Metrology for MEMS – more than just a trend

The complexity of integrated circuits is increasing significantly – and is an amazing innovation factor. At the same time, this development presents a considerable challenge for the industry in various areas. It requires constantly changing demands on production parameters, process control and quality assurance. Only variable and expandable systems are suitable for this purpose – such as optical surface measurement in the form of multi-sensor devices.

Microsystems technology is present in all areas and has become an omnipresent cross-sectional technology. For example, smartphones can be equipped with wafer-level microphones, RF filters, CMOS image sensors or GPS and MEMS acceleration sensors. Microsystems technology can also be found in health care applications, sensors in digital cameras, gyroscopes for stabilization or control. It offers more function in the same space and makes mobile applications possible, also thanks to the lower energy consumption.

Especially in the MEMS industry, a bundle of measurement tasks has to be processed due to the high product complexity. It is commonly used to determine roughness, contour, topography and film thickness, as well as special tasks such as the measurement of membrane bow, stress measurement on coated wafers or the parallelism measurement of periodic structures.

Manufacturers in the field of microsystems technology are already having extremely high demands on the pre-product wafer. Small deviations in the manufacturing tolerances influence the quality in the downstream, cost-intensive process steps and can lead to losses in yield as well as reduced efficiency and reliability of the end products. Therefore, the process tolerances must be monitored continuously during production. Many manufacturers rely on high-quality, non-contact and non-destructive multi-sensor measuring technology from FRT for this task. The devices of our MicroProf® series combine several measuring tasks in one system, offer a significantly higher resolution than conventional capacitive measuring technology and operate according to the standards of the international industry association SEMI. The determination of the parameters in one fully automatic multi-sensor device saves investment, installation space and time for process control.

The starting product in microsystems technology manufacturing is the so-called ingot, a block made of silicon or a compound material such as sapphire or gallium arsenide (GaAs), for example, from which individual raw wafers are sawn. The width and depth of the saw marks must be monitored. Optical multi-sensor measuring systems can not only visualize the saw contour three-dimensionally, but also characterize it quantitatively metrologically over several areas. This enables better control of the sawing process and the monitoring of tool wear.

Metrological measurements are also necessary for further processing steps (grinding, lapping and polishing) of the raw wafers. It is essential to ensure that the thickness is maintained over the entire wafer in the range of a few micrometers and that roughness parameters are at the specified value. Highest precision in the nanometer range is in demand for thin wafers for the production of 3D IC assemblies that are becoming increasingly popular on the market. Key technology for these are deep trenches and TSV (Through Silicon Via), contacting through the different levels of the components.

Also, certain measuring tasks cannot be solved by one sensor alone, since the desired parameters are not directly accessible. The multi-sensor arrangement alone does not help here as well. But FRT also offers the right solution for this: hybrid metrology. Due to the multi-sensor concept we pursue, the 3D surface measuring devices of the proven MicroProf® series can be equipped with point and field-of-view sensors for topography measurement as well as with film thickness sensors. This makes it possible to solve a measuring task with different sensors by performing a measurement with each sensor and combining the different results. The decisive step is now that the measuring instrument, or rather the recipe used, knows the complete measuring task and implements it completely. This means that not only the measurements with all necessary sensors are carried out automatically, but the software also records the different measurement results and calculates the desired parameters from them.

By adding the thermal unit to the MicroProf®, you can perform measurements of the surface topography of components under controlled thermal load. This is essential because changes in the components due to thermal stress can lead to functional faults or even breakdowns. Fully automatic measurements of the surface topography at different temperatures as well as dwell times at constant temperatures are fully adjustable. The thermal unit is available as an extension for all FRT measuring instruments and is mounted as a separate module like a normal sample holder.

FRT offers both manual and fully integrated measurement solutions with robotic wafer handling, recipe creation, automatic evaluation of measurement data and a SEMI-compliant SECS/GEM interface for connection to the Fab Host. Thanks to the modular multi-sensor concept, the devices can also keep up with ambitious roadmaps of the industry.

We certainly have a solution for your specific task. Do not hesitate to contact us if you have any questions. Our experts will be glad to take care of your request and develop individual solutions for you.

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