Wafer Stress Analysis Using MTI Instruments Proforma 300iSA
Wafer processing involves several stages that can lead to mechanical changes in the wafer structure. These changes, or stresses, may result in deformities, making the wafer either unusable or only marginally usable. To evaluate these stresses and determine the wafer’s quality, wafer stress measurement is essential.
The Proforma 300iSA wafer characterization tool offers a powerful solution for wafer stress analysis. It allows for the analysis of a wafer both before and after processing. By comparing these two states, the Proforma 300iSA effectively evaluates the wafer’s stress levels and mechanical alterations, providing accurate wafer stress measurements.
How Wafer Stress Measurement Works with the Proforma 300iSA
The Proforma 300iSA software expects the customer to provide the material elasticity constants and to define them in advance using the “Setup” menu of the tool. These constants are crucial for precise wafer stress measurement. In the user manual for the 300iSA (section 4.9.3), there is a screen capture of how this can be done, and there are examples of some silicon wafer values. Once these values are entered, they can then be selected in the “Analysis” menu under the “Material types” section.
NOTE: the stress analysis features will not activate until the material type is selected.
Under the “Lot Numbers” section, the before and after wafer runs need to be specified for analysis.
The tool will now display several extra tabs in addition to “Setup” and “Saved Results”, which are the default. The first new tab: “Data change” shows a delta of the two wafer runs:
Data Change – delta of two wafer runs
The next tab “Lot Summary” is similar to “Data Change” above except it displays the raw data:
The “Stress Plot” tab shows stress in two separate plots: mm Vs. mm and MPa’s Vs. mm:
The Stress Plot tab shows stress in two separate plots: mm vs. mm and MPa’s vs. mm
The “Stress Summary” tab shows the raw data used for the stress analysis:
The “Stress Summary” tab shows the raw data used for the stress analysis
In conclusion, the Proforma 300iSA software tool provides comprehensive wafer stress analysis. It not only evaluates the mechanical changes in the wafer but also exports raw data for further analysis with other plotting programs. The key to successful wafer stress measurement is the accurate input of wafer elasticity constants, which serve as the foundation for the analysis.