Methods of producing plasma enhanced chemical vapor deposition silicon nitride thin films with high compressive and tensile stress
Michael BelyanskyM. A. ChaceOleg GluschenkovJ.J. KempistyN. KlymkoAnita MadanAnupama MallikarjunanS. MolisPaul RonsheimY. WangDoohwan YangY. Li
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Various methods of generating high stress in thin plasma enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) films are reported. Besides the mainstream variation of plasma power and other process parameters, novel techniques such as creation of high density layers in multilayer PECVD structures or exposure of SiN films to ultraviolet radiation are shown to increase intrinsic film stress. Thin PECVD SiN films have been analyzed by a variety of analytical techniques including Fourier transform infrared spectroscopy, x-ray reflectivity (XRR), time of flight secondary ion mass spectrometry, and transmission electron microscopy to collect data on bonding, density, chemical composition, and film thickness. The level of bonded hydrogen as well as film density has been found to correlate with film stress. Creation of multilayer structures and high density layers help to build up more stress compared to a standard single layer film deposition. Both the density and number of layers in a film, characterized by XRR, affect the stress. Higher density layers affect diffusion profiles and show impurity oscillations corresponding to a multilayer film structure. Ultraviolet cure allows the film to achieve higher level of tensile stress at relatively low temperatures (400–500°C), comparable to the result of film high temperature annealing.Keywords:
X-ray reflectivity
Films of tantalum pentoxide (Ta2O5) with thickness of 10–100 nm were deposited on Si wafers and have been compared using spectroscopic ellipsometry (SE) and x-ray reflectivity (XRR). (Ta2O5) was chosen for comparison work based on various criterions for material selection outlined in this article. Measurements were performed at six positions across the sample area to take into consideration thickness and composition inhomogeneity. SE and XRR fitted curves required the incorporation of a linearly graded interface layer. SE systematically measured higher values of film thickness as compared to XRR. A linear equation was established between the thickness measurements using SE and XRR. The slope of the linear equation established was found to be 1.02±0.01. However, the intercepts were found to be 1.7±0.2 and 2.6±0.3 when the interface was excluded and included, respectively. These differences in the values of intercepts were attributed to the uncertainties in the determination of the interface layer.
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Tantalum pentoxide
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In this study ZnO thin film was fabricated by sol-gel spin coating method on glass substrate. X-ray reflectivity (XRR) and its optimization by simulated annealing (SA) technique have been used for characterization and extracting physical parameters of the film. The model independent information was needed to establish data analyzing process for XRR before optimization process. This independent information was extracted from wavelet transform of Fresnel reflectivity normalized XRR. This transformation yields thickness of each coated layer. This information was a keynote for constructing optimization process. Specular XRR optimization yielded structural parameters such as thickness, roughness of surface and interface and electron density profile of the film. Acceptable agreement exists between results obtained from wavelet transformation and XRR fitting.
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With the increasing miniaturisation, the use of thin silicide films in VLSI technology becomes more important X-ray reflectivity (XRR) is a non-destructive method for the characterization of layer thickness, surface and interfacial roughness of thin films. We have used XRR for the characterization of thin CoSi/sub 2/ and PtSi layers. The silicide films were prepared by rapid thermal annealing and XRR war used before and alter silicidation to measure the layer thickness. The XRR results are compared with results obtained on the same films by Rutherford backscattering spectrometry (RBS), cross-sectional transmission electron microscopy (XTEM), profilometry and atomic force microscopy (AFM). By XRR we were able to accurately measure the thickness of silicide layers down to 3 nm.
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Abstract We review the use of specular X-ray reflectivity (XRR) for the characterization of thin-film and surface structures. Specular X-ray scattering at small scattering vectors allows characterization of electron density profiles perpendicular to the surface on the length scale of 0.1 to 100 nm. This allows measurement of surface morphology, thin films, multilayer structures, and buried interfaces. The technique is nondestructive and can be applied in situ in a variety of processing environments. In the first half of the article, we review the theory and methods of XRR, including analysis of XRR spectra by a multilayer optical approach and a discussion of surface roughness measurements by XRR and other techniques. In the second half, we present a wide range of examples of XRR applications in thin-film structures, dynamic processes, liquid surfaces, and macromolecular structures.
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In the first part of this chapter the theoretical principles of X-ray reflectivity (XRR) techniques are reviewed: in particular it is possible to distinguish between specular reflectivity, when X-ray intensity is measured at the reflecting angle equal to the incidence angle, and diffuse reflectivity, that involves off-specular scattering. Structural information can be extracted from XRR patterns, as thickness, density and roughness of each layer. The reflectivity signal depends on the electron density as a function of depth. The mass density and the atomic number control the amount of signal, that can be reduced by the roughness. In the second part of the chapter, examples of XRR applications on thin films and multilayer are reviewed, with particular attention to recent developments. Major advances in X-ray optics during the past years, in particular, monochromator crystals and multilayer X-ray optics, make XRR experiments widely accessible in laboratory, and not only to the synchrotron beamlines. In recent years, in-situ XRR measurements under controlled atmosphere, humidity and temperature were also performed. In the third part of the chapter, a comparison between structural and morphological results, obtained by XRR and other standard techniques, is discussed. Finally, an overview regarding the improvements that are expected in the next future is also given.
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In this Letter, we present a method for the decoration of layer-by-layer (LbL) structures by heavy metal ions, which allows X-ray reflectivity (XRR) measurements at the solid/water interface. The improved contrast has allowed us to obtain well-structured X-ray reflectivity curves from samples at the liquid/solid interface that can be used for the film structure modeling. The developed technique was also used to follow the formation of complexes between DNA and the LbL multilayer. The XRR data are confirmed by independent null-ellipsometric measurements at the solid/liquid interface on the very same architectures.
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For realizing highly reliable Cu wiring in 3D/2.5D-IC, SiNx films formed by the reactive sputtering deposition and the plasma-enhanced chemical vapor deposition (PECVD) at low substrate temperatures are characterized and compared by use of X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The film density obtained by XRR shows clear difference between the sputtering and PECVD films. Si-H bonding concentrations obtained by analyzing FT-IR spectra show good correlations with the film densities independent of deposition methods and conditions. Lower density properties of PECVD films could be attributed to higher density of residual Si-H bonds in the films.
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X-Ray Calc is a fast and convenient tool for the simulation of X-ray reflectivity (XRR). The software was developed with the aim of simplification and acceleration of the XRR simulation through a user-friendly interface and optimized computation core. X-Ray Calc implements the recursive approach of calculation of XRR based on Fresnel equations and proposes special instruments for the modeling of periodical multilayer structures. X-Ray Calc computes XRR as a function of wavelength or grazing angle and can be used for the simulation of the performance of X-ray mirrors. Computer modeling and fitting to experimental grazing incidence X-ray reflectometry (GIXR) is a powerful tool. It could be used for a comprehensive analysis of the structure of single- and multi-component layered nanomaterials. This method allows for the obtaining of information about thickness, roughness, and density of individual layers in coatings by the fitting of the modeled GIXR to the experimental ones.
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