17 Interconnect Quality and Reliability of 3D Packaging
539
mapping representing the angle between [101] direction of Cu and
¯
101
direction
of Cu 6 Sn 5 . Figure 17.11b is a histogram orientation distribution corresponding to
Fig. 17.11a. It indicates that most of the IMC grains have very strong orientation
relationship between the [101] direction of Cu and
¯
101
direction of Cu 6 Sn 5 . A
similar crystallographic orientation relationship also exists in the same kind of pure
Cu and pure Sn diffusion couple, see Fig. 17.11c, d. The reason of preferred orientation relationship between [101] direction of Cu and
¯
101
of Cu 6 Sn 5 is attributed to
low misfit energy. The misfit between Cu and Cu 6 Sn 5 is 0.24%. The misfit direction
lies on (001) plane of Cu.
(010) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
(343) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
¯
34 ¯
3
Cu 6 Sn 5
//(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
(101) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
(141) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
¯
14 ¯
1
Cu 6 Sn 5
//(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
An EBSD study indicates that the roof-top or prism-type Cu 6 Sn 5 are elongated
along two perpendicular <110> directions on the (001) plane of Cu, which also corresponds to low misfit directions of the Cu 6 Sn 5 . This study implies that if we can control
the orientation of the UBM, i.e., (001) oriented Cu, the crystal orientation of Cu 6 Sn 5
can also be controlled with preferred texture, resulting in unique grain morphology,
i.e., roof-top, compared to randomly-oriented scallop-type Cu 6 Sn 5 grains. This orientation relationship might be potentially useful in controlling the texture of columnar
grains based microbumps, which is essentially dependent on the texture of Cu 6 Sn 5
grains (Fig. 7.12).
(a)
(b)
Fig. 17.12 Top view of exposed Cu 6 Sn 5 grains after deep etching of eutectic SnPb solder joint
reflowed at 200 °C for 30 s: (a) scallop-type Cu 6 Sn 5 grains on polycrystalline Cu substrate;
(b) rooftop-type Cu 6 Sn 5 grains on (001) Cu [20]
539
mapping representing the angle between [101] direction of Cu and
¯
101
direction
of Cu 6 Sn 5 . Figure 17.11b is a histogram orientation distribution corresponding to
Fig. 17.11a. It indicates that most of the IMC grains have very strong orientation
relationship between the [101] direction of Cu and
¯
101
direction of Cu 6 Sn 5 . A
similar crystallographic orientation relationship also exists in the same kind of pure
Cu and pure Sn diffusion couple, see Fig. 17.11c, d. The reason of preferred orientation relationship between [101] direction of Cu and
¯
101
of Cu 6 Sn 5 is attributed to
low misfit energy. The misfit between Cu and Cu 6 Sn 5 is 0.24%. The misfit direction
lies on (001) plane of Cu.
(010) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
(343) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
¯
34 ¯
3
Cu 6 Sn 5
//(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
(101) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
(141) Cu 6 Sn 5 //(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
¯
14 ¯
1
Cu 6 Sn 5
//(001) Cu
¯
101
Cu 6 Sn 5
//[101] Cu
An EBSD study indicates that the roof-top or prism-type Cu 6 Sn 5 are elongated
along two perpendicular <110> directions on the (001) plane of Cu, which also corresponds to low misfit directions of the Cu 6 Sn 5 . This study implies that if we can control
the orientation of the UBM, i.e., (001) oriented Cu, the crystal orientation of Cu 6 Sn 5
can also be controlled with preferred texture, resulting in unique grain morphology,
i.e., roof-top, compared to randomly-oriented scallop-type Cu 6 Sn 5 grains. This orientation relationship might be potentially useful in controlling the texture of columnar
grains based microbumps, which is essentially dependent on the texture of Cu 6 Sn 5
grains (Fig. 7.12).
(a)
(b)
Fig. 17.12 Top view of exposed Cu 6 Sn 5 grains after deep etching of eutectic SnPb solder joint
reflowed at 200 °C for 30 s: (a) scallop-type Cu 6 Sn 5 grains on polycrystalline Cu substrate;
(b) rooftop-type Cu 6 Sn 5 grains on (001) Cu [20]