Experimental study on isolation edge effects in the short channel characteristics of metal oxide semiconductor field effect transistors (MOSFETs)

We investigate experimentally the isolation edge shape effects an the short channel characteristics, i.e. the gate length dependence, of metal oxide s emiconductor field effect transistors (MOSFETs) for various isolation struc tures, as compared with a reference MOSFET without influence of the isolati on edges. For shallow trench isolation (STI), the effect, which is enhanced for gate lengths around the onset of the short channel effect and causes t he threshold voltage (V-th) to shift to the lower voltage side than that by the shea channel effect, is more prominent for the trench edge with the de eper dip. On the other hand, for the local oxidation of silicon (LOCOS) iso lation with an elevated field oxide edge (i.e. the bird's beak), the effect , which is also enhanced around the appearance point of the short channel e ffect, causes the V-th values to go in the opposite direction to the case o f STI. These results indicate that the isolation edge effect depends on the gate length and can be decribed in terms of the surface potential at the i solation edge being modulated by the mixing between the short channel and t he isolation edge effect. (C) 1999 Elsevier Science B.V: All rights reserve d.