The properties of aluminum, platinum silicide and copper based contacts for silicon high-power devices

Abstract

Electrical, thermo-electrical and thermo-mechanical properties were compared for PtSi, aluminum (Al, PtSi–Al, PtSi–AlCuSi, PtSi–TiW–AlCuSi), and copper based contacts (TiW–Ni–Cu, TiW–Ni–Cu–Ni–Au, PtSi–TiW–Ni–Cu, PtSi–TiW–Ni–Cu–Ni–Au). High-power 2.5 kV/150 A P-i-N diode with both lapped and etched anode surface was used to characterize the performance of the contacts in the conditions of free floating silicon in pressed package. The devices with PtSi contacts have the lowest forward voltage drop, but do not survive the operation in pressed package under thermal cycling. The copper based contacts with PtSi layer give lower voltage drop and better thermo-mechanical ruggedness compared to that of aluminum. These features are conserved even with passivation against corrosion using Ni–Au. The contacts without the PtSi layer have high voltage drop and fail under thermal cycling. The composition of the contact layer is shown to influence the thermal behavior of device voltage drop. The crossing point current is found to decrease with increasing contact layer thickness. The lowest magnitude gives the aluminum contact.