Consolidated Vacuum Corporation (CVC) Vacuum Evaporation System

STANDARD OPERATING PROCEDURE

TABLE OF CONTENTS:

1. SUMMARY .............................................................................................................................. 2 2. INTRODUCTION .................................................................................................................. 3 3. LOCATION OF EQUIPMENT, ACCESSORIES, TOOLS, AND SUPPLIES ............... 4 4. PERSONAL SAFETY EQUIPMENT .................................................................................. 5 5. PRIMARY HAZARDS AND WARNINGS ......................................................................... 5 6. OPERATIONAL PROCEDURE CHECKLISTS ............................................................... 5 Procedure 1. Preparation .................................................................................................................. 7 Procedure 2. Sample Loading .......................................................................................................... 8 Procedure 3. Chamber Pump Down .............................................................................................. 11 Procedure 4. Evaporation .............................................................................................................. 12 Procedure 5. Unload Sample and Shut Down ............................................................................... 12 7. HELPFUL HINTS, COMMON QUIRKS, AND TROUBLESHOOTING .................... 13

8. ENVIRONMENTAL HEALTH ......................................................................................... 13

2

1. SUMMARY

Equipment CVC Vacuum Evaporation System

Picture

Specification Vacuum chamber system for use in thermal evaporation of metal. Rotary

vane roughing pump used in conjunction with a high vacuum diffusion pump to achieve pressures as low as 2x10-6 Torr.

Location EEB room B029, EE MicroFabrication Laboratory (EE-MFL), UW

Contact Access Prof. R. Bruce Darling, Dept. of Electrical Engineering 206-543-4703 bruced@u.washington.edu

Technical same as above

Emergency same as above

Document History

Date Rev .

Authors

1999-06-07 2017-11-01

0.0 1.0

Mike Goettemoeller, Chris Morris, Shane Rowell Jenny Wan, R. B. Darling

3

2. INTRODUCTION

This Standard Operating Procedure (SOP) provides information on the operation of the vacuum system including pumps and gauges for the CVC vacuum system for evaporation of thin film metals. The actual process of metal evaporation is covered in a separate SOP. The system is composed of several different systems mounted on the same frame, each of which have their own reference material or manual. However, these manuals are somewhat dated and do not refer explicitly to the current configuration. The purpose of this SOP is to provide concise, step-by-step instructions for the successful operation of the system as it currently exists. The vacuum system consists of three main components: a rotary vane roughing pump, a high vacuum diffusion pump, and some pressure gauges.

The roughing pump is designed to work in the viscous flow regime, or vacuum pressures between atmospheric and about 50 mTorr. Rotary vanes sweep air in a circular chamber from the vacuum inlet to the outside air discharge. The excavation of air at the inlet creates a low pressure area, which draws more air into the pump. When the roughing pump achieves low enough pressures at the inlet, the air flow is no longer viscous, and other means are required to continue pumping.

The diffusion pump is designed to operate with an outlet pressure of less than 100 mTorr and can achieve vacuums on the order of 10-6 Torr. A silicone oil is vaporized by an internal boiler. The oil vapor is propelled by downward-facing jets at supersonic speeds. The downward stream of oil vapor entrains air molecules and forces them toward the outlet, located at the bottom. Water-cooled walls then condense the oil so it can be revaporized.

The roughing and diffusion pumps work in tandem as shown in Fig. 1. The roughing pump (shown on the lower right) is used both for excavating the bell jar chamber, and for providing the reduced foreline pressure that the diffusion pump needs to operate.

Figure 1. Schematic diagram of the roughing pump and diffusion pump system.

It is important to note that although the roughing pump fulfills both tasks, it cannot do them at the same time. The reason is that if the diffusion pump outlet line (hereafter referred to as the foreline) experiences too high of a pressure, the oil in the diffusion pump could be forced back up into the chamber. The valves depicted in the figure allow the roughing pump to be switched between its two tasks. The details about how to operate these valves, and how to avoid filling the

4

vacuum chamber with oil, are covered in the procedure checklists.

The third main part of the system are the pressure gauges. Two gauges are used to measure the pressure in the bell jar: a thermocouple gauge for rough (higher pressure) vacuum and an ion gauge for high vacuum. The thermocouple gauge measures the temperature of a heated filament whose rate of cooling depends upon the gas pressure around it. An ion gauge works by accelerating electrons from a hot filament toward a collector electrode, which ionizes any gas molecules in the vicinity. The ionized gas contributes to a current through the electrode, which is proportional to the gas pressure. In addition to the bell jar gauges, a thermocouple gauge is also used to measure the pressure in the foreline.

3. LOCATION OF EQUIPMENT, ACCESSORIES, TOOLS, AND SUPPLIES

The CVC Vacuum Evaporation System is located in room B029 of the EE building at the University of Washington. It is located toward the far left corner of the room as seen from the entrance to the laboratory. Various reference manuals should be located in the proximity of the system. There is also a CVC logbook which should be used to record the details of each use. Such details should include the date, the names of the operators, the base pressure levels achieved and the approximate pumping time to reach them, the source and substrate materials, the current and time for each layer, and any anomalies encountered during the operation of the system. Recording any suspicious or unusual behavior as it happens greatly assists in troubleshooting and maintaining the system.

4. PERSONAL SAFETY EQUIPMENT

No personal protective equipment is needed for the routine operation of this system. Powder free latex gloves are required for inserting and removing material from the bell jar to keep finger print oils off of the internal surfaces.

5. PRIMARY HAZARDS AND WARNINGS

If hazards are to be interpreted as harmful to the operator, the only hazard associated with the operation of the vacuum system is the handling of liquid nitrogen (LN2). Severe cold burns can occur if LN2 contacts the skin. Care must be used when pouring so that spills don’t fall on other people. Other hazards are associated with the actual evaporation process, including possible electrocution from the unprotected variacs (located on the front of the system) or internal electrical connections. The details of such hazards should be covered in the SOP on aluminum or chromium evaporation.

Similarly, if warnings are interpreted as being harmful to the equipment, the primary warning is to avoid too high of a foreline pressure when the diffusion pump is in operation. The pressure should never exceed 200 mTorr when the diffusion pump is on. If the pressure does rise above 200 mTorr, diffusion pump oil may be forced back into the bell jar, completely contaminating the ultra-clean environment. NEVER HAVE THE FORELINE AND ROUGHING VALVES OPEN AT THE SAME TIME, as this is one way to rapidly increase the foreline pressure. 6. OPERATIONAL PROCEDURE CHECKLISTS

Procedure 1. Preparation

5

Turn on the power switch to CVC evaporator (located on backside of the main frame). You will have

to physically walk around to the back of the unit. The switch is located on the right rear edge near the

top.

Turn on the power to upper crystal monitor (Gun 1 Controller); the power button is located under flap.

Insure that all four valves are completely closed (by turning clockwise) on the valve control panel,

shown in Figure 2 below.

Figure 2. Valve Control Panel.

Turn on the roughing pump, using the push button labeled ROUGING PUMP on the front control

panel, shown in Figure 3. This is important to do before turning on the diffusion pump because the

outlet of the diffusion pump (or foreline) needs a lower pressure to operate. The roughing pump will

require several minutes to warm up after starting.

Figure 3. Front Control Panel.

6

Fully open the FORELINE VALVE by turning the knob shown in the upper right of Figure 1 counter

clockwise as far as it will turn. The foreline pressure, reported by the thermocouple gauge, shown as

TC1 gauge in Figure 4 below, should start to fall, and ultimately reach 20 – 50 mTorr after a few

minutes.

Figure 4. TC1 Gauge (Top) and Ion Gauge (Bottom).

Turn on the cooling water by opening the two valves shown with yellow handles in Figure 5. The

utility drop shown is located behind the left corner of the CVC system. The valves have yellow

handles and are in the open position when the handles are parallel to the pipe to which they are

attached. The order in which they are opened does not matter, but they must all be opened. Note that

there are three other valves, also with yellow handles, which isolate the water pressure gauges and the

water filter; these are normally left open.

7

Figure 3. Cooling Water Valves.

Check the quick cool valve located beside the diffusion pump, shown in Figure 6 below, and make sure

it is fully closed (turned fully clockwise).

Figure 4. Diffusion pump and quick cool valve.

After the foreline pressure has been been pumped down to about 50 mTorr, as measured on the TC1

foreline thermocouple gauge, turn on the diffusion pump by pressing the button labeled DIFFUSION

PUMP on the control panel in Figure 3. When the diffusion pump is turned on, the heating element in

its bottom will start heating the oil, and initially this heat will cause the foreline pressure to rise,

possibly to about 100 mTorr or more. This is normal, but it’s also important to make sure that the

pressure does not rise above 200 mTorr, which will force the oil up towards the bell jar. With the

8

roughing pump applied to the foreline with the foreline valve open, the roughing pump should keep the

foreline pressure below 200 mTorr.

Note: Care must be taken to observe TC1 foreline pressure while switching to the diffusion pump. IF

THE FORELINE PRESSURE EVER RISES ABOVE 200 mTorr WHILE THE DIFFUSION PUMP IS

RUNNING, OIL MAY BE FORCED BACKWARDS INTO THE BELL JAR AND CONTAMINATE

THE SYSTEM. If the foreline pressure does rise rapidly after turning on the diffusion pump, shut it off

immediately. Wait until the foreline pressure drops below 50 mTorr again, and try turning on the

diffusion pump again.

Procedure 2. Sample Loading

1. Vent the Chamber:

Make sure the high vacuum (HI-VAC) gate valve and roughing valve are both closed completely. Also

make sure nitrogen valve is closed completely. Bring system to atmospheric pressure by slowly

opening the Air Inlet valve. Observe the chamber pressure gauge to see when the pressure rises to

atmospheric pressure, approximately 760 Torr. While not in use, system should remain under rough

vacuum to reduce contamination.

Once vented, raise the bell jar by pressing and holding the RAISE CHAMBER button. If the shutter is

open, close it.

2. Crystal Monitor Programming

In order to monitor the thickness of the film being evaporated, the crystal monitor must first be zeroed

out, and programmed to measure the specific material being evaporated.

Turn on the Gun 1 Controller. The T/X light should not be blinking. If the T/X light blinks, it means

the crystal is no longer oscillating and needs to be replaced. The used life of the crystal can be checked

by pushing in the T/X button. The used life will be shown in the readout as a percent. The crystal

should generally be replaced if the used life is more than 10%.

Put thickness monitor in AUTO mode. Press the CONTROL PWR switch, which is located under the

flip-down panel at the bottom of the thickness monitor’s front panel, to AUTO.

Put monitor in PROGRAM mode. If the orange Program light on the monitor’s front panel is not on,

press the KEY BOARD switch to PROG once.

Program the density and Z-ratio for the layer being deposited. Using the keypad and the selector

buttons on the monitor front panel, enter the density and Z-ratio of the material to be deposited. For

V2O5 for example, the density is 3.36 g/cm3. Since Z-ratio is unknown, we use 1.0 for it.

Switch the monitor into LOCK mode. Press the KEY BOARD switch to PROG once again. At this

time, the orange Program light on the front panel should go off.

Put monitor in MANUAL mode. Press the CONTROL PWR switch to MAN. After this step, the

orange MAN POWER light and the green DEPOSIT light should come on.

Reset thickness value. Press the ZERO button located on the front panel.

A quick way of checking the crystal is to gently blow some air on it which will condense moisture.

The thickness display should show a slight increase from the condensed moisture. Make sure to ZERO

out the thickness reading again after checking.

9

3. Source and Sample Loading:

The source stage holds three independent source boats, also referred to as filaments. Each source boat

is mounted to a pair of copper electrodes. For V2O5 deposition, due to reduction of source powder at

high temperature under vacuum, each source boat can only support 25nm thick film. User should

decide how many boats to use for the target thickness. Load V2O5 powder to desired boats.

Figure 5. Copper electrodes which mount the source filaments or boats.

Check the boat holder carefully. Make sure each of the boats and their mounting electrodes are

insulated from the grounded stage to avoid electrical shorts. Reposition the bottom plate if necessary to

insure a gap between the copper electrodes and the chamber frame. Figure 8 below shows one

common point where a short is possible if the stage is not carefully positioned.

10

Figure 6. A common point where the copper electrode can short to the bottom plate of the frame or the vertical strut.

Load the wafers. The system can hold up to three 4-inch wafers or six 3-inch wafers, depending upon

which aluminum insert is used. Kapton tape can be used to fix the wafers to the wafer holder if

necessary to avoid falling off.

Check the microscope slides for the view port. Make sure it is possible to see through them and watch

the boats. They do not need to be perfectly transparent, since the deposited metal film will create

mirror surfaces on them, and the image of the incandescent source boat can be viewed as a reflection.

Use a clean tissue to wipe off the top surface of the feedthrough ring before lowering the bell jar. The

L-gasket on the bottom of the bell jar should be properly coated with vacuum grease for sealing, so do

not wipe any of this grease off or leaks can result. Press the LOWER CHAMBER button to lower the

bell jar slowly. Keep an eye on the bell jar wall to make sure it does not bump the sample holder on the

way down. Stop pressing the button when the bell jar is a few centimeters above the baseplate. Adjust

the position of bell jar and make sure it is centered onto the baseplate, then fully lower the chamber.

Usually, the bottom of the bell jar will have to be pushed back about a centimeter to center it on the

feedthrough ring.

Procedure 3: Chamber Pump Down

NOTE: Pumping down the chamber involves operating both the foreline and roughing valves. It is

again important to note that THESE VALVES MUST NEVER BE OPENED AT THE SAME TIME!

DOING SO WILL CAUSE THE FORELINE PRESSURE TO RISE AND FORCE OIL INTO THE

BELL JAR CHAMBER. This will contaminate the system, for which cleaning can take several days.

Make sure the Air Inlet valve is closed. Fully close the FORELINE VALVE by turning the knob in the

upper right of Figure 1 clockwise as far as it will turn. Then, open the ROUGHING VALVE by

turning the knob in the upper left of Figure 1. This will allow the roughing pump to rough out the

chamber.

11

The chamber pressure is initially monitored by the thermocouple gauge next to the crystal monitor

control box. The pressure should begin to drop as the rough pump evacuates the chamber.

At the same time, monitor the foreline pressure of the diffusion pump. It will slowly start to rise,

because the roughing pump is no longer roughing out the foreline. If the pressure on the foreline rises

above 200 mTorr, the roughing pump must be switched back to the foreline to evacuate the backlog of

gas which has accumulated there. To do this:

o First, close the ROUGHING VALVE completely;

o Then, open the FORELINE VALVE completely;

o Allow the roughing pump to bring the foreline pressure (the reading of TC1) back down to about

50 mTorr;

o Observe the chamber pressure at the same time to identify any possible leaks.

After the foreline has been pulled back down to about 50 mTorr, the roughing pump can be switched

back to finish roughing out the chamber by reversing the above sequence of valves.

Continue roughing the bell jar until the thermocouple gauge reads about 50 mTorr. The roughing pump

may need to be cycled back and forth between the bell jar and the foreline one or more times, to keep

the foreline pressure below 100 mTorr (thus insuring that you are well under 200 mTorr). The number

of “cycles” should be recorded in the log book.

Once the chamber pressure is down to about 50 mTorr, switch the roughing pump back to the foreline:

o First, close the ROUGHING VALVE completely;

o Then open the FORELINE VALVE completely.

Next, gently open the gate valve by slowly turning the large crank on the valve control panel (see

Figure 2) counter clockwise. The bell jar chamber pressure should start to fall, and the foreline

pressure should start to rise as the gas is moved from the chamber into the foreline by the diffusion

pump. If there is a sudden change of pressure in any of the two pressure gauges, something may be

wrong and you should close the gate valve. Then try opening it again slowly. Most of the time, this

step should proceed smoothly. Once the majority of the gas in the bell jar chamber has been removed

by the diffusion pump, the gate valve can be opened all of way. The gate valve should normally be

open all of the way to allow the diffusion pump to have its maximum pumping effectiveness during an

evaporation.

Turn on the ion gauge to monitor the chamber pressure. The ion gauge filament should light up after

pressing the ION button on the front panel. If the chamber pressure is too great for the ion gauge, it

will automatically shut off the current to the filament.

The diffusion pump will need to run for 2-3 hours to bring the bell jar chamber pressure down to the

10−6

Torr range, which is what is needed to begin an evaporation run.

Procedure 4: Evaporation

Once the chamber has been evacuated to approximately 5×10−6

Torr, the system is ready to begin

evaporating the source material. Depending on which boat the user wants to evaporate, put the

corresponding lead into the red connector of the transformer, shown in Figure 9 below. Note that the

lead to the black connector in the back of the transformer remains there, as this is the common lead for

all three of the source boats. Also note that the transformer is a 10:1 step down, and the current shown

on the meter on the control panel is the primary side current. Thus a reading of 10 Amps on the meter

means that 100 Amps is flowing through the corresponding filament or source boat.

12

Figure 7. Source boat #2 connected to the transformer.

Start the crystal monitor by pressing the Layer 1 button on front panel.

Make sure shutter is in the CLOSED position.

Turn the filament on by pushing the FILAMENT NO. 1 button on the control panel. A red light on this

button should then light up. Check the electrical connections by quickly ramping up and then down the

current to about 5 Amps with the FILAMENT NO. 1 variac knob and observing the current reading on

the meter. Possible shorts or opens can be identified in this manner.

Increase the current through the filament by slowly turning the FILAMENT NO. 1 variac knob (the

right knob on the evaporator’s panel) in a clockwise direction. Care must be taken not to increase the

current through the filament too rapidly. This ensures that the thermal expansion of the Tungsten boat

occurs slowly, and that it does not get cracked by thermal shock.

For most materials, the evaporation will start at around 100 ~ 150 Amps. Open the shutter when the

source material has begun to create an observable evaporation rate on the crystal monitor.

Increase the current further to achieve a reasonable evaporation rate. The maximum current that can be

applied is around 200 Amps for most tungsten source boats. Wait until the desired thickness has been

reached and close the shutter.

Slowly decrease the current to zero through the filament by turning the FILAMENT NO. 1 variac knob

counterclockwise.

Procedure 5: Unload Sample and Shut Down

After the evaporation is complete, the samples can be removed, and the system can be shut down.

Turn off the filament by pushing the FILAMENT NO. 1 button on the control panel. The red light on

the button should go off.

Wait about 30 minutes for the hot components of the evaporator to cool down. This step will prevent

unwanted oxidation of the freshly evaporated metal surfaces.

Fully close the HI-VAC gate valve and turn off the diffusion pump.

After a few minutes, the quick cool water valve can be opened to cool down the diffusion pump more

quickly. After the diffusion pump has cooled, remember to turn off the quick cool valve and then turn

13

off cooling water using the yellow handled valves on the utility drop.

Fully close both the foreline and roughing valves.

Bring the bell jar chamber up to atmospheric pressure by venting slowly with air by opening the AIR

INLET valve. Once vented, raise the bell jar by pressing the RAISE CHAMBER button.

Unload the samples. Be sure to use powder-free nitrile gloves for handling the sample holder and

samples.

Clean the top surface of the feedthrough ring with a cleanroom tissue again. Lower the bell jar by

pressing and holding the LOWER CHAMBER button. Be careful to lower the chamber slowly,

guiding it down to be centered onto the feedthrough ring without bumping the internal support

structures while on the way down.

Once the bell jar is again seated on the feedthrough ring, open the roughing valve. Watch the pressure

on the thermocouple gauge until it reads 100 mTorr. Close the roughing valve after desired pressure is

reached.

Power off the roughing pump and then turn off the main power to the system. Insure that all vacuum

valves are fully closed, all pumps and main power are turned off, the crystal monitor is turned off, and

the cooling water is turned off at both valves on the utility drop.

7. HELPFUL HINTS, COMMON QUIRKS, AND TROUBLESHOOTING One of the most common problems with any vacuum system is leaks. A common place for this to occur is around the L-gasket seal between the glass bell jar and the top metal surface of the feedthrough ring. If the desired chamber pressure cannot be obtained within reasonable times (check the log book for past pump-down times), one can suspect a leak through the seal of the bell jar. If the chamber pressure rises rapidly upon closing the gate valve (which prevents the diffusion pump from pumping down the chamber), that would confirm that there is a leak associated with the bell jar. A first suggestion would be to repressurize and raise the bell jar, and clean and re-grease the L-gasket. A special type of grease must be used; contact technical support if this gasket needs to be re-greased. Another possible source of leaks could be within the vacuum lines and valves, but these are less likely and considerably more difficult to service. There is also the possibility of experiencing long pump down times if the bell jar was not stored under vacuum. Apparent leaks may be caused by vapors out gassing from the bell jar surfaces. The wafers loaded in the system can also contribute significantly to out gassing effects, especially if they have been exposed to the atmosphere for several weeks. Adding more LN2 to the liquid nitrogen trap can

significantly reduce the amount of water vapor within the chamber, which reduces the pump down time.

8. ENVIRONMENTAL HEALTH There are no significant known environmental health issues associated with the operation and use of this equipment.