Copper grains

It has been observed by some experimenters, but not by the others, that the experimental lattice constant a in crystals of ordinary size was different from that, a + A a, found in extremely small crystals. A recent example72 refers to vacuum-deposited copper grains whose diameter D (they were, of course, not spherical) varied from 24 to 240 angstroms. The lattice constants calculated from the (111) reflexions increased from 3.577 to 3.6143 angstroms when the grain volume decreased, but the particle size had no definite effect on the reflexions from the 220 plane. 

Properties of nanoscale materials may be very different from those of the bulk material. For instance, small particles may melt at much lower temperatures than the bulk and are often much harder 6 nm copper grains are five times as hard as bulk copper. 

FIGURE 17.29 Stress-induced pitting. The copper grain growth makes copper to reduce its volume slightly and leave some voids. It is visible in the middle of a long copper line. 

During electroless deposition of copper in HF solution, the nucleation process dominates initially for about 60 s to produce nanometer-sized nucleus deposits then growth of the copper grains takes over. ° As soon as nuclei of metal deposits are formed, the kinetics of deposition is changed as the metal nuclei act as catalytic sites for further metal deposition. The rate of deposition increases with increasing HF concentration. The silicon surface roughens as the deposition continues due to the corrosion reactions. 

C, onto vertical stationary copper wire electrodes which were not previously covered by copper thin hlms. The parallelism between the process of the copper electrodeposition and the hydrogen evolution can be easily seen in Fig. 14a. From this hgure, both the sites of the formation of hydrogen bubbles (i.e., sites at which the hydrogen evolution starts) and the agglomerates of copper grains between them can be noticed. 

Figure 14. (a) Copper deposit obtained at an overpotential of 1,000 mV Time of electrolysis 10 s, (b) the positions of formation of hydrogen bubbles and agglomerates of copper grains, and (c, d) the details from Fig. 14a and b. (Reprinted from Ref.18 with permission from Springer). 

Hence, increase the temperature led to a redistribution of evolved hydrogen from those creating a honeycomb-like structure (holes formed due to the attachment of hydrogen bubbles with cauliflower-like agglomerates of copper grains between them) to those making a copper structure with the dominant presence of cauliflower-like forms and irregular channels between them. 

Anti-suppressor is used to refine copper grain size and increase copper s ductility. The concentration of the anti-suppressor in our system is shown in Fig. 3 as a function of plating time. We were able to control this additive s concentration within its range over a long period of time with automatic addition of a constant amount of additives. This means that during system standby period there was no additive consumption, and also there was no self-induced decomposition during... 

Figures 14 and 15 show micrographs from FIB/SEM analyses of copper deposition in 0.5 pm trenches using the MREF waveform. The surface copper film thickness can be reduced or nearly eliminated by decreasing of the charge ratio (QJQa), as shown in Figure 16 and 17. Figure 18 shows the microstructure of the copper grain structure in the trench under MREF waveform.

Fig. 5. Plot of copper grain grooving data as surface diffusion.

The copper grain size and concentration of carbon atoms in the films are dependent of CH4 concentration in the gaseous phase (Fig. 3). The carbon content increased progressively from 25 to 75 at.% as the CH4 concentration in the gaseous phase increased from 60 to 100%. Copper grain size became less than 5 nm due to the increase of carbon content in the films from 60 to 75 at.%. 

Figure 3. Copper grain size and concentration of carbon atoms vs. concentration of CH4 in gas phase for a-C H,Cu coatings deposited by PECVD.

To gain more detailed view on the structure of Cu inside pores, the SEM was used for the cleaved samples. Fig. 3 presents the cross-section SEM images of the different porosity n+-type PS samples after Cu corrosive deposition. The size of copper grains on the surface of PS layer differs from that inside of pores. Very important result presented in Fig. 3 is the decrease of the thickness of PS layer after Cu deposition. It means that PS layer is etched because of interaction of silicon with the solution. Etching of PS is increased with the growth of PS porosity. 

The cauliflower-like agglomerates of copper grains were formed at an overpotential of 550 mV, where there was no hydrogen evolution (Fig. 5.1a). The very branchy 3D (three dimensional) dendrites were formed at an overpotential of 650 mV where hydrogen evolution was very small and corresponds to of... 

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