A new MOS transistor design with self-registering source-drain and gate contacts

This paper describes a new method for fabricating MOSFETs with self-registering contacts to the source-drain and polysilicon gate regions. Contacts to the source-drain and gate regions are made through a second level of polysilicon which is directly deposited in contact with the doped source-drain and gate regions. Isolations are obtained by selectively oxidizing the entire layer of the second level polysilicon using a thin layer of silicon nitride as an oxidation mask. Metal is only needed in the areas where interconnects cross over the source-drain or gate regions. For an MOS circuit with buried contacts, this approach requires one less mask than the conventional approach since no buried contact masking is needed. Metal silicide can be incorporated into the second level of polysilicon to reduce the lire resistance of this interconnecting layer. Refractory metal or refractory metal silicide can also be used as the gate material. Some experimental results on devices fabricated using the new process will be presented.