MoSi Film Research Articles

Measuring Hot-Spot Interaction Length in Single-Strip SNSPD

Superconducting nanowire single photon detectors (SNSPD) functionality is based on the local suppression of the superconducting order parameter upon photon absorption, causing a change in resistance which can be detected as a DC voltage pulse. Finding the size and the profile of the superconducting order parameter suppression area (the so-called “hot-spot”) experimentally is a challenging task. Here, we report the results of a quantum detector tomography on micron-length SNSPDs. The high internal detection efficiency of our SNSPDs allowed us to extract single and double photon efficiencies from the count rate vs radiation power dependence and extract hot-spot interaction length. We investigated a series of SNSPD samples made of NbN films with different sheet resistance and a MoSi film, with various widths of the stripe. The experimental results confirmed that regardless of the material or the film resistance, the hot-spot interaction length coincides with the strip width which is a promising feature for making a 2-photon counter with high fidelity.

Comparison single- and double- spot detection efficiencies of SSPD based to MoSi and NbN films

In this work, we present results of quantum detector tomography of superconducting single photon detector (SSPD) based on MoSi film, and compare them with previously reported data on NbN. We find that for both materials hot spot interaction length coincides with the strip width, and the dependence of single and double-spot detection efficiencies on bias current are compatible with sufficiently large hot-spot size, approaching the strip width.

Characterisation of amorphous molybdenum silicide (MoSi) superconducting thin films and nanowires

We report on the optimisation of amorphous molybdenum silicide thin film growth for superconducting nanowire single-photon detector (SNSPD) applications. Molybdenum silicide was deposited via co-sputtering from Mo and Si targets in an Ar atmosphere. The superconducting transition temperature (Tc) and sheet resistance (Rs) were measured as a function of thickness and compared to several theoretical models for disordered superconducting films. Superconducting and optical properties of amorphous materials are very sensitive to short- (up to 1 nm) and medium-range order (∼1–3 nm) in the atomic structure. Fluctuation electron microscopy studies showed that the films assumed an A15-like medium-range order. Electron energy loss spectroscopy indicates that the film stoichiometry was close to Mo83Si17, which is consistent with reports that many other A15 structures with the nominal formula A3B show a significant non-stoichiometry with A:B > 3:1. Optical properties from ultraviolet (270 nm) to infrared (2200 nm) wavelengths were measured via spectroscopic ellipsometry for 5 nm thick MoSi films indicating high long wavelength absorption. We also measured the current density as a function of temperature for nanowires patterned from a 10 nm thick MoSi film. The current density at 3.6 K is 3.6 × 105 A cm−2 for the widest wire studied (2003 nm), falling to 2 × 105 A cm−2 for the narrowest (173 nm). This investigation confirms the excellent suitability of MoSi for SNSPD applications and gives fresh insight into the properties of the underlying materials.

Superconducting single-photon detector made of MoSi film

We fabricated and characterized nanowire superconducting single-photon detectors made of 4 nm thick amorphous MoxSi1−x films. At 1.7 K the best devices exhibit a detection efficiency (DE) up to 18% at 1.2 wavelength of unpolarized light, a characteristic response time of about 6 ns and timing jitter of 120 ps. The DE was studied in wavelength range from 650 nm to 2500 nm. At wavelengths below 1200 nm these detectors reach their maximum DE limited by photon absorption in the thin MoSi film.

플라즈마 처리에 의한 마스크 특성 변화

We have studied surface roughness, contamination of impurity, bonding with some gas element, reflectance and zeta potential on masks to be generated or changed during photolithography/dry or wet etching process. Mask surface roughness was not changed after photolithography/dry etching process. But surface roughness was changed on some area under MoSi film of Cr/MoSi/Qz. There was not detected any impurity on mask surface after plasma dry etching process. Reflectance of mask was increased after variable plasma etching treatment, especially when mask was treated with plasma including gas. Blank mask was positively charged when the mask was treated with Cr plasma etching gas( sccm/He:20 seem, source power:100 W/bias power:20 W, 300 sec). But this positive charge was changed to negative charge when the mask was treated with gas for MoSi plasma etching, resulting better wet cleaning. There was appeared with negative charge on MoSi/Qz mask treated with Cr plasma etching process condition, and this mask was measured with more negative after SC-1 wet cleaning process, resulting better wet cleaning. This mask was charged with positive after treatment with plasma again, resulting bad wet cleaning condition.

Development of a magnetron sputtering apparatus equipped with superconducting bulk magnets for the preparation of optical multilayer films

We have constructed the two-cathode superconducting permanent magnet bearing magnetron sputtering apparatus with the aim at fabricating Mo/Si multilayer films to serve as an optical mirror at extreme ultraviolet wavelength of 10–14nm. By using the magnetized bulk superconductor, the magnetic field generated immediately above the target can be increased 20 times as strong as that in a conventional magnetron sputtering. This strong magnetic field enables us to perform sputtering in a low gas pressure and with a long throw distance. In the present study, we deposited about 10nm thick Si and then 10nm thick Mo layer on the Si wafer and studied the effect of deposition conditions on an interdiffusion layer formed between Si and Mo layers by measuring the grazing incident X-ray reflectivity. As a result, we could successfully reduce the interdiffusion layer thickness down to 0.6nm, when the deposition was made at the Xe gas pressure of 0.02Pa, a throw distance of 450mm and discharge voltage of 2kV. To the best of our knowledge, this is the lowest thickness of an interdiffusion layer of Mo–Si film ever reported. This promises us to increase the reflectivity towards 70%, when a multilayer film is ready to be synthesized in the present superconducting magnetron sputtering apparatus.

Investigation of Pulsed Laser Removal of Cr and MoSi Film on a Quartz Substrate

Cr and MoSi film removal from a quartz substrate was investigated using a Nd:YAG laser repair system with a wavelength of 532 nm and pulse duration of 4 ns. Characteristics of the debris, removal size, and transmittance were clarified from the results of scanning electron microscope (SEM) observation and optical measurements. The debris resulting from Cr and MoSi removal consisted of spherical particles and pulverized powder, respectively. The difference in removal size between Cr and MoSi was consistent at about 200 nm. In order to obtain the optimum optical transmittance, it was found that the laser energy required for Cr removal is 1.45 times higher than that required for MoSi removal. An approximate formula for estimating the actual laser energy required was proposed. The actual laser energy was estimated to be 1/500 in comparison with the operational energy measured using an in-house power monitor. An ablation model for the removal mechanism based on melting and vaporization was constructed. The saturated formula was in agreement with the results of experiments.

High-performance VLSI photomask with a molybdenum silicide film

A molybdenum silicide (MoSi) film deposited on a quartz substrate offers major advantages as a high-performance photomask material for VLSI fabrication. There is no missing pattern due to exfoliation after ultrasonic cleaning with a frequency of 28 kHz and 300 W of power, and after being scrubbed over fifteen cycles with a high-pressure water jet. Reflectivity and optical density of the MoSi film are not affected by acidic chemicals. Dry etching with CF 4 + O 2 gas plasma can be performed at a rate of 70 nm/min, which is about five times as fast as the etch rate for chromium (Cr) masks. Moreover fabrication of submicron patterns using poly(buten-1 sulfone) (PBS) resist, a positive electron beam resist with very poor resistance to dry etching, has been realized. In addition a photomask with a MoSi film is easier to repair by focused ion beam than one with a Crfilm because of the higher sputter yields for a MoSi film.

Fabrication technologies for advanced 5X reticles for 16M-bit dynamic random access memory

Fabrication technologies for advanced photomasks with a molybdenum silicide (MoSi) film have been developed by using a variable-shaped electron-beam (e-beam) system. These technologies were applied to the fabrication of 5X reticles for 16M-bit DRAMs. The variable-shaped e-beam system is very effective in increasing the throughput for writing reticles which have a great number of figures, such as 16M-bit DRAMs. The average writing time was 100 min, which was ∼ (1)/(3) of the time when using a conventional raster-scan e-beam system. Photomasks with the MoSi film have advantages in comparison with those with conventional chromium (Cr) film. Pattern defects did not appear during the photomask cleaning because of strong adhesion of the MoSi film to the quartz substrate. Moreover, an accurate feature size on the photomasks was obtained, because the MoSi film was easily dry etched. The feature size accuracy obtained was 0.03 μm in 3σ all over the 5 in. blanks.

Laser-Initiated Aluminothermic Reaction Applied to Preparing Mo-Si Film on Silicon Substrates

ABSTRACTMo-Si films on silicon substrates has been prepared by the CO2 laser-initiated aluminothermic reaction. The features of these films have been characterized by RBS, AES, etc. The formation mechanism is discussed.

Temperature Effects on Internal Stress in Molybdenum Thin Films on Single-Crystal Silicon Substrates

Molybdenum thin films were deposited with an electron beam gun onto (100)- oriented silicon substrates. The samples were then annealed in vacuum, and the internal stresses in the molybdenum thin films were studied as functions both of the annealing temperature and of the substrate temperature during deposition. Silicide formation and the film thickness after annealing were monitored by the Rutherford backscattering spectrometry technique, and the stress was determined from the substrate curvature which was measured from Newton's ring interference fringes. It was found that, when the substrate temperature was kept at 400°C during deposition, MoSi2 was formed after annealing at temperatures above 500 °C. This MoSi2 exhibited large tensile stresses of about 2 × 1010 dyn cm−2 for annealing above 700 °C, whereas at the lower annealing temperature of 500 °C the stresses were compressive. No detectable silicides were observed when the substrates were kept at temperatures below 150 °C. The Mo-Si film stresses were tensile for substrates kept at room temperature during deposition and compressive for substrates kept at 150 °C.