of the narrow end (on the source flange side of the isolator) should be noted for re-installation. For re-installation also note that the isolator shield can be rotated to any orientation, the rotational orientation does not matter. Magnetron cover securing ring support legs

Isolator shield

Isolator

Magnetron cover securing ring and securing screws

Gas feed pipe

Figure 14: Removing the isolator shield

iv) The isolator can now be seen. This should be white in colour, so any build up of deposited material can be clearly seen. If such material is present, the isolator should be gently cleaned with an abrasive. v) Re-assembly of the isolator shield is the reverse of removal, taking note of the notes for re-assembly above.

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Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U-B Version: 4.00

Section

6

Options Oxford Applied Research supplies a number of options for the NC200U-B source. The table below shows these options. Details of these options can be found in the respective manuals. If you require further information or pricing please contact your local representative. Option Quadrupole Mass Filter

RF sputtering upgrade Nanocluster deposition system

Description The QMF200 quadrupole mass filter has been specifically designed for the purpose of highresolution analysis and filtering of nanoclusters between 100 and 1x106a.m.u. It is compatible with the NC200 and can be tailored to the deposition system. The electronics unit allows control either from a front panel or a PC equipped with the optional software package. Other options to this item include a differential pumping T-piece and an inline filter to remove neutral clusters from the beam axis. For sources supplied with only the DC mode power supply, it is possible to purchase the necessary power supplies for RF mode operation from OAR. This allows the sputtering of targets of insulating materials. The Nanodep60 integrates the NC200U-B and QMF200 with a full deposition system. The system configuration provides for numerous entry ports for the addition of a variety of other deposition sources and analysis tools for optimal process flexibility. A heated rotary work-table substrate manipulator, substrate ion cleaning facility and system load-lock are among the options available.

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Part no. QMF200

NC200RFU

Nanodep60

Oxford Applied Research Gas Condensation RF/DC Nanocluster Source NC200U Version: 4.00

Section

7

Specifications Mounting flange: Differential pumping flange: Vacuum gauge flange: Minimum water cooling flow rate: Water cooling fittings: Gas inlet fittings: Target diameter: Maximum target thickness: Minimum target thickness: Maximum power handling: Maximum separation between target & aperture: Minimum separation between target & aperture: Maximum bake out temperature:

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NW150CF NW150CF NW34CF 1 l/min ¼” Swagelok ¼” VCR 50.8mm (2”) 6mm 1mm 1000 W DC 600 W RF 198mm 48mm 250oC

Section

8

Oxford Applied Research Nanotech House, Nursery Rd North Leigh Business Park Witney Oxfordshire OX29 6SN United Kingdom Telephone: (0)1993 880005 Fax: (0)1993 880060

http://www.oaresearch.co.uk e-mail: [email protected]

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