Si Multilayer Structure Research Articles

New methods of X-ray reflectometry of solids and solid thin films

X-ray reflectometry makes it possible to determine optical constants of materials in the corresponding range of wavelengths and the thickness of thin films on the basis of measurements of reflection coefficients in relation to the grazing angle. New reflectometry methods based on measurements of either the derivatives with respect to the grazing angle or the ratios of reflection coefficients for two characteristic wavelengths are suggested. Calculations and measurements indicate that the method suggested makes it possible to enhance the sensitivity of reflectometry and the accuracy of measuring the optical constants. Practical implementation of the method is based on an unconventional system of selecting monochromatic beams with the use of semitransparent crystals. The results of reflectometry studies of GaAs single crystals and a Ga0.25Si0.75−Si multilayer structure on a Si substrate are reported.

Reliability of Electrodeposited Copper and Ecrcvd Siof Films for Multilevel Metallization

AbstractThe effect of a post plasma treatment on the dielectric properties and reliability of fluorine doped silicon oxide (SiOF) films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) was studied. Also, the thermal stability of an electrodeposited Cu / sputtered Ta interconnect system with SiOF intermetal dielectrics was examined by annealing in a vacuum furnace. The stability of the dielectric constant of SiOF films was improved by O2 post plasma treatment. Surface modification by the plasma treatment was effective in prevention of water absorption. The Cu/Ta/SiOF/Si system was thermally stable at least up to 500°C for 3h. For the Cu/Ta/SiOF/Si multilayer structure, the plasma treatment seemed to play a big role in suppressing the interdiffusion between SiOF and metal interconnects. By C-V measurement, the electrical stability of the Cu/Ta/SiOF/Si multilayer structure was found to be stable up to 500°C for 2 h.

Thermal stability enhancement of Cu/WN/SiOF/Si multilayers by post-plasma treatment of fluorine-doped silicon dioxide

The effect of a post-plasma treatment on the dielectric property and reliability of fluorine doped silicon oxide (SiOF) film was studied. Also, the thermal stability of the Cu/WN interconnect system with SiOF interlayer dielectrics was examined by rapid thermal annealing. The surface roughness of SiOF films increased with increasing plasma treatment power due to ion bombardment effect during the plasma treatment. As the plasma treatment power increased, the dielectric constant increased from 3.16 to 3.43, while the change in the relative dielectric constant of the plasma treated films decreased in magnitude after treatment at 100 °C for 30 min in boiling water. Furthermore, the chemical properties of the plasma treated SiOF layers near the top surface tend to resemble those of thermal oxides after plasma treatment with sufficient plasma power, apparently due to the reduction in the Si–F bonding in the films. In the case of a Cu/WN/SiOF/Si multilayer structure, surface oxidation and densification due to the plasma treatment seemed to play an important role in suppressing the interdiffusion between SiOF and metal interconnects.

Influences of intermediate Si-Ni thin film conditions on adhesion of Ni-TiN gradient thick films

The influences of the intermediate thin film properties, that is internal stress and preferred orientation, on the adhesion of thick film were studied. The intermediate layers were designed Si and Ni multilayer structures, which were formed by the ion beam and vapor deposition method. Si films were prepared by evaporation of Si and simultaneous irradiation with Ar ions on to WC-Co substrates after surface cleaning by Ar ion beam irradiation. After the preparation of Si films, Ni films were also prepared by evaporation of Ni and Ar ion irradiation simultaneously. The internal stresses and preferred orientations of both films were controlled by changing the ion beam energy. Ni-TiN gradient thick films were formed on to these Si-Ni multilayer films by the cathodic arc ion plating method. It was found that the improvements of the internal stress and the preferred orientation conformities at the interface between the intermediate films and the thick films were important factors for high adhesion of thick film. The Ni-TiN gradient thick film reached a thickness of 600 μm with an adhesion high enough for practical use.

Oxygen δ-Doped Si Multi-Layers Grown by Molecular Beam Epitaxy

An oxygen δ-doped Si multilayer structure has been grown by molecular beam epitaxy (MBE). Thermal oxidation of a Si layer prepared by an MBE system at a low oxygen partial pressure resulted in a thin ordered oxide layer with a very flat surface. On the ordered oxide, Si was epitaxied through the solid phase epitaxy. Five periods of Si(2 nm)/SiOx(1 nm) multilayers were grown successfully. The O-doped Si layer (SiOx) was composed of 7 atomic layers and the crystalline structure of the SiOx layer was the same as that of the Si substrate but had a relatively transverse displacement. The in-plane stress restricted the number of the oxide layers grown to a thickness of less than 6 atomic layers. This structure may be the gateway for realizing Si-based quantum wells.

Reliability of Cu/WN thin Films Deposited on Low Dielectric Constant SiOF ILD

ABSTRACTThe effect of the post plasma treatment on the dielectric properties and reliability of fluorine doped silicon oxide (SiOF) films was studied. Also, the thermal stability of a Cu/WN interconnect system with SiOF intermetal dielectrics was examined by RTA. The surface roughness of SiOF films increased with the increasing plasma treatment power due to ion bombardment effect during the plasma treatment. As the plasma treatment power increased, the dielectric constant increased from 3.16 to 3.43, while the change in the relative dielectric constant of the plasma treated films by the boiling treatment was decreased in magnitude. Furthermore, the chemical properties of the plasma treated SiOF films near the top layer tend to resemble those of thermal oxides by the plasma treatment of sufficient power because of the reduction in the Si-F bonding in the films. In the case of Cu/WN/SiOF/Si multilayer structure, surface oxidation and densification due to the plasma treatment seemed to play an important role in protecting the interdiffusion between SiOF and metal interconnects.

Quantification of germanium and boron in heterostructures Si/Si 1− xGe x/Si by SIMS

The use of secondary ions mass spectrometry (SIMS) generally leads to very high sensitivity and depth resolution for silicon-based components. Low concentration elements such as dopants, are easy to quantify in silicon, whereas high concentration elements are subject to “matrix effects”, i.e. the intensity does not vary linearly with the concentration. Matrix effects are presently studied in SiGe alloys using two primary beams O 2 + and Cs + and a CAMECA IMS4F instrument. Rapid thermal chemical vapor deposition grown Si/Si 1− x Ge x /Si multilayer structures with x varying from 0 to 23.5% are preliminarily characterized by Rutherford backscattering spectrometry (RBS) in thickness and atomic composition. The linear variation of the SIMS intensity ratio I Ge +/ I Si + with the RBS concentration ratio x/(1− x) is confirmed for both O 2 + and Cs + beams. However, the linearity does not imply the absence of matrix effects. A variation of the ionization yields with Ge concentration and a similar behavior for τ Ge+ and τ Si+ actually lead to an exact compensation of the intensity ratio variation. At any energy, O 2 + experiments systematically over-estimate the real Ge concentration, whereas matrix effects under Cs + beam are weak. For polyatomic MCs + ions, strong matrix effects are observed in Si 1− x Ge x alloys. A quantitative analysis of major constituents and a dopant (boron) is used to determine the depth profiles of a thin base of a SiGe HBT heterostructure. Two different procedures are used depending on the primary beam. Consistent results are obtained for the concentrations of the major elements. The fully autonomous SIMS analysis with the Cs + beam is still penalized by the lack of sensitivity for boron in the secondary positive mode. © 1997 Elsevier Science S.A. All rights reserved.

Selforganization phenomena in heteroepitaxial growth

Three dimensional finite element (3D FE) calculations are performed to explain the physical origin of selforganized growth of island structures (that are of equal shape, of equal lateral dimensions and interdistances) in a strained film growing heteroepitaxially on a misfitted substrate. The selforganized island growth is a result of the inhomogeneous strain distribution in the 3D laterally limited islands that leads to a strain dependent locally varying adatom incorporation rate R(r). Based upon the same argument of locally varying strain distribution we may also explain further Selforganization phenomena, that are experimentally observed in, for example, (Si-Ge) n Si(001) multilayer structures, such as: (i) the flattening of a Si capping layer on top of an islanded Ge/Si structure and (ii) the vertical alignment of islands in (Si-Ge) n layers.

Efficiency of TiN diffusion barrier between Al and Si prepared by reactive evaporation and rapid thermal annealing

TiN layers prepared by reactive evaporation and rapid thermal annealing were tested as diffusion barrier between Al and Si. First, Rutherford backscattering spectroscopy (RBS) analysis of Al/Ti(N)/Ti/Si and Al/Ti(N)/Si multilayer structures showed that Si does not diffuse out up to a sintering temperature of 550 °C. However, as the temperature increases beyond 450 °C, Al starts to react with TiN. This reaction leaves less than half the TiN original thickness after a 30 min anneal at 550 °C. The RBS results indicate that TiN, crystallized at a temperature around 850 °C, forms a good barrier between Al and Si. Electrical measurements on various microelectronic devices were performed to verify this. Annealing of Ti(N) at 900 °C leads to a breakdown of p-MOS (metal–oxide–semiconductor) devices while n-MOS devices still work properly. Annealing at 800 °C gives good results on both MOS types except that the contact resistance of a p-type resistor is higher than desired. The electrical circuit failure is mainly due to dopant loss from the active area of the device into the titanium silicide which forms during the rapid thermal annealing at 800 or 900 °C of the deposited Ti(N) layers.

Refined RBS and AES techniques for the analysis of thin films used in photovoltaic devices

AbstractThe analytical potential of refined RBS and AES techniques is demonstrated by two examples: (i) thin FeSi2 absorber layers on Si and (ii) TiNiAg multilayer contact structures. Both systems have prospects as components in photovoltaic cell devices. In the case of RBS, the refinement concerns an improved mass resolution achieved by applying projectile ions of higher masses (15N, 22Ne) at higher energies (up to 25 MeV). For AES the principal component analysis (PCA) formalism is adopted starting with a peak‐to‐peak height normalization of the relevant Auger peaks in the measured spectra. This evaluation procedure, which takes advantage of the chemical information inherent in the Auger line shape, gives depth profiles of the elements with respect to their chemical bonding state.

Study of ion mixing during Auger depth profiling of Ge–Si multilayer system. II. Low ion energy (0.2–2 keV) range

Auger electron spectroscopy depth profiling was carried out on amorphous Ge–Si multilayer structures of 2 and 3 nm layer thicknesses using a dedicated Auger depth profiling instrument that rotates the specimen during sputtering and applies a grazing angle of incidence. Ion energy was in the range of 0.2–2 keV. The depth profiles of these multilayer systems are oscillating functions. The authors show that the amplitude of the oscillation versus the square root of the ion energy curve is linear in the energy range used. The depth profile cannot be described either by Gaussian broadening or the Liau model. Simulations using the dynamic transport of ions in matter code reproduce the slopes of the amplitude of oscillation versus the square root of ion energy curves, but the simulated and measured intercepts are different. The ratios of the measured and simulated intercepts are constant and do not depend on the layer thickness. This is used to give a recipe for a ‘‘normalization’’ of the simulated curves.

Diffusion Barrier Effects Against Cu of W-N Layer Formed by Electron Cyclotron Resonance Plasma Nitridation on W Layer

To improve the diffusion barrier effects of W against Cu, W-N/W multilayers formed by electron cyclotron resonance (ECR) N2 plasma exposure on W layers were investigated. Cu/W-N/W/Si multilayer structures were measured using secondary ion mass spectroscopy (SIMS), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), and electric resistance change. The W-N/W films showed a dramatic improvement in barrier properties over those of metallic W films. When the thickness of the W-N/W barrier layer was only 5 nm, the Cu/W-N/W/Si multilayer retained the multilayer structure even after annealing at 873 K for 1 h in H2 without increase of resistivity. The thickness of the W-N layer formed by ECR plasma nitridation was less than 1-2 nm, which provided an excellent barrier effect.

Solid state reaction of Co,Ti with epitaxially-grown Si1−xGex film on Si(100) substrate

The solid state reaction of Co,Ti with an epitaxially grown Si1−xGex strained layer is investigated in this article. The reaction was performed in a rapid thermal annealing system. The resulting films were characterized by Rutherford backscattering, Auger electron spectroscopy, x-ray photoelectron spectroscopy, x-ray diffractometry, and scanning electron microscopy. The electrical resistivity and Hall effect were measured in the temperature range of 77–300 K. Rapid thermal annealing of Co/Si0.8Ge0.2 at 650 °C results in a Co(Si0.9Ge0.1) film with cubic crystalline structure. At higher temperature CoSi2 is formed with Ge segregation towards the surface. After a multi-step annealing, a highly oriented CoSi2 layer can be grown. For TiN/Ti/SiGe, the ternary phase of Ti(Si1−yGey)2 is formed, with a smooth surface and with resistivity comparable to the lowest value exhibited by TiSi2. The Co/Ti/SiGe/Si reaction is studied for the first time, demonstrating that the uniformity of Co/SiGe reaction is improved by applying the Co/Ti bilayer. A TiN(O)/CoSi2(Ge)/Si multilayer structure is formed, and the CoSi2(Ge) layer exhibits a strongly textured structure. Low temperature measurement reveals that the CoSi2(Ge) layer has a re?istivity slightly higher than that of CoSi2.

Fabrication of p-channel polycrystalline Si1−xGex thin-film transistors by ultrahigh vacuum chemical vapor deposition

In this report, we present a novel approach for fabricating polycrystalline silicon-germanium thin-film transistors at low temperatures (≤550 °C). A bottom gate configuration is used for this approach, and an i-Si1−xGex/i-Si/p+-Si1−yGey multilayer is deposited sequentially on the gate oxide using an ultra-high vacuum chemical vapor deposition technique. The i-Si1−xGex serves as the channel while the i-Si is used as a buffer layer for allowing p+-Si1−yGey to be etched selectively on. p-channel thin-film transistors with a field-effect mobility of 13 cm2/V s were achieved using this method, which is superior to those grown by low pressure chemical vapor deposition. Our results indicate that the deposition of poly-Si1−xGex/poly-Si multilayer structure would be a promising way for polycrystalline thin-film device applications.

Study of ion mixing during Auger electron spectroscopy depth profiling of Ge–Si multilayer system

Auger electron spectroscopy depth profiling was carried out on a Ge–Si multilayer structure using a rotated specimen and grazing incidence angle. Under these sputtering conditions the depth resolution is determined mainly by atomic mixing. The dependence of the experimentally measured depth resolution on incidence angle and energy was compared with the simulation results from a trim code. It was found that the trends of the dependencies were the same, but the trim absolute values were different.

Auger in-depth profiling of Mo–Si multilayers

Auger in-depth profiles were measured on a Mo–Si multilayer structure, consisting of 45 periods of 3.3 nm molybdenum and 3.6 nm silicon layers, by means of Ar ion bombardment with rotated specimen and a glancing incidence ion beam probe. The relative sputtering yield of Si and Mo is determined in the ranges of 2–6 keV ion energy and 80°–87° incidence angle with respect to the surface normal. It is shown that the depth resolution depends strongly on the ion energy. The depth resolution changes immediately when the ion energy is changed. This observation is explained by the fact that the depth resolution in our experiment is limited by ion mixing and not by surface roughening. Attempts to determine the initial structure from the measured profile through application of Liau’s model on ion sputtering were not completely successful.

Selective Epitaxial Silicon and Selective Titanium Silicide in an Industrial Integrated Cluster Tool

ABSTRACTIntegrated processes for IC manufacturing are today of prime importance for obtaining such high performance results as uniformity on large diameter wafers, reproducibility, throughput and reliability. Using an industrial integrated cluster reactor we have obtained selective epitaxial Si and selective TiSi2 deposition. This is a 200 mm reactor in which epitaxial silicon has been obtained with <1% (1σ) thickness uniformity and <2% over a 25 wafer batch. Full selectivity of Si on oxide has been obtained below a 20 Torr working pressure using the DCS/H2 gas system. No loading effect has been detected. The main characteristics of this system are described with the most relevant results like: sharp interfaces obtained in Si0.7Ge0.3/Si multilayer structures grown at 650°C, abruptly doped epitaxial layers and residual defect density.TiSi2 has been selectively obtained with minimum substrate consumption using the H2/SiH4 (or DCS)/TiC14 chemistry. The elevated source & drain has also been successfully tested by selective Si epitaxy followed by “in situ” selective TiSi2 deposition to compensate for substrate consumption.

Ion bombardment induced silicide formation during sputter depth profiling of Ta/Si multilayer thin film structure as studied by x-ray photoelectron spectroscopy and auger electron spectroscopy

Auger electron spectroscopy (AES) and X-ray electron spectroscopy XPS sputter depth profiling with 3 keV Ar + ions of a Ta Si multilayer structure with 20 nm double layer thickness showed a pronounced asymmetric shape of the measured profiles of tantalum and silicon. In the region of the increasing slope of the silicon signal a sudden change in the gradient was observed. A detailed study of the chemical shift of Ta 4f peaks in the XPS spectra and the Si LVV peak in AES spectra with respect to standard TaSi 2, pure silicon and metalic tantalum revealed an ion-induced chemical bonding during profiling. The observed chemical shift in the region of the change in slope is attributed to TaSi 2 formation, resulting in a change in the sputtering rate. Crater edge profiling by scanning Auger microscopy reproduced the sputtering profiles with improved resolution.

多層薄膜構造のレーザ加工特性

Laser machining of multi-layer thin film is promissing to become an important processing in fabrications of electronic circuits. The various factors having influence on the characteristics of multi-layer thin film machining with a laser are evaluated theoretically and experimentally. The three dimensional heat diffusion equations including laser light absorption in multi-layer thin film structure are solved numerically to give the time evolution of temperature. Experiments were performed on amorphous Si (a-Si) multi-layer thin film structure of various thickness on transparent conductive oxide(TCO)/glass substrate to verify numerical results. The samples were irradiated with a Q-switched Nd : YAG laser at λ= 1. 06 μm and at λ =0.53, μm. The experimental results on the dependence of laser wavelength, laser pulse duration and laser irradiated energy on machining characteristics are in good agreement with the calculated results.