Metal Capping Layers

Even using a capping material, mechanical strength issues are still a concern. Good adhesion between all layers involved is critical. On the surface poor adhesion at either the metal-cap layer or the cap layer-polymer interfaces can lead to delamination during... 

Selective electroless deposition of cobalt alloys offers a novel approach for forming self-aligned metallic cap layers. Such films have better adhesion to copper than dielectric films. 

TiN film of approximately 300 A is typically used in the back-end interconnect process, as both the cap layer for the aluminum metal deposition sequence and an antireflective coating for the subsequent photolithography step. Since this TiN cannot be a substrate for oxide thickness measurement in ILD, the aluminum beneath the TiN must be used as the substrate. In other words, the TiN is a component of the film to be measured. Thus, its refractive index or thickness must be known to determine the unknown oxide thickness. However, the refractive index of TiN is not constant, but varies with thickness. As a result, the TiN thickness must be precisely controlled to enable the validity of the substrate modeling. 

In a representative work, Chen and Rosenzweig34 were able to alter the selectivity of CdS nanoparticles to respond either to Zn2+ or Cu2+ simply by changing the capping layer. They showed that, while polyphosphate-capped CdS QDs responded to almost all mono- and divalent metal cations (thus showing no ion selectivity), luminescence emission from thioglycerol-capped CdS QDs was quenched only by Cu2+ and Fe3+, but was not affected by other ions at similar concentrations. On the other hand, the luminescence emission of L-cysteine-capped CdS quantum dots was enhanced in the presence of zinc ions, but was not affected by cations like Cu2+, Ca2+, and Mg2+. Using this set of QD probes, the authors described the selective detection of zinc and copper in physiological buffered samples, with detection limits of 0.8 pM and 0.1 p,M for Zn2+ and Cu2+, respectively. This was claimed to be the first use of semiconductor nanocrystals as ion probes in aqueous samples. 

By using metal as the capping layer, SPPs have been demonstrated as an effective means for increasing the external quantum efficiency of ZnO. The use of thin spacer and metal alloy can eliminate the unwanted Forster energy transfer and support on-resonance SPP coupling. In addition, nanocrystalline Au can on one hand suppress the deep-level emission while on the other hand increase the band-edge emission of ZnO. Finally, the radiative SPP arising from MIM can be used to increase the forward emission of ZnO. 

The Ta Iiner/Si02 cap layer delaminated from the parylene-N ILD after removal of the copper metal. 

Bioassay for p-damascenone. Figure 2 shows a flowchart of the bioassay for p-damascenone. Sample extracts (0.5 mL) were placed in 5 mL. 1 M citric acid and heated 12 min at 90 C in 16 x 125 mm culture tubes covered with a vented metal cap. Preliminary experiments showed little change in the p-damascenone formed after 8 min. Loss of free p-damascenone due to volatilization was prevented by cooling to room temperature in ice water. Then 0.5 mL methanol plus 1.0 mL Freon-113 was added with mixing. The Freon layer was removed, and a series of three-fold dilutions were made from it. Thus each sample in the series was 1/3 the concentration of the previous. These were stored until charm analysis. 

To analyse the degradation of the sample it was characterised directly after the Teflon deposition and after a gap of one month. Meanwhile, the device was stored in a dark ambient atmosphere in a shielded metal box like the OFET presented in Table 18.3. Just after the deposition of the capping layer, there could be a small decline in the on-current at -40 V gate-source voltage observed, as shown in Figure 18.19. 

Figure 3-4. A cross-section of a double-layer metal with capping layer, barrier layer, and tungsten-filled via holes [250].

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