01/30/2018

Metrology Know-How: Measuring solutions for all wafer applications

Semiconductors and MEMS are becoming more and more miniaturized. This increases the demands on the metrology used to control the quality of the wafers in the processes.

The production is carried out on wafers with 150, 200 or 300 mm diameter. The wafers (e.g. silicon, sapphire or glass) are given an almost perfectly flat surface by various etching, grinding and polishing processes. A number of global and local wafer parameters are available to characterize wafer topography and thickness. These include flatness, roughness, waviness, TTV (total thickness variation), Bow, Warp, Sori, Taper, LTIR, LTV, LFPD and many more used for process monitoring and quality control. The graphical visualization of the local wafer parameters allows the user to identify regions on the wafer that are outside the specifications. The thickness variations are in the range of a few µm. On these wafers the components and structures are produced by a repeated sequence of structuring, etching and deposition processes. Each of these process steps affects the TTV as well. TTV is therefore the most important parameter to be measured together with the surface topography.

The MicroProf® surface measuring tool with TTV setup developed for this application measures a complete wafer surface quickly and determines TTV, flatness or waviness with very high accuracy and reproducibility. With a maximum sample diameter of 300 mm, the system achieves a resolution of less than 10 nm for thickness measurement. At the same time, roughness and topography on both sides of the sample can be measured with high resolution. A special sample holder picks up the component in such a way that it only sits on the outer edge. The sensors are arranged above and below the sample. The lower sensor remains fixed and is automatically at the correct working distance due to the sample holder. The upper sensor is approached via the z-axis in the same way as the standard tools. The variation of the absolute thickness can be measured over the full sample area. The bow of the sample and the height variation of the scan table do not affect this, because a differential measurement is carried out between the fixed sensors.

The MicroProf® is equipped with optical multi-sensor measuring technology and optional atomic force microscopy. In addition to flatness and TTV measurement, the measuring system also enables the inspection of the smallest structures on the wafer. In addition to doping, grinding or etching processes, coatings whose thickness has to be measured are also applied during the wafer production. Optical film thickness sensors, which can be integrated into the MicroProf®, are suitable for solving this measuring task - even retrospectively as the measuring task occurs.

The following metrology tasks are possible: wafer thickness, TTV, Bow, Warp, 3D topography, profiles, parallelism, flatness, roughness, waviness, layer thickness, step heights and widths, pitch, bumps, contour, edge structures, vias, trenches, geometry, slope angle, coplanarity, overlay, critical dimensions and defect inspection.

FRT also offers the right solution where multi-sensor systems alone do not help: hybrid metrology. Due to our multi-sensor concept, the 3D surface measuring tools of the established MicroProf® series can be equipped with point and area sensors for topography measurement as well as with film thickness sensors. This makes it possible to solve a measuring task with different sensors by carrying out a measurement with each sensor and combining the different results. The decisive step is that the measuring tool or the recipe used knows the complete measuring task and executes it completely. This means that not only the measurements with all the necessary sensors are carried out fully automatically, but the software also acquires the various measurement results and calculates the desired parameters from them.

Whether you need a separate non-contact wafer measuring tool for your laboratory or a fully integrated tool for your production department in the front-end or back-end, FRT offers the appropriate standard and special solutions to improve your production efficiency. The degree of automation reaches from manually operated measuring tools like the MicroProf® 300, which automatically perform predefined programs, to fully automated wafer handling including automatic pre- and fine alignment in the MicroProf® MHU. In addition, the tool can be equipped with powerful image acquisition hardware for intelligent pattern recognition. FRT systems can be configured to handle SEMI compliant and non-standard wafers often used in the MEMS industry. FRT also offers a variety of solutions for the growing market segment of 3D IC manufacturing from thin film measurement over trench measurement to inspection of critical dimensions in the whole manufacturing process.

For semiconductor applications FRT offers its own class of tools for clean room manufacturing: the MFE series, with the MicroProf® FE and MicroProf® FS. MFE measuring tools can process 200 mm and 300 mm wafers in one system (FOUP, SMIF and open wafer cassettes possible). The included SEMI-compliant software package enables interactive or automated use, easy creation of measurement and evaluation recipes and integration into existing production control systems via the SEMI-compliant SECS/GEM interface. This interface transfers measurement information to the next step in the production line.

Whether laboratory, development, quality assurance or production - FRT offers the right measurement technology for your application. Do not hesitate to contact us if you have any questions. Our experts will be glad to help you solve your measurement tasks by creating the best possible system configuration for you. In our opinion, a complete solution consists not only of hardware and software development but also of additional support and effective technical customer service. FRT provides on-site support through a global network of subsidiaries and distributors. FRT Remote Support enables our experts to support customers worldwide.