Specific Process Knowledge/Characterization/Stress measurement/Stress origins: Difference between revisions
new page about stress origins more systematic than before |
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This means the stress depends both on inherent material properties and on deposition conditions. | This means the stress depends both on inherent material properties and on deposition conditions. | ||
Examples of materials with comparatively high atomic mobility include Au, Cu, and Ag. | Examples of materials with comparatively high atomic mobility include Au, Cu, and Ag. They will tend to exhibit more compressive stress. | ||
Examples of materials with comparatively low atomic mobility include Cr | Examples of materials with comparatively low atomic mobility include Cr and Ni - and Pt and Ru??. They will tend to exhibit more tensile stress. | ||
The differences in stress in these materials is definitely something we can recognize from first-hand experience at Nanolab, as Cr and Ni layers in combination with other metal layers in the PVD equipment cause a lot of flaking. | |||
You can increase the atomic mobility (and reduce the tensile stress) by increasing the temperature, and in sputtering you can decrease the pressure and add a bias to accelerate the sputtered atoms towards the growing film. In evaporation you could potentially add energy to the growing film by using ion bombardment apart from increased deposition temperature. | You can increase the atomic mobility (and reduce the tensile stress) by increasing the temperature, and in sputtering you can decrease the pressure and add a bias to accelerate the sputtered atoms towards the growing film. In evaporation you could potentially add energy to the growing film by using ion bombardment apart from increased deposition temperature. | ||
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In addition, all other things being equal the tensile stress decreases/compressive stress increases with smaller grain size. The grain size tends to increase for thicker layers, meaning that the tensile stress will tend to increase when a thicker layer is grown. This is apparently especially true for the many metals with low mobility that tend to form columnar grains during thin film growth. | In addition, all other things being equal the tensile stress decreases/compressive stress increases with smaller grain size. The grain size tends to increase for thicker layers, meaning that the tensile stress will tend to increase when a thicker layer is grown. This is apparently especially true for the many metals with low mobility that tend to form columnar grains during thin film growth. | ||
==Models of thin film growth and stress== | |||
These observations are based on a model of thin film stress developed by E. Chason and collaborators at Brown university. You can read about it in their many publications including [https://pubs.aip.org/aip/jap/article/119/19/191101/1032395/Tutorial-Understanding-residual-stress-in this tutorial]. | These observations are based on a model of thin film stress developed by E. Chason and collaborators at Brown university. You can read about it in their many publications including [https://pubs.aip.org/aip/jap/article/119/19/191101/1032395/Tutorial-Understanding-residual-stress-in this tutorial]. | ||