Higher hole mobility induced by twisted Direct Silicon Bonding (DSB)

Twisted Direct Silicon Bonded (DSB) substrate demonstrates a higher hole mobility advantage over (110) bulk substrate for PFET. The mobility shows a (110) layer thickness dependence with the thinner DSB layer having a higher hole mobility. 25% on-current improvement is obtained for thin DSB PFETs at long channel (L
g
= 2 μm), 10% higher at short channel (L
g
= 36 nm) compared to (110) bulk PFETs. Moreover, we found that the thinner DSB shows better V
t
roll-off characteristics. On the other hand, NFETs on DSB are as good as (100) bulk NFETs. Thin DSB substrate demonstrates 11% faster ring oscillator speed over thick DSB substrate and 30% faster over (100) bulk due to higher mobility and lower capacitance.