Chemical Vapor Deposition Of Si Research Articles

Nanometer-Scale Conversion of Si3N4 to SiOx for Applications in Lithography, Micromachining, and Selective-Area CVD

We present the use of scanning probe oxidation of Si3N4 masks for performing nanolithography, nanomachining, and nanoscale epitaxial growth on silicon. Three most unique features of this approach are presented: (i) exceptionally fast oxidation kinetics using silicon nitride masks (∼30 μm/s at 10 V for a ≈5 nm thick film), (ii) selective-area anisotropic etching of Si using a Si3N4 etch mask, (iii) selective-area chemical vapor deposition of Si using a SiO2/Si3N4 bilayer growth mask.

Chemical vapor deposition of Si on chlorosilane-treated SiO2 surfaces. I. Suppression and enhancement of Si nucleation

We have investigated the nucleation processes in chemical vapor deposition (CVD) of Si on SiO2 surfaces that were treated with different chlorosilane gases SiHnCl4−n, where n=0, 1, or 2. These gases chemisorb on the SiO2 surface in a self-limiting manner. At 493 K, the saturation coverage was reached at 4×108 L exposure for the SiH2Cl2 gas, and at 2×109 L for the SiHCl3 and SiCl4 gases. CVD of Si was carried out on the chlorosilane-saturated SiO2 surfaces using Si2H6 as a source gas at 853 K. It has been found that the SiCl4 and SiHCl3 treatments effectively passivate the nucleation centers on the SiO2 surfaces, while the SiH2Cl2 treatment drastically enhances Si nucleation. The reaction mechanisms causing these differences are discussed, considering the structural changes of the adsorbed chlorosilane fragments at the CVD temperature. Application of the SiCl4 treatment to the patterned SiO2 mask for selective-area epitaxial growth of Si is demonstrated.

Chemical vapor deposition of Si on chlorosilane-treated SiO2 surfaces. II. Selective deposition in the regions defined by electron-beam irradiation

This article reports a selective-area deposition process using chlorosilane-treated ultrathin SiO2 masks on which the patterns are directly defined by irradiation of a focused electron beam (EB). Three different chlorosilane gases (SiH2Cl2, SiHCl3, and SiCl4) were first adsorbed on the SiO2 surfaces, and the regions with reactive sites were defined by taking advantage of electron-stimulated desorption (ESD) of the surface adsorbates. For the SiHCl3- and SiH2Cl2-treated surfaces, the nucleation density was remarkably high in the EB-irradiated regions. Such nucleation enhancement was less significant for the SiCl4-treated surface. For the purpose of direct patterning and selective growth, we conclude that SiHCl3 is the optimum treatment gas because it effectively suppresses Si nucleation outside of the EB-irradiated patterns. The overall ESD sensitivity of the SiHCl3-adsorbed mask was 50 mC/cm2, and a significant nucleation enhancement was observed by irradiation of 7 mC/cm2. We also report an extension of this selective-area processing to window opening through the ultrathin SiO2 mask layer. The factors limiting the minimum feature size of the grown Si structures and the opened windows are discussed.

Application of hot-wire chemical vapor-deposited Si:H films in thin film transistors and solar cells

This paper shows a wide range of applications of the hot-wire chemical vapor deposition (HWCVD) method to either deposit photosensitive hydrogenated amorphous silicon (a-Si:H), polysilicon (poly-Si) and heterogeneous Si materials, dielectric hydrogenated amorphous silicon nitride (a-SiNx:H) of device quality, or to carry out hydrogen passivation treatments. Various choices of deposition parameters, i.e. process temperature, wire temperature and filament materials, have been investigated to decide the growth rate, substrate material and device configuration. The main feature of our poly-Si films is the compact nature, which manifests itself in anti-ferromagnetically-coupled defect dimer formation and hydrogen diffusion through compact sites. Very thin grain-boundary defects, purely intrinsic nature and very low oxygen incorporation, both during and post-deposition, have resulted in poly-Si films of device quality. Thin film transistors (TFTs) and solar cells have been fabricated using the above-mentioned HWCVD-deposited materials. Highly stable TFTs in the inverted staggered configuration, using heterogeneous Si, showed a field effect mobility of 1.5 cm2 V−1 s−1, whereas top-gate TFTs using poly-Si on glass showed a mobility of 4.7 cm2 V−1 s−1. The paper demonstrates the application of HWCVD a-SiNx as a dielectric material in bottom-gate TFTs, and complete TFTs have been successfully fabricated by the HWCVD process (except the contact layers). Solar cells in an n–i–p structure on plain stainless steel (SS) substrate showed efficiencies of 7.2% for a-Si:H and 4.4% for poly-Si i-layers. An a-Si/poly–Si tandem cell, with all-HWCVD i-layers, on a SS substrate without a back reflector and texturization yielded an efficiency of 8.1%. This was achieved at a deposition rate of 10 Å s−1 for poly-Si.

Scanning probe oxidation of Si 3N 4 masks for nanoscale lithography, micromachining, and selective epitaxial growth on silicon

For studying the physical, chemical, and electronic properties of ultrasmall man-made structures, the major challenge is to fabricate highly uniform structures and control their positions on the nanometer length scale. Local oxidation of metals and semiconductors using a conductive-probe atomic force microscope (AFM) or other scanning probe microscopes in air at room temperature has emerged as a simple and universal method for this purpose. Here the uses of scanning probe oxidation of Si 3N 4 masks for performing nanolithography, nanomachining, and nanoscale epitaxial growth on silicon are reviewed. The three most unique features of this approach are presented: (1) exceptionally fast oxidation kinetics using silicon nitride masks (∼30 μm/s at 10 V for a ∼5-nm-thick film); (2) selective-area anisotropic etching of Si using a Si 3N 4 etch mask; and (3) selective-area chemical vapor deposition of Si using a SiO 2/Si 3N 4 bilayer growth mask.

High temperature chemical vapor deposition of silicon on Fe(100)

Oxidized silicon is a promising candidate for the adhesion promotion of polymeric coatings on iron and steel. Therefore, the surface of iron must be covered by silicon and silicon oxide. This can be done by the chemical vapor deposition (CVD) of silane gas, a process which might be applied in industry easily. Because of these reasons the CVD of Si on the Fe(100) surface was studied at the deposition temperature of 770°C. The silane partial pressure ranged from 0.02 to 0.2 mbar while the total pressure was constant 990 mbar. It was found that the morphology of the surface changes from a very thin two-dimensional (2D)- to a complex and thick three-dimensional (3D)-structure with increasing deposition time. This is connected with a change of the chemical structure and a change in the reaction mechanism. Different processes like passivation of the surface by oxidation and surface diffusion influence the deposition. Models are proposed to describe the mechanism of growth of the surface layer.

Effects of Growth Kinetics and Surface Emissivity on Chemical Vapor Deposition of Silicon in a Lamp-Heated Single-Wafer Reactor

Chemical vapor deposition of Si in a lamp-heated single-wafer reactor is studied by monitoring the growth rate of films deposited on bare S. silicon-on-insulator (SOI), and oxidized Si wafers. The growth rate is consistently higher for deposition of polycrystalline Si than for epitaxy of Si. due to different kinetics dictating the two depositions. Epitaxy of Si on SOI shows a higher overall growth rate than on hare Si. Likewise, deposition of polycrystalline Si on oxidized Si wafer with a 4000 Angstrom thick oxide has a higher growth rate than on that with 15 Angstrom oxide. These are attributed to surface emissivity variation during Si deposition. The difference in kinetics plays a more dominant role than the surface emissivity variation in affecting the growth rate for the depositions studied.

Nanoscale selective-area epitaxial growth of Si using an ultrathin SiO2/Si3Ni4 mask patterned by an atomic force microscope

We report selective epitaxial growth of Si using an ultrathin bilayer mask. The key feature of this process is direct writing of nanoscale patterns by means of local anodic oxidation of a Si3N4 layer using an atomic force microscope operated in air. Windows for selective growth are defined by wet etching of the locally oxidized regions. High growth selectivity upon chemical vapor deposition of Si is accomplished by employing the bilayer mask structure which is formed by oxidizing the Si3N4 surface and then selectively desorbing SiO2 in the windows. High-quality homoepitaxial growth is verified by transmission electron microscopy. We also report a simple plasma-treatment technique which solves the problem of retarded SiO2 desorption in the nanoscale windows.

Fe 3Si surface coating on SiFe steel

Fe 3Si layers were prepared using chemical vapor deposition of Si on the surface of GO steel and its subsequent heat treatment. The changes in the structure and phase composition after different heat treatment conditions have been analyzed. The coating is characterized by high hardness, good corrosion resistance, high electrical resistivity, and the spin texture which differs from the steel substrate.

Controlled bond formation between chemical vapor deposition Si and ultrathin SiO2 layers

This article reports that chemically active sites on SiO2 surfaces can be either passivated or introduced intentionally by treating them in a proper chlorosilane gas, SiHnCl4−n (n=0,1,2). Our experiments of Si chemical vapor deposition on SiO2-covered Si have shown that Si deposition is suppressed on SiCl4- and SiHCl3-treated samples, while an SiH2Cl2 treatment drastically enhances Si nucleation. Thus, the chlorosilane treatment is a unique way for us to control the interface bonds between the SiO2 surface and the Si deposits on it. We also demonstrate resistless selective-area deposition using a SiHCl3-treated ultrathin SiO2 mask layer. Patterns are defined on the mask surface by direct electron-beam irradiation which induces Cl desorption thereby forming chemically reactive surface defects.

Chemical vapor deposition of Si nanowires nucleated by TiSi2 islands on Si

Silicon “nanowires” can be formed by chemical vapor deposition of Si onto Si substrates on which nanometer-scale, Ti-containing islands have been grown. At the growth temperatures used, the Ti-containing islands remain solid and anchored to the substrate, while the Si nanowires grow out from the islands, which remain at their bases. The nanowire growth mechanism, therefore, differs from the usual vapor-liquid-solid process and provides a potential route for the formation of oriented Si nanostructures or semiconductor-metal-semiconductor structures compatible with Si integrated circuits.

Interaction of phosphine with Si(100) from core-level photoemission and real-time scanning tunneling microscopy

In this paper, we investigate the interaction of phosphine $({\mathrm{PH}}_{3})$ on the $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ surface at temperatures between 635 and 900 K. The hydrogen desorption, growth mode, surface morphology, and chemical composition and ordering of the surface layer are examined by synchrotron radiation core-level photoemission and real-time high-temperature scanning tunneling microscopy. The $\mathrm{P} 2p$ core-level spectra indicate that decomposition of ${\mathrm{PH}}_{n}$ is complete above $\ensuremath{\sim}550$ K and the maximum P coverage is strongly influenced by the growth temperature, which governs the coverage of H-terminated sites. The scanning tunneling microscopy (STM) images taken at real time during ${\mathrm{PH}}_{3}$ exposure indicate that a surface phosphorus atom readily and randomly displaces one Si atom from the substrate. The ejected Si diffuses, nucleates, and incorporates itself into islands or step edges, leading to similar growth behavior as that found in Si chemical vapor deposition. Line defects both perpendicular and parallel to the dimer rows are observed on the nearly P-saturated surface. Perpendicular line defects act as a strain relief mechanism. Parallel line defects result from growth kinetics. STM images also indicate that incorporating a small amount of phosphorus eliminates the line defects in the $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}n$ surface.

Solid phase epitaxy for low pressure chemical vapor deposition Si films induced by ion implantation

This work investigated the ion implantation induced solid phase epitaxy (SPE) of Si thin films prepared by low pressure chemical vapor deposition (LPCVD). Previous studies indicate that the residual layer at the interface between the Si thin film and single crystalline substrate is the major obstacle to the SPE process of Si film. In this work, Ge + and Si + ion were implanted to completely amorphize the Si film prepared by LPCVD. Ion implantation also mixed the interfacial oxide layer and its effects on subsequent epitaxial growth of Si film subjected to various annealing conditions were discussed as well. In addition, the specimen surface was modified by inductive couple plasma (ICP) process. The ICP modification using nitrogen gas could form a vacancy source on the sample surface to enhance the atomic diffusion rate and change the stress state in the vicinity of surface, thereby accelerating the SPE process.

Ellipsometric investigation of nucleation sites for chemical vapor deposition of Si on SiO2 and Si3N4 surfaces

The nucleation of polycrystalline silicon by chemical vapor deposition on stoichiometric and silicon-rich silicon dioxide and silicon nitride films was studied using real time ellipsometry. The time of the appearance of the first stable Si nuclei, the incubation time (tinc), was found to vary with the Si content within a film type (oxide or nitride) and also tinc varied for different film types with the shortest tinc for Si-rich silicon nitride films. Differences between Si bound (to O or N) and free Si (bound to Si) were observed with free Si being more effective at promoting nucleation. Anion screening effects might also yield second order reactivity differences.

Visualizing radical-surface interactions in plasma deposition processes: reactivity of SiH/sub 3/ radicals with Si surfaces

There is a need for improving our fundamental understanding of the radical surface interactions during plasma enhanced chemical vapor deposition of Si. Toward this goal, we have calculated the interaction energy between SiH/sub 3/ radicals and various Si surfaces, and mapped the changes in this energy as a function of position on the surface. Application of this analysis to the SiH/sub 3/ radical impinging on a variety of Si surfaces, coupled with detailed investigation of the radical impingement dynamics, proved valuable in understanding and visualizing the driving forces that determine the nature of the radical-surface interactions during plasma deposition of Si.

Thermal Conductivity of Diamond Films: 0.5 μm to 0.5 mm

AbstractA review of the thermal properties of chemical‐vapor‐deposited (CVD) diamond ranging in thickness from 0.5 μm to 0.5 mm is presented. The typical columnar microstructure of the material has a strong influence on the thermal properties, causing a steep gradient in both the in‐plane (κ‖) and normal (κ⊥) conductivities, as well as considerable anisotropy. Data for κ‖ from above room temperature down to liquid helium temperatures for high‐quality thick samples has revealed several types of phonon scattering centers preferentially located along grain boundaries. This model of dirty grain boundaries provides a framework for understanding the conductivity of thinner, lower‐quality material. The general difficulty of identifying microscopic sources of thermal resistance in CVD diamond is discussed, especially in view of the tendency for the concentrations of many types of defects to be highly correlated with each other. Finally, recent work on interfacial resistance between CVD diamond and Si substrate shows that the columnar microstructure has a strong influence for high‐quality films as thin as 2 μm.

Effect of boron-doping on the growth rate of atmospheric pressure chemical vapour deposition of Si

Abstract In this study an analytical approach is made to understand the mechanisms of boron-doping of Si using B2H6 and SiH4 in a H2 atmosphere. A simple model, namely that every boron atom on the surface creates a two-dimensional nucleation site for Si, is used to explain the observed growth enhancement of Si at low temperatures and high B-doping levels. An excellent agreement between experimental data and the model is found. This result also gives deeper insights into the growth limiting steps of atmospheric pressure chemical vapour deposition of undoped Si.

Rapid Thermal Processing: Fixing Problems with the Concept of Thermal Budget

Until now, kinetic effects in rapid thermal processing have been assessed using the concept of thermal budget, with the idea that thermal budget minimization should minimize dopant diffusion and interface degradation. This work highlights shortcomings with that principle. Experiments directly comparing the rate of Si chemical vapor deposition with that of dopant diffusion show how thermal budget minimization can actually worsen diffusion problems rather than mitigate them. We present a straightforward framework for improving the results through comparison of activation energies of the desired and undesired phenomena. This framework explains all the experimental results and provides strong kinetic arguments for continued development of rapid isothermal processing and small batch fast ramp methods.

Selective Nucleation-based Epitaxy (SENTAXY): A Novel Approach for Thin Film Formation

We have proposed a novel approach to form polycrystalline thin films called SENTAXY (Selective Nucleation-based Epitaxy). The location of the crystallites and boundaries with neighbors are generally random in polycrystalline films over amorphous substrates, because the formation of the films is initiated by the spontaneous nucleation of crystallites. The proposed method introduces artificial nucleation sites at which the crystallites nucleate selectively and grow epitaxially. As a result, it becomes possible to predetermine the location of crystallites and their boundaries. The principle of the method has been demonstrated in the chemical-vapor deposition of Si and the solid-state crystallization of amorphous Si films and has also been applied to other systems.

Problems with The Concept of Thermal Budget: Experimental Demonstrations

ABSTRACTUp to now, kinetic effects in rapid thermal processing (RTP) have been assessed using the concept of thermal budget, with the idea that thermal budget minimization should minimize dopant diffusion and interface degradation. This work highlights shortcomings with that principle. Experiments comparing directly the rate of Si chemical vapor deposition with that of dopant diffusion show how thermal budget minimization can actually worsen diffusion problems rather than mitigate them. We present a straightforward framework for improving the results through comparison of activation energies of the desired and undesired phenomena. This framework explains the experimental results and provides strong kinetic arguments for continued development of rapid isothermal processing and small batch fast ramp methods.