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A physically-based dynamic simulator has been constructed to investigate the time-dependent behavior of equipment, process, sensor, and control systems for rapid thermal chemical vapor deposition (RTCVD) of polysilicon from Si[H.sub.4]. The simulator captures the essential physics and chemistry of mass transport, heat transfer, and chemical kinetics of the RTCVD process as embodied in equipment. In order to complete the system-level description, reduced-order models are also employed to represent processes involving high complexity of physics. Integration of individual simulator elements for equipment, process, sensors, and control systems enables the evaluation of not only the deposition rate and film thickness, but also of a broad range of dynamic system properties such as equipment performance, gas flow conditions, wafer temperature variation, wafer optical properties (absorptivity/emissivity), reaction gas composition, total process cycle time, consumables volume, and reactant utilization. This makes the simulator directly applicable to the optimization of process recipes and equipment design, to process control strategy, and to fault classification. This case study of polysilicon RTCYD demonstrates 1) that integrated dynamic simulation is a versatile tool for representing system-level dynamics and 2) that such representation is pivotal in successful applications of modeling and simulation for manufacturing optimization and control. Index Terms - CVD, semiconductor process modeling, simulation.

Gas delivery from a liquid source, common in semiconductor manufacturing, raises contamination control concerns not only due to impurity levels in the source. In addition, the lower vapor pressure of impurity species compared to that of the host (source) species causes impurity concentrations in delivered gas to increase as the source is used up. A physics-based dynamic simulator to describe the time-dependent variation of impurity level in such a gas delivery system has been developed and applied to the important case of CHCl[F.sub.2] impurities in host CH[F.sub.3] liquid, as routinely used for dry etching processes. For a cylinder of CH[F.sub.3] liquid with 100 ppm of CHCl[F.sub.2] at 21.1 [degrees] C (70 [degrees] F), the concentration of CHCl[F.sub.2] in the delivered gas is initially [approximately]21 ppm, and rises slowly to [approximately]100 ppm with [approximately]25% of the initial material remaining. With further usage, the CHCl[F.sub.2] level increases quickly to [approximately]350 ppm when [approximately]15% of the initial source material is left; at this point, the source has reached the liquid-dry point, i.e., all the remaining source material is gaseous, and the impurity concentration in delivered gas remains constant at 350 ppm until all material is gone. The time-dependence of CHCl[F.sub.2] impurity concentration is also dependent on the operating temperature of the liquid source: for higher temperatures, the fast rise in impurity concentration and the liquid-dry point occur earlier, while the final impurity level after this point is lower. The dynamic simulator represents a useful tool for avoiding contamination problems with liquid delivery systems and for optimizing materials usage (for cost and environmental benefits) by structuring source usage procedures consistent with contamination-sensitivity of the process. The results also suggest benefits in materials usage if specific source temperatures (different from room temperature) were imposed. The physical basis of the dynamic simulator allows more general application to other systems. Index Terms - CVD, environmental factors, etching, semiconductor manufacturing, simulation.

In the semiconductor manufacturing industry, optimization of advanced equipment and process designs must include both manufacturing metrics (such as cycle time, consumables cost, and product quality) and environmental consequences (such as reactant utilization and by-product emission). We have investigated the optimization of rapid thermal chemical vapor deposition (RTCVD) of polysilicon from Si[H.sub.4] as a function of process parameters using a physically-based dynamic simulation approach. The simulator captures essential time-dependent behaviors of gas flow, heat transfer, reaction chemistry, and sensor and control systems, and is validated by our experimental data. Significant improvements in Si[H.sub.4] utilization (up to 7x) and process cycle time (up to 3x) can be achieved by changes in 1) timing for initiating wafer heating relative to starting process gas flow; 2) process temperature (650-750 [degrees] C); and 3) gas flow rate (100-1000 sccm). Enhanced gas utilization efficiency and reduced process cycle time provide benefits for both environmental considerations and manufacturing productivity (throughput). Dynamic simulation proves to be a versatile and powerful technique for identifying optimal process parameters and for assessing tradeoffs between various manufacturing and environmental metrics. Index Terms - CVD, environmental factors, semiconductor process modeling, simulation.

The rate of chemical transformation in a heterogeneous photocatalysis system involving TiO2 surfaces is dependent on the photoactivity of the absorbate molecules and the catalyst substrates. Electron transfer takes place between the absorbate molecules in an inert oxide substrate. The catalyst only creates a regulated atmosphere for a better molecular interaction and does not get involved in the photoexcitation or chemical reaction process.

Feature selection is one of the most important machine learning procedure, and it has been successfully applied to make a preprocessing before using classification and clustering methods. High-dimensional features often appear in big data, and it’s characters block data processing. So spectral feature selection algorithms have been increasing attention by researchers. However, most feature selection methods, they consider these tasks as two steps, learn similarity matrix from original feature space (may be include redundancy for all features), and then conduct data clustering. Due to these limitations, they do not get good performance on classification and clustering tasks in big data processing applications. To address this problem, we propose an Unsupervised Feature Selection method with graph learning framework, which can reduce the redundancy features influence and utilize a low-rank constraint on the weight matrix simultaneously. More importantly, we design a new objective function to handle this problem. We evaluate our approach by six benchmark datasets. And all empirical classification results show that our new approach outperforms state-of-the-art feature selection approaches. [ABSTRACT FROM AUTHOR]

CO chemisorption has been studied on TiO2(110) under surface conditions where oxygen anion vacancy sites are not present (oxidized surface), compared to conditions where the vacancy sites are present (annealed surface). The binding energy of CO on the nondefective TiO2(110) surface is 9.9 kcal/mole in the limit of zero coverage. CO...CO repulsive interactions have been observed at higher coverages. When anion vacancy sites are produced under controlled annealing conditions in vacuum at 900 K, a significant increase in the desorption temperature of a portion of the chemisorbed CO is observed. This observation, coupled with measurements showing that defective TiO2(110) does not have enhanced CO chemisorption capacity, suggests that CO adsorbs more strongly on lattice Ti sites in the vicinity of anion vacancy sites. It is postulated that enhanced CO bonding occurs via the interaction of the O moiety of CO with the anion vacancy site while primary adsorbate bonding occurs via the C moiety to Ti lattice sites. Neither CO2 production nor oxygen exchange in CO occurs when CO desorbs from defective TiO2(110). [ABSTRACT FROM AUTHOR]

We have investigated the adsorption and thermal conversion of molecular oxygen (O2) states on the TiO2(110) surface by making use of the distinct photodesorption behavior of each adsorption state. Oxygen chemisorbs at the oxygen vacancy defect sites on the annealed TiO2(110) surface at 105 K to a saturation coverage of less than 0.12 monolayers (ML), producing mostly the α-O2 species which is observed to undergo slow photodesorption. Upon heating this surface to above 250 K, the α-O2 is converted to the β-O2 state which can photodesorb at a significantly higher rate. The β-O2 species dissociates above 400 K to produce atomic oxygen, eliminating the oxygen anionic vacancies. Both the α- and β-photodesorption processes have a threshold energy at the TiO2 band gap (3.1 eV), indicating a substrate excitation mediated process. The photodesorption time-profile is fitted with an exponential decay function with a cross section of ∼8×10-17 cm2 for the α-O2 and ∼1.5×10-15 cm2 for the β-O2 species at a photon energy of 3.94 eV. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the first experimental observation of two chemisorption states for molecular oxygen on a TiO2(110) surface containing anion vacancy sites. The first molecular species can be photoactivated to oxidize coadsorbed CO to CO2 (α channel) and undergoes slow photodesorption. The second molecular oxygen species only undergoes fast photodesorption (β channel). Conversion from α-O2, to β-O2 occurs upon heating the surface to above 200 K. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have used multiple internal reflection infrared spectroscopy to investigate the interaction of digermane with Ge(111) at temperatures between 104–600 K. Digermane predominantly adsorbs molecularly on the surface below 120 K, displaying a vibrational spectrum similar to that of condensed digermane. At temperatures between 120–150 K, digermane dissociates via Ge–Ge bond scission to form adsorbed GeH3. Chemisorbed germyl GeH3 has a distinct symmetric deformation vibration at ∼772 cm-1, compared to a value of 721 cm-1 for molecularly adsorbed Ge2H6. At 200 K, Ge2H6 adsorption produces surface GeH3, GeH2, and GeH species with stretching vibrations at 2063, 2023, and 1968 cm-1, respectively. The surface GeH2 species is also identified by a characteristic scissor mode at ∼830 cm-1. Adsorption at 300 and 400 K produces only GeH2 and GeH, with a much lower concentration of GeH2 at 400 K. The surface GeH2 and GeH species are also generated by the successive decomposition of GeH3 upon heating. All surface hydrogen desorbs at ∼600 K. [ABSTRACT FROM AUTHOR]

Studies the adsorption and reaction of tetraethoxysilane with hydroxylated silicon oxide using transmission infrared spectroscopy. Importance of dielectric thin films; Methodology of the study; Discussion on the result of the study.