A formidable challenge in the present multi-step Cu CMP process, employed in the ultra-large-scale integration (ULSI) technology, is the control of wafer surface non-uniformity, which primarily is due to dielectric erosion and Cu dishing. In contrast with the earlier experimental and semi-theoretical investigations, a systematic way of characterizing and modeling dielectric erosion in both single- and multi-step Cu CMP processes is presented in this paper. Wafer- and die-level erosion are defined, and the plausible causes of erosion at each level are identified in terms of several geometric and physical parameters. Experimental and analytical means of determining the model parameters are also outlined. The local pressure distribution is estimated at each polishing stage based on the evolving pattern geometry and pad deformation. The single-step model is adapted for the multi-step polishing process, with multiple sets of slurry selectivities, applied pressure, and relative velocity in each step. Finally, the effect of slurry-switching point on erosion was investigated for minimizing dielectric erosion in the multi-step Cu CMP. Based on the developed multi-step erosion model, the physical significance of each model parameter on dielectric erosion is determined, and the optimal polishing practices for minimizing erosion in both multi-step and single-step polishing are suggested. / Singapore-MIT Alliance (SMA)

The use of bioenergy has been increasing due to efforts in fossil fuels replacement. Modern bioenergy technologies aim for high efficiency and low pollution levels, which increases the need for methods for the on-line characterization of biofuels. Dielectric methods have been identified as useful for the sensing of solid biofuels because they allow for rapid, nonhazardous, nondestructive, and bulk determination of material properties. The dielectric properties describe the interaction between the material and the electromagnetic waves. Dielectric properties are intrinsic of the materials and can therefore be used for the development of prediction models that can be applied regardless of the measurement technique. The study of the dielectric properties is also important as it improves the understanding of the dielectric behavior of the materials. This thesis focuses on the dielectric properties of solid biofuels and their use in the characterization of these materials. The work presented includes the development of new methods permitting the determination of the dielectric properties of solid biofuels with large particle size (waveguide method), broadband measurement of the dielectric properties (coaxial-line probe), and the use of a previously developed method for the accurate determination of the dielectric properties (free-space method). The results includes the dielectric properties of solid biofuels and their dependence on parameters such as frequency, moisture, density, and temperature. This thesis also presents semi-theoretical models for the determination of moisture content, which obtained a RMSEP of 4% for moisture contents between 34 and 67%, and an empirical model that resulted in a RMSEC of 0.3% for moisture contents between 4 and 13%. Finally, this thesis includes measurements of the influence of salt content on the dielectric properties and a discussion of its use for estimation of the ash content of solid biofuels. 

The objective of the research is to model the reliability and breakdown mechanism of back-end dielectrics in integrated circuits and to investigate the impact of physical design characteristics on the back-end dielectric reliability. As design and process complexities continue to increase, the reliability of the back-end dielectrics becomes marginal. This is mainly because the power supply voltage is not scaled at a rate comparable to feature size, which results in exponentially increasing electric fields among interconnect lines. Therefore, it is strongly desirable to be able to predict reliability or to detect design weaknesses to reliability failure during the pre-silicon verification stage. It is desirable to enable pre-silicon verification of back-end dielectric reliability based on physical design characteristics. In this research, it is shown that dielectric reliability can be modeled as a function of the critical circuit area based on the yield models. Defect clustering is taken into account by using the negative binomial statistics. The physical design characteristics will be investigated for their impact on back-end dielectric reliability. These characteristics include such factors as layout geometry, pattern density, pattern orientation, and via placement. The physical breakdown mechanism for porous back-end dielectric films is also to be investigated using Monte Carlo simulation. It is shown that the electric field is enhanced by porosity in ultra-low-k dielectric films. The electric field enhancement caused by the porosity is shown to accelerate the charge transport.

The dielectric waveguide is an important component used in the optical communication system. In this thesis, we conduct basic research on the propagation constant and the characteristic of the dielectric waveguide. We develop a method to expand 2-D rectangular dielectric waveguide modes with simple orthogonal bases. Furthermore, we improve the convergent rate by expanding waveguide modes with tensor product of properly chosen guiding-mode bases. We first derive the coupled differential equations of the two transverse magnetic field components which satisfy the continuous boundary conditions across all material interfaces. Then we investigate and verify the accuracy of this method on 1-D rectangular waveguide so that we can apply the technique to 2-D rectangular waveguides. By means of linear combination of simple 2-D orthogonal bases, we expand the mode of rectangular dielectric waveguide. Through rigorous mathematical closed-form integration, we obtain the equivalent matrix whose eigenvalues and associated eigenvectors become the mode propagation constants and mode field distribution functions of the underlying 2-D dielectric waveguide. Whenever symmetry exists we can reduce the size of the problem by choosing appropriate boundary conditions in accordance to particular mode polarization desired. This method provides at least four significant digits of propagation constant and detailed field description of the rectangular dielectric waveguide. We believe that it is an effective method for modal analysis of 2-D complex dielectric-waveguides.

The dielectric ridge waveguide is an important passive component used in the optical communication system. Compared to its cousins¡Xthe buried ridge waveguides, it is less expensive to process but harder to design due to its inherent complex field structure (it has a larger index contrast between the core and the cladding). Therefore, it is crucial to develop an efficient and accurate method to analyze the modal characteristic of ridge waveguides. We began with the expansion of one-dimensional three-layer dielectric slab waveguide using simple orthogonal basis functions. We examined both the step-index profile and the graded-index profile waveguides to confirm the feasibility of this method and to understand the level of accuracy our technique can reach. We then proceeded to derive the vector formulation of two-dimension dielectric waveguides and compared our results against the exact numerical solutions of optical fiber modes using Bessel functions. Our 2-D Cartesian mode solver gave up to 6 significant digits of the fiber propagation constants. Finally, for rectangular dielectric waveguides, we use the tensor product of 1-D guiding-mode bases as an improvement over the simple orthogonal bases to speed-up the numerical convergence and cut the storage requirement by a factor of ten without loss of accuracy which is around 4 to 5 digits over a wide range of parameters and mode types. We will use these bases to solve for the mode field distribution of ridge-waveguides and other complex structures.

In a conventional nonvolatile memory (NVM), charge is stored in a ploy-silicon floating gate (FG) surrounded by dielectrics. But, it will suffer some limitations for continued scaling of the device structure. Therefore, the nanocrystal nonvolatile memory devices have been investigated to overcome the limit of the conventional floating gate NVM in recently years. Nanocrystal charge storage offers several advantages, the main one being the potential to use thinner tunnel oxide without sacrificing nonvolatility. This is a quite attractive proposition since reducing the tunnel oxide thickness is a key to lowering operating voltage and/or increasing operating speeds. In this thesis, we have fabricated tungsten (W) nanocrystals nonvolatile memory devices. A thin tungsten silicide (W5Si3) layer was deposited on tunnel oxide layer first. The following oxidation was performed in furnace system. The W element tends to segregate downward and precipitate on the tunnel oxide after thermal oxidation. In addition, the silicon element is oxidized into silicon dioxide surrounded tungsten nanocrystals. Also, the carrier gas, such as O2 and N2, were also added as the tungsten silicide deposition. The memory effect and the electrical reliability for W nanocrystals surrounded in different dielectric were also investigated in this study. In addition, the formation mechanism of W nanocrystals with additional silicon oxide capped on tungsten silicide was also investigated. The thicker silicon oxide can effectively control the thermal oxidation condition and prevent thin film degradation. However, the overall oxidation cause the memory window reduction and the electrical characteristics degradation, resulted from the partially oxidation of W nanocrystal to metal-incorporated dielectric. By contrast, we also demonstrated the structure that deposited the charge trapping layer by co-sputtered W and dielectric material as SiO2 or Si3N4 to directly form the W nanocrystal embedded in dielectrics. Besides, the W and Si directly deposited by co-sputtered to adjust the two elements contained ratio had investigated as well in this study. Furthermore, the memory effect and electrical characteristics for germanium (Ge) element incorporated W nanocrystal memory were also discussed. The additional storage element contributes the memory effect. In summary, the memory effect for W nanaocrystal embedded in different dielectric, the effect of the thermal treatment for additional silicon oxide incorporation, and the contribution of the Ge element to the memory effect can be obtained from the fabrication of W nanocrystal memory were finished in this study.

In the generation of deep submicron semiconductor fabrication¡Atransmission delay is primarily caused by the parasitic resistance and capacitance (RC) in the multilevel interconnects. Besides¡Aelectromigration is also a serious issue for the reliability of devices . There are two principle methods of reducing the RC delay. The first method is to replace the Al wires with Cu interconnects which supply lower resistivity and high resistance to electromigration. The second method is to use a lower dielectric constant material as the inter-metal dielectric. But in Copper metallization¡Athe key issue of this technology is the formation of a thin barrier layer for Cu on the surface of the SiC film to prevent the absorption of water and diffusion of Cu. In this study¡Awe employed films SiC base compounds to investigate their chemical bonds, I-V characteristics comparisons with Al and Cu gate. On the other hand, because of serious C-V hysteretic phenomena, we try to analyze and build up models. There five models is reasonable for our experiment: (1) mobile ions, (2) dielectric polarization, (3) carrier injection, (4) gate-electrons injection, and (5) bound charges. They happens in different materials and structures.

Bismuth layer structure ferroelectrics (BLSFs) have attracted intensive investigation for the potential use in nonvolatile ferroelectric random access memory (NvRAM/FeRAM) and high temperature piezoelectric devices. In this thesis, there are three kinds of Bi-layered structure ferroelectric ceramics materials prepared by solid-state reaction methods. Investigations have been made on the crystal structure, surface morphology, and dielectric properties of these ferroelectric materials. In the chapter3 of this thesis, ferroelectric materials are SrBi2Ta2O9-based ceramics. One of the materials is SrBi2Ta2O9 composition with excess x wt% Bi2O3 (x=0, 2, and 4). Even 1280oC is used as the sintering temperature of stoichiometric SrBi2Ta2O9 composition, the X-ray diffraction patterns will show that the SrBi2Ta2O9 phase is coexisted with the raw material of Ta2O5 and the secondary phases of SrBi2O4 and BiTaO4. For SrBi2Ta2O9 composition with excess 2wt%- or 4wt%-Bi2O3-doped and sintered at 1040oC, the Ta2O5, SrBi2O4, and BiTaO4 phases are eliminated and only the SrBi2Ta2O9 phase is observed in the X-ray diffraction patterns. The other of SrBi2Ta2O9-based ceramics was doped with V2O5. V2O5 is used to substitute Ta2O5 of the SrBi2Ta2O9 ceramics to form SrBi2Ta2-xVxO9 composition, where x=0.1, 0.2, 0.3, and 0.4. For all SrBi2Ta2-xVxO9 composition, the crystal intensities of the (00l) planes (l =6, 8, 10, 12, and 14) increase with the increase of sintering temperature and saturate at 1050oC-sintered ceramics, and the increase in the crystal intensities of the (008) and (0010) planes are more obvious. For the same sintering temperature, the crystal intensities of the (00l) planes increase with the increase of V2O5 content and saturate at SrBi2Ta1.7V0.3O9 ceramics. In the chapter4, ferroelectric materials are SrBi4Ti4O15-based ceramics. One of the materials is (Sr1-xBax)Bi4Ti4O15 (x=0, 005, 0.1, 0.15, and 0.02), and BaO is used to substitute SrO. Dielectric properties were investigated in the temperature of 25oC~ 805oC at 1MHz. It is found that Curie temperatures are shifted to higher temperature as the BaO content increased. For (Sr1-xBax)Bi4Ti4O15 ceramics sintered at 1150oC, the Curie temperature for x=0, 0.05, 0.1, 0.15, and 0.2 are 645oC, 665oC, 705oC, 725oC, and 745oC, respectively. The other is non-stoichiometric compositions SrBi4Ti4O15+x Bi2O3, (x= -0.04, -0.02, 0, 0.02, and 0.04). From the observations of SEM, the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics reveal a two-phased grain growth, the bar-typed and the irregularly disk-typed grains coexist; The other ceramics will reveal the irregularly disk-typed grains. From the X-ray diffraction patterns, Bi2Ti2O7 and SrTiO3 phases are observed in the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics. Except the SrBi3.96Ti4O14.94 ceramics, the other ceramics have revealed an unapparent splitting peak in the (119) plane. In the chapter5, ferroelectric materials are (Na0.5Bi0.5)TiO3-BaTiO3-based ceramics. The 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 (x= 0, 1, 2, and 3) ceramics were fabricated by two different processes. The first process is that (Na0.5Bi0.5)TiO3 and BaTiO3 composition was calcined at 850oC and 1100oC, respectly, and then the calcined (Na0.5Bi0.5)TiO3 and BaTiO3 powders were mixed in according to 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions. The second process was that the raw materials were mixed in accordance to the 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions and then calcined at 900oC. The sintering process was carried out in air for 2h from 1120oC to 1240oC. As the sintering temperatures are higher than 1160oC, the maximum dielectric constants of ceramics made by the second method are higher than those of ceramics by the first method, and the maximum dielectric constant of this ceramics will reveal in the x =1 ceramics. Both ceramics reveal a broaden dielectric constant-temperature curves. The other is (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3 compositions, where x= 0.03, 0.05, and 0.07, formatted by two different methods given above. The dielectric-temperature curves of (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3-based ceramics are almost unchanged as the measured frequency changed from 10 kHz to 1MHz.

Recently, Iwamoto[1] has proposed a passive-matrix LCD called VA-STN-LCD (Verically Aligned Super Twist Nemetic LCD), in which excellent electro-optic (EO) performance under high-multiplexing conditions has been demonstrated. It was pointed out that such a high EO performance was realized by achieving a pretilt angle of about 80 degree. In this study, we want to learn the different EO characteristic of separate pretilt angle and separate chiral-doped concentration of Negative Dielectric Anisotropy nemetic liquid crystal in vertically aligned cell.

With combination of the both ferroelectric and ferromagnetic and mutural coupling properties, multiferroics attracts a lot of researcher¡¦s attentions. Among these very popular materials, such as REMnO (113 series, 125 series), BiFeO3 etc¡K , the BiFeO3 interests us the most for it manifests multiferroic effects above the room temperature. However, the pure BiFeO3 phase is very difficult to form and a serious lost of Bi creates complex grain boundaries that produces enormous electric leaking. In this study, Pb is doped into BiFeO3 in Bi sites and we hope this doping effect may increase the stability and the ferroelectricity of Bi1-xPbxFeO3. It is found that the crystal structure is changed dramatically, because of the doping of Pb, from the rhombohedra structure of the parent pure BiFeO3 to the cubic structure of Bi0.85Pb0.15FeO3. By the Pb doping, the compounds exhibit free from impurity phases and the dielectric constants are enhanced qualitatively to the doping levels.