Sensitivity analysis of ion implanted silicon wafers after rapid thermal annealing

In this study, we have investigated sensitivities of the ion implanted silicon wafers processed by rapid thermal annealing (RTA), which can reveal the variation of sheet resistance as a function of annealing temperature as well as implantation parameters. All the wafers were sequentially implanted by the arsenic or phosphorous implantations at 40, 80, and 100 keV with the dose level of 10¹⁴ to 2 × 10¹⁶ ions/cm². Rapid thermal annealing was carried out for 10 s by the infrared irradiation at a temperature between 850 and 1150°C in the nitrogen ambient. The activated wafer was characterized by the measurements of the sheet resistance and its uniformity mapping. The values of sensitivities are determined from the curve fitting of the experimental data to the fitting equation of correlation between the sheet resistance and process variables. From the sensitivity values and the deviation of sheet resistance, the optimum process conditions minimizing the effects of straggle in process parameters are obtained. As a result, a strong dependence of the sensitivity on the process variables, especially annealing temperatures and dose levels is also found. From the sensitivity analysis of the 10 s RTA process, the optimum values for the implant dose and annealing temperature are found to be in the range of 10¹⁶ ions/cm² and 1050-1100°C, respectively. The sensitivity analysis of sheet resistance will provide valuable data for accurate activation process, offering a guideline for dose monitoring and calibration of ion implantation process.     

An analytical model for breakdown voltage of surface implanted SOIRESURF LDMOS

An analytical model for the breakdown voltage of the surface implanted silicon-on-insulator (SOI) REduced SURface Field (RESURP) LDMOS is presented, which allows useful design curves of breakdown voltage in terms of the device parameters, including the substrate bias voltage. Improvement on both the breakdown voltage and the on-resistance of the device due to the surface implantation is demonstrated. Numerical simulations are shown to support the analytical results     

Improvement of imaging characteristics by pupil apodization in a laser scanning system for electro-photography

It is well known that imaging characteristics such as beam spot size and focal depth can be improved by applying apodization of amplitude and phase at the entrance pupil of an optical system. As an optical system for the electro-photography continuously requires highly resolved dot image and extended focal length to obtain more delicate expression with adequate production stability. Advantages from apodization technique can improve system performance and supply high degree of reliability of the optical system. However, issues on reduction in absolute optical power and on side-lobe of beam spot profile have been technical barrier for its useful implementation to imaging optics for commercial devices. Thorough this paper, theoretical feasibility of application of a pupil apodization to a laser scanning optical unit is mainly discussed in the aspects of optical power reduction and side-lobe of spot profile, as well as enhancement of optical resolution and focal depth. In addition, fundamental experimental results on beam spot profile through focal region are followed to uphold feasibility analysis.

     

A power MOSFET design methodology considering epi parametervariations

An optimum design method for power MOSFETs that maximizes the number of good dies is presented. From the device specification of the maximum voltage and current given, the target design value of the breakdown voltage required for the maximum number of good dies it determined by considering the variations of parameters such as thickness and resistivity of the epitaxial layer, chip area, and defect density during the manufacturing process. In the case of a 650-V/5-A power MOSFET, the optimum design target of the breakdown voltage is found to be 710 V, which gives 1213 good dies from a 5-in wafer with the defect density of 5/cm² when ideal junction termination is assumed. This maximum number of good dies is reduced to 855 in practice due to the nonideal junction termination with 80% of the ideal breakdown voltage, resulting in the target design voltage of 890 V     

Atomic-scale structure and morphology of ferric oxyhydroxides formed by corrosion of iron in various aqueous media

Fine particles of corrosion products consisting of one kind of ferric oxyhydroxide, either γ-FeOOH (lepidocrocite) or α-FeOOH (goethite), were directly prepared by dipping pure iron into aqueous solutions containing sodium chloride, sodium sulfate, or their mixed salts with sodium bicarbonate. Quantitative X-ray structural analysis using an in-house X-ray diffraction apparatus has been used for characterizing the atomic-scale structure of these ferric oxyhydroxide particles. The morphology of the γ-FeOOH and α-FeOOH particles was observed by transmission electron microscopy (TEM), and their bonding structures were analyzed using Fourier transform infrared spectroscopy (FT-IR). The realistic atomic-scale structures in the γ-FeOOH and α-FeOOH particles were estimated by fitting the interference functions with the help of the reverse Monte Carlo (RMC) simulation technique. The results showed that the linkages of fundamental FeO₆ octahedral units in the particles were deviated from the ideal crystal structure. The structural deviation is believed to be due to the incorporation of foreign anions during the formation of these particles in the aqueous solutions. The resultant atomic-scale structures in the γ-FeOOH and α-FeOOH particles were correlated with their morphology and bonding structure.     

Influence of silicate ions on the formation of goethite from green rust in aqueous solution

We investigated the influence of silicate ions on the formation of goethite converted from hydroxysulphate green rust, which was synthesized by neutralizing mixted solution of Fe₂(SO₄)₃ and FeSO₄ with NaOH solution, by O₂ in an aqueous solution. The pH and oxidation-reduction potential of the suspension and the Fe and Si concentrations in supernatant solutions were analyzed. X-ray diffraction results for the solid particles formed during the conversion were consistent with the results of the solution analyses. The results indicated that silicate ions suppressed the conversion from green rust to α-FeOOH and distorted the linkages of FeO₆ octahedral units in the α-FeOOH structure.     

Influence of silicon on local structure and morphology of γ-FeOOH and α-FeOOH particles

The extended X-ray absorption fine structure (EXAFS) method was used for investigating the local structures of lepidocrocite and goethite with and without silicon. The structure and morphology of these particles were investigated using X-ray diffraction and transmission electron microscopy, respectively. The bonding structure was examined by Fourier transform infrared spectroscopy (FT-IR). When silicon species was added, the structure and morphology changed while the linkage of FeO₆ octahedral units was distorted. The FT-IR spectra revealed the formation of the Fe-O-Si bond in particles containing silicate ions, and the characteristic bond affects the local structure and morphology of the particles.     

An analytical model for minimum drift region length of SOI RESURFdiodes

An analytical model for calculating the minimum drift region length of SOI RESURF diodes is presented with an expression for the maximum breakdown voltage of the device. The minimum drift region length is determined from the condition that the maximum breakdown voltage due to the one-dimensional field along the vertical path equals that of the lateral electric field along the surface. Analytical results agree well with the simulations using PISCES II, and qualitatively with the experimental results     

An analytical model for punch-through limited breakdown voltage of planar junction with multiple floating field limiting rings

An appropriate model for punch-through (PT) limited breakdown voltage of a planar junction is presented for the first time as a function of the normalized epitaxial layer thickness and the critical depletion width of the cylindrical junction at breakdown in non-PT case. The results are applied to the planar junction structure with a single ring, taking into account three different breakdown modes. The problem of the multiple ring structure is solved using the equivalent ring method, which allows determination of the PT limited breakdown voltage and optimized ring spacings for the structure. Comparisons with two-dimensional device simulations using MEDICI show a good agreement.     

Coarsening Behavior of Tricalcium Silicate (C3S) and Dicalcium Silicate (C2S) Grains Dispersed in a Clinker Melt

Microstructural evolution during the heat treatment of cement clinker was investigated. Two model specimens, which consisted of faceted tricalcium silicate (C₃S) and spherical dicalcium silicate (C₂S) grains dispersed in a liquid matrix, were prepared with 5 wt% of large seed particles. The seed particles of faceted C₃S grains grew extensively, whereas those of the spherical C₂S grains grew rather slowly, relative to the matrix grains. As a consequence, C₃S grains exhibited a bimodal size distribution that was typical of exaggerated grain growth, whereas C₂S grains retained a uniform and normal size distribution. These results suggest that the growth of faceted C₃S grains was controlled by the interface atomic attachment, such as two-dimensional nucleation, and that of spherical C₂S grains was controlled by diffusion through the liquid matrix. The dependence of growth mechanisms on grain morphology has been explained in terms of the atomistic structure of the solid/liquid interface.