Removable sidewall spacer for lightly doped drain formation using one mask level and differential oxidation

Claim 1

A process for forming lightly doped drains (LDDs) on both NMOS and PMOS devices together on a CMOS integrated circuit using only one mask level, comprising the following steps in the following sequence: forming gates for NMOS and PMOS devices on an integrated circuit substrate; forming disposable, cleanly removable sidewall spacers along the gate edges; protecting gates of a first conductivity type by covering them with a disposable barrier material; implanting heavily doped source/drain regions along sidewall spacer edges of gates of a second conductivity type, while gates of the first conductivity type are protected by the disposable barrier material; removing the disposable sidewall spacer from along the edges of the gates of the second conductivity type; implanting LDDs along the gate edges of the second conductivity while the gates of the first conductivity type are protected by a disposable barrier material; removing the disposable barrier material; driving in the source/drain regions and LDDs along the gate edges of the second conductivity type in a first thermal drive-in cycle in an oxidizing ambient to grow silicon dioxide over the surface of the substrate wherein the oxide over the source/drain regions and LDDs by the gates of the second conductivity type is thicker than the oxide over future source/drain regions by the gates of the first conductivity type; reforming disposable, cleanly removable sidewall spacers along the gate edges; implanting heavily doped source/drain regions along the edges of the sidewall spacers of gates of the first conductivity type; removing all disposable sidewall spacers from along the gate edges; implanting LDDs along the gate edges of the first conductivity type; and driving in the source/drain regions and LDDs along the gate edges of the first conductivity type in a second thermal drive-in cycle.