Notch profile improvement in 0.25 mu m dual-polysilicon gate etch

We observed a notch profile in the p-polysilicon gate while there is a foot profile in the n-polysilicon in the gate etch process using HBr gas plasma . These seems unusual since a notch profile is generated in n-polysilicon r ather than in a p-polysilicon because polysilicon structures become weaker with the increase of implant dose level. To understand this phenomena, we s tudied the transition process of the profile by the over etch process, whic h shows the phenomena is caused by a different etch rate and side-wall pass ivation mechanism between p- and n-polysilicon. Finally, a Cl-2 gas based i nter-step having medium selectivity between the main etch and the over etch was introduced to match the profile between n- and p-polysilicon.