Process for making a self aligned vertical field effect transistor having an improved source contact

DETAILED DESCRIPTION The above and other objects and advantages of the present invention are achieved by providing a self-aligned vertical field effect transistor wherein a nitride sidewall spacer is formed around a polysilicon gate, and an oxide sidewall spacer, which may be heavily doped with an n-type dopant, is formed covering the silicon nitride sidewall spacer.
The silicon nitride sidewall spacer allows the oxide sidewall spacer of a conventional self-aligned vertical field effect transistor process to be removed partially or completely before making ohmic contact to the source thus increasing the contact area between the source and the source electrode and eliminating reliability problems related to heavily doped oxide in contact with aluminum electrodes.