Couldn't you use a laser thermometer to take accurate readings? my understanding is that vacuum evaporation/deposition is a cold process so the temperature of the substrate might be the temperature of deposition.

If the operating temperature of the circuit is 0.3K the colder your substrate is, at deposition time the less bimetal stress it should produce. Does vacuum deposition work at .3K?

If I understood your question, you would like to know the temperature before processing your sample, not to measure it along the process.

I am not an expert in thin film technology, but as fas as I know the temperature depends strongly on the type of evaporation. For instance, e-beam evaporation heats the substrate, but the amount of heating depends strongly on the geometry. In contrast, sputtering is considered a cold technique, and substrate heating should be non-significant in most cases. Maybe this paper can give you more information:

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-49-24-4610

Can black-body radiation spectra work?

Generally in thermal evaporation process material that has to be evaporated is inserted in a spiral filament or a boat or a basket all are made of molybdenum or tantalum.The temperature of a material may not be measured directly because you are not allowed to keep any sensor besides to your material in the filament.i think you can measure the temperature of the filament keeping a thermo couple in the vicinity of the filament and monitor during material evaporation process. That may give an idea about the temperature.

Are you using an e-beam evaporator or a Joule-effect one?... Normally, the deposition temperature of an evaporator does not exceed the ambiant temperature. The only way to heat up the substrate is to use a resistance on the backside of the sample. I personally think you should consider the temperature around 20°C to 30°C.

Have you thought of using temperature dots for that? (they change color and would give you the highest temperature reached inside)

The sample temperature depends strongly upon how you deposit the materials and the geometry between the source and sample. Generally, the sample is heated radiatively by the hot evaporation source. The larger the distance the cooler the sample. The lower the power required to evaporate the material the cooler the sample. Higher vapor pressure materials require less power and lower dep rates require less power. I have done long high power runs where the temperatures increased by several 10's of degrees C. It also depends how you mount your sample. Is it mounted to something that can act as a thermal sink? Is the sample material thermally conductive (e.g., SiC) or insulating (e.g., glass)?

I imagine that you are doing relatively thin layers so I would not expect much of a temperature rise. One suggestion (assuming you are not rotating the substrate) .

is to do a run with a thermocopule mounted in contact with the surface of a similar substrate You may need to protect the thermocouple if bare, from the metal dep. There are other details to this of course but it may give you an estimate. The temperature dots may work as mentioned above assuming the metal dep on them does not obscure or change things.

another option is to deposit a thin film RTD (resistor) of Ni or Pt on a substrate, coat it with a very thin electrical insulator (SiN, SiO2, ?) and measure its resistance change during deposition. Perhaps this is too much for what you need. The blackbody calcs mentioned above may be able to give you a worts case estimate if you know your source temperature, the geometries and assume some emissivities.

Thanks a lot for your replies. I had two days off and were suprised concerning the amount of feedbacks. Thanks for that!

Well, we are doing thermal evaporation from a boat. The substrat holder is cooled down to 10 degrees C and the wafer on which the gates were evaporated is a 500µm thick GaAs wafer. The gates are 100nm "thick" and were evaporated with a rate of 2 Angstrom per second. I now will check the possibilities mentioned by you in order to get an estimation. Later on I will give a feedback.

I liked the answer offered by Daniel Poitras. I have done something similar myself in a plasma reactor. There is a way to determine the temperature at which evaporation occurs, the temperature is the "triple point' at which the solid becomes vapor without passing through the liquid phase, and this depends on the vacuum...

The deposition temperature is most likely the ambient temperature, as others have mentioned.

Yes, the temperature dots while running your boat at the same length of time and same power level required for the 100nm at 0.2nm/s but without the metal charge.

But the temp dots seem to be limited to ~38C minimum which may not be reached as you are cooling to 10C. Unless there are some that operate below room temp and are delivered with ice packs. If you can change your "cooling" temp to a level that moves your temperature range into the region of available temp dots, let's say 35-45C, and do a run as above, you should get an answer within the accuracy of the dots. I have seen 5F increments. Over this temperature range the thermal conductivity should not change much

Could you cool lower than 10C? A liquid nitrogen cold finger attached to a copper strap to your sample? Or a -140C probe cooler in the cold finger? Of course you would have to warm your sample before venting.

You are right, Brent. That could be very tricky since everything around is warmer than the 10°C. Unfortunately we have no possibility to cool the sample lower than that. Nevertheless the dots mentioned several times and they seem to be a good choice. But we are a federal agency and it would take its time to order such dots. In addition an order can be done in the beginning of the next year at the earliest. So we better use the things we already have. ;o)

Another way we're currently trying is to do stress measurements of a wafer with our Dektak before and after an evaporation of the same thickness. So maybe we can infer the deposition temperature from the stress.

Here is a paper where they evaporated a thermocouple on the surface of the substrate, measured surface temperature rise during deposition and compared to theoretical calculations.. The theory was not far off...

http://dx.doi.org/10.1116/1.1316375

We finished the stress measurements and analyzed them. Now (after theoretical considerations) we can say, that the surface temperature has to be almost exactly 20°C. And it matches all your suggestions pretty well.

Thanks a lot guys for support!

There are temperature sensitive paints and sticky dots that we have successfully used to measure temperature in such situations. The dots generally work best under high vacuum, and will not give you an exact number, but a +/-5C window is possible into the low 200C range.

We used the dots extensively while developing a metal deposition process with a polymer adhesive involved that could not withstand more than 200C (temp and vacuum resulted in a messy chamber and two pieces floating around in the chamber rather than one).

Brain is misfiring at the moment and I do not remember where I purchased the dots. Working on it though.

Omega TL-5-xxx temp labels give 5 dots in a temp range (ie 105,110,115,120,125C)

Wahl 101-8-xxx temp labels have 8 dots, but have several sizes on Kapton film.

Thanks, James!!!