Temperature dependence of doping element incorporation with the chemical vapour deposition of epitaxial silicon (IV). Incorporation of phosphorus in the Si-H-Cl-lP system

The lower temperature dependence of the phosphorus incorporation with the use of phosphine together with chlorosilanes (ΔH = −13 to −15 kcal/ mole) instead of silane (ΔH = −43 kcal/mole) is explained by introducing a special incorporation equilibrium of phosphine bound to the silicon surface. The source materials phosphorus trichloride and phosphorus pentachloride may be incorporated with this equilibrium.     

Temperature dependence of doping element incorporation with the chemical vapour deposition of epitaxial silicon (V). Incorporation of arsenic

Based on the knowledge previously obtained with regard to the incorporation of phosphorus as an equilibrium-determined process, theoretical values of the enthalpies of the different possible incorporation equilibria are calculated for the incorporation of arsenic into the growing silicon epitaxial layer. The sublimation enthalpies of elemental arsenic, the formation enthalpy of arsine and the enthalpy of solubility enter into the equation. The results compared to the present experimental data of other authors are discussed.     

Total pressure dependence of doping element incorporation during the chemical vapour deposition of epitaxial silicon

Starting from the literature on doping element incorporation at atmospheric and lower pressures the partial pressure of the dopants available within the deposition system is selected as a uniform basis of reference for the total pressure dependence of the doping element incorporation. It is shown that also at reduced pressures the incorporation equilibria of phosphor and arsenic, the author previously derived from the temperature dependence of the doping element incorporation may be used.     

Temperature dependence of photoluminescence from ordered GaInP2 epitaxial layers

The temperature behavior of the integrated intensity of photoluminescence (PL) emission from ordered GaInP₂ epitaxial layer was measured at temperatures of 10 ‐ 300 K. Within this temperature range the PL emission is dominated by band‐to‐band radiative recombination. The PL intensity temperature dependence has two regions: at low temperatures it quenches rapidly as the temperature increases, and above 100 K it reduces slowly. This temperature behavior is compared with that of disordered GaInP₂ layer. The specter of the PL emission of the disordered layer has two peaks, which are identified as due to donor‐accepter (D‐A) and band‐to‐band recombination. The PL intensity quenching of these spectral bands is very different: With increasing temperature, the D‐A peak intensity remains almost unchanged at low temperatures and then decreases at a higher rate. The intensity of the band‐to‐band recombination peak decays gradually, having a higher rate at low temperatures than at higher temperatures. Comparing these temperature dependencies of these PL peaks of ordered and disordered alloys and the temperature behavior of their full width at half maximum (FWHM), we conclude that the different morphology of these alloys causes their different temperature behavior. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition

A simple quantitative model for the surface adsorption of nitrogen has been developed to simulate the doping incorporation in intentionally doped 4H–SiC samples during epitaxial growth. Different reaction schemes are necessary for the two faces of SiC. The differences are discussed, and implications to the necessary model adjustments are stressed. The simulations are validated by experimental values for a large number of different process parameters with good agreement.     

Vapour phase growth of epitaxial silicon carbide layers

After a brief overview of different epitaxial layer growth techniques, the homoepitaxial chemical vapour deposition (CVD) of SiC with a focus on hot-wall CVD is reviewed. Step-controlled epitaxy and site competition epitaxy have been utilized to grow polytype stable layers more than 50 μm in thickness and of high purity and crystalline perfection for power devices. The influence of growth parameters including gas flow, C/Si ratio, growth temperature and pressure on growth rate and layer uniformity in thickness and doping are discussed. Background doping levels as low as 10¹⁴ cm⁻³ have been achieved as well as layers doped over a wide n-type (nitrogen) and p-type (aluminium) range.

Furthermore the status of numerical process simulation is mentioned and SiC substrate preparation is described. In order to get flat and damage free epi-ready surfaces, they are prepared by different methods and characterised by atomic force microscopy and by scanning electron microscope using channelling patterns. For the investigation of defects in SiC high purity CVD layers are grown. The improvement of the quality of bulk crystal substrates by micropipe healing and so-called dislocation stop layers can further decrease the defect density and thus increase the yield and performance of devices. Due to its high growth rate functionality and scope for the use of multi-wafer equipment hot-wall CVD has become a well-established method in SiC-technology and has therefore great industrial potential.     

Incorporation of dopants into epitaxial CVD-Silicon layers and incorporation equilibrium

Based on the temperature dependence of the layer growth rate influence on the incorporation of dopants into epitaxial silicon the range of validity of an incorporation equilibrium between dopants in the gas phase and in the layer is discussed. Additional to the borderline case of an infinitely low layer growth rate the incorporation equilibrium is equally important to high layer deposition temperature. For this region deducing the incorporation enthalpy from the temperature dependence of the incorporation of dopants proves adequate.     

Defects in epitaxial layers of silicon-germanium grown on silicon substrates

Crystal defects of various kinds found in epitaxially grown Si/Ge alloy layers on Si substrate, may be either inherent to the material and originating from atomic radii misfit, or can be traced to the growth process and controlled or eliminated by varying its parameters. A network of slip lines, becoming more pronounced with increased Ge content, indicates plastic deformation resulting from partial relief of stresses during the high temperature growth process. Electron microprobe and X-ray diffraction analysis indicate some Ge segregation in the fault vicinity, and a slight anisotropy in the lattice constant expansion due to the Ge.     

The influence of gas-phase etch removal,deposition temperature and substrate properties on the crystallographic perfection of silicon epitaxial layers

An investigation of the defect structure of silicon homoepitaxial layers, as influenced by gas phase etching, deposition temperature, and substrate properties, is presented. The minimum values of etch removal and deposition temperature necessary for sufficient layer perfection have been determined. The defect and impurity distribution in the substrate, as formed during a preceeding arsenic buried layer processing, have been evaluated and are discussed here with regard to their influence on the epitaxial layer perfection.     

Autodoping of epitaxial silicon layers (II) diffusion-induced autodoping

From discussing the influences of layer growth duration and deposition temperature on the slope of the steep autodoping profile branch adjacent to the substrate, it is concluded that there exists a special autodoping part, termed redistribution autodoping, which is independent on solid state diffusion effects, but should be restricted to the beginning of the layer growth.     

Autodoping during the deposition of epitaxial Silicon layers from the gas phase (I). Autodoping from the gas phase

The doping profile within the autodoping range of epitaxial layers deposited on lowresistance substrates, is considered the result of redistributing a substrate doping fraction through the substrate layer boundary, of incorporating a limited amount of dopants from the gas phase, originating from the preepitaxial process, and the result of incorporating dopants, externally admitted to the gas flow during the deposition. Assuming a special incorporation equilibrium to exist for the gas phase fraction of autodoping an analytic expression is derived, correlating the autodoping profile characteristic to the limited amount of dopants in the gas phase. The extent is discussed, to which the gas phase fraction of autodoping may be influenced by varying the deposition process.     

Effect of growth conditions on formation of grain boundaries in epitaxial silicon layers

The formation of grain boundaries of the general type, along with small-and large-angle symmetric grain boundaries with the 〈 〉 axis in the epitaxial layers grown onto bicrystal substrates by the method of thermal migration has been studied. The solvent was aluminum. It is shown that if the grain boundaries in the epitaxial layer are tilted to the crystallization front or if there is a temperature gradient tangential to this front, their orientation differs from their orientation in the substrate. The large-angle symmetric boundaries are more stable than the boundaries of the general type. The grain-boundary energy and rotation moment of large-angle symmetric boundaries are evaluated.     

Morphology of SiC epitaxial layers grown by temperature gradient zone melting (II). The dependence of the structural properties of the epitaxial layers on the growth conditions

In the present paper the relationships between the structural perfection of the layer, represented by the Tb average integral concentration (which is a criterion for the second phase quantity), the rocking curve half-width (a criterion for the general structural perfection of the layer) and the layer growth conditions, represented by the quantity, which is the most important characteristic of the growth process, namely the supersaturation are discussed. The considered model allows to conclude, that a optimal value of the supersaturation exists, at which the structural perfection is maximal.     

The incorporation of phosphorus in silicon; The temperature dependence of the segregation coefficient

An analysis is given of the temperature dependence of the segregation of phosphorous during chemical vapour deposition. The observed temperature dependence is compared with a theoretical expression which takes into account the ionization of P in the solid. From both expressions the differential heat of solution of P in Si can be calculated to be –14.9± 2.3 kcal, the uncertainty being mainly due to the unknown value of the bandgap of silicon at high temperatures. The heat of solution can be broken down - amongst others - into a binding part and a strain part for the incorporation of P in Si. The strain energy can be calculated to be 2.2 kcal, which gives an energy of 50.2 ± 0.6 kcal for the binding energy of the P-Si bond, close to the value of the Si-Si bond itself being 53.25 kcal.     

Ordered arrays of epitaxial silicon nanowires produced by nanosphere lithography and chemical vapor deposition

Gold dot arrays on (1 1 1) Si substrates obtained through nanosphere lithography (NSL) combined with sputtering and annealing in Ar at 1000 °C are used to catalyze vapor liquid solid (VLS) epitaxial growth of silicon nanowires (Si NWs) using chemical vapor deposition (CVD) with SiH₄ in Ar. The NWs grow primarily epitaxially on the underlying (1 1 1) Si wafer following the four independent 〈1 1 1〉 directions. The diameter distribution of the wires reflects the diameter distribution of the catalyst gold dot arrays and is therefore predictable. The wire length depends on the size of the gold catalyst for the same CVD parameters. The wire position is foreseeable within the limits of the pattern geometrical quality, but one-to-one growth of NWs to gold dots is not always observed, probably due to (very locally) the remaining presence of silicon oxide. Overall, this inexpensive patterning method for obtaining high-quality crystalline VLS Si NWs by CVD fulfills the requirements of many device applications, where patterning control, quality and reproducibility of the nanostructures are crucial.     

Doping of epitaxial CVD silicon with arsenic or phosphorus (i). Steady state conditions

A modified theoretical model of dopant incorporation is discussed, while comparing it with the Reif-Dutton model. In contrast to the Reif-Dutton model, which has been based on the adsorption step of dopant substances, the modified model is related to the real dopant incorporation step and its backreaction as the rate controlling factors. By that a thermodynamical decomposition equilibrium of the dopant source material may be established without being influenced by the dopant incorporation. Each component of the decomposition equilibrium acts as a source for making dopant atoms available for incorporation. Equivalent to the Reif-Dutton model the modified model describes the growth rate influence of the layer on the incorporation of dopants and additionally enables the temperature dependence, total pressure dependence and the specific features of dopant incorporation at high concentrations to be explained.     

Doping of epitaxial CVD silicon with arsenic or phosphorus (II). Non-steady state conditions

Theoretical expressions are developed suggesting how the non-steady state dopant incorporation is influenced by the parameters of the layer deposition process. Expressions for the transient doping profile are dealt with taking into account two different mechanisms of the overall rate controlling step. The one is based on the assumption made by Reif and Dutton that the adsorption step, which is followed by a solution equilibrium, is the rate controlling step, the other is based on the idea that the dopant incorporation reaction and its backreaction, following after the adsorption of dopant particles, are controlling the overall incorporation.     

Crystallographic defects in epitaxial layers of cadmium sulphide

Thin epitaxial films of CdS deposited in high vacuum on ionic single crystal substrates have been studied by transmission electron microscopy. The (100), (110) and (111) faces of NaCl and the (111) face of BaF₂ were used as substrate surfaces. Both cubic sphalerite and hexagonal wurtzite structure films have been produced. The orientations of the sphalerite structure films were (100) and (110) and were produced on substrate faces having the same two orientations. The wurtzite structure films were in (0001) orientation and grew on (111) oriented substrate faces. For a fixed rate of deposition both the number and type of defects found in the films appear to be dependent upon the growth temperature and the crystal structure. Annealing the films at a high temperature has been tested as a means for reducing their defect content and the effect is very different for the two crystal structures. A reduction in the defect content of the wurtzite structure films is induced but no change in the crystal structure occurs. In contrast to this, the sphalerite structure films undergo a progressive phase transformation to the wurtzite stucture while at the same time losing a high proportion of their defects.