Key Questions to Ask When Ordering sio2 sputtering

The life of a sputter target is typically quantified in terms of units of power and time, like kilowatt/hours. For a target being sputtered at 500 watts for a total duty cycle of 100 hours that&#;s 50 kilowatt/hours. Target life is also a function of the sputter yield of the material or how many target atoms are ejected for each gas ion (typically argon) that strikes the surface. For example when an argon ion with a mass of 39.948, hits a light material, like carbon, with an atomic mass of 12.01, about 3 carbon atoms are ejected. For materials like platinum with an atomic mass of 195.09, nearly 5 argon ions have to strike the target to get one platinum atom out (Ref 1).

Other factors that affect sputter yield include the bias voltage used to accelerate the argon ion to the target surface and the incident angle of the collision. In addition, there are big differences in sputter yield for metals verses oxides. Typically oxides will last many more kilowatt/hours than metals like aluminum.

One of our resident thin film deposition experts, Rob Belan, recommends that a target be replaced when the trench depth of the race track is ¾ of the total target thickness. For a ¼&#; thick target there will be 0.062&#; of material remaining at the bottom of the trench. He adds that if you are particularly careful you may be able to sputter the trench to a thickness of 0.031&#;, but beyond that you are risking a complete burn through.

A handy online calculator for sputter yield can be found at TU Wein&#;s Institute fur Angewandte Physik. I&#;m not sure how accurate it is, but it does list out several single element metals and their yields:

https://www.iap.tuwien.ac.at/www/surface/sputteryield

For a list of sputter yields using other ions, such as xenon and neon, there is an expansive data base on the web site of the National Physical Laboratory. Their data base also includes sputter yields at various powers (Ref 2).

So to determine when it is time to change out a sputter target you will need to have a depth gauge, either digital or dial. Check the depth of the trench in the race track after every deposition until you get a feel for the number of kilowatt/hours it takes to thin the target out to 25% of its original thickness (Ref 3). For those looking for an in-situ, real time method for measuring target thickness during sputtering, check out the publication from Alex Leybovich of TOSOH SMD who used ultrasonic time of flight measurements to monitor the health of sputter targets and target bonding during thin film depositions (Ref 4).

References:

1. Argonne National Laboratory, &#;Noble Gas Sputtering Calculations using TRIM,&#; https://www.osti.gov/biblio/
2. National Physical Laboratory of the UK, http://www.npl.co.uk/science-technology/surface-and-nanoanalysis/services/sputter-yield-values
3. MSC Direct, https://www.mscdirect.com/browse/Measuring-Inspecting/Dimensional-Measuring-Tools/Depth-Gages/?navid=&cid=ppc-bing-New%20-%20Measuring%20%26%20Inspecting%20-%20Product%20-%20PPC%20-%20Exact_I4PUCfCI_depth%20gauge_be__c_&mkwid=I4PUCfCI|dc&pcrid=&utm_source=bing&utm_medium=cpc&utm_campaign=New%20-%20Measuring%20%26%20Inspecting%20-%20Product%20-%20PPC%20-%20Exact&utm_term=depth%20gauge&utm_content=Depth%20Gages
4. In-situ real time sputtering source health monitoring using ultrasonics, Alex Leybovich, TOSOH SMD, Grove City, OH, , https://www.sciencedirect.com/science/article/pii/S?via%3Dihub

If you want to learn more, please visit our website Acetron.

Category: Deposition Equipment

Sub-Category: Sputtering Targets

Related Topics: Sputtering, Process

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A thin film is a metal or metal-ceramic layer of material that is deposited, atom-by-atom, on the surface of a substrate. The thin film forms a bonded layer that changes the part's appearance, durability or function. 

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Thin films don't affect dimensional tolerance or the substrate's desired textures. They are used to improve a product's color, light reflection or refraction, hardness or electrical insulation and conductance.

Thin film thickness ranges from fractions of a nanometer (1 nm = 0. m = 10 angstroms) to several micrometers (1 μm =  0. m). For reference, the diameter of a human hair ranges from 17-181 μm. A strand of spider web silk has a width of 3 to 8 μm.

The controlled synthesis of materials as thin films (a process referred to as "deposition") is a crucial need in many industries. For example, architectural glass, displays, touch panels and solar cells all contain thin films. A familiar example is a mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface.

Two basic methods are used to create thin films: 1) Chemical deposition, where a fluid precursor undergoes a chemical change at a solid surface and 2) Physical deposition, which uses mechanical, electromechanical or thermodynamic means.

A type of physical deposition is physical vapor deposition (PVD), which occurs in a vacuum. Sputtering is a type of PVD.

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