Wafer Stress Analysis Using MTI Instruments Proforma 300iSA
Wafer processing involves several stages that may translate into mechanical alterations. Sometimes these alterations can cause deformities that render the wafer either unusable or that put it marginally close to not being usable. To determine this, stress analysis can be used.
The Proforma 300iSA wafer characterization tool provides a software capability in which a wafer can be analyzed prior to processing and then after processing. The tool then evaluates how the wafer changed and hence, provides the resulting stress analysis.
The software expects the customer to provide the material elasticity constants and to define them in advance using the “Setup” menu of the tool. In the 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:
Lot Summary Tab
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 software tool provides wafer stress analysis, and it can export raw data that can be used by other plotting programs for further pre and post processing evaluations. The key requirement for this analysis being the availability of the wafer elasticity constants.