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. A superior optical performance and low defect levels of the interference filters, combined with maximized wafer throughputs is needed.

However, state-of-the-art deposition tools in semiconductor foundries lack a sufficient coating uniformity and optical performance as well as an in-situ thickness control. In the absence of such in-situ layer thickness control, the optical properties of filter stacks with up to hundreds of layers would 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 outstanding single layer quality in terms of thickness uniformity and optical properties as well as its low defect levels, the HELIOS 800 Gen II can pave the way to the next generation of highly resolved HSI sensors.

Imec and Bühler 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 Bühler 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 Bühler’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.

Andy Lambrechts, program director imaging technologies at imec: “Collaborating with Bühler 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.”

Stephan Mingels, team leader M2M development at Bühler:: “Imec enabled Bühler to gain additional experience in front-end semiconductor processing environments. Moreover, the access to imec’s facility including high-end metrology equipment, has been crucial to optimize the performance of the HELIOS 800 Gen II.”