Specific Process Knowledge/Thin film deposition/Temescal: Difference between revisions
| Line 120: | Line 120: | ||
We are still developing the QC procedure for the Temescal (September 2018). | We are still developing the QC procedure for the Temescal (September 2018). | ||
== | ==Avoid problems with the e-beam hitting the Cu hearth== | ||
[[File:Cu hearth.jpg|400px|right|E-beam impinging on the target from the filament and a 6-pocket Temescal copper hearth and filament box enclosed in its shields (from Scotech)]] | |||
[[File:Cu hearth 2.jpg|400px|right|Empty 6-pocket Temescal copper heath (from Fil-Tech)]] | |||
At the start of the deposition and for every 100 nm, please check that the e-beam hits the target material that you would like to evaporate rather than the heath next to the pocket or the bottom of the pocket. I.e., check that the e-beam sweep has not shifted, which could happen if the filament box has been distorted by heat for example, and also check that there is enough material in the pocket, so that you do not burn a hole in the bottom of the pocket. If you burn a hole in the bottom of the pocket, cooling water may leak into the chamber and it may flood! | |||
==Thickness measurement== | |||
The machine measures the thickness of the growing film with a Quartz Crystal Microbalance or QCM. The machine calls it the Xtal (crystal). This is a very thin piece of quartz that resonates at about 5-6 MHz when a voltage is applied across it. The resonance frequency varies with the mass of the crystal, and when material is deposited on one side of it, the frequency changes. This is measured by the crystal monitor, which can then calculate the deposited thickness. | |||
The thickness calculation depends on the material density as well as other physical factors. A so-called ''tooling factor'' is used to adjust the calculation based on the geometry of the setup, since the crystal is not in the same place as the wafer holders and the actual thickness deposited on the crystal is lower than on the samples. | |||
The tooling factor is calibrated for a particular deposition rate. It may not be perfectly accurate for other deposition rates, but should easily be within the 10 % accuracy that we test for in our quality control measurements. | |||
For very thin films the thickness measurement will be less accurate than for thicker films. | |||
The machine gives a rough number for the crystal lifetime simply based on how thick a layer it calculates has been deposited on it. If many layers have been deposited and there is stress in the layers (e.g., in Cr, Ni, or Ru layers), there may be partial delamination, which can make the thickness measurement inaccurate. In this case the lifetime estimate given by the machine will be inaccurate. If you think the crystal is not measuring correctly, please let us know. We exchange the crystals usually around 20 % lifetime use. | |||
*Stuff that we say in the manual that you can see on Labadvisor | *Stuff that we say in the manual that you can see on Labadvisor | ||
*Stuff about the Hula | *Stuff about the Hula | ||
*Stuff about heating during deposition and water cooling and cooling times | *Stuff about heating during deposition and water cooling and cooling times | ||