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 of 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.
Messaufgabe 3D: Stufenhöhe
Messaufgabe 3D: Rauheit (Bondpads oder abgeschiedene Schichten)
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 ConfoVIZ© measurement and analysis software allows for automatic pattern recognition as well as the measurement of vias, slots, overlays and other surface characteristics. In addition, the software also supports wafer map analysis which can be used to automatically measure dies on a wafer. Reproducibility and independence of the measurement results from the user can be achieved thanks to the automatic measurement algorithms. You can see at a glance whether process-related parameters on the relevant dies are within the tolerances. The results are statistically signifi cant thanks to the high number of measurements.
Automated measurements for reliable measurement processes
Operating the ConfoViz© software is intuitive, measuring with the ConfoViz© software can be pre-programmed and proceeds quickly. The user can position the measurement device close to recurring structures on a base substrate level, set the area to be measured and save this as a measurement plan. All parameters such as lighting periods, etc. are adopted by the system automatically and stored under the product number. For a repeat measurement, an untrained operator can call up a previously stored measurement plan and the measurements are repeated automatically. This results in the following advantages:
- Qualified personnel with metrological knowledge is only required to configure the measurement and evaluation once; after that, the company can carry out its own inspections.
- Follow-up measurements and evaluations are performed without any influence from the operator.
- Time-consuming programming of measurement plans becomes unnecessary.
- Downtime on production machines are reduced thanks to the high measurement speed.
- Because two measurement techniques are united in one device, only one operating interface must be instructed.
Characteristics tests made easy
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.
To arrange the data in a way that is more straightforward, the tolerance utilisation on test items is classified and depicted using a traffic light approach. This way, it is obvious whether items are within the tolerances and/or within the control limits or should be discarded at a glance. For industrial applications in which other evaluation tools are to be used as well, the ConfoViz© software provides diverse output formats such as PIF, G3D, STL and ASCII to name a few. With these, customers can continue to use the evaluation tools they are trained to use and have used before. Watch the video on the right to see the measurement system in action. >>