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Pilot line for micro-transfer-printing of functional components on wafer level

Periodic Reporting for period 2 - MICROPRINCE (Pilot line for micro-transfer-printing of functional components on wafer level)

Reporting period: 2018-04-01 to 2019-03-31

The primary objective of the MICROPRINCE project is to create the first worldwide open access foundry pilot line for microtransfer-printing (µTP) and to demonstrate its capability for heterogeneous integration of different functional components in an industrial environment. Five different target applications were selected to represent the possibilities of the technology for smart system integration (SSI) ranging from III/V Hall plates for current sensors, filter elements for optical sensors, µLEDs for automotive interior lightning as well as III/V-semiconductor-based emitters, modulators and sensors for photonic integrated circuits (PICs) in life science.
For the implementation of the pilot line and the process development for the selected target applications the following work was conducted till the end of M24:
Regarding the installation of the pilot line (WP1), all the selected tools (micro transfer printer, BCB coater/ developer and curing oven) were ordered and installed in the X-FAB MEMS cleanroom facility. Moreover, a Silane supply for an existing CVD chamber was established to allow the deposition of SiN on 8 inch source wafers. With respect to general process developments the following actionswere performed:
• DoEs on Nitride deposition and patterning for the tether formation,
• the release etch of Si-based coupons with KOH at X-FAB Erfurt,
• the release etch of GaAs and InP chiplets by HCl and FeCl3,
• the adhesive (BCB) deposition, annealing and curing process,
• the printing process itself,
• the adhesive patterning and
• the RDL formation to contact these coupons.
Moreover, in cooperation with the project partners TU Dresden and FhG IMWS work towards a µTP design aid tool and process characterization and reliability was done.
Concerning the transfer-printing of GaAs-based sensing elements in WP2, both current sensor ICs (target) and GaAs source wafers were prepared in this period and delivered to XMF. Based on this material, first release and printing experiments (on BCB) were performed. The characterization results indicated that GaAs transfer printed Hall elements provide increased signal to noise ratio (SNR) of a factor of five, compared to chips with Silicon Hall plates.
The main objectives of WP3 are the process development and industrialization for the printing of filters on optical sensors. To achieve this goal, source wafers carrying human eye response (HER) filter were fabricated at IOBJ. By further processing at ISIT (tether formation and release etch) these wafers were prepared for the transfer-printing. In addition, dummy devices (SiN based) were designed and applied for several DoEs to speed up the development of source wafer processes.
The objectives of WP4 (printing silicon photonics for data transmission) cannot be achieved in the MICROPRINCE project since HUAWEI stepped out of the project early in the 2nd project year.
Concerning WP 5 and the development of a LED driver IC for printed RGB µLEDs was completed and its capability was already demonstrated with a different packaging approach. Additionally, special GaN based blue LEDs for µTP were designed and fabricated in cooperation with the project partner TYN.
The main objective for WP6 is the heterogeneous integration of active components in a silicon photonic circuits. Therefore, initial printing tests at IMEC were prepared. The fabricated InP LEDs and PDs revealed promising performance with respect to bandwidth (3dB of ~50 nm), dark current (as low as 200nA) and responsivity (0.85 A/W). Moreover GaAs PDs were fabricated on die level.
In summary, the project is on track with respect to an accepted amendmentin which the leave of Huawei as well as minor scope modifications were addressed and explained. Accordingly, the main goal of building up a pilot line for heterogeneous integration and showing the applicability of µTP for different material classes and target applications will most likely be achieved.
With respect to the timeline of the MICROPRINCE project, summarized in the “ECSEL Grant Agreement”, the focus of the work performed in the 2nd project year was predominantly set on the installation of the pilot line and basic process developments for the different target application. For this purpose the following work tasks were fulfilled:
• Completion of the pilot-line installation (Silane supply, Coater/Developer, µTP tool & curing oven) and, thereby, achievement of MS4.
• Design and production of µTP test vehicles that allow a target-independent baseline process development.
• Process for a stamp master fabrication based on KOH was developed.
• Process characterization, first reliability evaluations and FEM simulations of the printing process were performed by the project partner FhG IMWS Halle.
• Programming of a first version of a design aid tool by TU Dresden.
• Source and target wafers for first printing and release developments at XMF were prepared.
• GaAs sensors with transfer-printed Hall elements were characterized and demonstrated an improved SNR about roughly a factor of five.
• For printed filters, the release of the source wafer was achieved with controlled under etch (of the anchor structures) and functional SiN-based tethers.
• The LED driver IC was designed, fabricated and demonstrated in an alternative packaging concept. Furthermore, the driver IC was completely characterized and qualified according to automotive standards.
• GaN blue LEDs that meet the requirements of µTP were designed and fabricated by Tyndal.
• InP LEDs and PDs as well as GaAs PDs for Si-photonics had been printed at imec (and XMF) and revealed a promising performance.
MICROPRINCE will strengthen the industrial competitiveness of the involved industrial partners by implementing the worldwide first open access pilot line for µTP. Thereby it will contribute to a stable and sustainable growth of the related business in Europe. For the project partner XMF the pilot line for µTP is an elementary step towards its vision to become a leading center for monolithic CMOS-MEMS integration as well as heterogeneous semiconductor integration.
Furthermore, the project offers the capability to develop and implement the next generation of different sensor applications for future markets in terms of fulfillment of standard requirements.
In more detail, the project will facilitate amongst others the production of significantly improved magnetic sensor systems for current measurements providing solutions with superior performance compared to actual market offerings. Furthermore, the project offers an innovative and unique solution for the integration of silicon photonics. Hence, less expensive and miniaturized photonic integrated sensors systems can be fabricated which are beneficial for various application and business areas like medical diagnostics, food inspection and bioprocess control.
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Group Picture at Kick-off Meeting