ON CONTACT RESISTANCE MEASUREMENT USING 4-TERMINAL KELVIN STRUCTURES IN ADVANCED DOUBLE-POLYSILICON BIPOLAR-TRANSISTOR PROCESSES

The contact between a polycrystalline silicon (polysilicon) layer and a silicon substrate is investigated for an advanced double-polysilicon bipolar transistor process. Contact resistances are measured using fo ur-terminal cross bridge Kelvin structures. The specific contact resis tivity of the interface and the sheet resistance of the doped substrat e region directly underneath the contact are extracted using a two-dim ensional simulation model originally developed for metal-semiconductor contacts. The extracted sheet resistance values are found to be large r than those measured using van der Pauw structures combined with anod ic oxidation and oxide removal. During the fabrication of the contacts , epitaxial realignment of the polysilicon in accordance to the substr ate orientation and severe interdiffusion of dopants across the interf ace take place, which complicate the characterization. The validity of the two-dimensional simulation model applied to the poly-mono silicon contact is discussed.