This paper reports for the first time the incorporation of in-situ reduced graphene oxide (rGO) into geopolymers. The resulting rGO-geopolymeric composites are easy to manufacture and exhibit excellent mechanical properties. Geopolymers with graphene oxide (GO) concents of 0.00, 0.10, 0.35 and 0.50% by weight were fabricated. The functional groups, morphology, void filling mechanisms and mechanical properties of the composites were determined. The Fourier transform infrared (FTIR) spectra revealed that the alkaline solution reduced the hydroxyl/carbonyl groups of GO by deoxygenation and/or dehydration. Concomitantly, the spectral absorbance related to silica type cross-linking increased in the spectra. The scanning electron microscope (SEM) micrographs indicated that rGO altered the morphology of geopolymers from a porous nature to a substantially pore filled morphology with increased mechanical properties. The flexural tests showed that 0.35-wt% rGO produced the highest flexural strength, Young’s modulus and flexural toughness and they were increased by 134%, 376% and 56%, respectivel
The reduction of graphene oxide during the processing of fly ash-based geopolymers offers a completely new way of developing low-cost multifunctional materials with significantly improved mechanical and electrical properties for civil engineering applications such as bridges, buildings and roads. In this paper, we present for the first time the self-sensing capabilities of fly ash-based geopolymeric composites containing in situ reduced graphene oxide (rGO). Geopolymeric composites with rGO concentrations of 0.0, 0.1 and 0.35% by weight were prepared and their morphology and conductivity were determined. The piezoresistive effect of the rGO-geopolymeric composites was also determined under tension and compression. The Fourier transform infrared spectroscopy (FTIR) results indicate that the rGO sheets can easily be reduced during synthesis of geopolymers due to the effect of the alkaline solution on the functional groups of GO. The scanning electron microscope (SEM) images showed that the majority of pores and voids within the geopolymers were significantly reduced due to the addition of rGO. The rGO increased the electrical conductivity of the fly ash-based rGOgeopolymeric composites from 0.77 S m −1 at 0.0 wt% to 2.38 S m −1 at 0.35 wt%. The rGO also increased the gauge factor by as much as 112% and 103% for samples subjected to tension and compression, respectively.
This study investigated the effects of tungsten (W) film morphology on the chemical mechanical polishing (CMP) of W. Chemical vapor deposited (CVD) W films with two distinctively different grain sizes were used for comparison. During polishing, W film thickness and optical reflectance, friction, and pad temperature were monitored in-situ. It was found that larger-grained W film took longer to pass the initial low removal rate stage. By correlating four different sensor signals, comparing friction dependency on film morphology, in slurry vs. DIW, it was concluded that W CMP comprises three main stages. First is the low rate initiation stage: grain is being partially planarized, reflectance increases, friction decreases. Second is the transition stage: rate is ramping, grain becomes fully planarized, optical reflectance reaches maximum, and friction becomes minimal followed by a significant rise caused by formation of tungsten oxide passivation layer on the planarized W surface. Third is the high and constant rate stage: passivation and removal occur in a repetitive cycle, friction is high and stable, optical reflectance changes as polishing reaches different film depths. In all three stages, pad temperature increases continuously as friction-induced heat dissipates, with the rate of temperature increase following that of friction magnitude. Metal CMP has enabled integrated circuit (IC) scaling as summarized in Table I. Depending on metal types and their different reactivity, different deposition methods are used. For example, aluminum (Al), a highly reactive metal, is deposited by high-temperature physical vapor deposition (PVD); whereas copper (Cu) as a noble metal is deposited by electrochemical plating (ECP) on top of a PVD Cu seed layer; W is deposited by CVD as its precursors and reaction by-product are in the gaseous phase. CVD cobalt is emerging as a replacement for Cu in back-end-of-line interconnects as it can fill much smaller line widths. Given their superior gap fill ability, CVD and atomic layer deposition (ALD) will become more common as IC scaling continues to 10 nm and beyond.CVD W and W CMP are widely used in IC manufacturing. W CMP was first introduced in 1995 as contact metal and enabled 0.35 μm technology yield and defect readiness.1 More recently, CVD W and W CMP enabled FinFET replacement metal gate (RMG) 2 when PVD Al could no longer fill in the small gate in the 3D structure. In addition to contact metal and gate metal in logic devices, W is widely used in memory, where 3D NAND involves many steps of CVD W and W CMP. CVD W grain size and crystalline orientation are dependent on many parameters, including the sub-layer films, ALD W nucleation, and CVD W deposition precursors and deposition temperature.3 For instance, CVD W is mostly dominated by alpha phase with (110) orientation >80% at 400• C, with some portion of beta phase (114) if CVD W temperature is higher.4 Different types of W applications have different sub-layers and deposition conditions. For CVD W used in contact, sub-layers in...
It is well known that chemical mechanical polishing (CMP) pads play a dominant role in the overall performance of the polishing process. It is critical to have a fundamental understanding of the impact of the change in the pad mechanical properties on the CMP performance. The stabilization of material removal rates and planarization efficiency (PE) are demonstrated by modification of pad mechanical properties such as storage modulus. For all the pads, removal rate and PE values are compared between wafers polished for a longer time (90 seconds) versus shorter time (15 seconds). It is concluded that for longer polish time, higher removal rate and lower PE results from a drop in the storage modulus. This decrease in the storage modulus is a consequence of an increase in the polish temperature with time. Results indicate that by minimizing the change in storage modulus with temperature, the impact of longer polish time on CMP performance can be minimized.
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