08/22/2017

Silicon goes 3D - TSVs and Trenches as the key technology of a new generation of semiconductors

Most of the pressure comes from the cost side as usual. But there are many reasons for developments in the area of ​​3D IC. Moore’s Law goes on for a while, but is limited, more than Moore is announced. The demand for smaller component sizes is unbroken. There are also problems with the bandwidth of the circuits, the thermal management and the signal paths. More functions of a component move from the PCB to the IC, which is to the wafer level. MEMS has made it, 3D structures are now feasible. Key technology for these are deep trenches and TSVs (Through Silicon Vias), contacting through the various levels of components. From outside is too big, too slow, too complicated. Of course, contact surfaces of different sizes meet here. Interposers are a solution which, like with gear units, implements support, packed with TSVs.

In combination with the white light interferometers WLI PL and WLI FL, the established devices of the MicroProf® series offer optical and non-contact innovative solutions in the field of TSV for production, research and development where other processes reach their limits. Etch trenches produced by plasma dicing, for example, have depths of 50 to 200 µm, which are far beyond the reach of AFM or profilometer tips. Due to their aperture, many optical methods such as confocal microscopy are not suitable for this measurement because light cannot get back into the sensor from the bottom of the trenches due to the shadowing on the side walls. In addition, the etching process leads to a roughening of the surface in the etching trenches and thus to high differences in the reflectivity between the substrate surface and the bottom of the trenches, which can lead to measurement problems. Thanks to its parallel illumination, the WLI PL is excellently suited for the measurement of such deep trenches with a high aspect ratio, since a large proportion of the light reaches the bottom of the etching structure and the depth can thus be measured. Depending on the surface properties, structures with minimum widths from 2 to 3 µm and aspect ratios of up to 50:1 (depth to width) can be captured. The use of a special measuring mode enables the measurement in two measuring steps. With a shorter measuring time, the substrate surface and the bottom of the structures are recorded in such a way that an optimal adaptation of the measuring parameters to the different surface conditions is achieved.

Another problem for measurement technology is often the small lateral dimension of the structures, since the optical resolution of the methods is usually not sufficient to dissolve them. For example, trenches can have trench widths of less than 1 µm. The WLI FL uses a special algorithm to determine the depth of etching structures with widths down to 0.7 µm, which is already below the optical resolution limit of the measurement method. In this case, the aspect ratio can be up to 3:1. This opens up dimensions that have never before been reached in this way. With this method, all currently used variants of TSVs can be measured, including vias with diameters of less than one micrometer that are no longer optically detectable. It is remarkable that the individual via is actually measured and not a statistical effect.

All devices of the MicroProf® series offer a complete analysis of topography and TTV. Depending on the individual requirements, it is possible to choose between semi-automatic or fully automatic EFEM (equipment front end module), which also supports the processing of thin wafers. Due to the multi-sensor concept pursued, the devices can be retrofitted with different sensors, e. g. IR sensors for the determination of film thickness, at any time. Thus, nothing stands in the way of a combination of different measuring tasks in one device. Use these advantages for yourself.

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.