Tunable and Switchable Multiple-Cavity Thin Film Filters

A novel angle-tuned thin film filter with low angle sensitivity

Hydrogenated silicon (Si‐H) thin films were deposited from a mixture of pure silane (SiH4) and hydrogen (H2) gases in a home‐built plasma enhanced chemical vapour deposition (PECVD) system using the layer‐by‐layer (LBL) deposition technique. In the LBL process, the deposition was performed by periodically alternating the deposition of Si:H layer with the hydrogen treatment process of the growth surface. In this work, the effects of the H pasma treatment time to Si‐H layer growth time ratio on the film properties were studied. The LBL deposited Si‐H films studied in this work were deposited using different Si‐H layer growth times ranging from 2 minutes to 7 minutes with the hydrogen plasma treatment time on the growth surface fixed at 3 minutes. Optical transmission spectroscopy, X‐ray diffraction (XRD), micro‐Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) measurements were done on these films to investigate the optical, structural and morphological properties of the films. The films deposited by this technique produced the highest deposition rate of 6.3 A/s when the growth time of the Si‐H layer was fixed at 5 minutes. These films were amorphous in structure and had large optical energy gaps irrespective of the Si‐H layer deposition time. High concentration of cone‐like structures was observed in the AFM images for the films deposited using the higher Si‐H layer deposition times.Hydrogenated silicon (Si‐H) thin films were deposited from a mixture of pure silane (SiH4) and hydrogen (H2) gases in a home‐built plasma enhanced chemical vapour deposition (PECVD) system using the layer‐by‐layer (LBL) deposition technique. In the LBL process, the deposition was performed by periodically alternating the deposition of Si:H layer with the hydrogen treatment process of the growth surface. In this work, the effects of the H pasma treatment time to Si‐H layer growth time ratio on the film properties were studied. The LBL deposited Si‐H films studied in this work were deposited using different Si‐H layer growth times ranging from 2 minutes to 7 minutes with the hydrogen plasma treatment time on the growth surface fixed at 3 minutes. Optical transmission spectroscopy, X‐ray diffraction (XRD), micro‐Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) measurements were done on these films to investigate the optical, structural and morpho...

We report on a novel method and system for investigation of hydrogenated nanocrystalline silicon (nc-Si:H) thin films' piezoresistive effect, and a measurement system for gauge factor of nc-Si:H thin films is designed based on four-point bending method. nc-Si:H thin film resistor is deposited onto glass beam by plasma-enhanced chemical vapor deposition (PECVD) technique. Fractional strain of strained nc-Si:H thin films is measured by PSD sensor based on laser triangulation method, and relative change in resistance of strained nc-Si:H thin films is read out by Wheatstone bridge, when nc-Si:H thin film resistor is under a uniform stress. All signals, including converted and conditioned signal outputting from PSD sensor and output of Wheatstone bridge, are acquired by PXI data acquisition system with industry's most accurate 7½-digit digital multi-meter, and then gauge factor of nc-Si:H thin films is achieved by programming. The experimental results show that the measurement system for nc-Si:H thin films' gauge factor has solved the problem of thin film materials' gauge factor measurement, and based on the system the level of automation, precision and efficiency in measurement has been improved, and more importantly, the measurement system has provided the experimental basis for investigation of nc-Si:H thin films' piezoresistive effect.

Hydrogenated silicon (Si:H) and germanium (Ge:H) are assessed for use as the resistive sensing layer in uncooled infrared microbolometer applications. N-type doped Si:H and undoped Ge:H thin films have been deposited using plasma enhanced chemical vapor deposition (PECVD) and monitored during growth using in situ, real time spectroscopic ellipsometry (RTSE) to track changes in the growth evolution and structure occurring within a single film as a function of thickness. Amorphous germanium (a-Ge) films prepared by sputtering and amorphous n-type doped silicon carbon alloy films (a-Si_1-xCx:H) films prepared by PECVD have also been studied by ex situ spectroscopic ellipsometry. Variations in the electrical properties of interest including film resistivity, temperature coefficient of resistance, and 1/f noise character in the form of the normalized Hooge parameter have been tracked as a function of the structure of the material as determined by deposition conditions and characterized by spectroscopic ellipsometry. Such notable variations observed include the effects of transitioning from amorphous to microcrystalline material in n-type Si:H; the addition of carbon to increase disorder in n-type a-Si:H; effects of process parameters for sputtered a-Ge; and a comparison of n-type a-Si:H, ntype a-Si_1-xCx:H, and undoped a-Ge:H properties for films all prepared by PECVD.

Non-uniform distribution in µc-Si1−xGex:H and its influence on thin film and device performance

Developed large area (45s45cm) PECVD (Plasma Enhanced Chemical Vapor Deposition) method was applied to prepare p type microcrystalline silicon thin films (µ-Si:H) on borofloat glass substrates for use of silicon thin film solar cells. The resistivity, thickness and index distribution of large area µc-Si:H thin films prepared at various deposition conditions including flow ratio of source gases, pressure and temperature were measured by four-probe mapping, ellipsometry mapping and VIS-NIR spectrometer method. The homogeneity contour was illustrated to be sensitive to process parameters especially the flow ratio of source gases. This can be one of important factors to affect large area µc-Si:H thin film performance especially in production process. Pin structure on glass substrate and silicon ribbon substrate was prepared with optimized deposition conditions.

We have used mass spectroscopy to observe and analyze, in real-time, gas phase reactants and product species in plasma enhanced chemical vapor deposition (PECVD) of silicon. We describe a doubly differentially pumped mass spectrometry system to sample the exhaust stream of a large area plasma CVD reactor operating at 0.4–1.5 Torr. We show real-time quantitative analysis of silane consumption and hydrogen production for deposition of hydrogenated amorphous silicon and for pulsed-gas selective area silicon deposition. The ability of mass spectrometry to observe process faults in real time is also demonstrated. Mass spectroscopy is a useful nonintrusive process-state sensor for real-time metrology of plasma deposition, for example, to quantify gas phase species, and to characterize reactions occurring on the substrate surface. Based on our results, we discuss potential advanced manufacturing applications of real-time mass spectrometry in amorphous silicon and selective area silicon plasma deposition, including indirect wafer-state sensing, fault analysis and classification, and run-to-run and real-time process control.

The effect of power density and thickness on aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) formed with plasma enhanced chemical vapor deposition (PECVD) was studied by using N2-protected conventional furnace reaction and optical microscopy. With the deposition power density ranging from 0.05 to 1.00 W/cm2 and the thickness from 500 to 5000Å, it was found that a low power density as well as a large a-Si thickness could result in a decrease of activation energy and therefore a significant reduction of the AIC reaction temperature. Scanning and transmission electron microscopy and X-ray diffraction were used to check the crystallinity and quality of the AIC thin films. High quality polysilicon thin films were achieved at an AIC reaction temperature as low as 120°C.

Fully microcrystalline silicon, μc-Si, thin films (<100 nm) have been deposited at low temperature (60 °C) on Corning glass and plastic flexible polyimide substrates by plasma enhanced chemical vapor deposition (PECVD) using SiF 4 -H 2 -He, The effect of deposition temperature on the structure, i.e., crystallinity and density, of μc-Si films is investigated by spectroscopic ellipsometry in the 1.5-5.5 eV energy range. Modeling of spectroscopic ellipsometry data is used for highlighting crystallinity of the substrate/film interface, i.e., the absence of any amorphous incubation layer. It is found that film crystallinity does not depend on film thickness, and it increases with the decrease of deposition temperature. The temperature dependence is explained on the basis of a like-Arrhenius kinetic analysis of the etching process by atomic fluorine and hydrogen of both μc-Si and a-Si phases.

High mobility single-crystalline-like silicon thin films on inexpensive flexible metal foils by plasma enhanced chemical vapor deposition

Microstructure characterization of microcrystalline silicon thin films deposited by very high frequency plasma-enhanced chemical vapor deposition by spectroscopic ellipsometry

The amorphous silicon (a-Si) grown by plasma enhanced chemical vapor deposition (PECVD) has been widely applied in advanced semiconductor devices. However, it still suffers from the bubble defects when the deposition temperature goes above 450 °C. In this work, we have investigated the influence of underlying materials on the formation of bubbles of a-Si. The a-Si was deposited on different dielectric substrates, including silicon nitrides (SiN) and silicon dioxide (SiO2), using PECVD technique at a substrate temperature of 500 °C. A large number of bubbles of the a-Si has been observed on the thermal ALD deposited SiN underlayer, and some of them even burst. In contrast, no bubble defects were observed at the a-Si grown on PECVD SiN and PECVD SiO2 films. Such deviation may be attributed to the quality of the underlying material, which induces the H/H2 diffusion during the growth of a-Si and results in bubbles. A solution based on the model has been used to suppress the formation of such bubbles. An inserting layer of SiO2 was introduced in between SiN and a-Si to improve the density of the lower layer material and the adhesion between the two materials. As a result, there is no bubble defects at the surface of a-Si observed using optical microscope. Our work reveals the mechanism of the formation of bubble defects and paves a new method to eliminate the bubbles defects and to form high-quality a-Si, which shows potential in the manufacture of semiconductor devices.

Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies

The characteristics of organic–inorganic hybrid low-k thin films by PECVD

A low temperature amorphous silicon (a-Si) thin film transistor (TFT) and amorphous silicon PIN photodiode technology for flexible passive pixel detector arrays has been developed using active matrix display technology. The flexible detector arrays can be conformed to non-planar surfaces with the potential to detect x-rays or other radiation with an appropriate conversion layer. The thin, lightweight, and robust backplanes may enable the use of highly portable x-ray detectors for use in the battlefield or in remote locations. We have fabricated detector arrays up to 200 millimeters along the diagonal on a Gen II (370 mm x 470 mm rectangular substrate) using plasma enhanced chemical vapor deposition (PECVD) a-Si as the active layer and PECVD silicon nitride (SiN) as the gate dielectric and passivation. The a-Si based TFTs exhibited an effective saturation mobility of 0.7 cm2/V-s, which is adequate for most sensing applications. The PIN diode material was fabricated using a low stress amorphous silicon (a-Si) PECVD process. The PIN diode dark current was 1.7 pA/mm2, the diode ideality factor was 1.36, and the diode fill factor was 0.73. We report on the critical steps in the evolution of the backplane process from qualification of the low temperature (180°C) TFT and PIN diode process on the 150 mm pilot line, the transfer of the process to flexible plastic substrates, and finally a discussion and demonstration of the scale-up to the Gen II (370 x 470 mm) panel scale pilot line.