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130 Cha pte r T h ree
but the process is very slow and may not produce a perfectly conformal coating. Laser-
assisted chemical vapor deposition (CVD) of Mo or W is considerably faster and is used
for filling deep vias. There are also different metal-ceramic composites with lower CTEs
(<<16 ppm/°C). It is difficult to fill deep, blind vias with an aspect ratio > 5:1. Specialized
processes are required for filling such deep vias. Figure 3.61 shows the SEM pictures of
different TSVs [74] fabricated this way.
10 mm
(a)
50 mm
(b)
FIGURE 3.61 (a) Small copper-ceramic–fi lled via. (b) A via with partial copper plating and
a composite fi lling. [74]
