By Vvon Engineering Team | Published | Updated
Compare thermal evaporation, electron-beam evaporation and sputtering against film materials, substrates, process control and installation requirements.
Nanotechnology RFQ checklist (TXT)
Choose between thermal and electron-beam evaporation from the film materials, substrate and process requirements. Both evaporate source material under vacuum; the heating method and source arrangement affect which processes are practical. A higher-temperature source is not automatically the best choice for every layer or substrate.
Thermal and electron beam evaporation look similar from outside the chamber. Both produce a vapour from a source at the bottom and condense it on a substrate at the top, in a line-of-sight geometry, at high vacuum. What differs is how the source gets hot, and that difference decides almost everything else.
Start with the films, substrates and acceptance measurements. Thermal evaporation may suit the proposed source materials; electron-beam heating broadens the materials that can be considered. Confirm source compatibility, substrate heating, uniformity and film requirements with the manufacturer. Use the comparison below rather than selecting from the deposition-method name alone.
Some modular systems offer multiple source configurations. For example, Moorfield's MiniLab 080 describes thermal and electron-beam options. Check the exact source, stage, monitoring, pumping and control schedule in the offer; the family name does not establish which options are installed.
Provide the materials and layer stack, substrate size, temperature restrictions, batch size, film-thickness and uniformity requirements, and available utilities. State whether transfer under a controlled atmosphere or a load lock is needed. Compare deposition systems and send a process brief.
| Decision | Thermal evaporation | Electron-beam evaporation |
|---|---|---|
| Source and materials | Check the material with the boat, basket or crucible and its heating range. | Check material, liner, source configuration and the proposed operating conditions. |
| Substrate and film | Specify the layer stack, temperature restrictions, thickness and uniformity. | Specify the same requirements and ask how the source and geometry affect the sample. |
| Equipment package | Identify sources, shutters, monitoring, stage, pumping and controls. | Identify the same functions, plus the electron-beam source, power supply and cooling scope. |
| Acceptance | Agree representative substrates and measurable film outputs. | Compare the proposed process on the same application brief. |
Use Moorfield's material selector as an initial reference and obtain application confirmation for the selected system. For conformal-film questions, the separate ALD and CVD guide addresses different deposition routes; the sputtering-target guide addresses target selection after the process has been chosen.
In thermal evaporation the charge sits in a resistively heated boat, basket or coil, usually tungsten, molybdenum or tantalum, sometimes alumina coated. Current through the boat heats the boat, and the boat heats the charge. Everything is limited by what the boat itself can survive.
In electron beam evaporation a filament outside the line of sight emits electrons that are bent by a magnetic field into the surface of a charge sitting in a water-cooled copper hearth, often with a crucible liner. The energy goes into a small spot on the charge, so the charge can be far hotter than the hearth around it. That is the whole trick, and it is why an electron beam source reaches materials a boat never will.
Before comparing anything else, write down every material the group expects to deposit over the life of the tool, including the ones that are somebody's idea rather than a current project. Then check each against the source.
| Material group | Thermal-source purchase check | Electron-beam purchase check |
|---|---|---|
| Gold, silver, aluminium, indium, tin | Confirm the source material, wetting behaviour, charge and required rate. | Compare the proposed source against the same film and operating-cost requirements. |
| Chromium | Ask which rod, basket or other source arrangement supports the proposed process. | Confirm the source and deposition conditions for the required film. |
| Titanium, nickel, palladium, platinum | Confirm each material separately; a single boat specification does not establish compatibility for the whole group. | Ask for the liner, power and process configuration proposed for each material. |
| Tungsten, molybdenum, tantalum | Check whether the offered source can reach the necessary evaporation conditions. | Higher source temperatures can broaden the material choice; confirm exact source capability. |
| Oxides and fluorides | Assess the individual compound, source and required film composition rather than rejecting the whole group. | Confirm material, liner, process atmosphere and film-composition requirements. |
| Organics and temperature-sensitive materials | Check source control, decomposition and substrate-temperature limits. | Ask whether radiation and heating from the proposed process are acceptable for the material. |
For aluminium and other materials that may interact with the source holder, ask the manufacturer to recommend a compatible boat or liner and operating conditions. Include replacement parts and contamination checks in the process plan. Do not assume one source material is suitable for every charge.
Both methods can use quartz-crystal monitoring for rate and thickness. Confirm whether the offered system provides monitoring alone or closed-loop control, then validate the reading against the deposited film on representative substrates.
Uniformity across a substrate is set by geometry. The flux from a small source falls off with angle and with distance, so a substrate held closer gets a thicker film in the centre. Moving the substrate further away flattens the profile at the cost of rate and of material utilisation, which matters when the charge is platinum. Substrate rotation, a planetary fixture and a correction mask are the three tools available, and a planetary fixture is the one most often left out of a research tool and most often wanted later.
An evaporated film picks up whatever else is in the chamber, and the sources of that are predictable.
One useful effect works in your favour: titanium getters. Depositing titanium improves the chamber vacuum while it runs, which is part of why a titanium adhesion layer deposited immediately before gold gives a cleaner interface than the same two films deposited in separate runs.
Evaporation is directional. Atoms arrive from a small source along a straight path, so vertical sidewalls receive very little material and the film breaks at a step. For a conformal coating that is a defect. For lift-off it is the entire mechanism.
In a lift-off process the metal on top of the resist and the metal in the opened window need to be discontinuous, so that solvent can reach the resist. A directional source with an undercut resist profile gives exactly that. A conformal process coats the resist sidewall, seals the pattern and turns lift-off into an exercise in ultrasonic agitation and lost devices.
So the questions are: does the process need to cover topography, or does it need to avoid covering it? If contacts are patterned by lift-off, an evaporator is the right tool and its directionality is a feature. If films must coat a trench or a released structure, an evaporator is the wrong tool no matter how good it is.
There are cases where neither evaporator will do the job, and buying one anyway is a slow way to arrive at the same conclusion.
For noble-metal contacts patterned by lift-off, a compatible thermal evaporator may meet the need. Refractory materials may favour electron-beam evaporation, while alloy or compound films may favour a validated sputtering or reactive-deposition process. Denton Desktop Pro is a magnetron sputtering system, not a thermal evaporator. Desk V is primarily an electron-microscopy sputter coater with a carbon-evaporation option; it should not be specified as a general-purpose gold-contact evaporator without manufacturer confirmation.
Where the budget only stretches to one chamber, buy the chamber with spare ports and a feedthrough count you do not need yet. Compact systems such as the Moorfield Nanotechnology MiniLab 026 and the nanoPVD-S10A Benchtop PVD System are worth comparing on that basis rather than on the first process alone. Adding a second source, a substrate heater, an ion source or a load lock to a chamber that was specified with room for them depends on the chamber design, controls, safety review and manufacturer-approved upgrade path. Adding them to a chamber that was bought to a minimum specification usually means buying the chamber again.
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