Specific Process Knowledge/Thin film deposition/Temescal: Difference between revisions

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 [http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=429 E Beam Evaporator (Temescal) in LabManager]
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+==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.
+[[File:Sell_quartz_crystal_microbalance.jpg|100px|right|thumb|Quartz crystal microbalance with gold electrode. Image from RLC on EC21.com]]
+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.
+<br clear="all" />
+== Heating during deposition ==
+If the material you are depositing requires a lot of heat to evaporate, the substrates may get warm during the deposition.
+A temperature test of a 100 nm Al deposition at 10 Å/s showed that the back of the wafer stays below 37 <sup>o</sup>C. The same is true for 10 nm Ti/90 nm Au at 10 Å/s. In contrast, deposition of 100 nm Nb at 2 Å/s heated the substrate above 104 <sup>o</sup>C (but less than 110 <sup>o</sup>C). Deposition of 60 nm W at about 1 Å/s heated the substrate to above 110 <sup>o</sup>C.
+You may be able to get some idea of how much the substrate will be heated by looking at the temperature required to give a reasonable vapor pressure for the evaporation. You can find a collection of Honig's vapor pressure curves at the bottom of [https://old.mcallister.com/vacuum.html this page (external link)].
+Please ask us if you need to test the heating of the substrates before making a deposition with the metal you need (contact thinfilm@danchip.dtu.dk).
+==The e-beam and the Cu hearth==
+[[File:Cu hearth.jpg|200px|left|thumb|E-beam impinging on the target from the filament and a 6-pocket Temescal copper hearth and filament assembly enclosed by shields (from Scotech)]]
+[[File:Cu hearth 2.jpg|100px|right|thumb|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 assembly 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!
+<br clear="all" />
 == Process information ==
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 We are still developing the QC procedure for the Temescal (September 2018).
-==The e-beam and the Cu hearth==
-[[File:Cu hearth.jpg|200px|left|thumb|E-beam impinging on the target from the filament and a 6-pocket Temescal copper hearth and filament assembly enclosed by shields (from Scotech)]]
-[[File:Cu hearth 2.jpg|100px|right|thumb|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 assembly 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!
-<br clear="all" />
-==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.
-[[File:Sell_quartz_crystal_microbalance.jpg|100px|right|thumb|Quartz crystal microbalance with gold electrode. Image from RLC on EC21.com]]
-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.
-<br clear="all" />
-== Heating during deposition ==
-If the material you are depositing requires a lot of heat to evaporate, the substrates may get warm during the deposition.
-A temperature test of a 100 nm Al deposition at 10 Å/s showed that the back of the wafer stays below 37 <sup>o</sup>C. The same is true for 10 nm Ti/90 nm Au at 10 Å/s. In contrast, deposition of 100 nm Nb at 2 Å/s heated the substrate above 104 <sup>o</sup>C (but less than 110 <sup>o</sup>C). Deposition of 60 nm W at about 1 Å/s heated the substrate to above 110 <sup>o</sup>C.
-You may be able to get some idea of how much the substrate will be heated by looking at the temperature required to give a reasonable vapor pressure for the evaporation. You can find a collection of Honig's vapor pressure curves at the bottom of [https://old.mcallister.com/vacuum.html this page (external link)].
-Please ask us if you need to test the heating of the substrates before making a deposition with the metal you need (contact thinfilm@danchip.dtu.dk).