A "Check" link appears at the top of each run description page. By selecting that link, you invoke the process rule checker and get a page reporting the results of a simulation and analysis of the run's processing sequence.

The report begins with a list of warnings about suspicious sequence characteristics. In particular, the warnings may include reports of incompatible equipment, missing clean or photoresist strip steps, steps with temperatures too high for the materials present on the wafers, or other conditions that probably indicate sequence errors. Please note that the a processing sequence may contain errors that the process rule checker does not report.

In addition to the list of warnings, the process rule checker produces a schematic diagram of the cross sections that may be present on the wafers after each processing step. The diagrams show layers of materials and estimates of thickness of each layer.

The example diagram above appears in a sequence for a sequence that deposits 1 µm of silicon dioxide and then performs a photolithography step. If your browser includes and enables Javascript, you can get more information about the layers by moving your cursor over them. When the cursor is over a layer a short description should appear on your browser's status line (usually at the bottom of the window). For layers of materials, like the ones that appear in the diagram above, the short description gives the step number that created the layer, the thickness, and the material.

The diagrams occasionally display layers that don't really correspond to materials. If the next processing step is a 1 µm silicon dioxide etch, for example, the simulator will list the following step description:

There are several features to note about the description above. First, observe the "Selectivity" table. This shows the selectivity information that is available for this particular etch process. The "Calculated depths" table to the right of the "Selectivity" box shows the depths of different materials that the simulator predicts can be removed by this processing step. In this particular case, the selectivity table tells us that this etch should remove half as much photoresist as silicon dioxide. The depth of silicon dioxide has been set to 1.1 µm, so the calculated depth for photoresist is .55 µm.

Looking at the cross section diagram appearing after the etch step, we find that the thickness of Shipley 1813 photoresist has been decreased by .55 µm. The 1.0 µm of silicon dioxide that was exposed has been removed, but this particular etch could have removed an additional 0.1µm of silicon dioxide. If the process library included information about the selectivity of this particular etch process with respect to silicon, then the etch would have removed some of the underlying silicon substrate. Because the selectivity information here is incomplete, though, the unresolved part of the etch is reported in the diagram in the layer labeled "Etch 3". The number 3 refers to the step number in this run's processing sequence. Moving the mouse over the etch layer shows the remaining calculated depths for the etch. Users should pay careful attention to these etch layers to make sure that they follow expectations.

Finally, there are some processes offered by the MEMS Exchange that the simulator does not understand. Bonding processes, for example, make the simulator cry uncle. Rather than simply ignore these processes, however, the simulator will display an additional layer labeled with the step number. These extra layers hinder the subsequent simulation of etches and depositions, but they serve to alert the user to processes that may need extra consideration.