6. Reliability lifetime of the device, as well as during fabrication. We wil a There are several failure mechanisms that can occur during the look at reliability in more detail next lecture For metallization, the key problems are Electromigration(material transport along the metal line due to a high current density)-reduce this by adding 0.5%Cu to Al Stress-induced voiding or hillock formation Corrosion(of Al, AlSiCu, or Cu to form oxides) Interdiffusion of the metal, which can degrade the transistors(a problem with Cu)-reduce with diffusion barriers ll/703 3.155J6.l521 What is the best metal, taking all these factors into account? Al-Si-Cu lines(low resistivity)with multilayers of Ti/tin to reduce diffusion and electromigration- now replaced by fully-encapsulated Vias(not needed in Cu metallization, where we make vias by dual-damascene process) Poly-Si gate contacts(avoids spiking, adequate conductivity )or Silicide/metal gate contacts(e.g. PtSi, TiSi, made by reacting metal with silicon) For gaas AuGeN alloys on n-GaAs, AuZnualluys on p-GaAs6. Reliability There are several failure mechanisms that can occur during the lifetime of the device, as well as during fabrication. We will look at reliability in more detail next lecture. For metallization, the key problems are: Electromigration (material transport along the metal line due to a high current density) - reduce this by adding 0.5%Cu to Al Stress-induced voiding or hillock formation Corrosion (of Al, AlSiCu, or Cu to form oxides) Interdiffusion of the metal, which can degrade the transistors (a problem with Cu) - reduce with diffusion barriers 11/17/03 3.155J/6.152J 25 What is the best metal, taking all these factors into account? For Si: Al-Si-Cu lines (low resistivity) with multilayers of Ti/TiN to reduce diffusion and electromigration - now replaced by fully-encapsulated Cu W vias (not needed in Cu metallization, where we make vias by dual-damascene process) Poly-Si gate contacts (avoids spiking, adequate conductivity) or Silicide/metal gate contacts (e.g. PtSi, TiSi2 made by reacting metal with silicon). For GaAs: AuGeNi alloys on n-GaAs, AuZn alloys on p-GaAs. 11/17/03 3.155J/6.152J 26 13