The far infrared instrument SAFARI spectrometer on board the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) provides moderate resolution spectra (R~300) with simultaneous coverage over 34 to 230 μm. With the high sensitivity TES detectors, the SAFARI can reach the sensitivity down to ~7×10-20 W/m2. In order to provide accurate calibration for the TES readout circuit, a calibration source assembly (CSA) is developed to provide a stable and absolute flux radiation to the spectrometer over the whole spectral range. The CSA has a primary function during observations to take periodic reference measurement to correct for drift, subtracting backgrounds, etc from the detector. The CSA is composed of three microlamps and one integrating sphere. The microlamps are made of resistance wires by microlithography to mimic square blackbody sources. By combining an 81K microlamp and a 24K microlamp, a reasonably flat spectrum can be produced at the output of the integrating sphere. The radiation to the transition edge sensor detector pixel is around 1×10-16 W. The integrating sphere can also provide a uniform output to cover the size of SAFARI field of view including the target and sky pixels. In this paper, the CSA design and the prototype results of the microlamp and the integrating sphere are presented.
We develop a continuous wave terehertz (THz) imaging system operating at 288 GHz. This imaging system simply consitutes three parts including the source, two optical lenses, and the detector. The entire size is smaller than the tranditional pulsed THz imaging system. In this developed system, the THz wave is generated by a horn attenna which concentrates the wave in an azimuth angle of 3° ~ 5°. The source originates from a singnal generator, and then the frequency increases to 288 GHz after passing through an 8X multiplier. Next, THz wave is focused by a THz lens on the test sample. By controling the sample position in the x-z plane, we can scan it pixel-by-pixel in which each step along the x- or z- axes is 0.1 mm. After penetrating the test sample, another lens collects the transmitted THz wave and focuses them into the thermal detector. This detector can disply the collected THz power. Finally, by drawing the detected power of each pixel, a transmitted-intensity figure for all pixels is obtained. The resolution of this THz imaging system is about 1~2 mm at present. We have measured human molar tooth and obtained its transmitted figures. Besides, we also develop a technology to adjust the positions of the source and detector by a system containing one laser, one beamsplitter, and two mirrors. The relative positions between the source and detector is very important. The input of the source and the output of the detector are small so that they have to aim at each other very accurately in order to collect maximum transmitted power in the detector.
The modified transmission line theory is used to calculate equivalent refractive indices of the extreme ultraviolet (EUV) mask multilayer (ML) over wavelengths from 13.35 to 13.65 nm for finite-difference time-domain (FDTD) simulation. Generally speaking, a fine mesh requiring huge memory and computation time are necessary to get accurate results in an FDTD simulation. However, it is hard to get accurate results for ML simulation due to the thin thickness of each layer. By means of an equivalent refractive index, the ML can be treated as one layer with the bulk effective material. Using FDTD simulations, we study the reflectivities of 40 Mo/Si ML and bulk material cases. The ML structure and bulk material with periodic excessive surface roughness as well as patterned with periodic contact holes are also studied by using two- and three-dimensional FDTD simulations. The simulation cases for a single wavelength and for a full-bandwidth EUV light source with a 6 ML system are studied. The results from each simulation show that the root mean square error between ML simulations and the bulk material simulations are confined within 3.3%, and all cases indicate that the FDTD computation time of bulk material is about half as compared with a 40-ML simulation.
KEYWORDS: Semiconducting wafers, Maskless lithography, Lithography, Photomasks, Data processing, Manufacturing, Electron beams, Data centers, Lenses, Microelectromechanical systems
Electron-beam lithography is promising for future manufacturing technology because it does not suffer from wavelength
limits set by light sources. Since single electron-beam lithography systems have a common problem in throughput, a
multi-electron-beam lithography (MEBL) system should be a feasible alternative using the concept of massive
parallelism. In this paper, we evaluate the advantages and the disadvantages of different MEBL system architectures,
and propose our novel Massively Parallel MaskLess Lithography System, MPML2.
MPML2 system is targeting for cost-effective manufacturing at the 32nm node and beyond. The key structure of the
proposed system is its beamlet array cells (BACs). Hundreds of BACs are uniformly arranged over the whole wafer area
in the proposed system. Each BAC has a data processor and an array of beamlets, and each beamlet consists of an
electron-beam source, a source controller, a set of electron lenses, a blanker, a deflector, and an electron detector. These
essential parts of beamlets are integrated using MEMS technology, which increases the density of beamlets and reduces
the system cost. The data processor in the BAC processes layout information coming off-chamber and dispatches them
to the corresponding beamlet to control its ON/OFF status. High manufacturing cost of masks is saved in maskless
lithography systems, however, immense mask data are needed to be handled and transmitted. Therefore, data
compression technique is applied to reduce required transmission bandwidth. The compression algorithm is fast and
efficient so that the real-time decoder can be implemented on-chip. Consequently, the proposed MPML2 can achieve 10
wafers per hour (WPH) throughput for 300mm-wafer systems.
When EUV light is used to inspect mask defects, the reflective photons reveal information for both the mask structure
and the mask defects. The number of reflective photons has to be enough for generating sufficient detector signals. A
modeling technique based on Feynman path integral is utilized to calculate the number of reflective extreme-ultraviolet
(EUV) photons scattered from photomask surfaces. For a 2D semicircular silicon defect, the capability of predicting the
moving direction for each reemitting photon and the intensity of photons in different direction has been demonstrated.
KEYWORDS: Sensors, Monte Carlo methods, Electron beams, Signal detection, Lithography, Electron beam lithography, Detector arrays, Optical simulations, Semiconducting wafers, Silicon
Multiple-electron-beam-direct-write lithography is one of the promising candidates for next-generation lithography
because of its high resolution and ability of maskless operation. In order to achieve the throughput requirement for highvolume
manufacturing, miniaturized electro-optics elements are utilized in order to drive massively parallel beams
simultaneously. Electron beam drift problems can become quite serious in multiple-beam systems. Periodic recalibration
with reference markers on the wafer has been utilized in single-beam systems to achieve beam placement accuracy. This
technique becomes impractical with multiple beams. In this work, architecture of a two dimensional beam position
monitor system for multiple-electron-beam lithography is proposed. It consists of an array of miniaturized electron
detectors placed above the wafer to detect backscattered electrons. The relation between beam drift and distribution of
backscattered-electron trajectories is simulated by an in-house Monte Carlo electron-scattering simulator. Simulation
results indicate that electron beam drift may be effectively estimated from output signals of detector array with some
array signal processing to account for cross-coupling effects between beams.
The Finite-Difference Time-Domain (FDTD) method is used to study the scattering effects of extreme ultraviolet (EUV)
mask. It requires significant amounts of memory and computation time as the fine grid size is needed for simulation.
Theoretically, the accuracy can be increased as the mesh size is decreased in FDTD simulation. However, it is not easy
to get the accurate simulation results for the multilayer (ML) structures by FDTD method. The transmission line theory
is used to calculate the equivalent refractive index for EUV mask ML to simulate the ML as one layer of bulk artificial
material. The reflectivities for EUV light with the normal incidence and small-angle oblique incidence in the bulk
artificial material and EUV mask ML are simulated by FDTD method. The Fresnel's equation is used to evaluate the
numerical errors for these FDTD simulations, and the results show good agreement between them. Using the equivalent
refractive index material for EUV multilayer mask can reduce the computation time and have the accuracy with tolerable
numerical errors. The ML structure with periodic surface roughness is also studied by this method, and it shows that only
half of computation time is needed to substitute ML to a bulk equivalent refractive index material in FDTD simulations.
This proposed method can accelerate the simulations of EUV mask designs.
Extreme ultraviolet (EUV) lithography is one of the promising candidates for device manufacturing with features smaller
than 22 nm. Unlike traditional optical projection systems, EUV light needs to rely on reflective optics and masks with an
oblique incidence for image formation in photoresist. The consequence of using a reflective projection system can result
in horizontal-vertical (H-V) bias and pattern shift, which are generally referred as shadowing. Approaches proposed to
compensate for shadowing effect include changing mask topography, modifying mask focus, and biasing features along
the azimuth angle, which are all rule-based. However, the complicated electromagnetic interaction between closely
placed circuit patterns can not only induce additional optical proximity effect but also change the shadowing effect.
These detailed phenomena cannot be completely taken into account by the rule-based approaches. A fully model-based
approach, which integrates an in-house model-based optical proximity correction (OPC) algorithm with rigorous three-dimensional
(3D) EUV mask simulation, is proposed to simultaneously compensate for shadowing and optical proximity
effects with better pattern transfer fidelity and process windows. Preliminary results indicate that this fully model-based
approach outperforms rule-based ones, in terms of geometric printability under process variations.
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