Showing papers on "Grain growth published in 1997"

Microstructure control in semiconductor metallization

Abstract: The microstructure of semiconductor metallization is becoming increasingly important as linewidths decrease below 0.5 μm. At these dimensions, reliability and performance are greatly influenced by specific microstructural features rather than only by the average material properties. In this article, we address the prospects for controlling the microstructure of thin film interconnection metals as linewidths are predicted to decrease below 0.1 μm by the year 2010. First, we evaluate the sources of energy available to drive microstructure changes in thin films, both during and after deposition. The internal energy sources considered are grain boundaries, interfaces, surfaces, strain, solidification, crystallization, solute precipitation, and phase transformations, with energy densities ranging from less than 1 meV/atom to greater than 100 meV/atom. The external energy sources considered are particle bombardment during deposition, mechanical deformation, and radiation damage, which may deliver energies greater than 100 eV/atom. Second, we review examples of microstructure changes in terms of these energy sources. These examples include the dependence of Al–Cu and Ti fiber texture on the roughness of SiO2, orientation change and abnormal Cu grain growth coupled to the precipitation of Co in Cu–Co alloys, and in-plane orientation selection during phase transformation of TiSi2 in very narrow lines. A substantial degree of microstructure control is also achieved in films deposited with off-normal incidence energetic particle bombardment, which has been used to produce both in-plane and out-of-plane crystallographic orientations in metals (Mo, Nb), nitrides (AlN), and oxides (ZrO2). Drawing on these examples, we discuss the prospects for microstructure control in future semiconductor metallization with respect to the list of energy sources, the decreasing dimensions, and the changing fabrication processes. One mechanism in particular, discontinuous precipitation of supersaturated solute atoms, is highlighted as having a substantial amount of stored energy available to drive microstructure evolution, and may provide a means to more fully control the microstructure of semiconductor metallization.

Plastic behavior of nanophase Ni: A molecular dynamics computer simulation

Abstract: We report molecular dynamics computer simulations of low temperature-high load plastic deformation of Ni nanophase samples with several mean grain sizes in the range of 3–5 nm. The samples are polycrystals nucleated from different seeds, with random location and orientation. Among the mechanisms responsible for the deformation, grain boundary sliding and motion, as well as grain rotation are identified. No dislocation activity is detected, in contrast to the behavior of coarse grain metals. Interpreting the results in terms of grain boundary viscosity, a linear dependence of strain rate with the inverse of the grain size is obtained.

Comparison between Static and Metadynamic Recrystallization-An Application to the Hot Rolling of Steels

Abstract: An investigation has been performed to simulate the microstructural evolution during the hot strip rolling of steels. During this research, the controlling softening and recrystallization mechanisms after the hot deformation of austenite were first determined using single-hit and double-hit compression techniques. Based on the experimental flow and softening data, several mathematical expressions have been proposed to quantify the boundary conditions and overall kinetics for static and metadynamic recrystallization, respectively. The static model is expressed as a function of initial grain size, strain, strain rate and temperature, while the metadynamic one only depends on the strain rate and temperature. Together with industrial mill processing parameters, these models were incorporated into an integrative analysis of the hot rolling of plain carbon steel strips. The simulation results indicate that metadynamic recrystallization is dominant and leads to the full softening during rough rolling, where processing temperatures are high and strain rates relatively low. Metadynamic recrystallization can also occur between the initial finishing stands, when larger reductions are applied to the steel band. In general, however, static recrystallization becomes more and more important in the finishing mill. Partial static recrystallization may take place in the later stages of finish rolling, which can be attributed to the decreasing processing temperatures, reduced stand strains and much shorter interstand times. The evolution of the austenite microstructure during hot rolling can be characterized by the grain refinement associated with recrystallization and the subsequent grain growth. Although grain growth is significant during rough rolling, grain refinement with minimum interstand grain growth plays a key role during finish rolling.

Phase reaction and diffusion path of the SiC/Ti system

Abstract: Bonding of SiC to SiC was conducted using Ti foil at bonding temperatures from 1373 to 1773 K in vacuum. The total diffusion path between SiC and Ti was investigated in detail at 1673 K using Ti foil with a thickness of 50 µm. At a bonding time of 0.3 ks, TiC at the Ti side and a mixture of Ti5Si3C x and TiC at the SiC side were formed, yielding the structure sequence of β-Ti/Ti+TiC/Ti5Si3C x +TiC/SiC. Furthermore, at the bonding time of 0.9 ks, a Ti5Si3C x layer phase appeared between SiC and the mixture of Ti5Si3C x and TiC. Upon the formation of Ti3SiC2 (T phase) after the bonding time of 3.6 ks, the complete diffusion path was observed as follows: β-Ti/Ti+TiC/Ti5Si3C x +TiC/Ti5Si3C x /Ti3SiC2/SiC. The activation energies for growth of TiC, Ti5Si3C x , and Ti3SiC2 were 194, 242, and 358 kJ/mol, respectively.

Influence of melt depth in laser crystallized poly-Si thin film transistors

Abstract: The influence of film thickness and incident excimer laser energy density on the properties of poly-Si thin film transistors has been investigated and a coherent pattern of behavior has been identified which establishes controlled melt-through of the film as a key condition for achieving high quality devices. The conditions were correlated with the appearance of large grains and gave consistent results from both n- and p-channel devices, with carrier mobilities of more than 150 and 80 cm2/V s, respectively, and leakage currents of less than 2×10−14 A/μm. From a study of static irradiations, using a semi-Gaussian laser beam, the results are shown to be consistent with the super lateral grain growth (SLG) model. The trailing edge of the beam, when used in a swept mode, has been demonstrated to play an important role in extending the size of the energy window for this effect by re-setting the material into the SLG regime.

Examination of the Zener relationship between grain size and particle dispersion

Abstract: Zener-Smith proposed the original relation R = 4r 3f v in 1948, where R and r are the mean radii of the matrix grains and dispersed particles, and f v is the volume fraction of dispersed particles. They derived the relation under the assumption that the configuration of the grain boundary was independent of particle distribution. In the present work a modified relation R=4r/3f 2/3 v has been obtained by assuming that (1) the grain boundary is roughened by particle pinning, and (2) the amplitude of the roughness is λ/2, where λ is the inter-particle distance. Experimental data on the radii of austenite grains and the dispersed cementite particles in high C high Mn steels are shown to agree well with the modified relation.

Thermal stability of submicron grained copper and nickel

Abstract: The features of structure and thermal stability of submicron grained copper and nickel processed by severe plastic deformation are considered. The results of studies by various techniques: transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, electrical resistance and microhardness are presented. The investigations have shown that thermal stability of submicron grained materials is determined not only by a mean grain size but also by the density and distribution of the grain boundary dislocations. The relaxation of the grain boundary dislocations precedes the grain growth starting at 175°C and influences on thermal stability.

Grain Growth and Control of Microstructure and Texture in Polycrystalline Materials

Abstract: You need not be an expert in material science or engineering to benefit from Grain Growth and Control of Microstructure and Texture in Polycrystalline Materials. This unique book presents up-to-date information on the grain growth process in an easy-to-understand format. It goes beyond the recent advances in this area achieved with stimulation models of microstructure and texture by focusing on quantitative, rather than qualitative, issues. Nowhere else will you find such an accessible single-volume resource that covers:

Control and characterization of abnormally grown grains in silicon nitride ceramics

Abstract: The intrinsic grain growth behavior of β-Si 3 N 4 was investigated by annealing fine-grained β-Si 3 N 4 ceramics with 0–30 wt% β-nuclei. The development of bimodal microstructures was observed in annealed materials with 0.1–10 wt% nuclei, caused by the abnormal grain growth of nuclei due to the large driving force. This driving force was related to the difference in nuclei and matrix grain solubility in the liquid phase. The driving force for abnormal grain growth was also related to the stable morphology of β-grains of about 4 in aspect ratio. The fact that the driving force was constant in materials with 0.1–3 wt% nuclei is explained by the constant diffusion space for nuclei. Nuclei addition exceeding 10 wt% decreased the driving force because of nuclei interaction. A unimodal microstructure was developed with 30 wt% nuclei addition.

Influence of the particle size on recrystallization and grain growth in Al-Mg-X alloys

Abstract: Recrystallization and grain growth studies of Al-Mg-X (where X is Mn, Zr or Sc) alloys have been carried out using a combination of optical and transmission electron microscopy of interrupted heating tests, changes in hardness, and in-situ observations in the transmission electron microscope. Nucleation sites have been identified as typically large (> 1 μm diameter) eutectic constituent particles, but also occasionally clusters of sub-micron dispersoids. By altering the density and size of the Mn-, Sc- and Zr-based particles with selected thermomechanical treatments, recrystallization could be suppressed up to temperatures near the melting point. These results can be explained by examination of the stored energy from cold work and the particle-substructure interactions due to the precipitate morphology. Implications of these results for grain size control in Al-Mg based alloys will be discussed.

Grain size dependence of dielectric properties of ultrafine BaTiO3 prepared by a sol-crystal method

Abstract: Ultrafine BaTiO3 prepared by a decomposition of an organometallic crystal with unity of Ba/Ti ratio (sol-crystal method) has been characterized. While the as-prepared product resulting from the decomposition of the organometallic crystal at room temperature was BaTiO3 with pseudo-cubic structure, the well-crystallized tetragonal polymorph was obtained by firing the as-prepared product above 1000°C. Residual organic compounds, CO2-3 and OH- ions in the samples prevent the grain growth and tetragonal distortion of BaTiO3. We obtained quite higher room temperature permittivity (3700) at 1 kHz for the sample fired at 1200°C than that (630) prepared by conventional solid-state reaction starting from BaCO3 and TiO2. Such a high value was probably due to the accomplishment of homogeneous cation stoichiometry, which was achieved by this preparation method via the organometallic crystal with stoichiometric Ba/Ti ratio.

Fabrication and mechanical properties of fine-tungsten-dispersed alumina-based composites

Abstract: The mechanical properties and microstructure of fine-tungsten-dispersed alumina-based composites, which were fabricated by hot pressing a mixture of fine α-Al2O3 and W powders, have been investigated Small W particles of approximately 140 nm average size were located within the Al2O3 matrix grains The mechanical properties were influenced by the metal content and sintering conditions When the appropriate W content and sintering condition were selected (typically 5–10 vol% W and sintered at 1400°C), the fracture strength was enhanced compared with that of monolithic Al2O3 The metal content dependence of Young's modulus and the Vickers hardness did not obey the rule of mixtures This may be attributed to the presence of localized residual stress caused by the incorporation of fine W dispersion into Al2O3 On the other hand, high-temperature (1600°C) sintering caused degradation in the properties of the composites due to the grain growth and chemical reaction of W dispersion, which was revealed by X-ray photoelectron spectroscopy analysis The relations between fabrication condition and mechanical properties are discussed