Quality control of semiconductors and wafer testing

Almost invisibly, microsystems are taking over an ever larger number of tasks in automotive, communications and medical engineering as well as in many other areas. The high density of functional integration of microsystems (e.g., capturing of several physical parameters by one chip) an ever smaller component area poses new challenges in measuring engineering.

With the WAFERinspect systems, Confovis is opening new horizons for the characterization of function-critical structures by combining 3D measurements with resolutions down to the single-digit nanometer scale thanks to the “structured illumination microscopy” confocal measuring technique and the traditional 2D measuring tasks such as CD (line/space, diameter) and overlay. As a result of increasing integration or the necessary structural design for converting physical magnitudes into electrical ones the structures to be measured no longer lie on the same level. This makes the CD determination by means of optical measuring methods more difficult and the definition of the actual width of the structure a challenge. The confocal measurement by the WaferInspect measurement system captures the design of the 3D structure in its entirety so that it can be analyzed extensively.

Measurements: Most different material combinations and no artefacts on steep flanks

The benefits of the patented ”structured illumination microscopy“ (SIM) confocal measurement technique can also be seen on typical wafer materials. The user has the advantage of a robust measuring technique and in this case, in particular, the use of non-polarized light, which makes measurements of most different combinations of material possible. Besides, most patterns on wafers have angles of > 80°, which with the technique from Confovis can be measured free of artefacts.

In addition, the wavelength of the light (528 nm, green) prevents the exposure of photoresist and is also of advantage for the analysis of transparent materials. Even “buried“ structures can be visualized and so the time-consuming FIB processing with subsequent REM analysis skipped. As a result of the above-mentioned benefits, latest process technologies can be measured reliably also in series production mode.

Measurement task 3D: step height and -width
Measurement task 3D: roughness (e.g. deposited layers)
Measurement task 3D: roughness (e.g. bond pads)

Recipes without programming

The intuitive operation of the ConfoViz© software makes the teaching of complicated script languages for the generation of recipes unnecessary. The procedure is as simple as you can imagine.

At first, the user picks and teaches a series wafer. Parameters such as thickness, diameter, flat/notch are selected according to Semi standard. Next, the positions for the fine alignment of the wafer are set. Any alignment mark can be used. Besides, it is possible to align wafers that do not contain structures, for example, render them usable also with KLA files.

When the alignment is complete and the coordinates transformed by the measurement system, the layout of the wafer is taught or loaded. Different layout formats are supported, e.g., GDSII. If no layout file is available, the DIE pitch is taught. For that, the diagonals of the DIEs are measured in 3 steps. The taught layout is now used for simple navigation and recipe generation.

To generate a recipe, it is enough to move to the required measurement position, define the measuring parameters for the structure to be analyzed, test the parameters and then select the appropriate DIEs with “DIE Select” on which the measurement will be made. The principle is the same for all measurement tasks that can be realized with the WAFERnspect system. Furthermore, selected DIEs can be saved and loaded and a list on coordinates loaded for measurement.

The use of measuring recipes makes all other measurements automatic procedures without operator intervention. The different steps are executed automatically by the measurement system and at the end the measuring values are saved and may be transferred to the host system, if required. Finally, the results are displayed on the wafer layout and shown red and green as permitted by the limit values.

Supported by the Free State of Thuringia and the European Social Fund
European Social Fund