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

Periodic Reporting for period 3 - MICROPRINCE (Pilot line for micro-transfer-printing of functional components on wafer level)

Reporting period: 2019-04-01 to 2020-09-30

The primary objective of the MICROPRINCE project has been to create the first worldwide open access foundry pilot line for micro-transfer-printing (μTP) and to demonstrate its capability for heterogeneous integration of different functional components in an industrial environment. Five different target applications were initially selected to represent the possibilities of the technology for smart system integration (SSI) ranging from III/V Hall plates for current sensors, optical filter elements for Human Eye Response (HER) sensors, μLEDs for automotive interior lightning as well as GaAs- & InP-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 the project: With respect to the pilot line installation the required tools for the adhesive deposition (coater/ developer), the micro-transfer-printing and the adhesive curing were specified, selected and installed in the XFAB MEMS cleanroom. Moreover, a Silane supply for an existing CVD chamber was established to allow the deposition of SiN on 8 inch source wafers. Based on these new equipment and already existing tools general process capabilities were investigated/ developed for a 3D-integration via µTP.
Moreover, in cooperation with the project partners TU Dresden a first μTP design aid tool was developed to relieve the co-design of source and target chips. Additionally, the new processes and materials were characterized and their reliability performance was tested in cooperation with the project partner IMWS. Concerning the transfer-printing of GaAs-based sensing elements in WP2, sensor ICs (target) and GaAs source chiplets with SiN tethers were prepared. Based on these materials, release and printing experiments (on BCB) were performed at XMF indicating issues with the chiplet warpage and, therefore, reduce print yields. Nevertheless, characterized samples 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 were process developments for the printing of filters on optical sensors. To achieve this goal, source wafers carrying HER filter were fabricated at the project partner OBJ. By further processing at ISIT (tether formation and release etch) these wafers were prepared for the transfer-printing. These print-ready filter devices were finally heterogeneously integrated at XMF. Optical measurements of the integrated sensors (Responsivity and dark current) indicated a full functionality of the HER sensors.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, a new LED driver IC for transfer-printed RGB μLEDs was developed. Additionally, special GaN based blue and green LEDs for μTP were designed and fabricated in cooperation with the project partner TYN. These LEDs were afterwards directly printed on the driver IC in the XMF MEMS clean room. After metallization and packaging, the integrated µLEDs were tested indicating a promising performance. The main objective for WP6 has been the heterogeneous integration of active components in silicon photonic circuits. Therefore, InP and GaAs photodiodes (PDs) have been fabricated and revealed promising performance with respect to bandwidth (3dB of ~50 nm), dark current (as low as 200nA) and responsivity (0.85 A/W). Moreover these PDs have been packaged on Si photonic circuits and functional integrated spectrometers were build. Accordingly, the main goal of the MICROPRINCE project of building a pilot line for heterogeneous integration and showing its applicability for different material classes and target applications by the generation of demonstrator devices has been achieved.
Within the funded MICROPRINCE project the following work has been done/ tasks have been fulfilled:

• Completion of the installation of a Pilot line for micro-transfer-printing (Silane supply, Coater/Developer, μTP tool & curing oven).
• Design and production of μTP test vehicles for the development of required baseline processes.
• Based on these test vehicles several process sequences have been developed including:
1) SiN deposition, stress optimization and patterning for the tether formation,
2) the release etch of Si-based coupons with KOH,
3) the release etch of GaAs and InP chiplets by HCl and FeCl3,
4) the adhesive (BCB) deposition, annealing and curing process,
5) the µTP process itself including the metrology of printed devices,
6) the adhesive patterning and the RDL formation to contact these coupons
7) the final passivation of the 3D-integrated stack.
• Process sequences for a stamp master wafer fabrication were developed.
• Process characterization, reliability evaluations and FEM simulations of the printing process were performed by XMF and the project partner FhG IMWS Halle.
• Creation of a first generation of design aid tool by TU Dresden.
• GaAs source wafers with SiN based tether structures were developed.
• GaAs sensors with transfer-printed Hall elements were characterized and demonstrated an improved SNR about roughly a factor of five.
• HER sensors based on printed filters were build and characterized. The test results demonstrate a full functionality of the filters/ sensors without major influences of the integration process on the PD performance.
• A new generation of LED driver IC was designed, fabricated and demonstrated. Furthermore, the driver IC was completely characterized and qualified according to automotive standards.
• Printable GaN blue and green LEDs were designed and fabricated by Tyndal and integrated by XMF.
• The functionality of the “integrated LED” driver package was shown and general characterization procedures were started.
• InP and GaAs PDs for Si-photonic based spectrometers were fabricated at imec and revealed a promising performance.
• The developed III/V- diodes were printed, wired and tested and, thereby, the functionality of the integrated spectrometers was proven.
MICROPRINCE has strongly strengthened the connection of the involved partners and will have a positive influence on the future industrial competitiveness since a new technology has been transferred into an industrial environment. Furthermore, the involved partners identified new market opportunities and started related projects based on their knowledge gained within MICROPRINCE. Thereby MICROPRINCE had created an noteworthy influence of the R&D activities of the related partners and can, thereby, 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 has proven an innovative and unique solution for the integration of silicon photonics. Hence, less expensive and miniaturized photonic integrated sensors systems could be fabricated based on the µTP process which will enable new medical diagnostic systems.
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Group Picture at Kick-off Meeting