EQUIPMENT & ACCESSORIES CATALOG EDITION IV SPUTTER COATERS, SEM/TEM CARBON COATERS


Techniques and Applications Rates of Sputtering


A question regularly asked is what difference is there in sputtering rates for each of the target materials. The following list gives the variance of the materials in relation to gold, assuming gold to be: 1, it is impossible to give actual coating rates as this varies with sputtering conditions.


Au Ag Co Cr


Cu Fe


Mo Ni


Pd Pt


Ta W


Gold


Silver Cobolt


Chromium Copper Iron


Molybdenum Nickel


Palladium Platinum Tantalum Tungsten


1.0 1.2 0.5 0.5 0.7 0.5 0.3 0.5


0.85 0.6 0.2 0.2


Figure 4 - Sputtering Rates for the EMS 7620 10


0 1 2 3 4 5 6 7 8 9


0 5 10 15 Plasma current (mA)


gold Au/Pd Platinum Nickel Silver Copper


20 25 Thickness of Coating


Experiments using interferometric techniques have shown that the thickness of Au/Pd coating sputtered in argon gas can be calculated at 2.5KV according to:


Th = 7.5 I t (angstroms) (V = 2.5KV, target to specimen distance = 50mm) t = time in minutes I = current in mA


Th = thickness in angstroms


Average coating times will be of the order of 2 -3 minutes using V = 2.5KV and I = 20 mA Platinum targets when fitted will give approximately half the deposition rate.


General Points for Improving Performance


1. Cleanliness, the work chamber must be kept clean! We advise that a separate carbon coater be used in applications where the maximum performance of the sputter coater is required • Clean the glass chamber with hot soapy water and dry thoroughly, solvents can be used but we have found this unnecessary and having greater danger to health and safety. If the deposit is stubborn, use a kitchen scouring pad such as the green Scotch Bright variety.


• Use Isopropyl alcohol on metal surfaces, not acetone which has greater danger to health and safety.It will also take longer to out gas and reduce the vacuum performance.


2. Vacuum, Never leave the chamber under vacuum without isolating the roughing pump from the coater, this is usually done with a manual valve (Quorum high vacuum sputter coaters have useful “pump hold” facility that allows the vacuum chamber to be held under vacuum when the instrument is not in use). Failure to do so will increase the risk of suck back of hydrocarbons (pump oil) in to the sputter chamber and increase contamination. • Always ensure the system is dry and pumping to its correct vacuum level before working with samples, failure to do so will result in poor sputter rate and contamination.


• Ballast rotary pumps on a regular basis and ensure they are serviced at regular intervals.


TEM image of 2nm sputtered platinum film


3. Sputter gas, Always use high purity argon gas of the grade known as “White spot” this will ensure fast sputter rate and good pump down time.


4. Rotary planetary specimen stages are essential for ensuring even coatings on specimens with irregular surfaces.


13


Carbon-coated Formvar film. Coated with 2nm of platinum (Pt) using the EMS 7640 Sputter Coater. Settings: 800V 10mA using argon gas and vacuum of 0.004 bar. Image courtesy of Topcon Electron Beam Services Corporation.


Platinum coating using SC7640


Borosilicate glass with surface imperfections (dark spots). Coated with 3nm of platinum (Pt) using the EMS 7640 Sputter Coater. Settings: 800V 12mA using argon gas and vacuum of 0.004 bar. Image provided by Gala Instrumente GmbH.


Gold/palladium coating of 6" wafer


This wafer was wafer-coated with 3nm of gold/palladium (Au/Pd) using the EMS 7640 Sputter Coater. Settings: 800V 12mA using argon gas and vacuum of 0.004 bar. Further tests revealed that coating was of an even thickness right to the edge of the 6" wafer. Work was done by Dr Jost Gabler of Gala Instrumente GmbH.


Rate (nm/min)


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