18 Fault Isolation and Failure Analysis of 3D Packaging
601
18.4.1.1 Nanosecond (ns) and Femtosecond (fs) Laser Ablation
Techniques
As illustrated in Table 18.4, the laser ablation techniques have the fastest material
removal rate, thus could provide a very short TPT. However the relatively low spatial
resolution and laser induced thermal damage in the μm range heat affected zone may
limit its application as an independent cross section technique [49]. Plasma FIB or
ion milling is needed to clean up laser prepared samples. Integrating femtosecond
(fs) laser ablation with conventional FIB and Scanning Electron Microscopy (SEM)
is an alternative advanced cross sectional technique comparable with the plasma FIB
and SEM method [49]. Compared with the conventional nanosecond laser ablation
technique, fs laser ablation technique combining with SEM and FIB has much better
location control, very little laser induced damage to the sample, as well as a high
material removal rate of up to 10
3
μm
3 /s. It has been demonstrated that the system
could perform artifact free TSV cross sections with comparable TPT to the plasma
FIB system [49].
18.4.1.2 Plasma Focused Ion Beam (FIB)
Commercially available Plasma-FIB system is equipped with an inductively coupled
plasma (ICP) source providing a focused Xe beam in a wide beam current range from
several pA up to 2 μA [48]. Compared with the conventional Ga ion beam based
FIB system with maximum beam current of ~65nA, the TPT of sample preparation
process by plasma-FIB system with similar sample finish could be 20–100 times
faster.
Plasma FIB combined with scanning electron microscopy (SEM) technique has
been used to reveal subtle defects in a large cross sectional area, like delamination
and cracks in TSVs, micro-bumps, stacked dice with high quality and fast TPT [48].
18.4.1.3 Broad-Beam Ion Milling
Unlike the advanced plasma-FIB and fs laser systems, broad-beam ion milling is a low
cost sample preparation technique for 3D packages. Units could be cross sectioned
either by conventional mechanical technique or laser milling close to the area of
interest before performing ion milling. It can produce about 1 mm
2 cross sectional
area with artifact free final finish within a couple of hours. Curtaining artifacts in
FIB cross sections are minimized in the ion milling method because of the large area
with homogenous ion dose and milling with varied incident angles. The ion milling
technique has been applied to perform TSV cross sections with artifact free sample
finish and fast TPT [50]. Figure 18.28 presents Scanning Electron Microscopy (SEM)
images of TSVs in a 3D package, cross sectioned by ion milling technique [50]. A
large area of artifact free cross sectional view in the 3D package is disclosed within
601
18.4.1.1 Nanosecond (ns) and Femtosecond (fs) Laser Ablation
Techniques
As illustrated in Table 18.4, the laser ablation techniques have the fastest material
removal rate, thus could provide a very short TPT. However the relatively low spatial
resolution and laser induced thermal damage in the μm range heat affected zone may
limit its application as an independent cross section technique [49]. Plasma FIB or
ion milling is needed to clean up laser prepared samples. Integrating femtosecond
(fs) laser ablation with conventional FIB and Scanning Electron Microscopy (SEM)
is an alternative advanced cross sectional technique comparable with the plasma FIB
and SEM method [49]. Compared with the conventional nanosecond laser ablation
technique, fs laser ablation technique combining with SEM and FIB has much better
location control, very little laser induced damage to the sample, as well as a high
material removal rate of up to 10
3
μm
3 /s. It has been demonstrated that the system
could perform artifact free TSV cross sections with comparable TPT to the plasma
FIB system [49].
18.4.1.2 Plasma Focused Ion Beam (FIB)
Commercially available Plasma-FIB system is equipped with an inductively coupled
plasma (ICP) source providing a focused Xe beam in a wide beam current range from
several pA up to 2 μA [48]. Compared with the conventional Ga ion beam based
FIB system with maximum beam current of ~65nA, the TPT of sample preparation
process by plasma-FIB system with similar sample finish could be 20–100 times
faster.
Plasma FIB combined with scanning electron microscopy (SEM) technique has
been used to reveal subtle defects in a large cross sectional area, like delamination
and cracks in TSVs, micro-bumps, stacked dice with high quality and fast TPT [48].
18.4.1.3 Broad-Beam Ion Milling
Unlike the advanced plasma-FIB and fs laser systems, broad-beam ion milling is a low
cost sample preparation technique for 3D packages. Units could be cross sectioned
either by conventional mechanical technique or laser milling close to the area of
interest before performing ion milling. It can produce about 1 mm
2 cross sectional
area with artifact free final finish within a couple of hours. Curtaining artifacts in
FIB cross sections are minimized in the ion milling method because of the large area
with homogenous ion dose and milling with varied incident angles. The ion milling
technique has been applied to perform TSV cross sections with artifact free sample
finish and fast TPT [50]. Figure 18.28 presents Scanning Electron Microscopy (SEM)
images of TSVs in a 3D package, cross sectioned by ion milling technique [50]. A
large area of artifact free cross sectional view in the 3D package is disclosed within