Consolidated Vacuum Corporation (CVC) Vacuum Evaporation System STANDARD OPERATING PROCEDURE

TABLE OF CONTENTS: 1. 2. 3. 4. 5. 6.

SUMMARY ................................................................................................. 2 INTRODUCTION........................................................................................ 3 LOCATION OF EQUIPMENT, ACCESSORIES, TOOLS, AND SUPPLIES .... 4 PERSONAL SAFETY EQUIPMENT ............................................................ 5 PRIMARY HAZARDS AND WARNINGS...................................................... 5 OPERATIONAL PROCEDURE CHECKLISTS ............................................. 5 Procedure 1. Diffusion pump warm up........................................................ 7 Procedure 2. Chamber pump down ............................................................. 8 Procedure 3. Ion gauge operation .............................................................. 10 Procedure 4. System shutdown ................................................................. 11 7. HELPFUL HINTS, COMMON QUIRKS, AND TROUBLESHOOTING ......... 12 8. ENVIRONMENTAL HEALTH ................................................................... 12

1. SUMMARY Equipment Picture

CVC Vacuum Evaporation System

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. EE/CSE B029, EE MicroFabrication Laboratory (EE-MFL), UoW Access Prof. Bruce Darling, Dept. of Electrical Engineering (206-543-4703, [email protected]). Technical Mr. Kevin Kerkof, EE-MFL (206-616-6981, [email protected]). Emergen Mr. Kevin Kerkof, EE-MFL (206-616-6981, cy [email protected]). Date Rev Authors . 1999-06- 0 Mike Goettemoeller, Chris Morris, Shane 07 Rowell

Location Contact

This Document

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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 metal evaporation. 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 special type of 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

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Figure 1 Schematic diagram of the roughing pump and diffusion pump system required low outlet pressure for the diffusion pump (shown on the lower left). 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 cycle between its two tasks. The details about how to operate these valves, and how to avoid filling the vacuum chamber with oil, are covered in the procedure checklists. The third main part of the system is the pressure gauges. Two gauges are used to measure the pressure in the bell jar: a Bourdon gauge for rough (higher pressure) vacuum and an ion gauge for high vacuum. The Bourdon gauge mechanically magnifies the deflection of a membrane caused by pressure, so that a needle moves around a circular display. 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 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 MicroFabrication Laboratory (EE-MFL) in the Electrical Engineering/Computer Science and Engineering (EE/CSE) building at 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. The logbook should be used to record the details of each use. Such details should include the date, operator name, time 4

required to reach desired vacuum levels, and any anomalies encountered during the operation of the system. Recording all 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, the diffusion pump oil may be forced into the bell jar, completely contaminating the ultraclean environment. NEVER OPEN THE FORELINE AND ROUGHING VALVES AT THE SAME TIME, as this is one way to rapidly increase the foreline pressure.

6. OPERATIONAL PROCEDURE CHECKLISTS To the authors’ knowledge, no consolidated procedure exists for the operation of the vacuum pumps and the pressure gauges installed on this particular system. The operation of equipment is described in detail in following sections. This procedure is organized into four sections, which discuss the diffusion pump warm-up, chamber pump down, ion gauge operation, and system shutdown.

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Figure 2 Valve control panel

Figure 3 Front control panel

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Figure 4 Ion gauge control panel

Figure 5 Plumbing stack showing the three CVC system cooling water valves

Procedure 1. Diffusion pump warm up The diffusion pump must first warm up for 30 minutes before it will work properly. This is because it works in part based on the difference in 7

temperature between the hot boiler and the cooled section near the top of the pump.  Turn on the main power switch for the CVC system on the (standing in front of the system) left rear edge, near the top. You will have to physically walk around to the back of the unit.  Open the FORELINE VALVE by turning the knob shown in the upper right of Figure 2 counter clockwise as far as it will turn.  Turn on the roughing pump, using the push button labeled ROUGING PUMP on the front control panel (see 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.  Turn the pressure sensor switch to TC1 (the dial in the upper left of Figure 4), which monitors the foreline pressure with a thermocouple. The red markings on the top of the gauge in Figure 4 are the readings of this gauge, in mTorr. The pressure should begin to drop.  Turn on the cooling water by opening the three valves in Figure 5. The plumbing stack shown is located behind the left corner of the CVC system. The valves have yellow handles and are in the open position when they 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.  When the foreline pressure is roughed out to 50 mTorr (the pressure reading of TC1), turn on the diffusion pump by pressing the button labeled DIFFUSION PUMP on the control panel in Figure 3. NOTE: Care must be taken here to observe the TC1 pressure while switching on the diffusion pump. If there is too much air pressure in the inlet to the diffusion pump, the foreline pressure (the outlet) may rise too quickly. IF THE FORELINE PRESSURE EVER RISES ABOVE 200 mTorr WHILE THE DIFFUSION PUMP IS RUNNING, OIL MAY BE FORCED BACK UP TOWARDS THE BELL JAR, RUINING 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. The diffusion pump must warm up for 30 minutes. In the meantime, you can record appropriate information in the log book. You can also vent the bell jar to open it (using the air inlet knob on the valve control panel in Figure 2), load wafers, check evaporation sources, the crystal monitor, etc. These procedures should be outlined in the SOP on aluminum or chromium evaporation. Procedure 2. Chamber pump down

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Once the diffusion pump has warmed up for 30 minutes, you are ready to pump down the system. This procedure involves roughing out the bell jar, switching the roughing pump back to the diffusion pump foreline, and opening the gate valve to allow the diffusion pump to pull the bell jar down to the desired vacuum level. The pressure monitoring of the bell jar will eventually involve the ion gauge, which will be covered in the next section. This procedure 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 ruin the system.  Close the FORELINE VALVE by turning the knob in the upper right of Figure 2 clockwise as far as it will turn.  Open the ROUGHING VALVE by turning the knob in the upper left of Figure 2. This will allow the roughing pump to rough out the chamber. Also, make sure the AIR INLET valve is closed (the valve on the lower left of Figure 2).  The chamber pressure is initially monitored by the Bourdon gauge next to the crystal monitor control box. Recall that a Bourdon gauge is an entirely mechanical pressure gauge, only good down to about 10 mTorr. The pressure should begin to drop.  At the same time, watch the foreline pressure of the diffusion pump. It will slowly start to rise, because the roughing pump is no longer roughing out the foreline. When this pressure on TC1 rises above 100 mTorr, you must switch the roughing pump back to the foreline. To do this: •

Close the ROUGHING VALVE completely

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Open the FORELINE VALVE.

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Allow the roughing pump to bring the foreline pressure (the reading of TC1) back down to 50 mTorr.

Then, switch the roughing pump back to the chamber by following the check list boxes at the beginning of this section.  Continue roughing the bell jar until the Bourdon gauge reads about 50 mTorr. You will probably have to cycle the roughing pump back and forth between the bell jar and the foreline one to three 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 about 50 mTorr, move the roughing pump back to the foreline: •

Close the ROUGHING VALVE completely 9

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Open the FORELINE VALVE.

 Fill the liquid nitrogen cold trap with liquid nitrogen (LN2). This will help remove extra water vapor from the bell jar, reducing the load on the diffusion pump. Filling the LN2 cold trap involves filling the funnel on the back of the CVC system two or three times.  Open the gate valve carefully by slowly turning the large crank on the valve control panel (see Figure 2) counter clockwise. 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. Most of the time, this step should proceed smoothly. After slowly turning about five to seven turns, you may open it more rapidly the rest of the way. Procedure 3. Ion gauge operation The chamber pressure on the Bourdon gauge will quickly bottom out once the diffusion pump is working on the chamber. When this occurs, the ion gauge is necessary to continue to monitor the bell jar pressure.  Before starting the ion gauge, make sure that the Range Selector knob located in the upper right-hand corner of the panel is set to 10-4. Also, the emission control knob located in the lower left-hand corner of the panel should be off.  Set the meter selection knob located in the upper left-hand corner to the PRESS position.  Power on the ion gauge by rotating clockwise the Power On knob located in the lower right-hand corner of figure 4. Rotate the knob clockwise until the deflection needle reads zero on the upper scale (black) of the gauge display.  Set the meter selector switch to the EMISS position. Make certain the pressure in the bell jar is less than 1 mTorr (as read from the Bourdon gauge) before selecting this position.  Turn the emission control switch on by rotating clockwise the Emission Control button. Rotate clockwise until the gauge display needle is stable between the two triangles (red) located on the top scale of the gauge display, preferably on the lower first triangle.  Turn the meter selector switch back to the PRESS position. The chamber pressure is now read from the gauge given the current range selection. The units are in Torr.  As the pressure drops, the sensitivity of the gauge must be increased. This is performed using the Range Selector switch. Before switching the Range Selector switch, the pressure must read less than 1 on the current range setting or the protection circuit will trip. If a trip occurs, press the Reset 10

button located directly below the gauge display and restart procedures from the beginning of this section.  Once a pressure of about 5 x 10-6 Torr is obtained, evaporation may be performed following procedures outlined in the SOP on aluminum or chromium evaporation. Procedure 4. System shutdown Following evaporation, samples must be removed and the system must be shutdown properly. This section describes the proper procedure.  Turn off the ion gauge by turning counterclockwise the Emission knob followed by turning the Power On knob. The range selector should be set to the 10-4 position, ready for the next use. Also, turn the upper left knob to the TC1 position. This will again monitor the foreline pressure.  Close the gate valve completely by turning the crank clockwise. Make sure the valve is closed tightly.  Turn off the diffusion pump using the button on the front control panel.  Wait 30 minutes for the bell jar to and samples to cool. Cooling water should remain on, and the roughing pump should remain on the foreline of the diffusion pump by keeping the foreline valve open. This is a good time to record entries on the log book. •

An alternative for cooling down the system involves the quick cool valve, a brass knob located in front of the diffusion pump, near the floor. The knob is mounted on the front of the system frame. Opening this valve will admit water to additional coils around the boiler of the diffusion pump. This will more rapidly cool it down. You should wait a few minutes after turning off the diffusion pump before opening this valve, until the sound from the boiling oil stops. This method should cool the diffusion pump in about 15 minutes.

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After this time, the quick cool knob should be closed, because the pump will not operate for the next user if this valve remains open.

 After 30 minutes (or 15 minutes if you used the quick cool method), turn off the cooling water (using the three valves in Figure 5), and close the FORELINE VALVE on the valve control panel.  Use the air inlet valve, located on the lower left corner of the valve control panel to bring the bell jar up to atmospheric pressure.  Raise the bell jar, remove samples, and lower the bell jar as described in the SOP on aluminum or chromium evaporation. If you used the quick cool 11

method and only waited 15 minutes, care should be taken for this step because several parts inside the bell jar may still be hot.  Close the air inlet valve.  Rough the bell jar to 100 mTorr: •

Open the Roughing Valve.

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Watch the pressure on the Bourdon gauge until it reads 100 mTorr.

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Close the roughing valve.

 Power off the roughing pump using the button on the front control panel.  Power off the CVC system by moving the breaker switch, located on the back side of the system, to the off position.

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 O-ring seals between the glass bell jar and the metal surfaces. If the desired chamber pressure cannot be obtained within reasonable times (check log book for past pump-down times), one can suspect a leak within 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, probably around one of the O-rings. A first suggestion would be to repressurize and raise the bell jar, and clean and re-grease the O-ring. A special type of grease must be used; contact technical support for what this grease is. Another possible source of leaks could be within the vacuum lines and valves, but these are 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.

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