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CVC Electron Beam Evaporator
I. Introduction
The electron beam (E-beam) evaporator is used to coat samples with various metals. A high-intensity beam of electrons is focused on the center of a crucible containing the material to be evaporated. The energy from the electron beam melts a region of the source metal. Material evaporates from the source and covers the sample with a thin layer.
Unlike sputtered films, evaporators only coat the surface facing away from the substrate. E-beam evaporators will provide very little coating to the sides of any features that are perpendicular to the surface of the substrate.
In a typical process, the chamber is pumped down to a pressure of 5 x 10 -7 Torr to increase the mean free path. The mean free path of a gas molecule is the average distance the molecule travels before it collides with another molecule. This prevents air molecules from interrupting metal atoms as they travel from the evaporation source to the substrate. Then, the metal is heated to the point of vaporization by a high-intensity beam of electrons. This causes the metal to evaporate, and the metal molecules travel in a straight line to be deposited on the substrate. Typical deposition rates range from two to five angstroms per second.
II. Machine Specifications
The E-beam can be used to evaporate:
- Titanium
- Chrome
- Gold
- Nickel
- Platinum
- Aluminum
- Copper
- Iron
- Silver
- Tungsten
- Tin
- St
- Palladium
- Germanium
- Vanadium
- NiCr
- Niobium
- Bismuth
- Indium
- Other metals*
*Please consult MiRC staff to process other metals.
III. System Components
A. Ion Gauge
The ion gauge is used to display the chamber pressure when the chamber is under high vacuum. The pressure is measured in Torr.
B. Valve Controller
The valve controller controls the valves that are used to control the chamber pressure. The gauge in the middle of the controller shows the chamber pressure in torr. The lights on the left side of the gauge show the status of the system's valves. A valve is open if the light is on.
C. IC5/Deposition Controller
The Deposition Controller is the system that allows the operator to setup, program, start, and stop the e-beam system.
D. Crucible Selector
The crucible selector moves the selected crucible into position for evaporation
E. Power Supply Controller
The power supply controller controls the electron-beam power supply. The power supply itself is located in the black box on the floor on the right side of the evaporator. Refer to the instructions below when operating the power supply. For more detail on the power supply lights, see the troubleshooting section.
F. XY Sweep
The XY Sweep controller controls the position of the electron beam. For proper operation, the beam must move in a circle inside the crucible. The beam should not touch the edges of the crucible
G. Shutter and Hoist Control
The shutter control opens and closes the shutter. Ordinarily, the shutter is controlled by the disposition monitor. The shutter is closed while the metal that is being evaporated is being heated. Once the metal is evaporating at the correct rate, the shutter is opened, exposing the sample to the evaporation. Once the desired amount of metal has been deposited, the shutter is closed to prevent further deposition.
H. Miscellaneous
- The E-beam system holds six separate evaporation sources, allowing for evaporation of multiple materials in a single run.
- It has the capability to process a variety of sample sizes ranging from less than one cm 2 to 4" wafers.
- It uses a cryo-pump for rapid pump down.
- Electron beam power is automatically controlled for uniform evaporation with little operator work.
- The E-beam system can process up to 20 3" (or less) samples simultaneously using a multiple-sample dome wafer holder (see instructions under Additional Features).
IV. Operating Instructions
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Loading the Evaporator
- Attach the sample to be processed to one of the sample holders that are kept in the drybox near the doorway. Remember that it will be mounted upside down.
- Just below the viewport there are two knobs. The knob on the left controls the viewport block. Turn this knob clockwise until it stops. Now check that there is no glow inside the chamber. A glow indicates that the metal inside the chamber is still hot and the chamber cannot be vented until the metal has cooled.
- Press STOP on the valve controller.
- Wait five seconds and then press VENT on the valve controller. (It takes at least 15 seconds for the chamber to vent.)
- The system has a sensor so that the hoist cannot be raised until the pressure inside the chamber equals atmospheric pressure. When you hear nitrogen exiting the seal (The needle on the gauge in the middle of the valve controller will be all the way to the right before you can hear the nitrogen exiting.), raise the chamber with the HOIST UP button. If you still hear nitrogen entering the chamber, press the STOP button on the valve controller.
- Inspect each material to be evaporated. You can switch crucibles by pressing the buttons on the crucible selector. Switch to the first material you will be using and make sure that the crucible is centered in the wedge shaped exposure area. If it is not, move the crucible plate to center.
Caution: An overfilled crucible can become jammed in the electron gun and cause serious damage to the gun.
- Put the sample holder, upside down, into the square holder at the top of the evaporator.
- Check to be sure that the mirror behind the gun is aligned. If the mirror is too close the crucible, the electron beam will hit it causing it to break. The base of the mirror should be behind the opening in front of the mirror. The electron beam comes through this opening. You will need to be able to see the exposed crucible through the viewing port on the front of the bell jar. Stand in front of the evaporator and look at the mirror from directly in front of it. You should be able to see the exposed crucible.
- Test the shutter. To do this, switch the shutter control to MANUAL and test it using the OPEN / CLOSE switch. Be sure that the shutter will not hit the mirror. Put the shutter in AUTOMATIC mode when you are done testing
- Before pumping the chamber down, it is a good idea to make sure the deposition sensor is working.
- Look at the bottom of the deposition controller screen. If "XTAL Fail" appears in the display, this means that the sensor crystal needs to be replaced. If this is the case, see the section "Replacing the Sensor Crystal" below.
- Vacuum around the chamber seal with the cleanroom vacuum. It is very important that you use the soft rubber tip on the vacuum so that the seal area is not scratched. If you cannot find the soft rubber tip, contact a MiRC staff member
- Lower the hoist by pressing and holding down the HOIST DOWN button. You may have to push the bell jar to the side by hand to make it set properly. Be careful not to put your fingers under the bell jar as it comes down.
- Press START on the valve controller to pump the chamber down
Caution: Be certain that there is nothing in the "throat" (the hole in the base of the chamber) before lowering the hoist. Objects such as metal pellets that fall into the throat can destroy the hi-vac valve.
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Programming the Deposition Controller
- If the deposition controller is not on, turn it on by pressing the ON / STBY button in the lower right corner of the controller.
- Press F6 (Program), then F2 (Process Directory). The controller will display a list of materials.
- You will need to set up each material that you are going to use. use the arrow keys to highlight the material that you want to set up.
- Press F5 (Process). The controller will display the settings for the material
- After you have set up the material, press F6 (Process Directory) to return to the list of materials.
- Set up any other materials you are using the same way
- Highlight the first material you are depositing and press F4 (Select Active). This will set it as the active process. The number of the active process is displayed at the top of the screen.
- Press F6 (Program), then press F6 (Operate)
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Running the Process
- The ion gauge will display the chamber pressure. Most people wait until the pressure is in the 5x10 -7 to 2x10 -6 Torr range to start depositing. However, if you are not concerned with the deposition quality, you can start at higher pressures. If you want a low pressure, please remember that it may take 30 - 45 minutes for the system to reach the pressure you want.
- Turn the keylock on the electron beam controller to ON and press the green ON button next to it.
- Before proceeding, you must wait for the power supply's cooling fans to reach operating speed. This will take about a minute. The power supply (the big black box beside the evaporator) will make a clicking sound.
- Press the "HI VOLTAGE" ON button. All four lights above the buttons should be lit (green) when you do this. If they are not, consult a MiRC staff member before proceeding. The voltage will appear on the digital display and should be in the 1kV range
- Press the "FILAMENT" ON button. The digital display should light up; however, not much current at all will appear. This is because the power does not actually turn on until a program is running.
- The knobs labeled "Position" and "Amplitude" control the position and amplitude of the motion of the electron beam. The lights above them show the position of the beam. The latitude knobs control the front to back motion and the longitude knobs control the left to right motion. Set both latitude and longitude so that their amplitude is about three lights wide and roughly center them with the position knob. However, if you are going to be depositing gold or any other material, which uses a narrow mouthed crucible, the amplitude should be set to one light wide and centered. If you are unsure which type of crucible is being used, contact a MiRC staff member before continuing in this process.
- When you are ready to start, press START on the deposition controller
- Look through the viewing port on the front of the bell jar. The beam pattern should be centered in the crucible. (The crucible is the bowl that contains the material being melted.) It should be big enough to heat the metal evenly, but should not touch the crucible itself. If on part of the crucible begins to glow brightly (it would be sparking brightly and usually occurs when the beam is moved into the orange and/or red ranges on the positional controllers), the beam is hitting it. The beam must be centered in the crucible. Also, when a process starts, the power will come up slowly, and the crucible will slowly bgin to glow. Pay attention to where the glow begins, but realize that it will take a little time for the crucible to come up to the desired temperature. DO NOT UNDER ANY CIRCUMSTANCES leave the e-beam system alone at this point. If you move the beam back too far, it will hit the mirror and break it.
- Crucible during evaporation. Note that the brightest glow comes from the metal in the crucible. Only a dim glow should come from the crucible itself.
- After the process is complete, you can deposit another metal by pressing the button for the material on the crucible selector, then selecting F6 (Program), then F2 (Process Directory) on the deposition controller. Highlight the metal you want to evaporate next and press F4 (Select Active). Then press F6 (Operate). Narrow the beam down to a few bars with the XY sweep controls and press START on the deposition controller. Align the beam as described in the previous step.
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Unloading the Evaporator
- On the electron beam controller, turn the "FILAMENT," "HI VOLTAGE," main power, and keylock off in that order.
- Wait for the last crucible used to stop glowing. If you vent the system while it is still hot, you will destroy the metal and may shatter the crcubile.
- Press STOP on the valve controller.
- Press VENT on the valve controller.
- The system has a sensor that will not allow the hoist to be raised until the pressure inside the chamber equals atmospheric pressure. When you hear nitrogen escaping from the seal (this takes about 15 seconds), raise the hoist with the HOIST UP button. If you can still hear the hiss of the nitrogen entering the system, press the STOP button on the valve controller.
- Remove your sample from the chamber.
- When you are finished, vacuum the inside of the chamber with the soft tip on the vacuum.
- Press and hold HOIST DOWN to lower the hoist.
- Press START on the valve controller.
- Return the sample holder to the dry box.
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Replacing the Crystal
- Pull the metal ring out of the top of the sensor unit.
- Pull the metal piece out of the back of the metal ring.
- Remove the sensor crystal.
- Put the new sensor crystal in with the white side facing the hole in the metal ring. Extra crystals are in the drawer in the desk on the left side of the filament evaporator.
- Put the metal piece back into the metal ring so that the contacts are against the patterned side of the crystal.
- Put the crystal holder assembly back into the sensor head.
- Throw the old crystal away.
V. Additional Features
A. 4" Wafer Holder
B. Multi-sample dome
C. Backside Heater
VI. Troubleshooting
Q:I can't turn the "HIGH VOLTAGE" on. What's wrong?
A: There are four lights above the HV display. They should all be lit. If one is out, wait a minute then press OFF . Wait a few seconds, then try to turn it on again. In case that doesn't work, here is more information on each light:
AIR/CAB - if this light is off, the step above should have fixed it.
VAC - make sure the chamber is pumped down and the ion gauge is on
If one of the other lights is oyt, or if you can't get it working with the information above, contact MiRC staff and do not do anything .
Q:I cannot turn the "FILAMENT" on. What do I do?
A: Is one of the lights at the top of the FILAMENT box off? If the WATER light is off, check the water switch near the shutter control below the chamber. It should be on (up). If the HVAC light is off, make sure the chamber is pumped down and the ion gauge is on. Press OFF wait a few seconds and try again. If it still will not come on, contact MiRC staff.
Q:The shutter did not open during my process. What might have caused this to occur?
A: Make sure that the shutter is set to AUT . If it is set to manual, it will not open.
Q:I did not get any deposition. Why?
A: Check to see if the shutter is set to AUT . If it is set to manual, the shutter will not open or close automatically, and therefore, you will not get any deposition.
Q:The power supply is clicking and the cut-back light is flashing. What is going on?
A: Is the system pumped down? If the pressure is high, and you turn the high voltage on, this will happen. If this is the case, turn the high voltage off and wait for the pressure to go down. If the pressure is under 1 x 10 -4 Torr, there should be no problem. If there is, there may be a problem with one of the power supply interlocks, or the filament leads may be shorted. If the interlock lights (the green lights at the top of the power supply controller) stay lit, there is probably a short circuit between one of the filament leads and the chamber. Try venting the system and looking for loose metal flakes behind the crucible holder. Pay special attention to the two copper leads that run from vacuum feedthroughs to the back of the crucible holder. If you see any flakes, vacuum them up, and do not let them fall into the hole under the crucible holder. If any flakes fall in, vacuum them out before pumping the system down. If this does not take care of the problem, stop processing and go find MiRC staff.
VII. DO's and DON'Ts
DO NOT
- attempt to open the chamber while a process is running.
- attempt to open the chamber if the chamber is not fully vented.
- proceed with processing in the face of an unknown error. Contact the trainer and/or maintenance staff first.
- use the machine if another user has placed a 'machine down' sign on it; ask the technical staff to verify that it is working.
- vent the chamber if the metal inside is still glowing.
- turn off the IC-5 Deposition Controller.
- turn off the cyro-pump
- proceed with processing in the face of an unknown error. Instead, go find the cleanroom staff.
DO
- ask the trainer, cleanroom / technical staff, and other users questions about anything that is not clear or that you do not understand.
VIII. Check-off requirements
To be checked off, you must be able to do, to demonstrate, and to know the following items if asked:
- Locate the relevant components of the system (ion gauge, etc.)
- Know the materials that can be deposited.
- Know the specific materials and processes you will be using the system for.
- Vent the chamber
- Load a sample
- Program the process
- Run a sample
- Center the beam so that it does not hit the crucible
- Unload a sample
- Demonstrate how to handle the following errors:
- XTAL fail
- No deposition occurred