“It’s still not clear to me why Intel went for so complicated anddifficult a technology solution,” Asenov tells me, “SOI finfetswould be much easier and better performers too.” The changing shape of Intel’s finfets as reported by Chipworks andanalysed by GSS has attracted a great deal of comment, says Asenovwho has now published some further analysis of the Intel finfet. Asenov’s analysis starts: ‘One interesting question arising from the related discussions washow much the processing-related variability in the individual finshapes, clearly visible in Fig 7 of the Chipworks blog, will result in variability in the electrical characteristicsof the individual fins,” says Asenov, “although in logicapplications multiple fins are connected in parallel, resulting inaveraging of their characteristics, in SRAM application thevariability in the single fin characteristics is of utmostimportance.’ Figure 1. TEM images of three Intel FinFETs with the GARANDsimulation domain overlaid . Asenov’s analysis continues: ‘It was fairly straightforward to introduce the different finshapes into GARAND and the results are illustrated in Fig.1, withthe simulation domain superimposed on top of the TEM image. Thecomplex 3D shape of the simulation domain can be appreciated infull in Fig.
2. Figure 2. The 3D simulation domain for Fin 1. Precise measurements of the FinFET dimensions were possible due tothe impressive atomic resolution of the fin image in Fig.
8 of theChipworks blog, which we interpreted as shown in Fig. 3. Figure 3. Close-up of the top of one fin from a Chipworks TEMshowing our estimation of the fin dimensions. As in our previous blog, in the simulations presented here weconsider that the fin itself is virtually undoped but there is apunchthrough stopper beneath the fin. Bright Led Strip
Low channel doping isbeneficial from the point of view of reducing therandom-dopant-induced statistical variability – a well-known SRAMyield killer. Figs. 4-6 show the current density in the three fins at differentgate bias conditions. The shape of each fin has a clear effect onwhere the current is flowing in each case. This is further visible in Fig. Bright Led Strip Manufacturer
7 where each fin is cut lengthwisedown the centre of the fin and iso-surfaces of current density areshown. In particular, the higher current density in Fin 3 due to ithaving a narrower top of the fin is evident. Figure 4. Current density across the middle of the three fins atgate voltage VG=0.0V Figure 5. Current density across the middle of the three fins atgate voltage VG=0.3V Figure 6. Led Wall Wash Light
Current density across the middle of the three fins atgate voltage VG=1.0V Figure 7. For each fin, cut lengthwise down the centre of the fin,iso-surfaces of current density are shown. VD=1.0V, VG=0.8V. At this point you are probably keen to see the differences in theelectrical characteristics of the three fins.
The channel lengthdependence of the on-current (VG=VD=1V) of the three fins iscompared in Fig. 8 to the channel length dependence of theon-current of rectangular fins with 10nm and 8nm fin width and thesame fin height. Because we don’t know the exact strain conditions in the IntelFinFETs we cannot guarantee the absolute value of the on-currents,but we are confident in the relative magnitudes. Surprisingly,despite significant differences in the shape of the three fins, thedifference in the on-current is within a 4% range. Moreinterestingly the rectangular fins yield approximately 12% higheron-current at comparable or better electrostatic integrity.’ Figure 8.
Dependence of on-current, ION, on gate length.