Vapor Deposition SiO2 Research Articles

Selective control of self-organized In0.5Ga0.5As/GaAs quantum dot properties: Quantum dot intermixing

Selective postgrowth control of the photoluminescence (PL) wavelength has been demonstrated for a single layer self-organized In0.5Ga0.5As/GaAs quantum dot (QD) structure. This was achieved by rapid thermal processing of dots using different dielectric caps. Selective band gap shifts of over 100 meV were obtained between samples capped with sputtered and plasma enhanced silica deposition, with the band gap shift under regions covered with plasma enhanced chemical vapor deposition SiO2 less than 70 meV. The effects of different caps on the PL linewidth were also observed. The differential band gap shift will enable the integration of passive and active devices in QD systems.

Photoemission of the SiO2–SiC heterointerface

Photoelectron spectroscopy has been performed on SiC surfaces to investigate the valence band characteristics during SiO2 formation. Various stages of the oxide development were investigated. The √3×√3R30° surface is used as the initial surface for the oxidation experiments. The substrates were exposed to a succession of a 30 s oxygen exposure, two 30 s oxygen plasmas, and finally, a plasma-enhanced chemical vapor deposition SiO2 deposition. Ultraviolet photoemission spectroscopy was employed to measure the valence band discontinuity for the oxide on n-type 6H and n-type 4H SiC substrates for each step in the oxidation process. X-ray photoemission spectroscopy was used to confirm the valence band offset. The valence band discontinuity was determined to be 2.0 eV. Furthermore, the location of the valence band maximum of the SiC to the conduction band minimum of the SiO2 is determined to be a constant (∼7.0 eV) between 6H and 4H SiC. Band bending effects are directly measured from ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy. From the UPS measurements of the band bending effects, the interface state density is determined to be ∼5×1012 cm−2.

Thermal stability and etching characteristics of electron beam deposited SiO and SiO2

We have studied the thermal stability and etching characteristics of electron beam deposited SiO and SiO2. Scanning electron microscopy, Auger, atomic form microscopy, and ellipsometry were used to analyze the surface morphology, roughness, and film composition as a function of annealing temperatures. Both SiO and SiO2 showed excellent thermal stability up to 400 °C anneal and refractive index, surface morphology and pattern edge definition of both films barely changed. For higher temperature anneal, based on Auger analysis results, the ratio of Si/O of SiO2 film stayed constant after 700 °C. However, the Si/O ratio of SiO film increased from 0.54 to 0.62 due to oxygen outdiffusion. Dry etch characteristics of SiO and SiO2 were investigated using SF6 and NF3 discharges in a Plasma Therm inductively coupled plasma system. Wet etches were performed using buffered HF and HF/H2O solutions. Dry etch rates of SiO2 were comparable with that of conventional plasma enhanced chemical vapor deposition SiO2. SiO2 etched faster than SiO under all etch conditions.

X-ray photoelectron spectroscopy studies of modified surfaces of α-Al2O3, SiO2, and Si3N4 by low energy reactive ion beam irradiation

Reactions of N2+ ion beams with oxide surfaces of α-Al2O3(0001) single crystal and chemical vapor deposition (CVD) SiO2, and reactions of O2+ ion beams with a nitride surface of Si-rich CVD Si3N4 were investigated as a function of ion beam energy (200–1000 V) and dose (1×1015–1×1017/cm2). The thickness modified by the irradiation of a reactive low kinetic energy ion beam was measured using high resolution cross-sectional images of transmission electron microscopy (HR-XTEM), and the formation of new bonding induced by chemical reaction was analyzed by x-ray photoelectron spectroscopy (XPS). New bonding of Al–O–N on α-Al2O3(0001) started to be observed at 600 V N2+ ion energy and a dose of 1×1016/cm2, and Al–N bonding could be found at an ion beam energy of 1 keV. The thickness of the aluminum oxynitride layer after 800 V N2+ bombardment has been determined to be 10–50 Å by HR-XTEM analysis. In the case of CVD SiO2 surface modification, new bonding related to nitrogen was not clearly resolved in the XPS spectra, irrespective of the change of ion beam energy from 200 to 1000 V and ion dose from 1×1015 to 1×1017/cm2. However, widening of the full width at half maximum of Si 2p core-level XPS spectra for the modified SiO2 surface and the peak position of N 1s around 399 eV were evidence of the existence of nitrogen-related bonding like Si–O–N in the modified CVD SiO2 surfaces. Moreover, it was very interesting that the Si 2p peak of elemental Si appeared in the sample irradiated at a dose of 1×1017/cm2. Its occurrence was considered to be due mainly to the preferential sputtering effect, and was found to be largely dependent on the ion beam energy as well as on the ion dose. In the surface modification of low-pressure CVD Si3N4 by direct ken O2+ ion irradiation, Si–O–N bonding could be successfully created at an ion beam energy of 200 V and it evolved significantly at ion beam energies higher than 500 V. From the above results, low energy reactive ion beam irradiation can successfully create new bonding structures on oxide and nitride surfaces due to a surface chemical reaction like nitridation or oxidation, and is expected to be very useful for the formation of new ultrathin functional layers on ceramic surfaces.

Process integration induced thermodesorption from SiO2/SiLK resin dielectric based interconnects

The thermodesorption from SiO2/SiLK resin dielectric assemblies at various stages of interconnect fabrication are studied by mass spectrometry. Species desorption from such an assembly is governed by the intrinsic material properties and the process step history, such as patterning chemistry and by environmental contamination. The thermodesorption of an as-cured SiLK resin film is compared to the desorption of species after different process steps. It is shown that as cured SiLK films contain very low amounts of moisture and volatile organic compounds. The plasma-enhanced chemical vapor deposition SiO2 hardmask is the main source of moisture in the SiO2/SiLK resin dielectric stack. Annealing at T⩾350 °C in both vacuum and nitrogen ambient conditions drastically reduces the species desorption. The origin and the kinetics of the desorbed species are described.

Remote plasma enhanced chemical vapor deposition SiO2 in silicon based nanostructures

In the depletion gate approach to silicon-based nanostructures, a deposited oxide covering tiny metallic or silicide gate structures must function as a metal-oxide-semiconductor field effect transistor gate oxide. Depending upon the implementation, it may form the Si/SiO2 interface or be placed upon a very thin thermal oxide. In the former case, bonding between the silicon and SiO2 must be nearly perfect in order to achieve the high mobility required for observing quantum effects. In the latter case, the deposited oxide must not allow leakage current to obscure effects being observed, nor degrade the previously established thermal interface during deposition. Remote plasma enhanced chemical vapor deposited (RPECVD) silicon dioxide has been studied for use in silicon-based nanostructures. For thin oxides deposited at low temperature, oxide surface roughness has been shown to perturb the potential landscape seen by an electron traveling in a silicon inversion layer. [M. J. Rack, D. Vasileska, D. K. Ferry, and M. Siderov, J. Vac. Sci. Technol. B 16, 2165 (1998).] We have further explored processing parameters that influence the deposited oxide surface roughness, presumably roughened primarily by gas phase nucleation, and examined the correlation between roughness and oxide reliability. We found that processing conditions that reduce the oxide roughness and unwanted oxidation of the depletion gate structures are not necessarily those that produce the best silicon/oxide interfaces, nor the most defect-free bulk oxides in our RPECVD system. Specific processes tailored for particular device strategies are presented. The low temperature process at 175 °C is extensively explored.

Polysilicon thin film transistors fabricated on low temperature plastic substrates

We present device results from polysilicon thin film transistors (TFTs) fabricated at a maximum temperature of 100 °C on polyester substrates. Critical to our success has been the development of a processing cluster tool containing chambers dedicated to laser crystallization, dopant deposition, and gate oxidation. Our TFT fabrication process integrates multiple steps in this tool, and uses the laser to crystallize deposited amorphous silicon as well as create heavily doped TFT source/drain regions. By combining laser crystallization and doping, a plasma enhanced chemical vapor deposition SiO2 layer for the gate dielectric, and postfabrication annealing at 150 °C, we have succeeded in fabricating TFTs with ION/IOFF ratios >5×105 and electron mobilities >40 cm2/V s on polyester substrates.

High-Quality CVD/Thermal Stacked Gate Oxide Films with Hydrogen-Free CVD SiO2 Formed in a SiCl4–N2O System

We have developed and evaluated chemical vapor deposition (CVD) SiO2 films formed in a hydrogen-free system in which tetrachlorosilane ( SiCl4; TCS) and nitrous oxide ( N2O) are used as low pressure CVD source gases. It has been found that the hot-carrier degradation, the constant current time-dependent dielectric breakdown (TDDB) and the charge-trapping characteristics are superior to those of conventional CVD SiO2 films formed from dichlorosilane ( SiH2Cl2; DCS) and N2O. We have concluded that TCS–SiO2 is appropriate for CVD stacked gate oxide films due to its low electron trap density and high reliability.

Thermal Annealing of Si+ Implanted Chemical Vapor Deposition SiO2

Ion implantation was used to bring silicon atoms into chemical vapor deposition SiO2. Two bands of photoluminescence spectra at about 540 and 640 nm were observed from the as-prepared samples. Thermal annealing behavior of the photoluminescence was studied. The possible origin of the photoluminescence is discussed.

Theoretical Analysis of Oxygen-Excess Defects in SiO2 Thin Film by Molecular Orbital Method

Energy states of oxygen-excess defects in SiO2 have been studied by theoretical analyses using molecular orbital calculation and discussed on the basis of comparison with photoluminescence of SiO2 thin films. Theoretical analyses have been carried out using both the semi-empirical and ab-initio methods, and have shown that the transition energy from the excited singlet state to the ground state is 2.32 eV with the STO-3G basis set and 2.40 eV with the 3-21G basis set, which are very close to the 2.4 eV photoluminescence peak measured in the photo induced chemical vapor deposition SiO2 thin film. This analysis and the effects of annealing in O2 and N2 atmospheres suggest that origin of the photoluminescence peak at 2.4 eV is oxygen-excess defect.

Wavelength resolved thermally stimulated luminescence of SiO 2 films

A wavelength resolved thermally stimulated luminescence (TSL) study has been carried out for the first time on X-irradiated chemical vapor deposition SiO 2 films deposited on a silicon substrate, from room temperature, to 400°C. Upon irradiation, the TSL glow curve features a prominent structure at a maximum temperature, T max, of approximately 62°C (heating rate = 1°C/s); the analysis of the emission wavelength shows a peak at 457 nm (2.71 eV). The shape of the TSL peak is complex, and cannot be described in the frame of classical first- or second-order kinetics. Moreover, T max has a strong and monotonic shift to higher temperatures after partial pre-heating treatments while the spectral emission is not modified: a similar phenomenon has already been observed in bulk fused silica of various types, different from crystalline quartz which does not present any shift of T max as a function of pre-heating. These results suggest that the TSL peak is characterized by a distribution of trap parameters: specifically, a continuous distribution of trap energy or of the frequency factor can be taken into account. Considerations on the characteristics of the trap parameter distribution are made.

Improvement in dielectric properties of low temperature PECVD silicon dioxide by reaction with hydrazine

The dielectric properties of plasma-enhanced chemical vapor deposition (PECVD) SiO2 deposited at 150°C were improved by reaction with anhydrous hydrazine vapor at 150–350°C. The permittivity and loss decreased ~32% and ~86%, respectively, after reaction with hydrazine at 150°C. The decrease in permittivity and loss correlated with a decrease in the dipole concentration (silanol + water). During exposure to humid conditions, water uptake in the SiO2 films degraded the dielectric properties. A nitrogen anneal at 350°C did not improve the dielectric properties of the PECVD SiO2. Although water was removed from the films, silanol remained. When the PECVD SiO2 deposited at 150° was reacted with hydrazine vapor at 150°C, both silanol and water were removed from the films. The dielectric properties and resistance to water absorption improved.

Performance improvement of amorphous silicon thin-film transistors with SiO2 gate insulator by N2 plasma treatment

We studied the performance improvement of hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) using atmospheric pressure chemical vapor deposition (APCVD) SiO2 as a gate insulator. The threshold voltage and the subthreshold swing decrease remarkably by N2 plasma treatment on the APCVD SiO2 surface even though the field effect mobility changes little, indicating that the interface state density around the Fermi level is reduced significantly by N2 plasma treatment. We obtained the high performance a-Si:H TFT with the field effect mobility of 1.25 cm2/V s, the threshold voltage of 3.5 V and the subthreshold swing of 0.45 V/dec.

Polycrystalline silicon ‘‘slit nanowire’’ for possible quantum devices

Polycrystalline silicon (poly-Si) ‘‘slit nanowire’’ was fabricated in a slit formed with 100 nm lithography, microwave dry etching of silicon substrate, conformable filling of the trench by chemical vapor deposition (CVD) SiO2, slit etching of the CVD SiO2, conformable deposition of doped amorphous silicon, followed by etchback and annealing. Observation with transmission electron microscope confirmed that a poly-Si slit nanowire, with a cross section of ∼5–8 nm×20 nm is fabricated. Appropriate annealing of the a-Si layer makes the poly-Si grains grow to more than 2 μm in length. This technique would make it possible to realize silicon quantum devices, and to fabricate conventional integrated circuit devices and light emitting slit nanowire devices on a same silicon chip, which would allow the fabrication of integrated optoelectronic circuits.

Photoluminescence and Its Excimer Laser Irradiation Effects in SiO2 Film Prepared by Photo-Induced Chemical Vapor Deposition

Defects and other imperfections in photo-induced chemical vapor deposition (photo-CVD) SiO2 films have been characterized by photoluminescence excited by ArF and F2 excimer lasers. Photoluminescence peaks have been observed at around 2.7, 3.5 and 4.4 eV and are characteristic of both the deposition temperatures of photo-CVD and excitation energy. The intensity of the photoluminescence peak at around 2.7 eV initially increases with ArF excimer laser irradiation but decreases after about 2000 shots. On the other hand, it decreases monotonously with F2 excimer laser irradiation. The origins of these peaks have been discussed in terms of various dependences of photoluminescence and absorption spectra.

Cap and capless annealing of Fe-implanted InGaAs

The distribution of Fe implanted at medium (1–4×1014 cm−2) and low (2×1012 cm−2) doses into InGaAs and annealed with or without a cap is investigated and the degree of compensation of such implanted regions is assessed. Secondary ion mass spectrometry profiles of low dose implanted Fe reveal a substantial role of the capping layer. Fe concentrations below as well as above the estimated metal vacancy concentration produced by implantation are observed. The effect of the cap strongly depends on the wet chemical surface preparation before insulator deposition. A correlation of the magnitude of the Fe accumulation at the InGaAs surface with defect related photoluminescence intensity is established. On the basis of the substitutional-interstitial diffusion model the barrier effects of the various caps for host and dopant atoms are analyzed. The best semi-insulating properties were obtained for plasma enhanced chemical vapor deposition SiO2 caped samples using a H2SO4:H2O2:H2O=1:1:125 surface preparation before deposition resulting in a 53% incorporation of Fe. A high electrical activation is proved directly by capacity-voltage profiles.

Water trapping of point defects in interlayer SiO2 films and its contribution to the reduction of hot-carrier degradation

The water-blocking effect of plasma chemical vapor deposition (CVD) SiO2 film is investigated. Using electron spin resonance measurements, point defects in the electron cyclotron resonance (ECR) plasma CVD SiO2 used in this work can be identified as dangling bonds belonging to Si atoms. The defect density is reduced by capping water-containing film on it, suggesting that the defect is capable of trapping water. The hot-carrier degradation in a metal-oxide-semiconductor (MOS) device is successfully prevented when ECR plasma CVD SiO2 is used as a water-blocking layer that keeps water in the overlayer from diffusing to the gate oxide. This result indicates that ECR plasma CVD SiO2 effectively blocks water due to the water trapping ability of the Si dangling bonds.

Electron beam patterning of SiO2

Maskless or ideally ‘‘resistless’ patterning of semiconductors is essential for in situ processes which require regrowth of semiconductor layers. If a practical method of patterning SiO2 were viable, many processing problems related to tasks currently utilizing organic resists could be eliminated. With the knowledge that etching selectivity can be induced in SiO2 by electron beam exposure, experiments were performed with the goal of gaining an understanding of some of the practical aspects of electron beam exposure and etching of SiO2. Electron beam energy optimization considerations for dose minimization were addressed followed by e‐beam exposure and etching of 100 nm films of thermal and remote plasma enhanced chemical vapor deposition SiO2. The etching characteristics of the respective oxides are presented and discussed.

Hydrogen sulfide plasma passivation of gallium arsenide

Improvement in the electrical properties of the GaAs surface has been accomplished using a room-temperature hydrogen sulfide plasma. The surface has then been protected by a 300 °C plasma enhanced chemical vapor deposition (PECVD) SiO2 film. This treatment is highly reproducible due to computer control of process parameters and long-lasting due to the SiO2 cap. Improved C-V characteristics were observed, showing interface trap densities in the high 1011 cm−2 eV−1 range. Photoluminescence (PL) measurements on the sulfided samples showed increased intensity over the untreated samples.

Chemical Vapor Deposition of SiO2 from Ozone-Organosilane Mixtures near Atmospheric Pressure

ABSTRACTThe kinetics of deposition of SiO2 by the reaction of tetramethylsilane (TMS) with ozone (O3) has been studied over the temperature range 180 – 380° C and compared with available data for the same process using tetraethoxysilane (TEOS). Both processes exhibit the same activation energy (17 kcal/mole) below 300 ° C which falls-off at higher temperatures due to transport limitations. Transition from first- to zero-order kinetics occurs with increasing concentrations of TMS and O3, which gives an overall O3/TMS consumption ratio of 10 at 258° C and5 at 325° C. TEOS is estimated to be 5 times more reactive than TMS above 300° C and over 10 times more reactive in the kinetically-limited regime below 300° C. Results suggest that O3-induced SiO2 deposition proceeds via surface reactions and is limited by heterogeneous decomposition of ozone.