High-throughput manufacturing of filter-on-chip CMOS sensors now possible

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Buhler Leybold Optics, a supplier of thin-film vacuum coaters and, imec have qualified Buhler’s HELIOS 800 tool to meet the stringent standards of the semiconductor industry and developed high performance filters for optical image sensors.

The enhanced tool will open up many new applications that require a precise deposition of high-quality optical stacks at high manufacturing speed. The development is expected to lead to a new generation of high-resolution low-cost hyperspectral imaging sensors.

The production of high-resolution low-cost filter-on-chip CMOS detectors for hyperspectral imaging sensors (HSI) for the visible (VIS) and the short-wave infrared (SWIR) range places high demands on thin-film deposition tools.

While a superior optical performance and low defect levels of the interference filters, combined with maximized wafer throughputs is needed, state-of-the-art deposition tools in semiconductor foundries tend to lack sufficient coating uniformity and optical performance as well as an in-situ thickness control. As a consequence, the optical properties of filter stacks with hundreds of layers need to be measured after the deposition of each individual layer. This dramatically reduces wafer throughput, making layer thickness corrections almost impossible.

An in-situ optical monitoring system in the HELIOS 800 Gen II sputter coater allows complex filter coatings with excellent precision in a single production step, in which batches of multiple wafers are processed. Combined with the single layer quality in terms of thickness uniformity and optical properties as well as its low defect levels, the HELIOS 800 Gen II is seen as helping to pave the way to the next generation of highly resolved HSI sensors.

Imec and Buhler Leybold Optics engaged in a joint development project, installing a HELIOS 800 Gen II in imec’s 200mm clean room. Within the framework of their collaboration, the HELIOS 800 Gen II was successfully upgraded to meet the extremely high standards of semiconductor manufacturing, with respect to contamination and particles levels. As a result, filters are now within the capabilities to be manufactured at high volume.

Currently, imec and Buhler are collaborating to further upgrade the HELIOS 800 Gen II to enable numerous other applications and to enable processing of more complex optical filter architectures, such as photonics devices. This know-how will also be transferred to Buhler’s new sputter coater HELIOS 1200, capable to process 300mm wafers.

The joint development project has been extended over the coming years, to enable the next generation of sensors and chips.

Commenting Andy Lambrechts, programme director imaging technologies at imec said, “Collaborating with Buhler has been of great value to imec. It enabled us to increase the quality of our hyperspectral detectors by decreasing the tolerances on the filters and facilitating more complex filter architectures. The system is available to partners for R&D projects with the support of imec in testing and qualification.”