Evaporator Maintenance and Troubleshooting Guide:
What regular maintenance work needs to be performed on the evaporator?
The oil in the mechanical pump (the orange pump on the floor) needs to be changed every 6-9 months. The oil in the diffusion pump (the silver unit attached by 4 screws underneath the high vacuum valve) needs to be changed every 9-12 months. And, as a precautionary measure, because graduate students using the evaporator have a habit of not cleaning it thoroughly, I recommend that every 3-4 months, you thoroughly clean the bell jar, trying to remove as much metal and organics as you can.
How do I change the oil in the mechanical pump?
From the evaporator supply cabinet, get the large metal pan, fresh vacuum pump oil, vacuum pump washing oil, the vacuum pump oil disposal can, and the funnel. The mechanical pump is resting on a block on the floor. Slide the pump forward so that the front of the pump is forward of the mechanical support. Place the pan under the front of the mechanical pump, and unscrew the black plastic plug from the front of the mechanical pump. The old mechanical pump oil will flow immediately when you unscrew the plug, so be sure the pan is positioned properly. When the flow slows, use the handle on the top of the mechanical pump to tip the pump forward, so that the remaining oil drains quickly. Once the flow has ceased, screw the plastic plug into the front. Then, unscrew the top plastic plug from the pump, and pour in vacuum pump washing oil, using the funnel. Fill the pump until the liquid level comes to the center of the gauge on the front. As a note, for a long time, the oil level will not appear at all on the gauge, but once it does, it will rise quickly. Screw the plastic plug back into the top, and turn on the mechanical pump. Let it run with the washing oil for 20-30 minutes. After that, turn off the mechanical pump, and drain the washing oil in the same manner that you drained the vacuum oil. Fill the pump with fresh vacuum oil to the line in the center of the gauge.
How do I change the oil in the diffusion pump?
From the evaporator supply cabinet, get diffusion pump oil. You will also need a container to dispose of the old diffusion pump oil, a bucket, an adjustable wrench, and a screwdriver. To change the oil in the diffusion pump, you will first need to get access to the diffusion pump. First, turn off the water flow through the water lines (yellow tubes), then remove the two water lines from the edge of the coil wrapping the diffusion pump. Water will spill out of them, so itís best if you put a bucket under you while you do that. Second, you will need to undo the upper clamp on the short section of thick rubber tubing, vent the system with the venting valve, and then undo the four support bolts that hold the diffusion pump in place. You will want 2 people doing that, because someone will need to hold the diffusion pump while the other person undoes the bolts. The diffusion pump will fall if it is not held by someone. Once the diffusion pump is free, remove the pieces from the center of the diffusion pump, and pour the old diffusion pump oil into the disposal container. Then, clean the body and the center pieces thoroughly with ethanol and dry them. Pour 150 cc of diffusion pump oil into the pump. Reassemble the diffusion pump, taking care to align the bottom component with the notch at the base of the pump. Replace the pump in the system. First, get the four support bolts started so that the pump is held by the system. Next, center the diffusion pump under the fitting, positioning it so it will form a seal. While positioning the diffusion pump, making sure that the tube off the side is replaced in the small section of rubber tubing. Once the diffusion pump is settled, begin tightening the support bolts evenly to create a strong vacuum seal. Reattach the water lines and restart the water, checking for leaks. Tighten the clamp attaching the short rubber tube to the diffusion pump. When everything is reattached, start the mechanical pump and monitor TC1. If it does not drop to 10 microns of vacuum, you should adjust the bolts supporting the diffusion pump, making adjustments until the vacuum returns. Then start the diffusion pump, let it warm up for 30 minutes. If the pressure is any higher than 1*10-6 torr, continue adjusting the support bolts.
What is the procedure for cleaning the bell jar and the faceplate?
One key is that acetone will dissolve the rubber in the gasket, causing the vacuum seal to be lost. So, if you are using acetone to remove organic, always be sure to only touch the glass portion of the bell jar. For the area around the gasket, and for the faceplate, clean with ethanol. A thorough scrubbing should remove all or most of the organics. If you are concerned about the presence of organics after that kind of cleaning, one way to get rid of them is to place an empty tungsten weighing boat in the system, and start up the system, evacuating the chamber. Once the pressure is as low as it will go, run the system with just the empty tungsten weighing boat. Any organics present will evaporate and be pulled out of the chamber by the diffusion pump.
The pressure is higher than 2*10-6 torr. How do I fix it?
Okay. First thing first, figure out what part of the system the leak is coming from. Using the mechanical pump, draw vacuum TC1. It should drop to 10 microns of vacuum in 5 or 10 minutes. Close the 3-way valve, and observe how quickly TC1 rises. If itís higher than 15-20 microns after 2 minutes, youíve got a leak in TC1. Repeat the procedure with TC2, draw the vacuum down to 30 microns, and then close the 3-way valve, and observe how quickly TC2 rises. If it rises above 50 microns in 2 minutes, you probably have a leak in TC2. If both systems pass the test, then the vacuum seals appear to be performing well. The next step would be to thoroughly clean the belljar and the faceplate, and then try again. The next step would be to run current through an empty tungsten boat, to evaporate any organics that are causing the increased pressure. Lastly, if none of those steps help, run the system overnight. If the evaporator has been used minimally for a while, running it continuously overnight can help improve the vacuum it draws.
The leak is in TC1, how can I fix it?
TC1 consists of several components: the mechanical pump, the rubber tube connecting the mechanical pump to the diffusion pump, the diffusion pump, and the lower half of the 3-way valve. A leak in TC1 is most commonly caused by degradation in the seals at the ends of the rubber tube, or from a small leak from where the diffusion pump seals against the bottom of the high vacuum valve. The first problem can be solved by replacing the rubber tubes, and checking the seals. The second problem is solved by adjusting the bolts positioning the diffusion pump, and finding the place that creates the best seal.
The leak is in TC2, how can I fix it?
TC2 contains the bell jar, the gasket, and the venting valve. A leak in TC2 is most likely due to improper seal around the gasket. To resolve this, thoroughly clean the faceplate and the gasket with ethanol, removing any visible dust from the gasket, and all organics from the faceplate. If those do not resolve the problem, check to make sure the venting valve is closing properly.
Help, Iíve done all that and I still canít isolate the leak! What now?
Youíre in for some real fun. You take apart the system, and cap it after each successive piece, to attempt to determine specifically where the problem lies. Youíll eliminate working pieces step by step as you cap them and the vacuum drops to a normal level. Eventually, you will find a piece that is leaking, and youíve got your problem.
What are other issues that arise with the evaporator?
Occasionally, the water lines will come loose from the drain. If not replaced, they can flood the cabinet area of the chemical hood, which is a big problem. To prevent this, occasionally check to make sure that the water lines are securely taped and directed down the sink in the back of the chemical hood. If the water gets switched off, you will have to restart it before the diffusion pump will switch on. The switch that is used to change the current from the Cr side to the Ag/Au side will occasionally wear down, as that switch is designed to be used to switch a boat from its primary battery to a backup. In that case, the switch must be replaced.
1) Turn on water for diffusion pump cooling system. Make sure that the tubes which go to the drain are properly placed or the chemical hood will flood.
2) Make sure all valves are in their proper positions. The high vacuum valve should be closed, the three-way valve should be set knob pointing horizontal, and the venting valve should be closed.
3) Turn on the mechanical pump and let it run for a few minutes. You will hear a change in the sound it makes when it is ready.
4) Turn the knob on the three-way valve pointing down (foreline position). The pressure in TC1 should immediately drop, quickly reaching a value between 10 and 25 microns of vacuum.
5) While the system is running, open the venting valve while monitoring TC1. If TC1 rises, the high vacuum valve is not properly closed. TC2 should rise quickly to atmospheric pressure, and there will be a pop when the pressure is equalized and the belljar is free. Carefully remove the belljar. Lift it directly vertical, as there are vital components under the belljar when it is on the system. Place the belljar carefully on its side on the benchtop, preferably on top of a kimwipe.
6) Clean the belljar thoroughly. Acetone may be used to remove metal and organic from the inside of the belljar, but only ethanol should be used on the belljar near the gasket or on the faceplate.
7) After the belljar is clean, place your samples on the sample holding tray, ensuring that you leave a space directly beneath the thickness sensor. Position a tungsten boat with either gold or silver between the metal prongs on the right, and a chromium rod between the prongs on the left.
8) After the sample is placed and the metals are in position, carefully place the belljar back on the surface. Make sure that you place the belljar evenly to prevent chipping, and that you place it gently.
9) Turn the three-way valve so that the knob is pointing up (roughing position) and monitor both TC1 and TC2. The mechanical pump will make the same sound now as it did when it was first warming up, but that will stop shortly. TC1 should not increase significantly. TC2 should decrease steadily.
10) Once TC2 is around 50 microns, turn the three-way valve so the knob is pointing down (foreline position), and switch on the diffusion pump.
11) Let the system run for 10-15 minutes, and then open the high vacuum valve. The pressure in the chamber will drop. You should wait at least 60-90 minutes after you open the high vacuum valve before you deposit.
12) 10 minutes before you deposit, get 1 L of liquid nitrogen and pour it into the funnel in the system. That will ensure the cold cathode gauge is functioning properly during deposition.
13) Turn on the thickness monitor, press stop and then start, which should reset it to zero. Input the density of the metal by using the buttons on the monitor.
14) Double check to make sure the variac is at 0. Set the current switch to deposit the desired metal. Adjust the cover so that it is over the source to be deposited.
15) Turn on the high current switch. Slowly increase the variac to a number that will give you the proper deposition rate for the metal you are depositing. Optimal rates are 0.1 Angstrom per second for chromium and 1 Angstrom per second for silver and gold. If you are unsure where to position the variac, either consult with other group members, or check the log book to see what current levels were used in recent depositions.
16) After 1-2 minutes at the proper current, the source will be ready for deposition. Shift the cover to the other side, and watch the thickness monitor. Adjust the variac up or down as needed to get the proper deposition rate.
17) When the thickness of the layer reaches the desired thickness, put the cover back over the deposition source, turn the variac down to zero, and switch off the high current power.
18) If more than one deposition is required, repeat steps 12-17 until you are finished depositing.
19) Following the final deposition, let the system run for 10 minutes. Then, close the high vacuum valve tightly and shut off the diffusion pump.
20) Turn on the nitrogen flow and open the venting valve. When the pressure equalizes, the belljar will make a popping sound.
21) Remove the belljar, handling it with utmost care, and then remove and properly store your samples.
22) Place the belljar on the face plate, and then turn the three-way valve so that the knob is pointing up (roughing position). Let the system run until TC2 is below 50 microns.
23) Turn the three-way valve horizontal (closed position) and shut off the mechanical pump.
24) Turn off the water flow at the faucet.