he roughness average value Ra and the ten-point height value RZ were used to estimate the height values of the islands. To get an even film a layer thickness of at least 2 nm is necessary for plane sample and the planetary drive stage and 5 nm for highly structured samples. The WD distance can be varied between 30 and 100 mm. At lower working distance the layer growth but also the heat impact in increased. The minimum sputter current for a stable plasma for different material is also shown in Table 2.
|Material||Island radius [nm]||Ra [nm]||RZ [nm]||pAr [mbar]||WD [mm]||Current [mA]|
|Au||13.5||0.74||3.7||< 1e–2||30–100||> 15 mA|
|W||8.3||0.14||0.7||< 1e–2||30–100||> 90 mA|
|Pt||5.9||0.37||1.6||< 1e–2||30–100||> 15 mA|
|Au/Pd||5.7||0.24||1.3||< 1e–2||30–100||> 15 mA|
|Pt/Pd||5.3||0.18||0.9||< 1e–2||30–100||> 15 mA|
|Ir||4.2||0.20||0.7||< 1e–2||30–100||> 80 mA|
Table 2: Summary of the optimized sputter parameters. Material = material of sputtered target; Island radius = mean island radius in nm; Ra = roughness average in nm; RZ = ten-point height in nm; PAr = Argon pressure in mbar; WD = working distance in mm; Current = sputter current in mA.
Highly demanding samples concerning sputtering processes are lipids. They are biological and non-conductive samples which are highly temperature sensitive. The surface structure of lipids is most important for the different applications, what makes the Leica Microsystems DC magnetron sputter coater to the ideal device to sputter a thin conductive layer. In Figure 9 a completely artefact free high resolution SEM image of a highly structured pharmaceutical lipid sample is shown (10 nm Au/Pd sputtered).
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- Eisenmenger-Sittner C: Lecture notes of “Technologie Dünner Schichten”.
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- Melischnig A: DC magnetron sputtered thin films for HR-SEM.