Microstructure and electrical properties of diborides modified by rapid thermal annealing

Diborides of Ti, Hf and Zr are thermally, mechanically and chemically stable with good thermal and electrical conductivity. We tested their properties in front-end processes used in Si integrated circuits (IC). Films were deposited by e-beam evaporation either on Si, for the formation of contacts to the source/drain (S/D) regions, or on Si oxides, for the formation of metal gates in p-type metal-oxide-semiconductor (PMOS) transistors. We focused on their crystallization caused by rapid thermal processing (RTP) at temperatures up to 1100 degrees C. Transmission electron microscopy was used for identification of nanocrystallites of TiB(2), ZrB(2), and HfB(2). The grain growth was correlated with temperature and time of RTP. Of all borides, HfB(2) resulted in the most complete crystallization with little amorphous phase left. There was no crystallographic degradation of the interface with Si or dielectrics, except for extreme thermal budgets. Complementary techniques were used for monitoring chemical stability and electrical parameters of test structures to assess the role of recrystallization in device behaviour.