William A. Tiller

Computer modeling of Si and SiC surfaces and surface processes relevant to crystal growth from the vapor

Abstract It has been shown that many-body effects are essential for the description of atomic clusters and surfaces for most real materials. We have developed Potential Energy Functions (PEFs) for both silicon and silicon carbide which include the many-body effect via a parameterized three-body term. Thus, our PEFs include both two-body and three-body terms parameterized to fit cluster and bulk thermodynamic data for their respective systems. Our computations utilize these PEFs in a two step process: (i) select initial positions for several hundred atoms to represent the surface element or defect desired, and (ii) relax the positions of all or a portion of the atoms to find the stable or metastable energy configurations. This paper focuses on the following useful information for Si and SiC (111) surfaces in contact with the vapor phase. (1) Equilibrium geometries for planar surfaces, ledges and kinks (i.e., surface reconstruction features), (2) adsorption or formation energies for ad-atoms and vacancies at various surface locations, (3) excess quantities such as surface, ledge and kink site energies, and (4) stress tensor components around the various surface features and their penetration into the subsurface region.

Theoretical analysis of requirements for crystal growth from solution

Abstract The necessary requirements which must be met for the obtaining of smooth-interface crystal growth from solution has been discussed and a general procedure has been outlined for growing such crystals in an isolated zone of well-defined and completely controllable environmental conditions. The analysis has been applied to the growth of GaAs, GaP, SiC, B 6 P, and ZnTe from solution.

Crystal growth of GaN by the reaction between gallium and ammonia

Abstract Optimum conditions for the growth of GaN crystals by flowing a mixture of NH3 and H2 over gallium are presented. Growth is thought to occur by a VLS mechanism. The addition of Bi or Sn to the solution was found to increase the number of crystallites nucleated. An unusual form of growth instability is described involving the flow of solution over the surface of the crystal in a thin film.

Thermodynamic and kinetic considerations on the equilibrium shape for thermally induced microdefects in Czochralski silicon

Using thermodynamic and kinetic considerations, we explain the quasiequilibrium, morphological, and structural characteristics of thermally induced oxide precipitates in Czochralski silicon. A model based upon the formation of Frenkel defects at the silicon/silica interface is used to explain the experimentally observed precipitate shapes: 〈110〉 coesite rods, (100) vitreous silica discs, and silica polyhedra at low, intermediate, and high temperatures, respectively.

On the growth rate of crystals from solution

Abstract Both a rigorous calculation and an approximate calculation of the crystal growth velocity as a function of time have been generated for the growth of a crystal layer from solution wherein the solution has been subjected to a variable cooling rate. The similarities and differences between these solutions have been compared and the conditions under which the approximate solution can be used is noted. The approximate solution is shown to be useful for a variety of situations wherein a rigorous solution is not possible; i.e., where fluid convection and interface attachment kinetics affect the crystal growth velocity.

Photon enhanced oxidation of silicon

Experiments have been conducted to show that at low laser power densities the enhanced oxidation rate of silicon is linearly proportional to the photon flux density for photon energies in the range 2.4–2.7 eV. The enhancement effect is greater for 〈100〉 Si than for 〈111〉 Si.

Refractive index, relaxation times and the viscoelastic model in dry‐grown SiO2 films on Si

Inert thermal anneals were performed at various temperatures to determine annealing kinetics of dry thermally grown SiO2 films on Si. Two stages of relaxation are demonstrated. The film relaxes quickly to an intermediate level, and then progresses more slowly toward full relaxation. The relaxation times to attain the fully relaxed refractive index, 1.460, and full ≤3% swelling were found to fall below typical oxidation times at T≥1150 °C, in concurrence with the experimentally observed breakpoint in the refractive index versus growth temperature data. It is concluded that the linear viscoelastic model is sufficient to quantitatively explain the breakpoints in refractive index for both wet and dry thermally grown oxide.

Film stress‐related vacancy supersaturation in silicon under low‐pressure chemical vapor deposited silicon nitride films

The effect of stress in silicon nitride films, deposited by the low‐pressure chemical vapor deposition process, on the point defect concentrations in silicon has been studied. The stress level in the nitride film is varied by controlling the ratio of flow rates of reactant gases R=fSiH2Cl2/fNH3, from 1/6 to 6. The stress in the nitride film is tensile and its magnitude increases with decreasing R. During anneals at 1100 °C in Ar with a high stress in the nitride, phosphorus diffusion in silicon is retarded, antimony diffusion is enhanced, and extrinsic stacking faults shrink faster than with a low stress. These results suggest that a vacancy supersaturation and a self‐interstitial undersaturation exist under the nitride and that the deviation from the equilibrium point defect concentrations are closely related to the stress level in the silicon nitride film. From the phosphorus junction profiles with varying shape width, an effective vacancy diffusivity of 3×10−10 cm2/s has been obtained.

Thermal oxidation of silicides

Kinetics of thermal oxide growth on silicides MoSi2, WSi2, TaSi2, and TiSi2 deposited over polycrystalline and single‐crystal silicon were investigated. Both steam and dry O2 oxidations in the temperature range of 750–1200 °C were examined. An oxidation kinetic model for silicides which accounts for diffusion processes of silicon through the silicide layer and oxidant through the growing oxide, and the interface chemical reaction was developed. This model uses the Deal–Grove silicon oxidation approach. The significantly larger linear rate constants and greatly reduced activation energies of the linear rate constants of silicides in relation to single‐crystal silicon oxidations are predicted by this model. The similarity of parabolic rate constants and their activation energies for silicon oxidations is also in excellent agreement with the model.

The influence of an interface electric field on the distribution coefficient of chromium in LiNbO3

Abstract The effective solute partitioning of chromium was investigated on single crystals of LiNbO 3 grown by the laser-heated pedestal growth (LHPG) technique. Electric field effects at the interface influence this solute partitioning, leading to an electric field-dependent effective solute distribution coefficient, k E . The LHPG technique made it possible to explore these field effects by controllably changing the growth velocity ( V ) and the temperature gradient ( G S , G L ) near the interface over a wide range. The electric field generated via the temperature gradient is associated with the thermoelectric power while an additional electric field is growth rate associated via a charge separation effect. By applying the Burton-Prim-Slichter (BPS) theory to our experimental data, we found the phase diagram solute partition coefficient to be k 0 ≈ 3.65, while the field-influenced solute partition coefficient ( V = 0) was k ′ EO ≈ 8.17 at G L ≈ 11500°C/cm. It is theoretically shown that the same considerations can be applied to all ionic partitioning at a solid-liquid interface.