Standard Operating Procedure
Bendix High Vacuum Thermal Evaporator
Located in the cleanroom (V113C), this basic thermal deposition unit is configured for four sources and is primarily
intended for optical thin-film coatings. The filaments would normally be loaded with both metals (such as aluminum) and dielectric materials such as magnesium fluoride (in a crucible) and sodium hexafluoroaluminate (cryolite) allowing fabrication of dielectric mirrors and filters. Unlike most of our other systems this is a completely manual system optimally suited for student laboratories.
This front view of the Bendix high-vacuum thermal evaporator system shows the major components including the vacuum chamber, controls stack (with gauges), and vacuum valves on the front panel.
The vacuum system
The filament deck holds four filaments separated by shields to prevent cross-contamination. Atop these is a shutter which covers the filament in use during outgassing as well as to stop deposition. The substrate deck holds twenty substrates up to 1.5" diameter or 1" square. In the center of this deck is the crystal holder for the XTM monitor.
This rare view of the system with all covers removed shows the diffusion pump and cold trap above it. The cold trap is filled with extremely cold liquid nitrogen (at a temperature of 77K) when the pump has been switched on but before the high-vacuum valve is opened.
Electrical Controls and Valves
The electrical control panel showing switches for both pumps (roughing and diffusion),
filament power, and bell jar lift controls. The roughing pump must be energized and water flow must be present before the diffusion pump can be energized or filaments can be powered.
The active filament is selected via the rotary switch on the control stack just below the gauges. Filament current is controlled via a variable autotransformer on the top deck of the unit and is monitored via an ammeter on the front of the unit. Short, straight filaments require control settings in the 20A-35A range while larger helical filaments require higher settings. Crucibles heated with helical filaments can require control settings of over 100A for high melting point, low vapour pressure materials.
Basic manual controls allow the user to first rough pump the chamber via the ROUGHING valve then pump the chamber to high vacuum using the High-Vacuum valve. The Foreline valve is open whenever the diffusion pump is used. The vent valve allows the chamber to be brought back to atmospheric pressure to raise it and load/unoad substrates.
The control stack features two Varian Multigauges. The one on the left indicates chamber pressure via both a thermocouple (TC) gauges and an ion gauge and the one on the right indicates foreline pressure via a TC gauge. Pressing the "CHANNEL" button (upper left on each gauge) allows the user to configure the display on each gauge - this button selects each function cyclically - when an unused channel (TC2, 3, or 4) is selected an "E03" error is displayed. For the chamber gauge (the left one), the only two valid options are to display the chamber pressure (from TC1) both on the bargraph and numerically on the main display or to display the TC1 pressure on the bargraph and the ion gauge pressure numerically on the main display (as shown above). The foreline gauge always displays the foreline pressure the the TC gauge on both the bargraph and numerically on the main display.
During chamber roughing, the chamber pressure is monitored using the TC alone: the user may use the bargraph or may select to have the pressure displayed numerically on the main display. When the chamber pressure is low enough (after rough-pumping) the high vacuum valve is opened and the chamber is pumped through the diffusion pump. ONLY after the high vacuum valve is opened, and the chamber TC1 bargraph has 'bottomed out' can the ion gauge be used by pressing the EMIS button on the chamber gauge. Only the chamber gauge features a BA (Bayert-Alpert ion) gauge. DO NOT turn the ion gauge filament ON until the chamber TC gauge 'bottoms out' to 1.0E-3 torr and the high-vacuum valve is open.
This stack also includes an Inficon XTM quartz-crystal deposition monitor allowing in-process monitoring of depositions, a filament selector (one of four filaments plus an OFF position) and a lamp indicating water failure to the diffusion pump. Filament #1 is on the LEFT side of the chamber, filament #4 is on the RIGHT side of the chamber.
The Inficon XTM Monitor allows the user to determine the rate of deposition (in Angstroms/second) as well as the total thickness of the deposit (in kilo-Angstroms) simultaneously. Before use the unit must be programmed with the density of the material being deposited (in grams/cm3) and a tooling factor. When first switched on the unit enters programming mode automatically (as evident by the PROGRAM lamp being lit). When materials are switched the unit must also be reprogrammed by pressing the PROGRAM button.
To set the density of the material, press the PROGRAM key (if not already in program mode) and then press the DENSITY button. Enter the density and press the ENTER key to store it. There is no decimal point key so the density of aluminum would be entered as '2', '7', '0', then enter. The decimal place is implied at two places. Next, enter the Z-ratio (a number ranging from 0.000 to 1.000) followed by the tooling factor. Tooling factors ranging from 10 to 200 percent are entered in a similar manner by pressing the TOOLING key beside the DENSITY key. This factor defaults to 100% at power-up, begin with a value of 120.0% with the crystal monitor located at the center of the substrate deck.
When a deposition is started (i.e. just before the shutter is opened), press the ZERO button to reset the display. It is also important to ensure the crystal is oscillating before the chamber is pumped. The XTAL lamp will blink if there is a problem with the crystal or the oscillator package.
- Turn the cooling water ON (the valve on the wall at the rear of the unit)
- Switch the main power shutoff on the wall behind the unit ON
- Press the ROUGHING PUMP power switch ON
- Turn the BACKING PUMP power switch ON (on the left side of the unit, beside the Ammeter)
- Ensure the HIGH-VACUUM and ROUGHING valves are both closed
- Open the FORELINE valve completely
NOTE: Ensure the foreline pressure drops below 100 millitorr before continuing
- Press the DIFFUSION PUMP power switch ON
NOTE: The Diffusion pump needs about thirty minutes to fully warm-up before use. During this time do not close the foreline valve as the pump oil will outgas
- Open the VENT valve to admit air into the chamber, wait until atmosphere is reached
- Raise the chamber via the switch on the switch panel
- Load substrates and evaporant (see notes on this procedure)
- Turn on the Inficon XTM monitor and ensure the crystal is operating (i.e. Ensure XTAL is not lit or blinking)
If a crystal error is indicated, check the wires as they may be loose. If the crystalk itself if faulty or has been used beyond 50%, replace it
- Close the chamber via the LOWER switch on the switch panel
- Close the VENT valve
- Close the FORELINE valve
- Open the ROUGHING valve
- The chamber pressure, indicated on the chamber TC, will begin to fall
During rough pumping of most systems, BACKING is usually necessary however this system features a separate backing pump rendering this operation unnecessary
- If using the optional liquid nitrogen cryotrap, fill the cryotrap during Rough pumping via the valve at the right-rear of the unit. Stop filling when liquid nitrogen overflows from the vent port (this only takes a minute)
- Rough pump the chamber to 1 millitorr on the chamber TC gauge (i.e. the chamber TC gauge 'bottoms out'). This may take a while depending on the cleanliness of the chamber. Be patient, there is no way of rushing this
- Close the ROUGHING valve
- Open the FORELINE valve
Opening the HIGH-VACUUM valve must be done slowly as follows to prevent backstreaming which contaminates the chamber, the work, and damages the pump components ...
- Slowly open the HIGH-VACUUM valve while watching the foreline pressure TC gauge. At about two turns counter-clockwise the foreline pressure will rise. Open the HIGH-VACUUM valve only enough to keep the foreline pressure below 100 millitorr. If the foreline pressure rises above 100 millitorr, close the valve slightly. In less than one minute the chamber pressure (indicated on the chamber TC gauge) will fall below measurable limits and the foreline pressure will fall again. Continue to open the HIGH-VACUUM valve until the foreline pressure does not rise again beyond the 100 millitorr limit then open it full counter-clockwise.
- Turn ON the ion gauge by pressing the EMIS button on the chamber gauge. Pressure will be displayed in a moment
- Do not run the ion gauge more than a minute at a time. Press the EMIS button to toggle the gauge filament off
- Pump the chamber to a pressure suitable for deposition (Below 2 * 10-5 torr). This usually takes less than 10 minutes
- Set the filament current control on the top deck (the variac) to ZERO
- Place the shutter over the filament to be used
- Select a filament (1-4) using the rotary selector under the gauges
- On the Inficon XTM thickness monitor, program the proper parameters (including density, Z-ratio, and tooling factor) to match the material in use
- Press the FILAMENT ON switch on the switch panel
- ZERO the thickness monitor
- Regulate current using the filament current control (variac) until a dull glow is observed through the chamber window. The current is displayed on the ammeter on the front panel of the unit. Most filaments require between 30A and 50A of current
- Outgas the material gently then open the shutter to begin the deposit. Filament current can be increased until a suitable deposition rate is obtained.
- When complete, close the shutter and set filament current to zero
- Turn the FILAMENT ON switch off and select filament zero (0)
- Close the HIGH-VACUUM valve. Ensure it is completely closed (it is stiff)
- Leave the FORELINE valve open
- Open the VENT valve. Watch the Foreline Pressure TC gauge to ensure it does not rise – if it does, the HIGH-VACUUM valve is not fully closed so tighten it!
- Wait until the chamber is back at atmospheric pressure (about two minutes) then raise the chamber and unload substrates
- Turn off the DIFFUSION PUMP power switch
- Leave the FORELINE valve open, the roughing pump ON, and the backing pump ON until the diffusion pump to cools (about 30 minutes)
- Close the FORELINE valve
- Open the ROUGHING valve and pump the chamber below 100 millitorr (Never leave a chamber at atmospheric pressure for long periods)
- Close the ROUGHING valve
- Shut off the roughing pump, backing pump, and turn off the MAIN SUPPLY on the wall behind the unit
- Turn off the water supply
Filament Loading Procedures
Use the nomograph to predict the quantity of evaporant required based on the material, source-to-substrate distance, and desired thickness as per the example.
- For aluminum, hang horseshoes on the filament as required using tweezers. Always add one extra.
- For Na3AlF6 press the powder into the helix until full. Put a cleanroom rag under the filament to catch any excess and change gloves when done: this material is toxic.
PDF Document outlining the basic procedures required to operate the Bendix System.
||Index of Refraction
||Deposition Rate (Angstroms/sec)
||15 - 25 typical, 35 Max
||5 - 10 typical, 50 Max
Updated 2018/05/23 by M. Csele
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