Identifier: Revision: Effective Date: Review Date:

SOP-005

0

1/16/2009

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Geology Dept. Document No.: EXACt - 005

Author: Miguel A. Santiago Rivera

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UUPPRR--NNSSFF EEaarrtthh XX--rraayy AAnnaallyyssiiss CCeenntteerr ((EEXXAACCtt!!)) Standard Operating Procedure for:

Operating the Denton Vacuum Desk IV - Carbon Coater

UPR-Mayaguez Campus, is an affirmative action / equal opportunity employer, is operating by the University of Puerto Rico.

UUPPRR--NNSSFF EEaarrtthh XX--rraayy AAnnaallyyssiiss CCeenntteerr ((EEXXAACCtt!!)) X – R a y L A B O R A T O R Y

__________________________________________________ DEPARTMENT OF GEOLOGY

F- 304 Geochemistry Facilities at Physics Building University of Puerto Rico – Mayagüez Campus

Revision Log

Revision No.

Effective Date

Prepared By Description of Changes

Affected Pages

R-0

January 20, 2009

Miguel Santiago

New Procedure

All

\

Operating the Carbon Coater – Denton Vacuum Desk IV

Table of Contents 1.0 PURPOSE . . . . . . . . 4

2.0 SCOPE . . . . . . . . 4

3.0 TRAINING . . . . . . . . 4

4.0 DEFINITIONS . . . . . . . 4

5.0 RESPONSIBLE PERSONNEL . . . . . 4

6.0 EQUIPMENT . . . . . . . 4

7.0 THEORETICAL BACKGROUND . . . . . 5

8.0 PROCEDURE . . . . . . . 9

9.0 RECORDS . . . . . . . 26

10.0 REFERENCES . . . . . . . 26

Operating the Carbon Coater – Denton Vacuum Desk IV

1.0 PURPOSE This procedure provides instructions for the operation of the Denton Vacuum LLC, for Model Desk-IV, carbon coater system. 2.0 SCOPE This SOP is a mandatory document and shall be implemented by all Researcher, Faculty member, Technician or Students participants when collection electron microprobe data. 3.0 TRAINING

3.1 All users of this SOP are trained by reading the procedure, and the training is documented in accordance with the GLP’s. 3.2 The Geology Task Leader will monitor the proper implementation of this procedure and ensure that relevant team members have completed all applicable training assignments in accordance with GLP’s.

4.0 DEFINITIONS

4.1 SOP - Standard Operational Procedure 4.2 GLP’s - Good Laboratories Practices 4.3 Machine Custodian —The Machine Custodian is responsible for

Denton Vacuum Desk IV maintenance and User instruction. This includes sample preparation.

5.0 RESPONSIBLE PERSONNEL

The following personnel are responsible for activities identified in this procedure. 5.1 Scientific Instrumentation Specialist 5.2 Faculty Member 5.3 Researcher 5.4 Student Participant

6.0 EQUIPMENT Description of equipment constituting the Carbon Coater – Denton Desk IV system is provided below. 6.1 Denton Vacuum Desk IV — The Denton Vacuum DESK IV Cold

Sputter/Etch Unit (Purchase Date: month/year: 08/2007 and Serial Number: 116123) is designed to deposit a conductive coating on an SEM sample and to provide some limited surface cleaning.

6.2 The Denton Vacuum DESK IV counts with; • Standard 6” diameter Pyrex Cylinder • Aluminum Baseplate. • Mechanical Pump • Vent Valve • Specimen Table • Sputter Cathode • Shutter • Gas Control Knob

6.3 Major components of the Carbon Coater

6.3.1 Programmable Logic Controller (PLC) at Denton Vacuum DESK IV

6.3.2 Denton Vacuum DESK IV - Carbon Accessory - Electron gun - Adjustable Power Knob - Ampere meter

7.0 THEORETICAL BACKGROUND

7.1 What is a carbon coating? Carbon evaporation has resulted in the production of preparation units (both dedicated units and sputter-coater attachments) which operate at mechanical pump vacuum (10-2 Torr). The nucleus of the low vacuum system is a carbon fibre filament source, which burns at very high temperatures over a short period of time. The mean free path of carbon particles evaporated conventionally at such vacuums (10-2 Torr) is less than 5mm, but the more energetic hot carbon particles resulting from the fibre system have a longer path length. Carbon Films, because of their mechanical stability, good electrical conductivity, and low background signal are commonly used in sample preparation techniques for Electron Microscopy (EM).Thin films of the order of up to 5nm (50A) are used in Transmission Electron Microscopy (TEM) as particle support and as isolating layers in auto-radiography. Thick films somewhat more than 5nm (50A) are used in Scanning Electron Microscopy (SEM) also for support, in addition to coating for X-ray Microanalysis. It may also be a requirement to subsequently treat support films by means of Glow Discharge.

In general, here is a need for all these films to be fine grain, even coating, with uniform and reproducible film thickness. The advent of Carbon fibre has resulted in a new principle for Evaporation of Carbon in EM applications. The basis is a carbon filament, which at high temperature burns very quickly somewhat in the order of 1 second, or less, from which has evolved the terminology Carbon 'Flash' Evaporation. The resulting short coating times and reduced total power input distinguishes it from the somewhat longer process of carbon rod evaporation. Evaporation under these conditions is not unidirectional as the particles engage in a number of collisions before they arrive at the surface, enhancing the possibility of a uniform coating, even on sculptured surfaces.

7.2 Physical Considerations The carbon particle evaporation is dependant on several factors., such as the surface area, temperature, and the length of the filament. The filament itself can take several forms including multi stranding and "made up form" carbon fibre. Although generally the "made up form" is more convenient.

Figure 1:

(i) Fibre (ii) String (iii) Cord.

Differing arrangements may be used to cover a range of applications. It is more convenient to have a fixed length filament for both mechanical simplicity, and in determining the requirements of the Power Supply, this also ensures for particular that high repeatability of Carbon Evaporation can be achieved. It is considered that a filament length of 10 mm (exposed length for evaporation, the actual length being somewhat longer to accommodate clamping) is satisfactory. The power supply requirements can now be determined which are two fold, it being necessary to flash the carbon filament rapidly with full applied power to ensure a good repeatability and also prior to this. To outgas the filament at the higher end of the red heat temperature band, for a time period and with variable current facilities to allow for the differing arrangements of filament.

In the vacuum range we are considering of 0.05 to 0.01 Torr where the mean free path lengths are relatively short, of the order of 1-5mm, then if the specimen is several times this spacing from the filament, the coating will not be as sensitive to vacuum. In general the outgassing would be 0.1 Torr with flash evaporation at 0.05Torr or better and it is good practice to repeat parameters to ensure consistent results. The filament itself tends to act as a point source and in the flash process 'breaks' as part of the process without fully evaporating along its complete length. The geometric arrangement is indicated in Figure 1, which has a shutter used during the outgassing process to avoid heat input to the specimen. The filament length (10mm) can normally be considered, as a point source and theoretically the thickness (t) of coating will vary inversely proportional to the height of the specimen to the filament squared. (t proportional to 1/h2). In practice due to the short mean free path, this relationship is somewhat less than indicated.

The apparent point source of the filament also suggests another consideration in coating a flat substrate, which is related to the angle for differing heights. If the angle is large, the variation of coating of a central area to that on an outer edge will be somewhat different. This is given in the table showing the percentage coating for angle of “Φ” which can also be related to the height “h” to radius “r”, although again due to collision with the short path length it is not as sensitive as may be anticipated for the table. However, it serves as a good basis for considering the height range requirement (usually variable) and specimen table diameter (usually fixed). It might be reasonable to consider a figure of 85% as the acceptable limit, with a ratio of 0.4. If we use a specimen table of diameter “d” of 50 mm (r = 25 mm) then “h” would need to be some 65 mm. In practice the system has a 50 mm diameter specimen table with variable height facility centering of 65 mm with a + -20 mm range giving 45 mm to 85 mm. As has been, already, mentioned however, in practice the coatings tend to be much more evenly deposited over this range. To test for uniformity of Carbon films, deposition on glass fibre filter paper positioned in the centre of the specimen table. The uniformity of thickness over the surface of the filter paper can then be visually assessed. Results from deposited films on filter paper demonstrate that the carbon deposit is relatively even over the surface of the 60 mm diameter specimen stage. Deposition is predominantly thicker however, in the direction parallel to the evaporation source.

8.0 PROCEDURE Note: All personnel performing work under the UUPPRR--NNSSFF EEaarrtthh XX--rraayy AAnnaallyyssiiss CCeenntteerr ((EEXXAACCtt!!)) quality program may follow this standard operating procedure (SOP) for carbon coating. May use their own procedure(s) as long as the substitute, only if, meets the minimum requirements prescribed by the UUPPRR--NNSSFF EEaarrtthh XX--rraayy AAnnaallyyssiiss CCeenntteerr ((EEXXAACCtt!!)) Plan or are better in the performing, and have been approved by the Director of the Department of Geology, UPR-Mayagüez Campus, before the commencement of the activitie(s). Note: UUPPRR--NNSSFF EEaarrtthh XX--rraayy AAnnaallyyssiiss CCeenntteerr ((EEXXAACCtt!!)) personnel may produce paper copies of this procedure printed from the controlled-document electronic file. However, it is their responsibility to ensure that they are trained to and utilizing the current version of this procedure. The author may be contacted if text is unclear. Note: Deviations from SOP’s are made in accordance with Department Director approval and documented in accordance with the GLP’s.

8.1 Introduction - The Denton Vacuum DESK IV Cold Sputter/Etch Unit is designed to deposit a conductive coating on a SEM sample and to provide some limited surface cleaning in some models. Procedure Users are responsible for determining what methods are appropriate for their work.

8.2 General Description - A standard 6” diameter Pyrex Cylinder with

top and bottom seals sits on an aluminum Baseplate. Metal chamber is optional with Turbo Pump option (TSC). A two-stage, direct-drive Mechanical Pump mounted in the cabinet evacuates the cylinder. An automatic Vent Valve is slaved to the mechanical pump. It will automatically open when the Mechanical Pump is turned OFF to vent the chamber to atmosphere. It will automatically close when the Mechanical pump is turned on.

An insulated Specimen Table with provisions for height adjustment is mounted within the Pyrex cylinder. Rotation is optional. The Sputter Cathode is clamped to an insulated aluminum plate in the chamber cover. The target supplied in the base system is gold or gold/palladium. A manual Shutter is provided to shield the Sputter Cathode from contamination during the Etch cleaning cycle. The shutter control knob is left of the chamber. Clockwise rotation of the knob will open the shutter and counterclockwise rotation will close it. A manual Gas Control is provided to control pressure in the cylinder. The Gas Control knob is to the left of the chamber.

For servicing and inspection convenience, all Fuses are mounted externally on the rear panel and the rear panel is hinged to provide access to internal components. There are six main operations for the system: Vacuum, Etch Enable (if equipped), Rotation (if equipped), Sputter Enable, Timed Etch (if equipped) and Timed Sputter. A Programmable Logic Controller (PLC) controls the system. A Touch Screen is used to interface with the PLC. Operator interface is through a graphics program that is running on the Touch Screen. This control system will be described in detail in the Operation section of this SOP.

8.3 Safety Considerations - Normal-operating conditions as performed by

trained Procedure Users present no safety hazards.

8.4 Performing the Standard Operation Procedure for Carbon Coater Denton Vacuum Desk IV

8.4.1 Environmental Conditions - Normal interior building temperature and humidity are acceptable for the operation of the Desk IV System. The system is designed and intended for use in the following environmental conditions. If not all specifications are met, system components may malfunction and can possibly cause injuries. • Altitude up to 2000 m • Temperature range from 5 to 40C • Maximum relative humidity 80% for temperature up to

31C decreasing linearity to 50% relative humidity at 40C • Mains supply voltage fluctuations not to exceed +/-10%

of the nominal voltage • Other supply voltage fluctuations as stated by the

manufacturer • Pollution degree 2 in accordance with IEC 664

8.5 ELECTRICAL REQUIREMENTS

8.5.1 Desk IV • 120-VAC; 10 Amps (standard); or 220-VAC; 8

Amps (non-US)

• Power cord provided with unit.

8.5.2 Carbon Rod Accessory and Carbon Yarn Accessory

• 120-VAC; 10 Amps (standard); or 220-VAC; 5 Amps (non-US).

• Power Cord provided with unit.

8.6 Safety Warnings

8.7 Mechanical Pump - The mechanical pump is mounted within the

cabinet and contains oil. 8.7.1 Remove the four screws at the top of the hinged rear panel,

and lower the panel to open. 8.7.2 Check the oil level in the mechanical pump view port. It

should be at the center of the red ring. 8.7.3 Should the pump require additional oil, proceed as follows

(see photos on next page): 8.7.4 Unscrew the exhaust filter and remove. The white bushing

remains on the exhaust port on the pump. 8.7.5 Remove the cap on the oil container and fill the pump,

through the exhaust port, until the oil reaches the center of the red ring on the sight glass (located on end of pump).

8.7.6 Check oil level again after running pump below 1 Torr. 8.7.7 Replace the exhaust filter.

8.7.8 Close the back panel. 8.7.9 Save all tubing, sponge and containers.

8.8 Sample Preparation - Samples to be examined with the Desk IV must be in a form or size that can be inserted into, or attached to, an Desk IV stage mount. To check your carbon evaporation technique, before coating samples, do the following:

8.8.1 Coat a glass cover slip with gold. 8.8.2 When the cover slip is over coated, the gold color will

change: • To copper with 100A of carbon • To orange with 150A of carbon • To purple with 200A

8.8.3 Operation – The Desk IV sputter head must be rotated to the

side. Replace the standard 6.0” diameter by 6.0” high Pyrex cylinder with the 6" D. x 9" H. Pyrex cylinder. Mount the Carbon Rod accessory plate to the top of the larger Pyrex cylinder. The Desk IV vacuum pumping system can be used to evacuate a Pyrex cylinder with a carbon evaporation source mounted in the metal cover.

The source can be mounted so as to vary the source-to-specimen distance from 3-1/2” to 5”. Two carbon rods are positioned in the center of the “yoke” to do the coating. One rod will have a point or reduced section. The other will have a full diameter section that has been carefully flattened on the end touching the point (or reduced section) of the other rod. Both carbon rods should be inserted, one after another, through the outside end of the fixed rod holder. First, the pointed rod should be inserted (point trailing) and pushed through with the flattened carbon rod to move into the moving rod holder. Continue pushing the rods until the spring is deflected about 1/8 inch. Tighten the thumbscrew holding the flattened carbon in the fixed holder.

If using a reduced section carbon rod, the spring should be moved out a little more than the length of the reduced carbon. With the carbon source loaded, place the Pyrex cylinder on the baseplate, seat the source head, and start pump down. Within two to three minutes, the chamber vacuum gauge should read about 50 mTorr. Turn on FILAMENT POWER on the Carbon Evaporation Module. Rotate powerstat clockwise to obtain 15 amp reading on ammeter. Carbon point should be bright red and outgassing. Increase filament power to 28 to 32 amps until a light spark is seen. DO NOT exceed 50 amps on the meter. At 4” source-to-specimen, about 1/8” length of .040 inches reduced section will deposit about 100 angstroms of carbon. For evaporating at relatively high pressure, it is good practice to check carbon film thickness. Coat a glass cover slip with gold. The gold color will change to copper when the cover slip is over-coated with 100 angstroms of carbon; to orange with 150 angstroms of carbon; to purple with 200 angstroms of carbon. At 50 mTorr, the average gas molecule travels about .04” between collisions. With a source-to-specimen distance of 4”, the carbon will make many collisions. It will arrive from all available directions. Above 75 mTorr, the thickness of the carbon film will diminish rapidly, as compared to the expected thickness. If the carbon chamber will not pump below 100 mTorr, check by substituting the Desk IV chamber. If that pumps down, then the trouble is probably with the “L” gaskets on the carbon chamber. Wipe them clean with a lint free cloth and acetone. Apply a thin coating of vacuum grease to the gasket on the glass side and on the baseplate side WARNING ! Use dark safety glasses to observe carbon evaporation. Intense brightness is harmful to eyes when viewed directly.

8.8.4 General Notes - The chamber should first be pumped to 50 mTorr or less. Denton Vacuum supplies a carbon of excellent quality. It is suggested that a low power setting, to degas the carbon, be used; slowly raise to evaporate. Degas the carbon (bright red) for 5 to 10 seconds. (Watch the chamber pressure rise, and then start to fall back.) Carbon may be evaporated slowly or rapidly. Normally, after degassing, the power is increased to where the carbon starts depositing. Length of evaporation time will depend on the desired thickness of carbon film. It should take from 30 seconds to totally evaporated the carbon. DO NOT take power too high for more than one minute. NEVER EXCEED 50 AMPS. A rapid evaporation (flashing) may be utilized by presetting the control to 75 percent of dial rotation, and then turning on the power. The flash will last from 1 to 2 seconds and help reduce heat damage.

8.9 Start UP Procedure - Before starting up the unit, make sure the following are provided:

8.9.1 120VAC, 60Hz, 10-amp service (220VAC, 50Hz, 8 Amps:

special order). 8.9.2 5-psig-argon gas (or room air, if deemed adequate). 8.9.3 All lines are properly connected and there are no loose

wires, hoses, or hardware. 8.9.4 Check rotary motion: (optional) 8.9.5 Make sure the small sprocket is spaced from feedthrough

nut by at least 1/16". 8.9.6 Make sure that the chain is not tight. It should be slightly

limp.

8.9.7 Check the mechanical pump oil level only after it has been running for a few minutes. This will give the oil a chance to be distributed throughout the pump and will give a more accurate level reading.

8.9.8 To start-up the system, use the following procedure: 8.9.8.1 Turn ON Main Power. 8.9.8.2 Press the START button on the touch screen. 8.9.8.3 Select the desired operating screen from the on-

screen menu.(Vacuum, Manual or Timed Sputter, Manual or Timed Etch )

8.9.8.4 Operation of the system is described in detail in the Operation section of this manual.

8.10 OPENING THE CHAMBER - Be sure that chamber is vented

(mechanical pump is off). 8.10.1 Grasp the under side of the sputter head between the

vertical post and the glass cylinder. 8.10.2 Lift vertically approximately one inch. When the sputter head

is clear of the top of the cylinder swing the head horizontally to the left.

8.10.3 When the head is clear of the top of the cylinder, stop, grasp the front edge of the sputter head and rotate the head counter-clockwise.

8.10.4 The sputter head will rotate so the target is facing at a 45-degree angle. To replace the sputter head on the cylinder reverse the procedure.

8.11 Main MENU - Access to all control screens is available on the Main Menu screen. Each system function is described in detail later in this section of the Operating Manual:

8.11.1 Vacuum – Provides access to the operation of the vacuum controls and a digital display of the vacuum pressure. Substrate Rotation control is also available from this screen.

8.11.2 Manual Sputter – Provides access to the manual operation of the sputter controls. Substrate Rotation and Gas Valve controls are also available from this screen.

8.11.3 Timed Sputter – Provides access to the timed operation of the sputter controls. Sputter Setpoint (%), Sputter Time (seconds) and Rotation Setpoint (%) are programmed from this screen.

8.11.4 Manual Etch – Provides access to the manual operation of the etch controls. Substrate Rotation and Gas Valve controls are also available from this screen.

8.11.5 Timed Etch – Provides access to the timed operation of the etch controls. Etch Setpoint (%), Etch Time (seconds) and Rotation Setpoint (%) are programmed from this screen.

All system controls are implemented by using the touch screen. All subsystem controls are available on individual control screens.

8.12 VACUUM - All vacuum pump operations are available on the Vacuum screen.

8.12.1 Select Vacuum from the Main Screen. 8.12.2 Current chamber pressure is displayed in mTorr. 8.12.3 ON/OFF operation of the Rough Pump is a push button on

this screen. 8.12.4 Buttons will switch to green when active. 8.12.5 ON/OFF operation of the Gas Inlet Valve is a push button on

this screen. NOTE: Gas flow must be manually adjusted on metering valve on the gas inlet.

8.12.6 Metering Valve adjustment knob is on top of cabinet to the left of the chamber.

8.12.7 ON/OFF operation of the Turbo Pump is a push button on this screen.

8.12.8 The Main button will return to the Main screen. WARNING! Five (5) minutes must elapse between turning off the turbo pump and turning off the mechanical pump, or the turbo pump will be damaged.

8.13 ETCH - Manual Etch operations are available on the Etch screen. 8.13.1 Select Manual Etch screen from the Main screen. 8.13.2 ON/OFF operation of the Etch Power Supply is a push

button on this screen. 8.13.3 Buttons will switch to green when active.

NOTE: Etch Set point should be set before power supply is turned ON. NOTE: Power Supply is interlocked to chamber pressure set point of 500 mTorr.

8.13.4 Power supply will NOT turn ON above this chamber pressure.

8.13.5 Etch Set point allows for adjustment of the power set point of the Etch Power supply.

8.13.6 Scroll buttons adjust the Etch Set point from 0% to 100%. 8.13.7 The current Etch Set point is displayed.

NOTE: 0 - 100% = 0 - 20 milliamps 8.13.8 Electrical Current output of the Power Supply is displayed in

milliamps. 8.13.9 Current chamber pressure is displayed in mTorr. The Main

button will return to the Main Screen.

8.14 SHUT-DOWN PROCEDURE 8.14.1 Turn off all sub-systems (sputter, etch, gas, rotation). 8.14.2 For DESK IV TSC option, turn off turbo pump, and wait five

(5) minutes before turning off mechanical pump, or the turbo pump will be damaged.

8.14.3 Turn off mechanical pump. WARNING! Five (5) minutes must elapse between turning off the turbo pump and turning off the mechanical pump, or the turbo pump will be damaged.

8.15 MANUAL ETCH - Manual Etch operations are available on the

Etch screen. 8.15.1 Select Manual Etch screen from the Main screen. 8.15.2 ON/OFF operation of the Etch Power Supply is a push

button on this screen. 8.15.3 Buttons will switch to green when active.

NOTE: Etch Setpoint should be set before power supply is turned ON. NOTE: Power Supply is interlocked to chamber pressure setpoint of 500 mTorr.

8.15.4 Power supply will NOT turn ON above this chamber pressure.

8.15.5 Etch Setpoint allows for adjustment of the power setpoint of the Etch Power supply.

8.15.6 Scroll buttons adjust the Etch Setpoint from 0% to 100%. 8.15.7 The current Etch Setpoint is displayed.

NOTE: 0 - 100% = 0 - 20 milliamps 8.15.8 Electrical Current output of the Power Supply is displayed in

milliamps. 8.15.9 Current chamber pressure is displayed in mTorr. 8.15.10 The Main button will return to the Main screen.

8.16 ROTATION - All fixture Rotation operations are available on the

Etch and Sputter screens. 8.16.1 ON/OFF operation of the Rotation Motor is a push button on

the screen. 8.16.2 Buttons will switch to green when active.Rotation Setpoint

allows for adjustment of the 8.16.3 Rotation speed. Scroll buttons adjust the Rotation Setpoint

from 0% to 100%. The current Rotation Setpoint is displayed. NOTE: 0 - 100% = 0 – 20 RPM The Main button will return to the Main screen.

8.17 MANUAL SPUTTER – Manual Sputter operations are available on the Sputter screen.

8.17.1 Select Manual Sputter from the Main screen. 8.17.2 ON/OFF operation of the Sputter Power Supply is a push

button on this screen. 8.17.3 Buttons will switch to green when active.

NOTE: Sputter Setpoint should be set before power supply is turned ON. NOTE: Power Supply is interlocked to chamber pressure setpoint of 500 mTorr. The Power supply will NOT turn ON above this chamber pressure.

8.17.4 Sputter Setpoint allows for adjustment of the power setpoint of the Sputter Power supply. Scroll buttons adjust the Sputter Setpoint from 0% to 100%. The current Sputter Setpoint is displayed. NOTE: 0 - 100% = 0 - 50 milliamps

8.17.5 Electrical Current output of the Power Supply is displayed in

milliamps. 8.17.6 Current chamber pressure is displayed in mTorr. 8.17.7 The Main button will return to the Main screen.

8.18 Time Etch - Timed Etch opera tions are available on the Timed Etch screen.

8.18.1 Select Timed Etch from the Main screen. 8.18.2 ON/OFF operation of the Etch Power Supply is a push

button on this screen. 8.18.3 Buttons will switch to green when active. 8.18.4

NOTE: Etch Setpoint and Etch Time should be set before power supply is turned ON.

NOTE: Power Supply is interlocked to chamber pressure setpoint of 500 mTorr. Power supply will NOT turn ON above this chamber pressure.

8.18.5 Etch Setpoint allows for adjustment of the Setpoint of the Etch Power supply. Scroll buttons adjust the Etch Time from 0 to 100%. The current Etch Setpoint is displayed.

8.18.6 Etch Time allows for adjustment of the Etch Timer setpoint of the Etch Power supply. Scroll buttons adjust the Etch Timer from 0 to 1800 minutes. The current Etch Timer setpoint is displayed.

8.18.7 Current chamber pressure is displayed in mTorr. 8.18.8 The Main button will return to the Main screen.

8.19 Sample Preparation

8.19.1 To check your carbon evaporation technique, before coating samples, do the following: 8.19.1.1 Coat a glass cover slip with gold. 8.19.1.2 When the cover slip is overcoated, the gold color

will change: • To copper with 100A of carbon • To orange with 150A of carbon • To purple with 200A

8.20 Operation - The Desk IV sputter head must be rotated to the side. Replace the standard 6.0” diameter by 6.0” high Pyrex cylinder with the 6" D. x 9" H. Pyrex cylinder. Mount the Carbon Rod accessory plate to the top of the larger Pyrex cylinder. 8.20.1 The Desk IV vacuum pumping system can be used to

evacuate a Pyrex cylinder with a carbon evaporation source mounted in the metal cover. The source can be mounted so as to vary the source-to-specimen distance from 3-1/2” to 5”.

8.20.2 Two carbon rods are positioned in the center of the “yoke” to do the coating. One rod will have a point or reduced section. The other will have a full diameter section that has been carefully flattened on the end touching the point (or reduced section) of the other rod.

8.20.3 Both carbon rods should be inserted, one after another, through the outside end of the fixed rod holder. First, the pointed rod should be inserted (point trailing) and pushed through with the flattened carbon rod to move into the moving rod holder. Continue pushing the rods until the spring is deflected about 1/8 inch. Tighten the thumbscrew holding the flattened carbon in the fixed holder. If using a reduced section carbon rod, the spring should be moved out a little more than the length of the reduced carbon.

8.20.4 With the carbon source loaded, place the Pyrex cylinder on the baseplate, seat the source head, and start pump down. Within two to three minutes, the chamber vacuum gauge should read about 50 mTorr.

8.20.5 Turn on FILAMENT POWER on the Carbon Evaporation

Module. Rotate powerstat clockwise to obtain 15 amp reading on ammeter. Carbon point should be bright red and outgassing. Increase filament power to 28 to 32 amps until a light spark is seen. DO NOT exceed 50 amps on the meter. WARNING ! Use dark glass to observe carbon evaporation. Intense brightness is harmful to eyes when viewed directly.

At 4” source-to-specimen, about 1/8” length of .040 inches reduced section will deposit about 100 angstroms of carbon.

8.20.6 For evaporating at relatively high pressure, it is good practice to check carbon film thickness. Coat a glass cover slip with gold. The gold color will change to copper when the cover slip is over-coated with 100 angstroms of carbon; to orange with 150 angstroms of carbon; to purple with 200 angstroms of carbon.

8.20.7 At 50 mTorr, the average gas molecule travels about .04”

between collisions. With a source-to-specimen distance of 4”, the carbon will make many collisions. It will arrive from all available directions. Above 75 mTorr, the thickness of the carbon film will diminish rapidly, as compared to the expected thickness.

8.20.8 If the carbon chamber will not pump below 100 mTorr, check

by substituting the Desk IV chamber. If that pumps down, then the trouble is probably with the “L” gaskets on the carbon chamber. Wipe them clean with a lint free cloth and acetone. Apply a thin coating of vacuum grease to the gasket on the glass side and on the baseplate side.

8.21 General Notes - The chamber should first be pumped to 50 mTorr or less. 8.21.1 Denton Vacuum supplies a carbon of excellent quality. It is

suggested that a low power setting, to degas the carbon, be used; slowly raise to evaporate. Degas the carbon (bright

red) for 5 to 10 seconds. (Watch the chamber pressure rise, and then start to fall back.)

8.21.2 Carbon may be evaporated slowly or rapidly. Normally, after

degassing, the power is increased to where the carbon starts depositing. Length of evaporation time will depend on the desired thickness of carbon film. It should take from 30 seconds to totally evaporated the carbon.

8.21.3 DO NOT take power too high for more than one minute.

NEVER EXCEED 50 AMPS. A rapid evaporation (flashing) may be utilized by presetting the control to 75 percent of dial rotation, and then turning on the power. The flash will last from 1 to 2 seconds and help reduce heat damage.

8.22 Timed of Operation

8.22.1 Pump system to less than 0 mTorr. 8.22.2 Set the desired Etch or Sputter power Setpoints. 8.22.3 Set the desired Etch or Sputter Time. 8.22.4 Turn the Gas Valve ON and adjust the gas flow to 50 mTorr

(for Desk IV TSC to 5 mTorr). 8.22.5 Turn ON Rotation (if equipped). 8.22.6 Turn power ON from the Timed Etch or Sputter screens. The

process will continue for the duration of the Etch or Sputter Timers. The power supply will turn OFF automatically at the end of the preset time. NOTE: Timer controls Power supply only. Gas, rotation, and pumps must be operated manually.

8.22.7 Etch or Sputter power Setpoints can be adjusted at any time during this timed operation.

8.22.8 At completion, reduce Setpoints to zero. 8.22.9 Turn Gas Control OFF 8.22.10 Turn Turbo pump OFF (Desk IV TSC). Wait five (5)

minutes, and then turn Mechanical Pump OFF. The Mechanical Pump will stop and the Vent Valve will open automatically to vent the chamber to atmosphere.

WARNING! Five (5) minutes must elapse between turning off the turbo pump and turning off the mechanical pump, or the turbo pump will be damaged.

8.22.11 Shut Down Procedure 8.22.11.1 Turn off all sub-systems (sputter, etch, gas,

rotation). 8.22.11.2 For DESK IV TSC option, turn off turbo pump, and

wait five (5) minutes before turning off mechanical pump, or the turbo pump will be damaged.

8.22.11.3 Turn off mechanical pump. WARNING! Five (5) minutes must elapse between turning off the turbo pump and turning off the mechanical pump, or the turbo pump will be damaged.

8.23 Summary - The Denton Vacuum DESK IV Cold Sputter/Etch Unit is designed to clean the surface of SEM specimens and to deposit a heavy metal conductive coating on the clean surface.

8.23.1 A standard 6” diameter by 6” high Pyrex Cylinder with top

and bottom Seals sits on an aluminum Baseplate. 8.23.2 The cylinder is evacuated by a two-stage, direct-drive,

Mechanical Pump mounted in the cabinet.

8.23.3 An automatic Vent Valve is slaved to the mechanical pump. It will automatically open when the Mechanical Pump is turned OFF to vent the chamber to atmosphere. It will automatically close when the Mechanical pump is turned on.

8.23.4 An insulated Specimen Table with provisions for height

adjustment is mounted within the Pyrex cylinder.

8.23.5 The Sputter Cathode is clamped to an insulated aluminum plate in the chamber cover. The target supplied in the base system is gold or gold/palladium (your choice). Other targets are available.

8.23.6 The Desk IV contains a single high voltage power supply.

The output of the power supply is connected to the substrate fixture for Etch and to the Sputter Cathode for Sputter deposition. Power output varies: Etch = 0 - 20 milliamps; and Sputter = 0 - 50 milliamps

8.23.7 A manual Shutter is provided as the etch electrode and to

shield the Sputter Cathode from contamination during the Etch cleaning cycle. The shutter control knob is left of the chamber. Clockwise rotation of the knob will open the shutter and counterclockwise rotation will close it.

8.23.8 A manual Gas Control is provided to control pressure in the

cylinder. The Gas Control knob is to the left of the chamber.

8.23.9 The Desk IV is provided with a vacuum gauge to provide vacuum pressure measurements in the vacuum chamber.

9.0 RECORDS The Procedure User is responsible for submitting the following records to the Machine Custodian/Lab. Instrumentation specialist to be storage at the UPR-NSF Earth X-ray Analysis Center (EXACt), F-304-D.

9.1 Log-Book or Notebook records of the sample handling and results of analysis relevant to Production of the Carbon Coater.

10.0 REFERENCES The following documents have been cited within this procedure by:

• http://erproject.lanl.gov/docs/Quality/SOP/SOP-09.02R1T.pdf • http://geology.uprm.edu/facilities/exact.html • http://geology.uprm.edu/facilities/labrules/exact.doc • Denton Vacuum Desk IV Operating Manual – Desk IV Cold Sputter/Etch

Unit and Accessories; http:// www.dentonvacuum.com

• www.wikipedia.com

• http://www.quorumtech.com/Manuals/Current_Technical_Briefs/TB-CARBON.pdf

• http://www.emitech.co.uk/vacuum-coating-brief.htm

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