LED & CMOS Structured Light Systems for Multi-modal Optical Lithography

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In recent years, microscopic active-matrix light-emitting diode (LED) arrays have emerged as a platform technology, which currently sees huge commercial interest for display applications, but which has also proven significant capability in other areas, including wireless optical communications, imaging and object location, and maskless lithography. These devices are fabricated through an integration process of the Gallium Nitride LEDs with complementary metal-oxide semiconductor (CMOS) driver electronics, thus providing direct digital electronic control with up to about 100 MHz signal rates. The application of micro-LED arrays to imaging/tracking and maskless direct writing has previously been investigated separately. Now, there is a timely opportunity to explore the combined capabilities of structured light metrology and micro-fabrication in one multi-modal setup whose operating modes are all crucially underpinned by micro-LED technology.This project is going to apply the principles of structured light imaging, for example so-called "single-pixel cameras", in LED-based direct writing. This approach allows detectors to be used whose capability goes vastly beyond the traditional camera systems that are currently used in direct writing tools. The applicant will explore the use of charged-coupled device spectrometers and CMOS single photon detectors, which will enable the detection and location of spectral or fluorescence lifetime features that are undetectable otherwise. The direct-writing capability can then be used to fabricate micro-structures in perfect automatic alignment with the detected features, thus creating technology demonstrations with significant relevance for industrial and R&D applications. Gallium Nitride LED arrays are available across a broad wavelength range, from deep ultra-violet to green emission, and the feature detection and direct writing functions can therefore readily be adapted to a range of different target markers and photoresists. In addition to the tracking and alignment function, structured illumination with LED arrays also holds promise for closed-loop process control. 3D imaging, either by pattern projection or through means of photometric stereo-imaging, can potentially be employed in the setup while a structure is being written, thus providing real-time feedback to the writing process.Research towards the above objectives entails numerous challenges, from the basic optics design of the setup, to noise effects specific to the structured light imaging methods, to systems integration challenges. There are a number of trade-offs to be investigated, e.g. illumination dose versus imaging quality, writing speed versus feedback accuracy, and possible application of compressive sensing. This project will provide insight into the parameter space of device operation and identify useful configurations.