Specific Process Knowledge/Thin film deposition/thermalevaporator

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Thermal evaporator- A system for deposition of metals

The main purpose of the thermal evaporator is to deposit Al for removing charging of the resist when doing EBL on isolating substrate.

It is not only usable for Al deposition. The thermal evaporator has room for two evaporation sources and thereby the possibility to make thin films of two different metals. At the moment not that many metals have been tested, so right now only Al and Ag can be evaporated. We have attempted to evaporate Au and Zn but these are not standard processes. If you would like to deposit these or other metals, please talk to the Thin Film group.

Compared to the Wordentec, the thermal evaporator is quicker to use if you only need to deposit on one wafer or on small samples, as it only takes about 15 minutes to pump down the chamber. You can also deposit thicker layers because the throw distance from source to sample is shorter, so the material use is more efficient: In the thermal evaporator, you get up to 200 nm per metal pellet, whereas in the Wordentec you get about 15 nm per pellet. However, the thickness uniformity is better for large samples in the Wordentec also because of the longer distance from source to sample.

So if you want a quick deposition process and/or a relatively thick metal layer, and your samples are small or the thickness uniformity is not critical, then the Thermal Evaporator is a very good choice for you. If you need to deposit on many wafers or you need a more constant layer uniformity across a full 4" or 6" wafer, then the Wordentec is best.

The user manual, APV, technical information and contact information can be found in LabManager:

Thermal Evaporator in LabManager

Process information

Materials evaporated in the Lesker Thermal Evaporator

Aluminium
Silver
(Zinc - we don't like to evaporate this material)
Chromium

We can also evaporate gold in this evaporator and can develop processes for other materials if requested.

Equipment performance and process related parameters

Purpose	Deposition of metals	Thermal evaporation of metals
Performance	Film thickness	10Å - 1µm (Al and Ag) up to 80 nm (Cr)
	Deposition rate	0.5-2 Å/s (Al), 5 Å/s (Ag) In general, 0.5-10 Å/s is possible We need to develop a new process for each rate
	Thickness uniformity	approx. 13 % variation on a 4" wafer with 100 nm Al * approx. 23 % variation on a 4" wafer with 100 nm Ag * approx. 10 % variation on a 6" wafer with 100 nm Cr *
	Pumpdown time	about 15 min
Process parameter range	Process Temperature	Approximately room temperature
Process parameter range	Process pressure	Below 4*10^-6 mbar
Substrates	Batch size	Up to 8" wafer Or several smaller pieces Deposition on one side of the substrate
	Substrate material allowed	Silicon wafers Quartz wafers Pyrex wafers
	Material allowed on the substrate	Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar Metals

* The variation is defined as (Max-Min)/Average for the various points measured on the wafer. The max. point was around the center and the min. somewhere along the edge. The exact location of the maximum thickness depends how the sample is placed relative to the point of maximum material flux. Measurement by Rebecca Ettlinger, Nov. 2018.

Quality control (QC) procedure for the Thermal evaporator

Quality control (QC) for the Thermal evaporator

QC Recipe:	Al	Ag
Deposition rate	1 Å/s	5 Å/s
Thickness	150 nm	150 nm
Pressure	Below 1*10^-5 Torr	Below 1*10^-5 Torr

QC limits	Temescal
Measured average thickness	± 20 %
Deposition rate deviation	± 50 % after stabilizing
Thickness deviation across a 4" wafer	± 30 %

Thicknesses are measured in 5 points with one of the Dektak instruments.
Additionally we monitor the state of the Al crucible and ensure that it does not contain too much Al as this can wet the outside and short circuit the heater.