MEMS technologies have been used successfully to miniaturize optoelectronic systems. Nonetheless alignment issues limit the level of miniaturization for complex optical systems. Especially off-axis optical designs such as used in Czerny-Turner spectrometers or "Schiefspiegler"-cameras offering completely reflective and thus chromatic aberration free optics are difficult to shrink. On the other hand multiple applications request extremely miniaturized and light weight modules for mobile devices, automotive or unmanned aerial vehicles.
A new concept for the efficient realization of complex optical systems has been invented and patented . For the so-called "place and bend assembly" a planar substrate is used which features preprocessed bending lines. Due to the progress in production technologies, 3D printing for small and medium volumes as well as other advanced plastic process technologies for high volumes with supreme accuracy are available. Optical, electronic as well as MEMS components can be placed on such a substrate using standard but precise planar technologies. Then the different parts of the substrate are bent and form the 3D body. Simultaneously the optical path inside is generated. This concept is not limited to rectangular shapes. It may also be possible to realize the "W-configuration" of a Czerny-Turner spectrometer in a very efficient way.
The first proof of concept has been achieved with a camera device realized from a 3D printed substrate. An entrance window, two spherical mirrors, an aperture stop and a detector array have been assembled using planar technology. Afterwards the substrate was folded and fixed. The functional capability has been demonstrated by capturing test images which have been optically evaluated. Challenges for the future development will be named and discussed.
Next generations of mobile phones will contain spectral analysers. Different concepts and system designs compete in this ultra-high volume market. Especially for the analysis of organic matter, which can be food, human skin or other items, the near infrared range offers substantial advantages, most of all a suitable penetration depth and relevant spectral information. On the other hand the spectrometer has to meet the requirements for the use in a mobile phone, i.e. size and price must drop significantly. The reliable operation, especially for the evaluation of the spectra with chemometric models, requires a very stable wavelength scale of the spectroscopic system. The deviation must not exceed 0.5 nm during operation under any condition and for each device used.
Resonant MEMS devices combine multiple advantages: Ultra compact designs can be realized, MEMS motions allow an operation using a single detector to meet cost issues even with extended InGaAs technology and the position feedback ensures a precise and long term stable wavelength scale. Based on such resonantly actuated MEMS components NIR spectrometers have been designed. Recent research work aims for extreme miniaturization of the optical bench. The presented assembly technology has been optimized for volume production. The outline from the previous published work will be shrunk to 10 x 10 x 5 mm3 with only a slightly reduced resolution. The new design will be optimized for cost efficient production as well.
A groundbreaking new approach  for the fabrication of complex photonic systems, especially such with off-axis optics, has been invented based on planar mounting in combination with a novel folding approach.
Up to now volume production of photonic systems has been optimized for on-axis lens based optical systems. Chromatic aberration limits the usage or spectral range of these systems. Applying mirrors instead of lenses may help to suppress chromatic aberrations and wavelength depending absorption. The assembly of reflective optics, often in an off-axis configuration, is a complex process. So far most tools for volume production apply stacking of components in planar technology. Off-axis systems are typically assembled by more or less manually alignment of the components, which is not in favor for mass and low cost production of these systems.
The novel approach utilizers a planar substrate featuring preprocessed bending lines. A high accuracy tool for planar assembly places the components onto the substrate. Then the sides of the substrate are bent leading to a predefined three dimensional body. The off-axis optical path inside is generated automatically.
This concept is not limited to rectangular shapes but can also be applied to more complex systems, for example the so called “W-configuration” for a Czerny-Turner spectrometer.
First tests of the “bend and place assembly” have been performed successfully on a camera setup to prove the working principle.
Scanning the retinae of the human eyes with a laser beam is an approved diagnosis method in ophthalmology; moreover
the retinal blood vessels form a biometric modality for identifying persons. Medical applied Scanning Laser
Ophthalmoscopes (SLOs) usually contain galvanometric mirror systems to move the laser spot with a defined speed
across the retina. Hence, the load of laser radiation is uniformly distributed and eye safety requirements can be easily
complied. Micro machined mirrors also known as Micro Electro Mechanical Systems (MEMS) are interesting
alternatives for designing retina scanning systems. In particular double-resonant MEMS are well suited for mass
fabrication at low cost. However, their Lissajous-shaped scanning figure requires a particular analysis and specific
measures to meet the requirements for a Class 1 laser device, i.e. eye-safe operation.
The scanning laser spot causes a non-uniform pulsing radiation load hitting the retinal elements within the field of view
(FoV). The relevant laser safety standards define a smallest considerable element for eye-related impacts to be a point
source that is visible with an angle of maximum 1.5 mrad. For non-uniform pulsing expositions onto retinal elements the
standard requires to consider all particular impacts, i.e. single pulses, pulse sequences in certain time intervals and
cumulated laser radiation loads. As it may be expected, a Lissajous scanning figure causes the most critical radiation
loads at its edges and borders. Depending on the applied power the laser has to be switched off here to avoid any retinal
Scatterometry proved to be a powerful technique for CD and profile metrology. In contrast to alternative methods like
scanning electron microscopy (SEM) it is an integral method that reconstructs structure parameters from a comparison
between measured and simulated spectra. It is well established in the field of line / space gratings and gaining importance
for crossed grating structures. The simulation tool MicroSim, which was developed at the Institute for Technical Optics
(ITO) in Stuttgart, has recently been extended to arbitrarily shaped crossed grating structures. Besides the shape also the
pitches and mode numbers in the two directions of periodic continuation can be selected freely. In this article, different
measurement configurations are discussed regarding as an example an asymmetric crossed grating structure. The depth
of an asymmetric etch ought to be measured as well as its width. For the depth a conventional spectroscopic
ellipsometric setup can be applied, whereas for the width an angle scan is proposed. In this configuration the wavelength
remains constant while the sample is rotated around its normal.
Scatterometry is receiving considerable attention as an emerging optical metrology in the silicon industry. One area of progress in deploying these powerful measurements in process control is performing measurements on real device structures, as opposed to limiting scatterometry measurements to periodic structures, such as line-space gratings, placed in the wafer scribe.
In this work we will discuss applications of 3D scatterometry to the measurement of advanced trench memory devices. This is a challenging and complex scatterometry application that requires exceptionally high-performance computational abilities. In order to represent the physical device, the relatively tall structures require a high number of slices in the rigorous coupled wave analysis (RCWA) theoretical model. This is complicated further by the presence of an amorphous silicon hard mask on the surface, which is highly sensitive to reflectance scattering and therefore needs to be modeled in detail. The overall structure is comprised of several layers, with the trenches presenting a complex bow-shape sidewall that must be measured. Finally, the double periodicity in the structures demands significantly greater computational capabilities.
Our results demonstrate that angular scatterometry is sensitive to the key parameters of interest. The influence of further model parameters and parameter cross correlations have to be carefully taken into account. Profile results obtained by non-library optimization methods compare favorably with cross-section SEM images. Generating a model library suitable for process control, which is preferred for precision, presents numerical throughput challenges. Details will be discussed regarding library generation approaches and strategies for reducing the numerical overhead. Scatterometry and SEM results will be compared, leading to conclusions about the feasibility of this advanced application.
Polysilicon recess etch process control in deep trench arrays of a DRAM requires reliable measurements of the recess depth directly in the trench array. Until now Atomic Force Microscopy (AFM) has been used for post etch depth measurements. However, with decreasing lateral trench dimensions, AFM may approach its limits especially with respect to the available bottom travel length. Consequently, alternative metrology methods are of interest. Scatterometry is an optical, model based measurement technique which potentially allows a full reconstruction of the measured structure. The measurement of the polysilicon recess presents a number of challenges: (1) the recess depth (150nm to 300nm) is much smaller than the total height of the complete structure (several microns), (2) spacer-like sidewall layers are present, while (3) unpredictable effects may be present (e.g. voids in the polysilicon fill) and would be difficult to include into a grating model. In addition, for measurements within the trench array 3D capability is required. In this work we analyze the capability of 2D and 3D scatterometry for polysilicon recess depth process control. We evaluate parameter sensitivities, parameter correlations, measurement robustness, depth correlation to the trench array, precision and accuracy for a wide range of process variations by comparing results obtained by scatterometry to those obtained by AFM and SEM cross sections. We show that a simplified grating model provides accurate measurements in lines/spaces structures (2D). However, in trench arrays (3D) the trench depth sensitivity is critical.