Towards In-Line Metrology Process Control For 3D Integration Technology

The aim of WP3 is to use a series of artefacts produced in WP1 and WP2 to demonstrate how industrial standard artefacts should be certified and tested to be traceable to the International System; this is a critical requirement in order to ensure reliable and transferable calibrations for Fabs. Good practice guides will then be produced for providing recommendations to standardisation bodies as well as for the semiconductor industry. In addition, WP3 will explore the application of the GUM to conformity assessment for the semiconductor industry. Indeed, in semiconductor manufacturing, the performance of metrology equipment directly impacts yield. Fabs and equipment suppliers depend on calibration standards to ensure that their metrology results are within tolerances and to maintain, for example, their ISO quality certifications. Calibration standards are used for making and maintaining measurement instruments in virtually all industries. Since most instruments do not work on first principles, they rely on reference artefacts, or standards, in order to be calibrated so that they can provide meaningful data.

The accuracy of the measurement thus directly depends on the accuracy of the calibration standard. For this reason, such a standard must have not only a nominal value close to the quantity to be measured but also a much smaller uncertainty. For semiconductor manufacturing, this means that these standards must have dimensional features comparable to device dimensions, often in the nanometre scale, with much smaller uncertainties than the tolerances of the devices. Calibration standards have been developed and enhanced by the semiconductor industry for all essential measurements, i.e. critical dimensions, thin films, surface topography, overlay, doping, and defect inspections. However, this task becomes more challenging as when the device features shrink, the device architecture becomes more complex and/or the tolerances become tighter.

In order to obtain accurate measurement results, or even to evaluate accuracy, it is necessary to establish traceability to the SI units. Calibration standards become much more valuable when they are made traceable to SI units because this provides the guarantee that the results from any metrology instrument in any place that have been calibrated with such standards, are matched. However, it is usually not straightforward to establish traceability for these quantities because the chain of comparison involved can be complex and the equipment required is not commonly available. In order to help the industry obtain and maintain traceable standards, some standards organisations have made available Standard Reference Materials that are traceable to SI units; unfortunately, the availability of these master standards does not always follow the pace of the development of device manufacturing technology. Furthermore, in the area of 3D integration, European companies are at the forefront of 3D TSV technology with R&D organisations such as CEA, FhG and IMEC being among the pioneers. On the industrial side, STMicroelectronics and AMS AG are leaders in their sector and equipment and materials suppliers such as, BESI, EV Group, Oerlikon, Suss MicroTec and SPTS have invested significant R&D efforts. However, Europe has a relative poor visibility in the standards area while some of the key challenges that remain for mass 3D-SIC commercialisation, i.e. cost control, design, mass production and testing, are all clearly related to standards. This will be addressed in this WP.