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A Complimentary Inspection Technique based on Computer Tomography and Plenoptic Camera for MEMS Components

Periodic Reporting for period 2 - CITCOM (A Complimentary Inspection Technique based on Computer Tomography and Plenoptic Camera for MEMS Components)

Periodo di rendicontazione: 2019-04-01 al 2020-12-31

The term micro-electro-mechanical systems (MEMS) was traditionally used for micro-fabricated devices that converted electrical signals in movement (micro-actuators) or movement into electronic signals. The last category represents currently the bulk of the MEMS devices (e.g. accelerometers, gyroscopes, inertial sensors, pressure sensors and microphones), which on a large scale find their way in automotive, gaming and mobile communication applications. However, presently the term MEMS is additionally being used for a much larger class of emerging devices and applications that are all being manufactured using micro-fabrication tools and equipment. These include miniaturized medical systems, micro-fluidic systems, Organ-on-Chip devices and implantable systems.
This new class of MEMS has been enabled by advancements in micro-fabrication materials and processing such as Deep reactive ion-etching (DRIE), and new materials like cavity SOI. Also the assembly of these devices into packages and printed circuit boards (PCBs) has seen a tremendous development and is an essential part of the total manufacturing cycle. One thing all of those microsystems and devices have in common is that they are all (highly) three-dimensionally complex.
This is a problem from a manufacturing point of view. Whereas the IC industry has developed many planar inspection tools, there is a more or less urgent need for tools, which can structurally inspect 3D micro-structures. At the moment many of these new systems are only inspected electrically and not structurally, which may leave critical defects unnoticed. This is especially problematic for automotive and medical applications where reliability is of primary concern. Manual inspection is presently the only alternative, adding to the cost.
It is the aim of the CITCOM project to fill this gap in the manufacturing cycle by increasing the TRL-level of 3D imaging and X-Ray inspection equipment suitable for in-line MEMS and microsystems production environments. This shall improve the level of acceptance and ease the implementation of this kind of equipment at manufacturer’s sites such as Microchip as a potential end-users within the project.
At the end of the project, the CITCOM system results in two modules ready to be applied within a MEMS manufacturing facility: A 3D vision in-line system to inspect 100% of production flanked by a side-line X-ray system, for selective and advanced analysis.
The optical module consists of a conventional micro-electrical wafer prober, which has been retrofitted by with a plenoptic camera. This technology resolves details at the micron scale in 3D, with high throughput, up to 80 fps. The chosen cameras are compact and have an extended depth of focus compared to microscope cameras with similar optical properties because the microlenses have various focal lengths. The combination of all these advantages renders this technology ideal for MEMS inspection (Figure 1).
The X-ray system mainly consists of X-ray source, detector and manipulator. Optimization of the system resulted in a maximal spatial resolution of 0.5 m, enabling detection of sub-micron defects. The manipulator, designed and developed specifically for CITCOM, can manoeuvre up to 8” wafers with three axis translations and one axes full rotation (Figure 2).
A dedicated software automates wafer handling and inspection on both systems. User interaction and direct control of the plenoptic system is provided through an industry-ready automation software, which has been extended to the CITCOM components and functionalities. A backend software guarantees integrated control of the imaging hardware, steers the image analysis workflow and relays information to all components. Automated analysis includes image reconstruction, stitching and noise filtering as well as metrology and automated defect recognition (ADR). The ADR applies Deep Learning to detect anomalies such as defects and foreign particles (Figure 3).
The system’s functionalities have been tested and successfully validated for reliability, robustness and performance on MEMS samples provided by end-user partners. The restrictions related to the COVID-19 pandemic, prevented to setup the systems in a real production environment. Thus, final validation has been conducted in a laboratory environment based on production-like samples and by applying production-like conditions and validation protocol, fully coordinated by the main end-user partner.
Reliability/ageing testing conducted on specialised laboratories on the samples provided by Microchip have shown that critical features which can be identified by the CITCOM technology, have a relevant impact on the MEMS life. By applying 100% in-line inspection and providing the tools to identify such defects at early production stage, the CITCOM system has the potential to significantly improve production efficiency and product yield and quality.
The economic benefit of the system was shown by benchmarking with state-of-art methods at Microchip Technology (i.e. human experts with high magnification microscopy). Life Cycle Assessment and Life Cycle Costing also showed a positive environmental impact. Finally, different recycling scenarios to be associated with the CITCOM technology have been proposed, to promote a circular economy approach.
The successful closure of the CITCOM project is underlined by the concrete intent shown by several partners to continue the collaboration beyond the end of the project. This phase will allow to test the setups in a real production environment and to finalise the technology toward commercialisation.
The project results have been promoted through participation to various workshops/conferences as part of dissemination and communication actions. An exploitation plan for the key results and developed technology has been prepared. Several partners involved into the project including a major end-user intend to bring the developed technology into a further finalisation and commercialisation phase, starting right after the end of the project.
X-ray systems of course exist already for analysis of single samples after component or equipment failure. However, as a system integrated next to a production line with software interfaces to the shop floor level it is a novelty, not to forget the automated defect recognition. With an optimized source/detector combination and the implemented large substrate handling system it achieves larger throughput than current systems on the market.
3D optical inspection systems in itself are not new either. However, the technology employed in CITCOM, based on plenoptic cameras, seamlessly integrated with the wafer prober and correlated 3D image and electrical and/or electromechanical data clearly goes beyond state of the art.
Based on end-user feedback we strongly believe that both systems will impact the actual production yield of complex MEMS and microsystems. Together with the activities on sustainability this will reduce waste and therefore having a positive impact on our environment.
Schematic of re-use/recycling strategy for MEMS and microsystems
Deep reactive ion etching (DRIE) structures by VTT
CITCOM nano focus X-ray system
Cross section of DRIE etched structures by VTT
CITCOM plenoptic system fully integrated in the micro-electrical wafer prober
A 2mm diameter MEMS ultra-sound catheter by Philips
Automated inspection features
Capacitive micromachined ultrasound transducers with flexible interconnects from Philips