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8/22/2019 Thermal Evaporation Procedure
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THERMAL EVAPORATOR
Document prepared by
Pavithra Prashanth
Equipment technologist
Center for Excellence in Nanoelectronics
Indian Institute of Science
mailto:[email protected]:[email protected]:[email protected]8/22/2019 Thermal Evaporation Procedure
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Bell jar
Substrate table
Crystal Monitor
Substrate holder andsample
Path of vapor
Clamps connected tohigh current source
Filament boat filledwith evaporant
High vacuum created byDiffusion pump backed byRotary pump
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A thermal evaporator uses an electric resistance heater to
melt the material and raise its vapor pressure to a useful range.
This is done in a high vacuum, both to allow the vapor to reach the
substrate without reacting with or scattering against other gas-
phase atoms in the chamber, and reduce the incorporation of
impurities from the residual gas in the vacuum chamber.
Thermal evaporation is the simplest way of depositing
material onto a substrate. One major disadvantage of this is that alot of material is lost in the process.
Optimization
Purity of the film depends on the purity of the source materialand the quality of the vacuum.
Thicknesses of the film vary due to the geometry of thechamber.
Collision with the residual gases aggravates no uniformity ofthe thickness.
Advantages
It is simple and cheap. Less substrate surface damage. Excellent purity of films.
Disadvantages
Limited to low melting point metals.
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Its not possible to evaporate the Dielectric materials. Filament limits the amount of material that can be deposited. Density is poor. Adhesion is poor. Step coverage is more difficult to improve.
Specifications of the system
Uses tungsten or Molybdenum filaments to heat evaporants. Ultimate chamber pressure 5x10-5mbar. Typical filament currents are 100-200Amps.
Exposes substrate to visible or IR radiation. Maximum deposition thickness that can be achieved is600nm.
Substrate temperature can be increased up to 150oc.
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Heating sources for Thermal Evaporation
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Crystal Monitor
Quartz crystal is used to monitor the thickness of thedeposited film and also to control the rate of evaporation.
Crystal has to be cleaned or changed periodically.Steps to use Crystal Monitor
Switch ON the crystal monitor. Select the film number depending on the material you are
going to deposit.
Enter the density of the material.Acoustic impedance
Tooling factor
When you start the evaporation press the Start button(set thethickness display to zero and open the shutter).
Once the desired thickness is achieved close the shuttermechanically.
Press the stop button.
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Material guide for Thermal Evaporator
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Vacuum Techniques Thermal Evaporator
Thermal Evaporator make Vacuum techniques
Crystal monitor make Model DTM -10
Heating filaments/boats Tungsten, molybdenum
Materials evaporated Low melting point metals
(Al, Cu, In, Au, Ag..)
Pressure in System 5X10-5m bar
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Operating procedure for Vacuum technique Thermal
Evaporator
Precautions
Only the trained and authorized users are permitted to operatethe instrument themselves.
Check if all the valves are CLOSED, before switchingON the system.
Procedure
1. Check if all the valves are closed. Switch ON the system mains.
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2. Switch ON the Rotary pump. Open the Gas ballast. Also switch
on the Pirani gauge (GH 1). Press to on rotary pump Green lightglows if rotary pump is on Press to on diffusion Green light glows
if diffusion pump is on.
Green light glows if
Diffusion pump is onGreen light glows if
rotary pump is onLT
indicatorHT indicator
Press to on rotaryPress to on
diffusion pump
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3. Close the Gas ballast after 5 minutes. When the pressure drops
below 0.02 mbar, open the Backing valve slowly. (The pressure
increases and again starts decreasing).
4. Once the pressure reaches 0.02 mbar, open the coolant watersupply. Switch ON the Diffusion pump. The diffusion pump needs
to be heated for about 20-25 minutes.
Roughing valve
Backing Valve
Pirani gauge Penning gauge
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5. Meantime, open the air admittance valve slowly, hoist up the
chamber. Clean the chamber and the boat/filament contacts,
replace the glass near the window, check the contacts, load the
metal (Al, Cu, etc.,) into tungsten boat/filament, load the samples,hoist down the chamber and close the air admittance valve.
6. After about 20-25 minutes Diffusion pump will becomeoperational. Close the Backing valve and open the Roughing valve
slowly. Switch on to GH2. Wait till the Pirani gauge reads
0.01mbar.
Air Admittance valve
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7. Once this vacuum is achieved, close the roughing valve and
open the Backing valve slowly. Then open the Baffle (main) valve
slowly. On the Penning gauge (Ring 1).
8. Then pour about 5 liters of Liquid Nitrogen, Wait pressure ofabout 5X10
-5mbar is reached on penning gauge (Ring 2).
Note: The penning gauge should not be kept on continuously.
9. If the evaporation of the metal is to be done at a certain
temperature, the Radiant Heater switch needs to be turned ON after
the above told pressure is reached and the temperature needs to be
set. The set temperature can be seen on the temperature controller.
9. Once the required pressure is reached switch on the crystal
monitor and enter the proper values, depending upon the material
to be deposited.
Crystal monitor
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10. Switch on the LT /HT Mains. Increase the voltage slowly.
During this time the shutter should be closed. The tungstenfilament (or tungsten boat) becomes red hot and the metal starts
melting or wets the filament. Open the shutter now and increase
the voltage.
11. Once the metal gets completely evaporated, decrease the
voltage to ZERO, switch off the LT Mains. After 5 minutes, close
the baffle valve and switch off the diffusion pump. Switch off the
Penning gauge.
LT and HT
mains
Hoist
u /down
Radiant heater
switch
LT and HT
switch
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12. Allow the substrate to cool down to room temperature.
13. Close the Backing valve. Open the air admittance valve slowly,
hoist up the chamber and remove the samples, hoist down thechamber, close the air admittance valve.
14. Open the roughing valve for about 15 to 20 minutes, to get a
pressure of 0.01 mbar which can be seen on the pirani gauge (GH
2). This is done to keep the system always in vacuum.
15. Close the Roughing valve. Open the Backing valve.
16. After 10 minutes, close the Backing valve and open the Gas
ballast for 5 minutes.
17. Close the Gas ballast and switch of the Rotary pump.
18. Switch off the mains.
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Aluminum film thickness measured using CrystalMonitor and Dektek profiler
Crystal monitor Thickness in nm Dektek Profiler Thickness in
nm
52 53
83 82
91 94
93 98
108 112
120 113
193 189
237 235