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Next: 5.3 Performance Degradation Mechanisms Up: 5.2 Statistical Process Influence Previous: 5.2.4 SiN-Semiconductor and Heterojunction

5.2.5 Contacts

In [50] the effect of the T-gate head shape above the gate foot on the capacitances was demonstrated, which has a similar impact as the gate length $ {\it l}_{\mathrm{g}}$ at the gate foot itself. Thus, the shape of the gate head statistically influences the device as much as the statistical gate length variations.

For the ohmic contacts a statistical variation is introduced by the alloying depth and actual contact geometry of the contacts. For the semiconductor line resistance indirectly the SiN/barrier interface influences the average mobility as the surface potential leads to a partially depleted barrier layer. Variations of geometry or even slight changes of the surface potential due to process induced remaining surface pollution will thus affect the current path and the average mobility leading to effective changes of the parasitic resistances $ {\it R}_{\mathrm{S}}$ and $ {\it R}_{\mathrm{D}}$.