Photochemical Vapor Deposition Research Articles

Fabrication of Silicon Dioxide by Photo-Chemical Vapor Deposition to Decrease Detector Current of ZnO Ultraviolet Photodetectors.

Zinc oxide (ZnO)-based semiconductor is a promising application for ultraviolet photodetectors (UV PDs). The performance of ZnO UV PDs can be improved in two orientations: by reduction of the dark current and by increasing the photocurrent. In the study, we used two processes to prepare ZnO UV PDs: photochemical vapor deposition to fabricate silicon dioxide as an insulator layer and a radio frequency sputter system to prepare the ZnO film as an active layer. The results show that the silicon dioxide layer can reduce the dark current. Moreover, a large photo–dark current ratio of the metal–insulator–semiconductor (MIS) structured PD is 200 times than the metal–semiconductor–metal (MSM) structured PD. When the silicon dioxide thickness is 98 nm, we can significantly enhance the rejection ratio. The silicon dioxide layer can reduce the noise effect and enhance the device detectivity. These results indicate that the insertion of a silicon dioxide layer into ZnO PDs is potentially useful for practical applications.

SiNx Deposition at Low Temperature Using UV-Irradiated NH3

Introduction Technology for depositing silicon nitride (SiNx) films at low temperature has been extensively studied. Plasma-enhanced chemical vapor deposition and photo-chemical vapor deposition can deposit SiNx films at low temperature (1-3). However, a substrate exposed to plasma or UV light is damaged (4). Deposition equipment with low plasma damage has also been developed (1-2); however, such damage is difficult to avoid. In this paper, we suggest a low-temperature SiNx film deposition technique that does not cause plasma or UV damage. Further, we deposited SiNx film to evaluate its characteristics. Experiment Fig. 1 shows a schematic diagram of the SiNx film deposition equipment. The equipment was constructed with a UV irradiation chamber and a tube reactor for SiNx film deposition. Ammonia (NH3) gas was excited by UV light and then supplied to the tube reactor. Si2H6 gas was directly supplied to the tube reactor without the UV irradiation. The UV light was emitted perpendicular to the NH3 flow in the UV irradiation chamber separate from the tube reactor and Si2H6. Because the UV light did not reach the substrate, the deposited films are not damaged and the film is not deposited the glass window for the irradiation chamber. The wavelength range of UV light of 160 – 210 nm included the absorption wavelength of NH3 (5). The deposition temperatures were 30˚C and 450˚C. We evaluated the effect of the UV-irradiated NH3 for the formation of high quality SiNx film. The nitrogen content of the films was analyzed by X-ray photoelectron spectroscopy (XPS). Result and discussions The effect of UV-irradiated NH3 is shown in Fig. 2. The vertical axes show the thickness and refractive index evaluated by ellipsometry. Horizontal axes indicates measurement positions shown in Fig. 1. NH3, N2 or H2 were supplied to the tube reactor with and without UV irradiation. A film having a refractive index near 2.0 was clearly deposited only when UV-irradiated NH3 was supplied. When N2 and H2 was supplied, regardless of the UV irradiation, almost the same films having thickness and refractive index were obtained. These results indicate that UV irradiation of N2 and H2 gas did not affect the reaction of not only N2 and H2, but also Si2H6. Fig. 3 shows composition ratio measured by XPS of the film deposited on the 300 nm thick SiO2. Figs. 3(a)-3(b) show that the film containing nitrogen was formed at 30°C and 450°C. The N/Si ratio of the film deposited at 450˚C with UV-irradiated was near 1.33, and the film’s depth profile had a region where no oxide was detected. These results show that the stoichiometric composition of the deposited film was close to Si3N4, and the film cannot be oxidized by the atmosphere of the clean room at R.T. Conclusion We suggested a low-temperature SiNx film deposition technique using UV-irradiated NH3 and demonstrated the deposition of SiNx films at low temperature. When UV-irradiated NH3 was used, nitrogen-containing film with an N/Si ratio close to 1.33 was clearly deposited at 450°C. In addition, the UV light introduced into the irradiation chamber excited only NH3 molecules, and it did not reach the substrate in the tube reactor. These results show that UV irradiation with NH3 is able to deposit SiNx films without UV damage at low temperature. Figure 1

Ultrasensitive determination of mercury in waters via photochemical vapor deposition onto quartz substrates coated with palladium nanoparticles followed by total reflection X-ray fluorescence analysis

We describe a method for ultrasensitive detection of mercury (Hg) by total reflection X-ray fluorescence following photogeneration of Hg vapor and trapping onto quartz substrates coated with nanostructured palladium. The nanostructured coating was characterized by transmission electron microscopy. Hg vapor was generated by online photo-UV reduction in the presence of acetic acid, which acts as a precursor for reducing species. Trapping of Hg occurred as a result of amalgamation. A trapping time of 30 min and an acetic acid concentration of 2 mol L−1 provided the best results. An enrichment factor of 127 and a limit of detection as low as 54 ng L−1 of Hg were achieved. The repeatability of the method (expressed as the relative standard deviation at a level of 1 μg L−1) was 3 %. The method was successfully applied to the determination of Hg in water samples spiked with 10 μg L−1 of Hg. Recoveries ranged from 96 to 101 %.

AlGaN/GaN high electron mobility transistors based on InGaN/GaN multi-quantum-well structures with photo-chemical vapor deposition of SiO2 dielectrics

AlGaN/GaN metal–oxide-semiconductor high electron mobility transistor (MOS-HEMT) based on InGaN/GaN multi-quantum-well (MQW) structure has been fabricated with SiO2 dielectric deposited via photo-chemical vapor deposition (PHCVD) using a deuterium lamp as the excitation source. High quality SiO2 was successfully formed by PHCVD and it exhibited exactly stoichiometric as gate oxide and passivation dielectric for MQW-based MOS-HEMT. The protection offered by the passivation of PHCVD of SiO2 may contribute to the significantly reduced current dispersion and improved RF performance. With 1-μm-long gate length at drain–voltage of 10 V, it exhibited a maximum drain current Id(max) of 966 mA/mm and a peak transconductance gm(max) of 127 mS/mm, while the unity gain cutoff frequency (fT) and maximum frequency of oscillation (fmax) are 13.9 and 33.9 GHz, respectively.

Room-temperature growth of high-quality ZnO nanocrystals using a dressed-photon-assisted near-field process

Single-crystalline ZnO nanocrystals were fabricated by room-temperature photo-chemical vapor deposition (PCVD). We further enhanced the growth of high-quality single-crystalline ZnO nanocrystals using dressed photons and phonons (DPPs). This resulted in greater position control and the growth of high-quality ZnO nanocrystals. The ZnO nanocrystals produced with DPPs had excellent cathodoluminescence characteristics, indicating that the near-field PCVD process could be a promising technique for nanophotonic integrated circuit production.

AlGaN/GaN heterostructure field-effect transistors with multi-MgxNy/GaN buffer and Photo-CVD SiO2 gate dielectric

We report the fabrication of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOS-HFETs) with multi-MgxNy/GaN as an epitaxial buffer and using SiO2 dielectric by photochemical vapor deposition (Photo-CVD) simultaneously for surface passivation and as gate insulator. High quality SiO2 dielectric was successfully deposited onto AlGaN by Photo-CVD compared with the traditional plasma enhanced chemical vapor deposition (PE-CVD). Compared to conventional AlGaN/GaN HFET, the MOS-HFET with Photo-CVD SiO2 exhibits lower leakage current, higher breakdown voltage and channel current. It was also observed that our MOS-HFETs presented pure 1/f noise with smaller trapping effects and improved immunity to the RF current collapse.

Optical and Structural Features of Silicon-Rich Hydrogenated Amorphous Silicon Nitride Thin Films

A systematic study of fabrication and effect of post-deposition processing on the optical and structural features of silicon-rich hydrogenated amorphous silicon nitride thin films deposited by Hg-sensitized Photo-Chemical Vapour Deposition technique is presented. Both deposition parameters and post-deposition thermal treatment resulted into substantial change in the refractive index associated with the densification of the film. Our studies reveal that the presence of hydrogen and its out-diffusion upon thermal treatment play a crucial role in the overall structural evolution, specially the stabilization of individual phases such as Si and Si3N4. We further report the room-temperature photoluminescence from as-deposited films, which is due to formation of silicon nanostructures in crystalline and amorphous forms. These studies are of great interest from the prospective of commercially viable Si-based technology.

Study of the optical response of Si-rich a-SiNx : H thin film near Si L2,3-edge using soft x-ray reflectivity

Angle-dependent soft x-ray reflectivity measurements in the photon energy range 82.67–248 eV near the Si L2,3 absorption edge have been performed on Si-rich a-SiNx : H (SRSN) thin film deposited by the Hg-sensitized photo-chemical vapour deposition technique. It is found that experimentally obtained δ (dispersion) values of the SRSN film lie in between that of pure silicon (Si) and silicon nitride (Si3N4). X-ray photoelectron spectroscopy measurements suggest that excess silicon is responsible for reducing optical constants values and hence by controlling the silicon amount one can tune the optical constants to desired values. We further compare the soft x-ray optical spectrum of the SRSN film with those of other silicon compounds such as silicon carbide (SiC) and silicon monoxide (SiO) near the Si L2,3 edge region to shows its possibility as a prospective material for the next generation 13.5 nm (91.85 eV) node extreme ultraviolet (EUV) lithography technology.

High temperature characteristics of ZnO-based MOS-FETs with a photochemical vapor deposition SiO 2 gate dielectric

The authors report the fabrication of ZnO-based metal-oxide-semiconductor field effect transistors (MOSFETs) with a high quality SiO 2 gate dielectric by photochemical vapor deposition (photo-CVD) on a sapphire substrate. Compared with ZnO-based metal-semiconductor FETs (MESFETs), it was found that the gate leakage current was decreased to more than two orders of magnitude by inserting the photo-CVD SiO 2 gate dielectric between ZnO and gate metal. Besides, it was also found that the fabricated ZnO MOSFETs can achieve normal operation of FET, even operated at 150 °C. This could be attributed to the high quality of photo-CVD SiO 2 layer. With a 2 μm gate length, the saturated I ds and maximum transconductance ( G m ) were 61.1 mA/mm and 10.2 mS/mm for ZnO-based MOSFETs measured at room temperature, while 45.7 mA/mm and 7.67 mS/mm for that measured at 150 °C, respectively.

Growth kinetics and compositional analysis of silicon rich a-SiNx:H film: A soft x-ray reflectivity study

We report soft x-ray reflectivity measurements near the Si L2,3 absorption edge for Si-rich silicon nitride thin film obtained by Hg-sensitized photochemical vapor deposition. We demonstrate that the precise analysis of optical index profile derived over extended energy region gives compositional details of the film. This nondestructive approach is used in Si-rich silicon nitride film to reveal buried Si-rich interfacial layer. Further, the combined study of soft x-ray reflectivity and optical density obtained from the reflectivity fitting at various photon energies provide a qualitative estimation of the film composition and its growth.

Phase evolution and photoluminescence in as-deposited amorphous silicon nitride films

A systematic study of hydrogenated amorphous silicon nitride films deposited by varying gas flow rate ratio ( R = SiH 4 /NH 3 ) using Photo-Chemical Vapour Deposition reveal that as R is increased, dominant phase changes from silicon oxynitride to silicon nitride with embedded silicon nanoclusters. The change in photoluminescence spectral features in these films is attributed to quantum confinement effect. The results suggest that hydrogen plays a crucial role in overall phase evolution and in-situ formation of Si nanoclusters embedded in silicon nitride matrix.

Preparation of solid acid carbon coating on the surface of TiO2 by photo-CVD of gaseous aromatic hydrocarbons

Abstract Properties of a solid acid carbon coating prepared on TiO2 powder surface using photochemical vapor deposition (photo-CVD) were evaluated. The TiO2 powder surface became brown during UV illumination under a flowing xylene and xylene sulfonic acid mixture. Observation by TEM revealed an amorphous carbon coating on the TiO2 powder. Sulfonate groups were identified on the coating using FT-IR. A chart of NH3-TPD measurements showed two peaks: that at high temperature was attributed to the coating’s strong acid. The carbon coating’s acidity was equivalent to that of the solid superacid carbon powder and the carbon-coated TiO2 decomposed cellulose.

A ZnO-based MOSFET with a photo-CVD SiO2 gate oxide

We demonstrate that a high quality SiO2 was successfully deposited onto ZnO by photochemical vapor deposition (photo-CVD). ZnO-based metal-oxide-semiconductor field effect transistors (MOSFETs) were also fabricated with such a photo-CVD oxide as the insulating layer. As compared with similar structure of ZnO-based metal-semiconductor FETs (MESFETs), it can be found that the gate leakage current was decreased to more than three orders of magnitude by inserting the photo-CVD oxide layer between ZnO and gate metal. With the 2 µm gate length, we also found that the saturated Ids and maximum Gm of the fabricated ZnO-based MOSFET were 61.1 mA mm−1 and 10.2 mS mm−1, respectively.

Flexible pentacene ion sensitive field effect transistor with a hydrogenated silicon nitride surface treated Parylene top gate insulator

We report on the realization of flexible ion sensitive organic field effect transistors based on pentacene on which Parylene-C was deposited as top gate dielectric. In order to create proton sensitive sites at the insulator/electrolyte interface, Parylene-C surface has been covered with a thin layer of hydrogenated silicon nitride (SiN:H) deposited by photochemical vapor deposition at moderate temperature. The combination of Parylene and SiN:H enables the realization of highly reproducible and good performance transistors as well as ion sensitive sensors with an excellent pH response both in the acidic and alkaline pH range in a nearly all plastic technology.

Photochemical Reaction of Ozone and 1,1,1,3,3,3-Hexamethyldisilazane: Analysis of the Gas Reaction between Precursors in a Photochemical Vapor Deposition Process

The photochemical reaction of 1,1,1,3,3,3-hexamethyldisilazane (HMDS) and ozone (O3) in the gas phase was analyzed as the side reaction in the photochemical vapor deposition (photo-CVD) process irradiated by ultraviolet light: the analysis was conducted by Fourier-transform infrared absorption spectroscopy (FT-IR) and mass spectrometry (MS). The final products of this photochemical reaction between HMDS and O3 are CO2, N2, and H2O, although this reaction is initiated at the Si–N–Si bond of HMDS with O3 and ultraviolet (UV) light, thus producing, as a reaction intermediate, a compound with carbonyl and/or carboxylic group followed by Si–N–Si scission.

Evaluation of implanted InSb p+n diodes passivated with composite anodic oxide/SiOxstack

This investigation presents detailed characteristics of an implanted planar InSb p+n diode with a junction area scaled down to 20 × 20 μm2. Low-temperature photo-chemical vapor deposition oxide stacked with an optimized thin anodic film, instead of a gate control structure, is used to control the planar surface potential of the implanted p+n diode under the weak inversion condition on the n-type surface and under weak accumulation on the p-type surface. The zero-bias resistance–area product is 7.6 × 104 Ω cm2 at 77 K. To the best of the authors' knowledge, this result represents the best performance of a small-area and implanted planar diode to date. The dark current is controlled by an internal shunt conduction mechanism, which seems to be related to the defects that are produced by the implantation. Low leakage current and high breakdown voltage have proven the feasibility of the composite anodic oxide/SiOx that is stacked as the passivation structure in small-pixel InSb p+n photodiodes for focal plane array applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dependence of the Deposition Rate on Probe-Substrate Separation in Nonadiabatic Near-Field Optical CVD

Photochemical vapor deposition in the optical near field was employed to fabricate nanometric Zn dots on a sapphire substrate. A nonadiabatic photochemical process was used to excite molecular vibrational states in optically inactive zinc-bis(acetylacetonate) (Zn(acac)2) vapor. Dependence of the deposition rate on the separation distance, d, between the apex of the fiber probe and the substrate was investigated. At d > 5 nm, the dissociation rates of Zn(acac)2 decreased with increasing d due to the transition probability of ground-state Zn(acac)2 to excited vibrational states induced by the nonadiabatic photochemical process. At d 2 molecules in the gap space between the fiber probe and the substrate.

Low-temperature Deposition of Hydrogenated Microcrystalline Silicon Thin Films by Photochemical Vapor Deposition Technique and Their Application to Thin Film Solar Cells

Hydrogenated microcrystalline silicon (µc-Si:H) thin films were prepared by mercury-sensitized photochemical vapor deposition (photo-CVD) technique at various deposition temperatures. Crystalline volume fraction showed a monotonic decrease with increasing temperature from 125 to 200 °C caused by the enhanced desorption of surface hydrogen atoms. Since a similar decrease has been reported at higher temperatures than 400 °C in plasma-enhanced vapor deposition technique, we conclude that photon energy from ultraviolet radiation serves to activate surface species in photo-CVD process. In spite of the low deposition temperature, the obtained films had excellent material properties. Then, thin film solar cells were fabricated on a Type-U substrate with various haze ratios provided by Asahi Glass using such films as the i-layer. A substrate with a high haze ratio of about 50% was effective in realizing a better light-trapping structure. By decreasing the deposition temperature of the i-layer to 140 °C, conversion efficiency was improved markedly due to the improved film quality brought about by the contributions of photons from ultraviolet radiation to the enhancement of the surface migration of the radicals for reducing defects in the resulting film. Consequently, a maximum solar cell efficiency of 7.4% was obtained.

Fabrication of fin field-effect transistor silicon nanocrystal floating gate memory using photochemical vapor deposition

The fin field-effect transistor (FET) silicon nanocrystal floating gate memory using the photochemical vapor deposition and the plasma doping processes was proposed. The silicon nanocrystals with a uniform size were formed on a vertical sidewall surface of the fin channel by the photochemical vapor deposition. The plasma doping was applied to form the junctions at the sidewall of the fin source-drain extension regions with a high aspect ratio. The FinFET silicon nanocrystal floating gate memory with a gate length of 100nm was successfully fabricated and it revealed a memory effect as well as a suppressed short-channel effect.

Noise Analysis of Nitride-Based Metal–Oxide–Semiconductor Heterostructure Field Effect Transistors with Photo-Chemical Vapor Deposition SiO2 Gate Oxide in the Linear and Saturation Regions

Low frequency noise of AlGaN/GaN metal–oxide–semiconductor heterostructure field effect transistors (MOS-HFETs) with photo-chemical vapor deposition (photo-CVD) SiO2 gate oxide was investigated as functions of gate bias (from Vgs=-6 to 4 V) both in the linear (Vds=3 V) and saturation (Vds=12 V) regions. In the linear region, it was found the measured noise spectra were fitted well by the 1/ f law up to 1 kHz. The normalized noise power density of the MOS-HFETs was proportional to Vgs-1 when -4<Vgs<0 V, and was independent of the gate voltage when 0<Vgs<4 V. The Hooge's coefficient α was estimated to be around 10-3. In the saturation region, it was found that the measured noise power density decreased monotonically with the increase of gate voltage.