Optical satellite communication is growing fast and among various applications it requires higher throughput optical feeder links. Optical feeder links for satellite communication necessitate very high data throughput, up to 1 Terabit/s and beyond. Amongst several multiplexing strategies, dense wavelength division holds a key position to enable overall throughput rates above 1 Terabit/s. As a consequence, hardware architectures capable of handling high throughput links must be devised. Complementary to the high throughput requirement, the devices should also cope with the high optical power levels needed in optical ground stations. Combination of spatial aperture multiplexing and free space bulk optics configurations of multiplexers with transmission diffraction gratings are presented as possible concepts. Besides wavelength multiplexing, it is essential to include the beam propagation effects in the performance analysis, since this may affect the overall feeder link properties. A modelling framework is presented that covers the multiplexing behavior as well as the beam propagation of the transmission gratings based concept. The modelling framework based on first principles of optical diffraction is general, and independent of the grating choice. The results suggest that the design of a free space bulk multiplexer for optical feeder link must be approached already at system level. Decisions about telescope sizing, channels distribution and modulation formats may affect the performance of the multiplexer, resulting in severe effects on the link performance. The work discusses the effect of each design parameter and proposes design guidelines for high power satellite communication beam multiplexing.
Nowadays most overlay metrology tools assess the overlay performance based on marker features which are deposited next to the functional device features within each layer of the semiconductor device. However, correct overlay of the relatively coarse marker features does not directly guarantee correct overlay of the much smaller device features. This paper presents the development of a tool that allows to measure the relative distance between the marker and device features within each layer of the semiconductor device, which can be used to improve the overlay at device feature level. In order to be effective, the marker to device feature distance should be measured with sub-nanometer measurement uncertainty over several millimeters range. Furthermore, the tool should be capable of profiling the marker features to allows prediction of the location interpretation of the optical diffraction based alignment sensors, which are sensitive for potential asymmetry of the marker features.
To enable this, a highly stable Atomic Force Microscope system is being developed. The probe is positioned relative to the wafer with a 6DOF controlled hexapod stage, which has a relatively large positioning range of 8x8mm. The position and orientation of this stage is measured relative to the wafer using 6 interferometers via a highly stable metrology frame. A tilted probe concept is utilized to allow profiling of the high aspect ratio marker and device features. Current activities are aimed at demonstrating the measurement capabilities of the developed AFM system.
With the device dimensions moving towards the 1X node, the semiconductor industry is rapidly approaching the point where 10 nm defects become critical. Therefore, new methods for improving the yield are emerging, including inspection and review methods with sufficient resolution and throughput. Existing industrial tools cannot anymore fulfill these requirements for upcoming smaller and 3D features, since they are performing at the edge of their performance. Scanning probe microscopy (SPM) has the ability to accurately measure dimensions in the micrometer to nanometer scale. Examples of applications are surface roughness, channel height and width measurement, defect inspection in wafers, masks and flat panel displays. In most of these applications, the target area is very large, and, therefore, the throughput of the measurement plays an important role in the final production cost. Single SPM has never been able to compete with other inspection systems in terms of measurement speed, thus has not fulfilled the industry needs in throughput and cost. Further increase of the speed of the single SPM helps, but it still is far from the required throughput and, therefore, insufficient for high-volume manufacturing. Over the past three years, we have developed a revolutionary concept for a multiple miniaturized SPM heads system, which can inspect and measure many sites in parallel. The very high speed of each miniaturized SPM unit allow the user to scan many areas, each with the size of tens of micrometers, in a few seconds. This paper presents an overview of the technical developments and experimental results of the parallel SPM system for wafer and mask inspection.
Applying aspherical and freeform optics in high-end optical systems can improve system performance while decreasing
the system mass, size and number of required components. The NANOMEFOS measurement machine is capable of
universal non-contact and fast measurement of aspherical and freeform optics up to ∅500 mm, with an uncertainty of 30
nm (2σ). In this machine, the surface is placed on a continuously rotating air bearing spindle, while a specially developed
optical probe is positioned over it by a motion system. A separate metrology system measures the probe and product
position relative to a metrology frame.
The prototype realization, including custom electronics and software, has been completed. The noise level at standstill is
0.88 nm rms. A reference flat was measured with 13 μm and 0.73 mm tilt. Both measurements show an rms flatness of
about 8 nm rms, which correspond to the NMi measurement. A hemisphere has also been measured up to 50° slope, and
placed 0.2 mm eccentric on the spindle. These measurements reproduce to about 5 nm rms. Calibration and software are
currently being improved and the machine is applied in TNO aspherical and freeform optics production.