Intermetallic compounds in 3D integrated circuits technology: a brief review

Figures & data

Figure 1. Schematic comparison of three-dimensional (3D) interconnections of (a) stacked die package by wire bonding; (b) package on package by ball grid array (BGA); and (c) wafer and/or dies interconnected with through-silicon via (TSV) [28].

Figure 2. Synchrotron radiation tomography of 3D ICs test sample with the blue arrows representing the electrical flow during device operation [48].

Table 1. Different adsorption and penetration energies of M atoms on the a-axis and c-axis of Sn solder [69].

M atoms	Ead /(eV)		Epe/(eV)
	a-axis	c-axis	a-axis	c-axis
Ni	−4.84	−5.18	0.57	0.06
Cu	−3.05	−3.58	0.61	0.18
Ag	−1.96	−2.65	0.78	0.43
Au	−2.11	−2.77	0.79	0.49
In	−1.27	−2.88	0.88	0.57

Figure 3. (a) Phase diagram [74] and (b) bonding profile of binary Cu-Sn couple [75].

Figure 4. Scanning electron microscopy (SEM) images of Cu/Sn diffusion coupled with Kirkendall void formation at the Cu₃Sn layer (a) without electromigration effect [76] and (b) with electromigration effect [95].

Figure 5. EBSD orientation maps (TD) of Cu-Sn IMCs (RD: reverse direction and TD: transverse direction) [96].

Table 2. Analysis of total IMC thickness with respect to different aging times, constant atmospheric condition and constant temperature for each solder joint.

Solder joint	Atmospheric condition	Annealing temperature (°C)	Aging time(hours)	Total thickness of IMCs (μm)(Cu6Sn5+ Cu3Sn)	Ref.
Sn3.5-Ag	Air	260	0.16	20.50	[100]
			0.50	29.30
			1.00	38.45
Sn0.7-Cu	Vacuum	240	24.0	3.77	[101]
			72.0	4.40
			120.0	4.85
Sn3.0-Ag0.5-Cu	Air	150	100.0	4.80	[102]
			200.0	5.50
			500.0	6.50

Figure 6. Schematic diagram of two β-Sn grain interconnects separated by grain boundaries with different electron flows: (a) forward direction and (b) reverse direction [112].

Table 3. Asymmetric growth of IMCs on the cold and hot sides.

Different sides	Growth of IMCs	Growth mechanism of IMCs	Morphology changes	Typical explanation
Cold side	Cu6Sn5 is enhanced	Reaction and thermo- migration-controlled	Scallop-like Cu6Sn5 transformed into layer-like	- Sufficient Cu atomic flux on the cold side
Hot side	Cu6Sn5 and Cu3Sn are hindered	Grain boundary and thermo- migration-controlled	Scallop-like Cu6Sn5 is maintained	- Insufficient Cu atomic flux on the hot side

Figure 7. (a) Schematic illustration of the asymmetric growth of IMCs during thermomigration and (b) SEM images of the asymmetric growth of Ni₃Sn₄ IMCs under thermomigration conditions at the hot end (190°C) and cold end (100°C) for 150 h [113].

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