3 Materials and Processing of TSV
51
Fig. 3.1 Schematic illustration of (a) a TSV assembly or TSV structure comprising of TSV, dielectric layer, barrier layer, seed layer and the filler, and (b) three major steps required for fabricating a
TSV assembly
concentrations; this is particularly useful as the TSV assembly usually has high
residual stresses and it is often exposed to large thermal stresses during fabrication
of transistors, etc., as well as during service [19, 20]. Therefore, fabrication of TSV
requires drilling small sized, slightly tapered, smooth holes of high aspect ratios in
Si wafer. For this purpose, laser drilling, powder blast micromachining, anisotropic
wet etching and plasma etch have been explored. However, as explained below, the
plasma-etching based Bosch-process type deep reactive ion etching (DRIE) method
is the most widely-used commercial method for creating holes or trenches in Si for
fabricating TSVs [21].
3.3.1.1 Laser Drilling
Laser drilling for fabricating TSVs is a process, where a hole or trench in Si is created
by focusing a high-powered laser beam at a desired location on a Si wafer. Due to
the excessive heating, Si below the laser beam melts and vaporizes, thus creating a
vertical trench with small diameter [22]. The typical diameter of the laser beam used
in this process is 10–20 µm [22, 23]. To confine the spread of the heat-affected zone
and remove the machined debris, a jet of coolant (e.g. deionized water) may also be
splashed onto Si wafer near the laser spot. As shown in Fig. 3.2, this process has been
successfully employed to drill blind holes of high aspect ratios and having diameters
in range of 10–80 µm in Si [24]. As multiple laser beams can be simultaneously
used, this process can be used to simultaneously drill multiple holes (see Fig. 3.2b)
and hence may also have very high throughput (>2000 holes/s [23]).
51
Fig. 3.1 Schematic illustration of (a) a TSV assembly or TSV structure comprising of TSV, dielectric layer, barrier layer, seed layer and the filler, and (b) three major steps required for fabricating a
TSV assembly
concentrations; this is particularly useful as the TSV assembly usually has high
residual stresses and it is often exposed to large thermal stresses during fabrication
of transistors, etc., as well as during service [19, 20]. Therefore, fabrication of TSV
requires drilling small sized, slightly tapered, smooth holes of high aspect ratios in
Si wafer. For this purpose, laser drilling, powder blast micromachining, anisotropic
wet etching and plasma etch have been explored. However, as explained below, the
plasma-etching based Bosch-process type deep reactive ion etching (DRIE) method
is the most widely-used commercial method for creating holes or trenches in Si for
fabricating TSVs [21].
3.3.1.1 Laser Drilling
Laser drilling for fabricating TSVs is a process, where a hole or trench in Si is created
by focusing a high-powered laser beam at a desired location on a Si wafer. Due to
the excessive heating, Si below the laser beam melts and vaporizes, thus creating a
vertical trench with small diameter [22]. The typical diameter of the laser beam used
in this process is 10–20 µm [22, 23]. To confine the spread of the heat-affected zone
and remove the machined debris, a jet of coolant (e.g. deionized water) may also be
splashed onto Si wafer near the laser spot. As shown in Fig. 3.2, this process has been
successfully employed to drill blind holes of high aspect ratios and having diameters
in range of 10–80 µm in Si [24]. As multiple laser beams can be simultaneously
used, this process can be used to simultaneously drill multiple holes (see Fig. 3.2b)
and hence may also have very high throughput (>2000 holes/s [23]).