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
Goto Acetron to know more.
Category: Deposition Equipment
Sub-Category: Sputtering Targets
Related Topics: Sputtering, Process
Intended application: Selecting the right target material first requires an in-depth understanding of the application requirements of the film. Different applications (e.g., photovoltaics, semiconductors, decorative coatings) have different requirements for the electrical, optical and mechanical properties of thin films. Therefore, defining the application purpose and performance requirements of the film is the first step in target selection.
Evaluate target properties: After determining the application needs of the film, the target needs to be selected based on its purity, compositional homogeneity, size and shape. For example, for highly transparent optical films, it is particularly important to select targets with uniform composition and high purity. For large-area coatings, target size and shape uniformity are critical to improving deposition efficiency and film uniformity.
For more information, please visit Rotary Metal Sputtering Targets.
Consider cost-effectiveness: When selecting targets, there is also a balance of cost-effectiveness to consider. While high-quality targets may cost more, they may be more economical in the long run by providing superior film performance and longer service life.
Equipment and target compatibility: Ensure that the specification, size and shape of the target purchased matches the equipment requirements, and that the physical and chemical properties of the selected material are suitable for the required application and equipment to ensure that it can be loaded and used correctly.
Sputtering method: For reactive sputtering or the preparation of thin films of specific compounds, targets matching the gases used in the sputtering process are required. High-frequency sputtering or magnetron sputtering are generally more suitable for using pure, homogeneous targets for stable deposition. Some sputtering methods may require targets of special shapes, sizes, or structures, such as magnetron sputtering, which improves target utilization. The choice of sputtering method needs to take into account the physical and chemical properties of the target to ensure that it is compatible with the process and that the desired film properties are obtained.
Conductivity: The higher the purity of the target, the higher the conductivity. In semiconductor and conductive film applications, trace impurities can significantly affect the conductivity of the material. High purity targets reduce these impurities and provide higher conductivity, which is critical for high performance electronics.
Specialized resources and guidance are critical to selecting the right target, and by partnering with AEM, a supplier of specialized sputtering targets, we will utilize our years of technical knowledge and experience to help you more accurately select the target that meets your needs.
Are you interested in learning more about rotary sputter target? Contact us today to secure an expert consultation!