[[microscope:sem:coating]]
 
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microscope:sem:coating [2013/07/11 05:15] – mcmastermicroscope:sem:coating [2013/07/12 04:07] – mcmaster
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 Ways to deposit material: Ways to deposit material:
   * Physical vapor deposition (PVD)   * Physical vapor deposition (PVD)
-    * Sputtering: electric field rips ion off of sacrificial electrode ("target") and deposits them on sample in plasma cloud+    * Sputtering: electric charges electrons which them bumps material off of sacrificial electrode ("target") and deposits them on sample in plasma cloud
     * Evaporation: material to deposit is heated to give off metal in gas form that condenses on the sample surface     * Evaporation: material to deposit is heated to give off metal in gas form that condenses on the sample surface
   * Chemical vapor deposition (CVD): generally not used for SEM sample prep?   * Chemical vapor deposition (CVD): generally not used for SEM sample prep?
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 ====== Sputtering ====== ====== Sputtering ======
  
-"The most common arrangement for a D.C. (Direct Current) sputter coater is to make the negative cathode the target material to be sputtered typically gold, platinium or with high vacuum sputter coaters, metals such as chromium and iridium)" [Principles]+"The most common arrangement for a D.C. (Direct Current) sputter coater is to make the negative cathode the target material to be sputtered typically gold, platinium or with high vacuum sputter coaters, metals such as chromium and iridium)" [Principles]  
  
 +"DC sputtering is common for conductors.  RF sputtering can be used for insulators too"
  
 +A magnet is often placed around the target: "Lorenz forces force electrons in the plasma into a helical path. The longer path results in more collisions with gas atoms (and thus more ions) [SJSU]
 +
 +Usually DC but sometimes RF power.  [SJSU] cites 13.5 MHz
 +
 +Sputtering should be done in pure argon, not air.  "Always use high purity argon gas of the grade known as 'White spot' this will ensure fast sputter rate and good pump down time" [Principles]
 +
 +"Average coating times will be of the order of 2 -3 minutes using V = 2.5KV and I = 20 mA" [Principles]
 +
 +"Step coverage is a measure of how uniform thickness is over the topography of the surface" [SJSU].  Higher pressure gives a more even surface.  Having a larger target also helps to create a more even film [Lab 7]
 +
 +Putting a negative bias on substrate can produce better films [Lab 7]
 +
 +Distance between target and substrate is typically a few cm [Techniques]
 +
 +Optimal temperature varies on a few parameter but 100 mTorr is a good rule of thumb [Techniques, Lab 7].  [SJSU] says its closer to 110 mTorr for Ar
 +
 +Reactive sputtering can deposit non-metallic compounds [SJSU] """
 +  * Oxides from O2 gas: Al2O3, Ta2O5, SiO2
 +  * Nitirdes from N2 or NH3: TaN, TiN, Si3N4
 +  * Carbides from CH3 or CH4: TiC, WC, SiC
 +  * Also combinations such as oxycarbides, oxynitrides
 +"""
 ===== Sample machine spec ===== ===== Sample machine spec =====
  
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 Material is typically evaporated in either a "boat" or a filament.   Material is typically evaporated in either a "boat" or a filament.  
 +
 +===== Carbon =====
 +
 +Can be deposited by quickly vaporizing a few strands.  This is done at about 200 mTorr.  Going lower to 150 mTorr with a higher current burst can be more gentle on samples but may not give as good of a surface [EFFA]
 +
  
 ===== Boat ===== ===== Boat =====
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 ===== Filament ===== ===== Filament =====
  
-Filaments are similar except that the material is placed inside a spiral.  This makes placing the sample a little easier as the evaporation can drift downward.+Filaments are similar except that the material is placed inside a spiral.  This makes placing the sample a little easier as the evaporation can drift downward.   
 + 
 +"Filaments work well with materials that melt, wet the filament, and then evaporate uniformly in all directions.  With materials that sublime you get shadowing from the wire"
  
  
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 Factors in choosing a coating material: Factors in choosing a coating material:
 +  * What type of detector are you going to use?  Secondary emission and other properties vary from material to material
   * Do you have equipment to sufficiently heat it?   * Do you have equipment to sufficiently heat it?
   * Do you have equipment to achieve the necessary vacuum?   * Do you have equipment to achieve the necessary vacuum?
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 Probably not usable due to rapid surface oxidation Probably not usable due to rapid surface oxidation
  
 +===== Chrome =====
 +
 +Less BSE than other materials but must be stored under vacuum to avoid corrosion and requires high vacuum to sputter [Principles]
 +
 +
 +===== Iridium =====
 +
 +Requires high vacuum to sputter [Principles]
  
 ====== References ====== ====== References ======
  
-Sputter Coater Principles ("Principles"): http://www.emsdiasum.com/microscopy/technical/datasheet/sputter_coating.aspx+  * Sputter Coater Principles ("Principles"): http://www.emsdiasum.com/microscopy/technical/datasheet/sputter_coating.aspx 
 +  * Lab 7: http://users.wfu.edu/ucerkb/Nan242/L07-Sputtering_a.pdf 
 +  * Sputter Deposition Techniques ("Techniques"): http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/sputtertech.html 
 +  * SJSU: http://www.engr.sjsu.edu/sgleixner/mate129/Continuing%20Ed/Deposition/sputtering.pdf 
 +  * EFFA Carbon Coater Instructions ("EFFA"): http://micron.ucr.edu/public/carboninst.pdf
  
 
 
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