Interconnections and Contacts

To complete the formation of an integrated circuit, one must interconnect the devices and finally get connections to the world outside the silicon chip. Until the 1970s, integrated circuits had two possible levels of interconnection: diffusions and metallization. The use of polysilicon as a gate material in MOS devices added a third level useful for interconnecting devices and circuits. In this section we discuss the various forms of interconnections and the problems associated with making good contacts between metal and silicon. Refractorv metal silicides and multilevel metallization used in VLSI processes are discussed, and an additional method for depositing patterned films, called liftoff is also introduced.