Solubility Of Carbon In Silicon Research Articles

Thermodynamic Studies of Carbon in Liquid Silicon Using the Central Atoms Model

The activity and solubility of carbon in liquid silicon were calculated using the ideal interstitial solution model. The central atoms model of binary interstitial solution was introduced into the study of carbon solubility in silicon for the first time. The temperature dependence of the carbon activity coefficient and solubility in liquid silicon was presented. Good agreement with the reported data in the literature proves the validity of central atoms model in the thermodynamic studies of a Si–C binary interstitial solution.

Epitaxy of carbon-rich silicon with MBE

At high concentrations, carbon in silicon shows some properties of technological interests like gap engineering, lattice engineering or the reduction of the so-called ‘Transient Enhanced Diffusion’ of some dopants. The carbon incorporation in concentrations above 1% is nevertheless a difficult task due to the low carbon solubility in silicon. Here, we present a systematic approach of the Si 1− x C x layer growth by Molecular Beam Epitaxy (MBE). To study the influence of the growth temperature on the carbon incorporation, we deposit 100 nm thick silicon layers with different carbon concentrations separated by a 100 nm silicon spacer for different temperatures, ranging from 370 up to 800 °C. In-situ Reflection High Energy Diffraction (RHEED), Secondary Ion Mass Spectroscopy (SIMS) and cross-sectional Transmission Electron Microscopy (TEM) have been performed to characterize the as-grown structures. We show the presence of two distinct growth phenomena, a ‘classical’ one, around 450 °C, where carbon is mainly substitutionally incorporated, defect free until 2%; and a second one, above 550 °C, showing an agglomeration of carbon in thin layers with presumably a very high local concentration, without any planar defects. We propose in this work a diagram of Si:C growth by MBE.

MBE growth and properties of supersaturated, carbon-containing silicon/germanium alloys on Si(001)

The growth and properties of Si1−yCy and Si1−x−yGexCy alloys pseudomorphically strained on Si(001) will be reviewed. Although the bulk solubility of carbon in silicon is small, epitaxial layers with more than 1% C can be fabricated by molecular beam epitaxy and various chemical vapor deposition techniques. One of the most crucial questions is the relation between substitutional and interstitial carbon incorporation, which has a large impact on the electrical and optical properties of these layers. The carbon substitutionality (fraction of substitutional incorporated carbon atoms) is strongly influenced by the growth conditions, such as growth temperature and Si growth rate. The mechanical and structural properties, and the influence of C atoms on band structure and charge carrier properties will be discussed. Further, we will show how lower carbon concentrations can influence dopant diffusion, without affecting strain and band alignment. We demonstrated that suppressed boron diffusion in carbon-rich epitaxial layers can be used to increase the performance of SiGe heterojunction bipolar transistors (HBTs). We demonstrate epitaxially grown SiGe:C HBTs with static and dynamic performance suitable for high frequency applications. Compared to SiGe technologies, the addition of carbon provides significantly greater flexibility in process design and offers wider latitude in process margins. The physical mechanism for suppressed boron diffusion in carbon-rich Si and SiGe (about 0.1% carbon) is an undersaturation of Si self-interstitials due to outdiffusion of carbon.

The Effect of Carbon/Self-Interstitial Clusters on Carbon Diffusion in Silicon Modeled by Kinetic Monte Carlo Simulations

AbstractA new model for carbon diffusion in silicon that explains carbon diffusion during annealing at 850°C and 900°C in superlattice carbon structures grown by MBE is implemented using the Monte Carlo atomistic simulator DADOS. Carbon concentrations in the delta layers are 2×1020 cm−3, exceeding by far the solid solubility. The simple kick-out mechanism which incorporates the well established values of the product of diffusivity and equilibrium concentrations of intrinsic point defects and in-diffusion experiments of carbon in silicon does not explain the observed C diffusion profiles. A more detailed analysis of the experiments shows that, in order to fit them, a more unstable Ci is required. Therefore, we include the formation of clusters in the simulations. The formation of carbon/Si self-interstitial clusters promotes the premature break-up of Ci and the increase of the Si self-interstitial concentration in the carbon rich regions and, consequently, provides a better fit to the experiments. The low solubility of carbon in silicon at the annealing temperatures explains why these clusters are formed, even under conditions where the self-interstitial concentration is below the equilibrium value.

Ternary SiGeC alloys: growth and properties of a new semiconducting material

The growth and properties of Si 1− y C y and Si 1− x− y Ge x C y alloys pseudomorphically strained on Si(001) will be critically reviewed. Although the bulk solubility of carbon in silicon is small, epitaxial layers with more than 1 at.% C can be fabricated by molecular beam epitaxy and different chemical vapour deposition techniques. One of the most crucial questions is the relation between substitutional and interstitial carbon incorporation, which has a large impact on the electrical and optical properties of these layers. We will show that the interstitial to substitutional carbon ratio is strongly influenced by the chosen growth conditions, like growth temperature and Si growth rate. In addition, angle-resolved X-ray photoelectron spectroscopy measurements indicate a surface segregation of interstitial carbon-containing complexes (more significant for higher growth temperature). Substitutionally incorporated C atoms allow strain manipulation, including the growth of an inversely strained Si 1− x− y Ge x C y layer. Local ordering effects due to atomic size differences and the growth on reconstructed surfaces, the mechanical and structural properties, and the influence of C atoms on band structure of Si and SiGe layers will be discussed.

Supersaturated carbon in silicon and silicon/germanium alloys

The growth and properties of Si1 − yCy and Si1 − x − yGexCy alloys pseudomorphically strained on Si(001) will be reviwed. Although the bulk solubility of carbon in silicon is small, epitaxial layers of more than 1 at.%C can be fabricated. Most of the incorporated C atoms occupy substitional positions and, therefore, allow strain manipulation; including the growth of an inversely strained Si1 − x − yGexCy layer. The mechanical properties as well as the influence of C atoms on band structure will be discussed. Finally we will present an atomistic picture of a fully strain-compensated SiGeC layer.

Carbon defects and defect reactions in silicon.

The energies of carbon defects in silicon are calculated, using an empirical classical potential, and used to infer defect properties and reactions. Substitutional carbon is found to react with silicon interstitials, with the carbon ``kicked out'' to form a (100) split interstitial. This interstitial can in turn bind to a second substitutional carbon, relieving stress, in three configurations with similar energies. The results here accord well with a variety of experimental data, including defect structures, activation energies for defect motion, and coupling to strain. A discrepancy with the accepted values for carbon solubility in silicon suggests a reinterpretation of the experimental data.

Reaction mechanism in carbon-liquid silicon systems at elevated temperatures

The mechanism of reactions which occur in the carbon-liquid silicon system at elevated temperatures is far from being understood although the reactions are utilised for producing manu interesting SiC materials. In the present paper the formation of fibrous β-SiC in this system, which occurs with the SILCOMP SiC/Si material, has been investigated by observing the evolution of the microstructure at successive stages of the reaction and by measuring the thermal effects accompanying the reaction. A model has been developed which permits a rational explanation of the main features of the reaction rate and of the microstructure of the products formed at the first and intermediate stages of the reaction; the microstructure is of a decisive importance for the formation of fibrous β-SiC in the final product. An explanation is given for: (1) the preferential formation of small β-SiC crystals disseminated at random in the Si matrix in localised zones which were previously occupied by the carbon fibres; (2) the high rate of reaction in spite of the low solubility of carbon in silicon at the temperatures, attained by external heating, which are usually used to produce SILCOMP (1680–1880 K). Because analogous reactions occur in the production of SILCOMP, REFEL SiC and other similar materials, the model developed may have a wider range of applications.

Solubility of Carbon in Silicon and Germanium

The solubility of carbon in silicon has been measured over the temperature range 1560 to 2900°C. The enthalpy of solution is 59±3 kcal/mole. A phase diagram for the system Si–C is presented, embodying these solubility data as well as the results of other high-temperature experiments with silicon carbide. It is found that SiC possesses a peritectic point at 2830±40°C. These studies were carried out in argon at pressures as high as 35 atmos. Solubilities of carbon in germanium were measured in the temperature range 2780 to 3170°C, at argon pressures up to 55 atmos, and a tentative phase diagram is given.